APPLICATION SCHEMES Kirk Key Interlock Company

“The key that ends costly mistakes”

D E
A-2 A-3

L-O-C L-O-C

A B
A2 A 3

C
L-O L-O

D E
A-2 A 3 A 5 A-4

L-O-C L-O L-O L-O-C

A-3 A-5

A-2 A-4

L-C L-C

A B
A2 A 4
C
A 1 A 1

L-O L-O

211Wetmore Ave. S.E., Massillon, OH 44646

Phone: 330.833.8223 • Fax: 330.833.1528
Toll Free: 1.800.438.2442

www.kirkkey.com
Table Of Contents
Purpose of Interlocking
Scheme# Function
Switch and Breaker
Scheme #1 Prevents opening of switch when breaker is closed.
Scheme #2 Prevents operation of switch when breaker is closed. Permits re-closing the breaker for servicing when switch is locked open.
Scheme #3 Prevents operation of switch when breaker is closed. Circuit cannot be cleared until proper supervisory key is obtained.

Grounding Switch with Main Switch

Scheme #4 Prevents closing of grounding switch when main switch is closed, and vice versa.

Isolating Switches and Breaker

Scheme #5 Prevents operation of disconnect when breaker is closed. Prevents opening fuse compartment door when disconnect is closed.
Scheme #6 Prevents operation of disconnect when any or all of a group of breakers are closed. Operates through transfer interlock, no sequence is
required for breaker closing.
Scheme #7 Prevents operation of disconnect when any or all of a group of breakers are closed. Breakers operated in prearranged sequence.
Scheme #8 Prevents operation of disconnects when breaker is closed. Permits servicing of breaker when disconnects are locked open.
Scheme #9 Prevents operation of disconnects when breaker is closed, and prevents access to breaker compartment with disconnects closed.

Isolating Switches and Breaker or Regulator with By-Pass Switch

Scheme #10 Prevents operation of breaker disconnects and by-pass disconnect under load. Provides for closing of by-pass disconnect before
breaker circuit is opened, or permits circuit breaker to be opened with by-pass disconnect remaining open.
Scheme #10A Prevents operation of voltage regulator disconnects and by-pass disconnect under load. Permits by-pass disconnect to operate only
when regulator is in neutral position. Permits isolating regulator for servicing.

Prevent Paralleling of Lines

Scheme #11 Prevents paralleling of two lines - single load, fed from either source.
Scheme #12 Prevents paralleling of two lines - single load, fed from either source - breaker on load side.
Scheme #13 Prevents paralleling of two lines - two loads, fed from either source (one tie breaker)
Scheme #14 Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Prevents operation of switch when breaker
is closed (on either source).
Scheme #15 Prevents paralleling of two lines - two loads fed from either source (one tie breaker). Prevents operation (open or closed) of
disconnect when breaker is closed (on either source). Prevents access to fuses when disconnects and breakers are closed.
Scheme #16 Prevents paralleling of three lines - three loads, fed from any source (two tie breakers).
Scheme #17 Prevents paralleling of four lines - four loads fed from any source (three tie breakers)
Scheme #17A Prevents paralleling of four lines - four loads fed from any source (three tie breakers). Also prevents opening of rear access doors when
breakers are energized.
Scheme #18 Prevents paralleling of three lines - three loads fed from any source (three tie breakers).
Scheme #19 Prevents paralleling of four lines - four leads fed from any source (four tie breakers).
Scheme #20 Prevents paralleling of three power sources through a common tie bus not normally in service. Permits feeding any load bus from
a second power source through the tie bus. Permits one power source to supply all three load buses through the tie bus.
Scheme #21 Prevents paralleling three power sources through a common tie bus not normally in service. Permits feeding any load bus from a
second power source through the tie bus only when authorized by a supervisor. Permits one power source to supply all three load
buses through the tie bus only when authorized by a supervisor.
Scheme #22 Prevents paralleling two incoming primary sources through primary tie bus disconnect. Prevents operation (open or closed) of the
disconnects under load. Permits one power source to supply both loads through tie bus.
Scheme #23 Prevents paralleling of two incoming primary sources through the primary tie bus disconnect or secondary tie bus breaker. Prevents
operation (open or closed) of disconnects under load. Permits one power source to supply both loads through either the primary or
secondary tie bus.
Scheme #24 Prevents paralleling of two incoming primary sources. Prevents operation (open or closed) of disconnects under load. Permits the
isolating of breakers for servicing. Permits one power source to supply both loads through tie bus.

Interrupter Switch
Scheme #25 Prevents opening fuse compartment door when the interrupter switch is closed. Prevents closing interrupter switch until fuse
compartment door is locked closed.
Scheme #26 Prevents operation (open or closed) of interrupter switch when breaker is closed. Permits the breaker to be serviced and operated
while the interrupter switch is locked open.
Table Of Contents
Purpose of Interlocking
Scheme# Function
Interrupter Switch
Scheme #27 Prevents operation (open or closed) of interrupter switch when breaker is closed. Prevents opening fuse compartment door when
interrupter switch is closed. Prevents closing interrupter switch until fuse compartment door is locked closed. Permits the breaker to
be serviced and operated while the interrupter switch is locked open.
Scheme #28 Prevents dropping load when shifting from one source to the other. Prevents opening both interrupter switches at the same time.
Permits both interrupter switches to be closed at the same time.
Scheme #29 Prevents paralleling two lines - requires dropping load when shifting from one source to the other. Prevents closing both interrupter
switches at the same time. Permits both interrupter switches to be opened at the same time.
Scheme #30 Prevents paralleling two lines - requires dropping load when shifting from one source to the other. Prevents closing both interrupter
switches at the same time. Permits both interrupter switches to be open at the same time. Prevents operation (open or closed) of
either interrupter switch when breaker is closed. Permits the breaker to be serviced and operated while both interrupter switches are
locked open.
Scheme #31 Prevents operation (closed, open or closed) of a three position interrupter switch when the breaker is closed. Permits the breaker to
be serviced and operated while the interrupter switch is locked open.
Scheme #32 Prevents operation (closed, open or closed) of a three position interrupter switch when the breaker is closed. Prevents opening fuse
compartment door when the interrupter switch is closed. Prevents closing interrupter switch until fuse compartment door is locked
closed. Permits the breaker to be serviced and operated while the interrupter switch is locked open.

Motor or Machinery Guard

Scheme #33 Prevents opening of guard when motor circuit is closed. Guard may be a door or fence gate that prevents access to moving parts, belts,
cutters, or any dangerous equipment.

Motor or Machinery Guard with Time Delay

Scheme #34 Prevents opening of guard (or door) for a predetermined time after removal of power (from motor, centrifuge, condensers, etc.)

Breakers and Generators

Scheme #35 Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Allows switching loads to a generator.

Scheme #36 Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Allows switching loads to two generators.

Capacitor Bank Access

Scheme #37 Prevents access to capacitor bank enclosure until capacitors have been grounded and discharged.

Scheme #38 Prevents access to capacitor bank enclosure until capacitors have been grounded and discharged - utilizing a Time Delay Key Release
Unit (TDKRU).

Uninterrupted Power Sources

Scheme #39 Prevents improper maintenance bypass of UPS equipment.

Scheme #40 Prevents improper maintenance bypass of UPS equipment.

Precipitator Access
Scheme #41 Prevents access to an electrostatic precipitator, scrubber, or baghouse until all power supplies have been de-energized and properly
grounded.

Scheme #42 Prevents access to an electrostatic precipitator, scrubber, or baghouse until all power supplies have been de-energized and properly
grounded.
Legend\Symbols

KIRK KIRK
Device normally open.
Detachable latch interlock,
Type D.
Device normally closed.
Interlock
Direction of key transfer. KIRK
Auxiliary switch 2 make,
Multi-cylinder 2 break. Type SS
A-1, A-2, A-3 Key interchange number. Detachable latch interlock,
Type D.
KIRK

KIRK

Interlock with key held.

Device in position as shown. KIRK

Transfer interlock, Type T. Interlock

KIRK
Auxiliary switch 3 make,
Interlock with key removed. 3 break. Type SSS
Device in position as
shown.
KIRK

KIRK
KIRK
Interlock used to lock Transfer interlock, Type T.
device open. 3 cylinder
L-O (with key removed)
Auxiliary switch
KIRK Type K
Interlock used to lock
KIRK
device open.
L-O
(with key held) KIRK

Key released after time delay.

KIRK
Interlock used to lock Transfer interlock, Type T. Time-delay key release unit
TM
device closed. 5 cylinder
L-C (with key removed) Initiating lock.

KIRK
Interlock used to lock
device closed.
L-C (with key held) Solenoid key release unit. Key
Padlock released when solenoid is E,
KIRK KIRK
Type P KIRK energized.
Interlock used to lock device
open and closed.
L-O-C
E
KIRK

KIRK
A3 Key Interchange number
(showing key held). Two key
Multi-lock interlock. Solenoid key release unit. Key
released when solenoid is E,
KIRK
energized.
KIRK

Initiating key
KIRK
Interlock with master lock. Interlock Key released when
(Also called apartment lock.) Auxiliary switch 1 make, solenoid is energized.
1 break. Type S E

E E
Key Removable Positions
A-2 A- 1
The “E” or “W” next to the interlock symbol indicates the position of the interlock bolt when the key is removable, “E” =
L-C A3
W
Extended, “W” = Withdrawn.

L-O For more information regarding key removable positions please reference the technical paper “How an Individual Key
Interlock Operates” on our website (Click on the 'APPS/Schemes' button, then click on 'Technical Papers', then click on
“How an Individual Key Interlock Operates”). Refer also to the Available Options on Data Sheets 1.1, 1.2, 1.3, 1.4, 1.5,
1.13 and to columns 8 & 9 on the Interlock Ordering Guide.
APPLICATION SCHEMES - Introduction
In order to lay out complicated interlock schemes, it is necessary to understand the simplest applications. On this page, the basic concepts of
interlocking are outlined and discussed.

Interlocking a Single Unit in One Position Interlocking Two Units in Two Positions

If it is desired to secure a device in the open position, an interlock is The other method for locking in both the open and closed positions
used as in Fig. 1. The possession of the key indicates requires two interlocks as show in Fig. 4. Possession of key A-1 indicates
that the device is locked open possession of key A-2 indicates that
the device is locked closed. The device is shown normally open;
therefore, key A-1 is free and the L-O interlock bolt is extended into its
recess provided in the movable member while key A-2 is held and the
A1 A-1 E A1 A-1 E L-C interlock bolt is withdrawn. To close the device, insert key A-1 in the
L-O lock and turn to withdraw bolt of L-O interlock, which permits the
L-O L-C device to be operated. Now the device can be moved to the closed
Fig. 1 Fig. 2 position. Key A-2 can be turned to extend the bolt of the L-C interlock
into its recess, which locks the device in the closed position.
that the device is in the open position and is locked by the extension of
the interlock bolt. When the key is inserted in the lock and turned to
withdraw the interlock bolt, the device is free to operate to the closed
position and the key is held in the lock. E E
A 1 A-1 A2

L-O L-C
When a device is to be locked only in the closed position an interlock is
used as shown in Fig. 2. The possession of the key indicates that the Fig. 4.
device is locked in the closed position, as the interlock bolt has been This releases Key A-2 from the L-C interlock. Meanwhile, key A-1 is held
extended to remove the key. When the key is inserted in the lock and in the L-O interlock since its withdrawn locking bolt cannot be
turned to withdraw the interlock bolt, the device is free to operate to extended.
the open position and the key is held in the lock.
This method is used more often than the single two-position interlock
Interlocking a Single Unit in Two Positions shown in Fig. 3, due to its adaptability to sequence operations. Also,
the possession of key A-1 or A-2 indicates that the device is locked
Two methods are used in interlocking a device in both open and open or locked closed, respectively.
closed position. The first method requires only one interlock as shown in
Fig. 3. The interlock bolt is extended in both the open and closed Sequence Interlocking
positions. This is accomplished with two recesses in the device that is
being interlocked - each coinciding with the locking bolt in one With the fundamentals developed above, it is quite simple to extend
position. the application to the interlocking of two or more devices in a desired
sequence.
A B

A 1 A-1 E
A-1 E A-1 E
A 1
L-O-C L-O L-O

Fig. 3 Fig. 5
Two devices are shown in Fig. 5. In operation they are not closed at
The possession of the key indicates that the interlock bolt is extended
the same time. With the interlocks arranged as shown, only one key is
and that the device is locked either in the open or closed position.
required in the interlocking system. Both devices are shown open;
Furthermore, the device cannot be operated until the key is inserted
therefore, the key is free. To close any one device, the key is inserted
and turned in the lock to withdraw the locking bolt. The key cannot be
and turned in that particular lock to withdraw the interlock bolt. The key
removed from the lock in an intermediate position, but in the fully
is held in this lock until the device is again locked open. This simple
open or closed positions only. However, in this application, possession
interlocking sequence lends itself to a multitude of applications. The
of the key gives no indication as to whether the device is locked
procedure is the same for two devices, neither of which is to be
closed or open.
opened at the same time.
Scheme 1 Scheme 3
To prevent opening of switch A when breaker B is closed. To prevent operation of switch A when breaker B is closed. Circuit
cannot be cleared until proper supervisory key is obtained.
A
B
A
B
A-1 E A 1 E

L-C L-O
W A-2 A 2
SUPERVISORY
Switch A and breaker B are in closed position. Key A-1 is held in breaker A-1 E A 1 E KEY

B interlock.
L-O-C L-O
1. Open breaker.
2. Turn key A-1 in L-O interlock on breaker B to lock open. Key A-
1 is now free.
3. Insert key A-1 in L-C interlock on switch A and turn to unlock.
4. Open switch A. Key A-1 is now held. Breaker B and switch A shown closed. Key A-1 held in breaker interlock.
Key A-2 retained by supervisor.
Reverse sequence to restore service.

1. Obtain key A-2 from supervisor.

2. Open breaker.
Scheme 2 3. Insert key A-2 in L-O interlock on breaker B and turn key A-1 to
lock open. key A-2 is now held and key A-1 is free.
4. Insert key A-1 in L-O-C interlock on switch A and turn to
To prevent operation of switch A when breaker B is closed. Permits re- unlock.
closing of breaker for servicing when switch is locked open. 5. Open switch A.
6. Turn key A-1 in L-O-C interlock on switch A to lock open. Key
A A-1 is now free.
7. Return key A-1 to breaker interlock and unlock for operation
B during servicing period.

Reverse sequence to restore service.

A-1 E A 1 E

L-O-C L-O Scheme 4

To prevent closing of grounding switch B when main switch A is closed,
and vice versa.
A
B A

A-1 A 1

L-O-C L-O B
A 1 E A-1 E
Switch A and breaker B are in closed position. Key A-1 is held in breaker
L-O L-O
B interlock.

1. Open breaker.
2. Turn key A-1 in L-O interlock on breaker B to lock open. Key A- Main switch A shown closed and grounding switch B shown open. Key
1 is now free. A-1 is held in main switch interlock.
3. Insert key A-1 in L-O-C interlock on switch A and turn to
unlock. 1. Open main switch A.
4. Open switch A. Key A-1 is now held. 2. Turn key A-1 in L-O interlock on main switch A to lock open.
5. Turn key A-1 in L-O-C interlock on switch A to lock open. Key Key A-1 is now free.
A-1 is now free. 3. Insert Key A-1 in L-O interlock on grounding switch B and turn
6. Return Key A-1 to breaker interlock and unlock for operation to unlock. Key A-1 is now held.
during servicing period. 4. Close grounding switch B.

Reverse sequence to restore service. Reverse sequence to restore service.

Scheme 5
To prevent operation of disconnect switch A when breaker B is closed. To service breaker:
To prevent opening fuse compartment door when the disconnect 1. Open breaker.
switch A is closed. 2. Turn key A-1 in L-O interlock on breaker to lock breaker open.
Key A-1 is now free.
3. Insert key A-1 in L-O-C interlock on disconnecting switch and
turn to unlock. Key A-1 is now held.
A 4. Open disconnect.
5. Turn key A-1 in L-O-C interlock on disconnect switch to lock
B open. Key A-1 is now free.
6. Return key A-1 to breaker interlock and unlock for operation
of breaker during servicing.

Reverse sequence to restore service.

A-1 A2 A-2 A 1

L-O
To open fuse compartment door:
L-O-C L-C L-O
1. Proceed from normal position with operations as in 1
through 4 above.
2. Turn key A-2 in L-O interlock on disconnect switch to lock
open. Key A-2 is now free.
3. Insert key A-2 in L-C interlock on fuse compartment door
and turn to unlock. Key A-2 is now held.
Breaker, fuse compartment door and disconnect switch are shown in 4. Open fuse compartment door.
closed positions. Key A-1 is held in breaker interlock and key A-2 is held
in disconnect interlock. Reverse sequence to restore service.

Scheme 6

To prevent operation of disconnect switch A when breakers B, C, D and Disconnect A and breakers B, C, D and E are shown in closed position.
E are closed. Breakers may be opened in any sequence. Key A-1 is held in transfer interlock. Keys A-2, A-3, A-4 and A-5 are held
in interlocks on breaker B, C, D and E.
NOTE: Electrical circuit is equivalent of Scheme 7.
1. Open breakers B, C, D and E.
W A-5
2. Turn key in L-O interlock on each breaker B, C, D and E to
A lock breakers open. Keys A-2, A-3, A-4 and A-5 are now free.
A-1
W A-4 3. Insert keys A-2, A-3, A-4 and A-5 in transfer interlock.
L-O-C
W A-3
4. Turn key A-1 in transfer interlock. Key A-1 is now free. Keys A-
2, A-3, A-4 and A-5 are now held.
W A-2 5. Insert key A-1 in L-O-C interlock on disconnect A and turn to
unlock. Key A-1 is now held.
A 1 E
6. Open disconnect A.
T
7. Turn key A-1 in L-O-C interlock on disconnect A to lock open.
Key A-1 is now free.
8. Insert key A-1 in transfer interlock and turn. Key A-1 is now
held, Keys A-2, A-3, A-4 and A-5 are now free.
B C D E 9. Return keys A-2, A-3, A-4 and A-5, as desired, to breaker
A2 A3 A4 A5 interlocks and unlock for operation during servicing.
L-O L-O L-O L-O
Reverse sequence to restore service.
Scheme 7 Scheme 8
To prevent operation of disconnect switch A when breakers B, C, D and To prevent operation of disconnects A and B when breaker C is
E are closed. Breakers must be opened in pre-arranged sequence. closed. To permit servicing of breaker when disconnects are locked
open.

NOTE: Electrical circuit is equivalent of Scheme 6.

A A B
A-1 A5

L-O-C
SUPERVISORY C
KEY

E E E E E
A2 A-1 A 1 A 1 A-2
B W C W D W E W
A-2 A-3 A-4 A-5 L-O L-C L-O L-O L-C
A 1 A2 A3 A4

L-O E L-O
E L-O
E L-O
E

Disconnect A and breakers B, C, D and E are shown in closed position. Breaker C and disconnects A and B are shown closed. One key A-1 is
Key A-1 is held in breaker B interlock, key A-2 is held in breaker C held in breaker L-O interlock and the other key A-1 is held in L-O
interlock, key A-3 is held in breaker D interlock and key A-4 is held in interlock on disconnect B. Key A-2 is held in L-O interlock
breaker E interlock. Key A-5 is held free in breaker E interlock or is on disconnect A.
retained by supervisor.
1. Open breaker.
1. Obtain key A-5 from supervisor. 2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
2. Open breaker E. is now free.
3. Insert key A-5 in L-O interlock on breaker E and turn key A-4 to 3. Insert key A-1 in L-C interlock on disconnect A and turn to
lock open. Key A-5 is now held. Key A-4 is now free. unlock. Key A-1 is now held.
4. Open breaker D. 4. Open disconnect A.
5. Insert key A-4 in L-O interlock on breaker D and turn key A-3 to 5. Turn key A-2 in L-O interlock on disconnect A to lock open.
lock open. key A-4 is now held. key A-3 is now free. Key A-2 is now free.
6. Open breaker C. 6. Insert key A-2 in L-C interlock on disconnect B and turn to
7. Insert key A-3 in L-O interlock on breaker C and turn key A-2 to unlock. Key A-2 is now held.
lock open. Key A-3 is now held. Key A-2 is now free. 7. Open disconnect B.
8. Open breaker B. 8. Turn key A-1 in L-O interlock on disconnect B to lock open.
9. Insert key A-2 in L-O interlock on breaker B and turn key A-1 to Key A-1 is now free.
lock open. Key A-2 is now held. Key A-1 is now free. 9. Insert key A-1 in breaker L-O interlock and turn to unlock for
10. Insert key A-1 in L-O-C interlock on disconnect A and turn to operation during servicing.
unlock. Key A-1 is now held.
11. Open disconnect A. Reverse sequence to restore service.
12. Turn key A-1 in L-O-C interlock on disconnect A to lock open.
Key A-1 is now free.
13. Insert key A-1 in L-O interlock on breaker B and turn to unlock.
Key A-1 is now held and key A-2 is now free.
14. Breaker B may now be operated for servicing.
15. Insert key A-2 in L-O interlock on breaker C and turn to unlock.
Key A-2 is now held and Key A-3 is now free.
16. Breaker C may now be operated for servicing.
17. Insert key A-3 in L-O interlock on breaker D and turn to unlock.
Key A-3 is now held and key A-4 is now free.
18. Breaker D may now be operated for servicing.
19. Insert key A-4 in L-O interlock on breaker E and turn to unlock.
Key A-4 is now held and supervisor Key A-5 is now free.
20. Breaker E may now be operated for servicing.

Reverse sequence to restore service.

Scheme 9
To prevent operation of disconnects A and B with breaker C closed. To Disconnects A and B, breaker C, and door are normally closed. Keys
prevent access to breaker compartment with disconnects closed. A-1 are held in L-O interlock on breaker C and L-O interlock on
disconnect B. Key A-2 is held in the L-O interlock on disconnect A. Key
A-3 is held in L-O interlock on disconnect B.

E 1. Open breaker.
A 1 2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
is now free.
L-O 3. Insert key A-1 in L-C interlock on disconnect A and turn to
unlock. Key A-1 is now held.
A B 4. Open disconnect A.
5. Turn key A-2 in L-O interlock on disconnect A to lock open.
C Key A-2 is now free.
6. Insert key A-2 in L-C interlock on disconnect B and turn to
unlock. Key A-2 is now held.
7. Open disconnect B.
8. Turn keys A-1 and A-3 in L-O interlock on disconnect B to
E E E E
lock open. Keys A-1 and A-3 are now free.
A-1 A2 A-2 A 1 9. Insert key A-1 in breaker L-O interlock and turn to unlock for
E
E
operation during servicing.
A-3 10. Insert key A-3 in L-C interlock (type D) on compartment door
L-C L-O L-C A3
and turn to unlock. Key A-3 is now held.
L-C 11. Open compartment door to service breaker.
L-O

Reverse sequence to restore service.

Scheme 10

To prevent operation of disconnects A and B and by-pass disconnect To transfer load from breaker and disconnects to by-pass switch:
C under load. Provides for closing of by-pass disconnect C before
breaker circuit is opened, or permits breaker circuit to be opened with 1. Obtain key A-3 which is free and insures that both
by-pass disconnect C remaining open. disconnects A and B are locked closed.
2. Insert key A-3 in L-C interlock on breaker D and turn to lock
Disconnects A and B and breaker D normally closed. By-pass closed. Key A-3 is held and key A-4 is now free.
disconnect C normally open. Keys A-1, A-2, and A-4 normally held in 3. Insert key A-4 in L-O-C interlock on by-pass disconnect C and
locks as indicated. Key A-3 normally free. turn to unlock. Key A-4 is now held.
4. Close by-pass disconnect C.
5. Turn key A-4 in L-O-C interlock on by-pass disconnect C to
lock closed. Key A-4 is now free.
E
A-4 6. Insert key A-4 in L-C interlock on breaker D and turn to unlock.
Key A-4 is held and key A-3 is now free.
L-O-C
7. Open breaker D.
8. Turn key A-1 in L-O interlock on breaker D to lock open. Key A-
C 1 is now free.
9. Insert keys A-1 and A-3 in L-C interlock on disconnect A and
turn to unlock. Keys A-1 and A-3 are now held.
10. Open disconnect A.
11. Turn key A-2 in L-O interlock on disconnect A to lock open.
A B Key A-2 is now free.
D 12. Insert key A-2 in L-C interlock on disconnect B and turn to
unlock. Key A-2 is now held.
13. Open disconnect B.
14. Turn key A-1 in L-O interlock on disconnect B to lock open.
Key A-1 is now free.
15. Insert key A-1 in L-O interlock on breaker D and turn to unlock
E E E W E E
A 3 A 1 A-2
to permit operation during servicing.
A 2 A1 A-3
E E
A 4
To open disconnects A and B and breaker D, leaving by-pass
L-O A-1 L-O L-O L-C
disconnect C open:
L-C L-C
1. Proceed from normal position with operations as in 7 to 15
above.
Scheme 10A Scheme 11
To prevent operation of disconnect A and B and by-pass disconnect C To prevent paralleling of lines A and B. Single load, fed from either
under load. Permits by-pass disconnect C to operate only when source.
regulator is in neutral position. Permits isolating regulator for servicing.

A-1 A 2

L-O L-C

C
A B
Disconnect C shown closed and disconnect D shown open. Key A-1 is
REGULATOR held in disconnect C interlock.

1. Open switch C.
2. Turn key A-1 in L-O interlock on switch C to lock open. Key A-1
is now free.
3. Insert key A-1 in L-O interlock on switch D and turn to unlock.
A-3 A1 A 1 A-2 A3 Key A-1 is now held.
4. Close switch D.
L-C L-O L-N L-C L-O
Reverse sequence to restore service through switch C.

Disconnects A and B are normally closed. Regulator is normally in

operation. By-pass disconnect C is normally open.

One key A-1 is held in regulator L-N (locked neutral) interlock and the
second key A-1 is held in L-O interlock on disconnect A. Key A-2 is held
in L-C interlock on disconnect C. Key A-3 is held in L-O interlock on
disconnect B.

1. Operate regulator to neutral position.

2. Turn key A-1 in L-N interlock on regulator to lock in neutral
position. Key A-1 is now free.
3. Insert key A-1 in L-O interlock on by-pass disconnect C and
turn to unlock. Key A-1 is now held.
4. Close by-pass disconnect C.
5. Turn key A-2 in L-C interlock on by-pass disconnect C to lock
closed. Key A-2 is now free.
6. Insert key A-2 in L-C interlock on disconnect B and turn to
unlock. Key A-2 is now held.
7. Open disconnect B.
8. Turn key A-3 in L-O interlock on disconnect B to lock open. Key
A-3 is now free.
9. Insert key A-3 in L-C interlock on disconnect A and turn to
unlock. Key A-3 is now held.
10. Open disconnect A.
11. Turn key A-1 in L-O interlock on disconnect A to lock open. Key
A-1 is now free.
12. Insert key A-1 in regulator L-N interlock and turn to unlock. This
permits regulator to be operated during inspection and
servicing.

Reverse sequence to restore service.

Scheme 12
To prevent paralleling of lines A and B. Single load, fed from either 3. Insert key A-1 in L-O-C interlock on disconnect A and turn to
source. To prevent operation of disconnect switches A and B when unlock. Key A-1 is now held.
breaker C is closed. 4. Open disconnect A.
5. Turn key A-1 in L-O-C interlock on disconnect A to lock open.
Key A-1 is now free.
A A B B 6. Return key A-1 to breaker interlock and unlock for operation
of breaker during servicing.

To transfer load from line A to line B:

C 1. Open breaker C.
2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
A2 A-1 A-1 A-2 is now free.
A 1 3. Insert key A-1 in L-O-C interlock on disconnect A and turn to
L-O L-O-C L-O-C L-O unlock. Key A-1 is now held.
L-O 4. Open disconnect A.
5. Turn key A-1 in L-O-C interlock and key A-2 in L-O interlock on
disconnect A to lock open. Keys A-1 and A-2 are now free.
6. Insert key A-1 in L-O-C interlock on disconnect B and turn to
unlock. Key A-1 is now held.
7. Insert key A-2 in L-O interlock on disconnect B and turn to
Breaker C and disconnect A are shown in closed position. Disconnect unlock. Key A-2 is now held.
B is shown in open position. Key A-1 is held in breaker C interlock. Key A- 8. Close disconnect B.
2 is held in L-O interlock on disconnect A. 9. Turn key A-1 in L-O-C interlock on disconnect B to lock
closed. Key A-1 is now free.
To service breaker: 10. Insert key A-1 in breaker interlock and turn to unlock. Key A-1
is now held.
1. Open breaker C. 11. Close breaker.
2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
is now free. Reverse sequence to restore service through line A.

Scheme 13
To prevent paralleling of lines A and B. Two loads, fed from either source. Breaker A is closed to supply load M. Breaker B is closed to supply load
N. Tie-breaker C is open. Keys A-1 are held in interlocks on both
breakers A and B. Tie-breaker C cannot be closed unless either A or B
is locked open.

To transfer load N to breaker A:

1. Open breaker B
2. Turn key A-1 in L-O interlock on breaker B to lock open. Key
A B A-1 is now free.
3. Insert key A-1 in L-O interlock on tie-breaker C and turn to
unlock. Key A-1 is now held.
C 4. Close tie-breaker C.

Reverse sequence to restore service.

M N Load M can be supplied through breaker B in a similar manner.

Scheme 14 Scheme 15 - (Continued)
To prevent paralleling of lines A and B. Two loads, fed from either source
(one tie-breaker). To prevent operation of disconnect switch D when
breaker A is closed. To prevent operation of disconnect switch E when
D E
breaker B is closed.
A-2 A 3 A 5 A-4

L-O-C L-O L-O L-O-C

D E
A-2 A-3
A-3 A-5

L-O-C L-O-C A-2 A-4

L-C L-C

A B
A2 A 3
A B
C A2 A 4
C
L-O L-O A 1 A 1

M N L-O L-O

Disconnect switches D and E and breakers A and B are closed. Breaker M N

A closed to supply load M. Breaker B closed to supply load N. Tie-
breaker C is open. Keys A-1 and A-2 are held in interlock on breaker A. Disconnect switch D and breaker A are closed to supply load M. Disconnect
Keys A-1 and A-3 are held in interlock on breaker B. Tie-breaker C switch E and breaker B are closed to supply load N. Tie-breaker C is open.
cannot be closed until either breaker A or B is locked open. Keys A-1 and A-2 are held in interlock on breaker A. Key A-3 is held in L-O
interlock on disconnect D. Keys A-1 and A-4 are held in interlock on breaker
To transfer load N to breaker A: B. Key A-5 is held in L-O interlock on disconnect E. Tie-breaker C cannot be
closed until either breaker A or B is locked open.
1. Open breaker B.
To transfer load N to breaker A, proceed as follows:
2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A-
1. Open breaker B.
1 and A-3 are now free.
2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A-1
3. Insert key A-1 in L-O interlock on tie-breaker C and turn to and A-4 are now free.
unlock. Key A-1 is now held. 3. Insert key A-1 in L-O interlock on tie-breaker C and turn to unlock.
4. Close tie-breaker C. Key A-1 is now held.
4. Close tie-breaker C.
Reverse sequence to restore service through breaker B. Load M can be
Reverse sequence to restore service through breaker B. Load M can be supplied through breaker B in a similar manner.
supplied through breaker B in a similar manner.
To service breaker B, proceed as follows:
1. Open breaker B.
To service breaker B: 2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A-1
and A-4 are now free.
1. Open breaker B. 3. Insert key A-4 in L-O-C interlock on disconnect E and turn to
2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A- unlock. Key A-4 is now held.
4. Open disconnect E.
1 and A-3 are now free.
5. Turn key A-4 in L-O-C interlock on disconnect E to lock open. Key
3. Insert key A-3 in L-O-C interlock on disconnect E and turn to
A-4 is now free.
unlock. Key A-3 is now held. 6. Return key A-4 to L-O interlock on breaker B and unlock for
4. Open disconnect E. operation of breaker during servicing.
5. Turn key A-3 in L-O-C interlock on disconnect E to lock open. Reverse sequence to restore service. Breaker A can be serviced in a similar
Key A-3 is now free. manner.
6. Return key A-3 to L-O interlock on breaker B and unlock for
operation of breaker during servicing. To enter fuse compartment on line B, proceed as follows:
1. Open breaker B.
Reverse sequence to restore service. Breaker A can be serviced in a 2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A-1
similar manner. and A-4 are now free.
3. Insert key A-4 in L-O-C interlock on disconnect E and turn to
unlock. Key A-4 is now held.
4. Open disconnect E.
5. Turn key A-4 in L-O-C interlock on disconnect E to lock open. Key
Scheme 15 A-4 is now free.
6. Turn key A-5 in L-O interlock on disconnect E to lock open. Key A-5
To prevent paralleling of lines A and B. Two loads, fed from either source (one is now free.
tie-breaker). To prevent operation of disconnect D when breaker A is closed. 7. Insert keys A-4 and A-5 in L-C interlock on fuse compartment door
To prevent operation of disconnect switch E when breaker B is closed. To and turn to unlock. Keys A-4 and A-5 are now held.
prevent opening fuse compartment door when the associated disconnects 8. Open fuse compartment door.
D or E and breakers A and B are closed. Reverse sequence to restore service. Fuse compartment on line A can be
entered in a similar manner.
Scheme 16
To prevent paralleling of lines A, B, and C. Three loads, fed from any Tie-breaker D interlock has a master or apartment lock and can be
source (two tie-breakers). unlocked for operation with either keys A-1 or B-1. Tie-breaker E has a
master or apartment lock and can be unlocked for operation with
either keys B-1 or C-1.
A B C
To transfer load M from Breaker A to breaker B:
1. Open breaker A
A1 A B1 B C1 C 2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A-
1 is now free.
3. Insert Key A-1 in L-O interlock on tie-breaker D and turn to
unlock. Key A-1 is now held.
D E 4. Close tie-breaker D.

Reverse sequence to restore service through breaker A.

A-1 B-1
B-1 C-1
To transfer load M and N from breakers A and B to breaker C:
L-O L-O
1. Close tie-breaker D as above.
2. Turn key B-1 in L-O interlock on breaker B to lock open. Key B-
1 is now free.
M N P
3. Insert key B-1 in L-O interlock on tie-breaker E and turn to
unlock. Key B-1 is now held.
4. Close tie-breaker E.

Breaker A is closed to supply load M. Breaker B is closed to supply load Reverse sequence to restore service (M and N through breakers A
N. Breaker C is closed to supply load P. Keys A-1, B-1, and C-1 are held and B).
in L-O interlocks of breakers A, B, and C. Tie-breakers D and E are Any of the loads M, N, or P can be transferred from its own supply to
locked open. any adjacent supply.

Scheme 17
To prevent paralleling lines A, B, C, and D. Four loads, fed from any To transfer load M from breaker A to breaker B:
source (three tie-breakers).
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A-1 is
now free.
A B C D 3. Insert key A-1 in L-O interlock on tie-breaker E and turn to unlock.
Key A-1 is now held.
4. Close tie-breaker E.
E E E E
A1 A B1 B C1 C D1 D
Reverse sequence to restore service through breaker A.

To transfer load M and N from breaker A and B to breaker C:

E F G 1. Close tie-breaker E as above.

2. Open breaker B.
3. Turn key B-1 in L-O interlock on breaker B to lock open. Key B-1 is
E E E
A-1 B-1 C-1
now free.
B-1 C-1 D-1 4. Insert key B-1 in L-O interlock on tie-breaker F and turn to unlock.
L-O L-O L-O Key B-1 is now held.
5. Close tie-breaker F.
M N P R
Reverse sequence to restore service (M and N) through breakers A and B.

To transfer load R from breaker D to breaker C:

Breaker A is closed to supply load M. Breaker B is closed to supply load
1. Open breaker D.
N. Breaker C is closed to supply load P. Breaker D is closed to supply
2. Turn key D-1 in L-O interlock on breaker D to lock open. Key D-1 is
load R. Keys A-1, B-1, C-1, and D-1 are held in L-O interlocks of
now free.
breakers A, B, C, and D. Breakers E, F and G are locked open. Breaker E 3. Insert key D-1 in L-O interlock on tie-breaker G and turn to unlock.
interlock has a master or apartment lock and can be unlocked for Key D-1 is now held.
operation with either key A-1 or B-1. Breaker F interlock has a master or 4. Close tie-breaker G.
apartment lock and can be unlocked for operation with either key B-1
or C-1. Breaker G interlock has a master or apartment lock and can be Reverse sequence to restore service through breaker D.
unlocked for operation with either key C-1 or D-1. Any of the loads M, N, P, or R can be transferred from its own supply to any
adjacent supply.
Scheme 17A

To prevent paralleling lines A, B, C, and D. To prevent opening All loads can be transferred as described in scheme 17.
rear access doors when breakers are energized.
To open rear access doors K-1, K-2, and K-3:
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock
open. Key A-1 is now free.
ACCESS ACCESS ACCESS ACCESS ACCESS ACCESS ACCESS ACCESS ACCESS 3. Open breaker B.
DOOR DOOR DOOR DOOR DOOR DOOR DOOR DOOR DOOR
#1 #2 #3 #4 #5 #6 #7 #8 #9 4. Turn key B-1 in L-O interlock on breaker B to lock open.
E E E E E E E E E
Key B-1 is now free.
K-1 K-2 K-3 K-4 K-5 K-6 K-7 K-8 K-9 5. Insert key A-1 and B-1 in transfer interlock.
L-C L-C L-C L-C L-C L-C L-C L-C L-C 6. Turn key A-1 in transfer interlock. Keys K-1, K-2, and K-
3 are now free. Keys A-1 and B-1 are now held.
7. Insert keys K-1, K-2, and K-3 in their respective rear
access door interlocks and turn to unlock. Keys K-1,
K-2, and K-3 are now held.
K3 W K9
W K6 W
8. Open the rear access doors.
K2 W K5 W W K8
Reverse sequence to restore service.
K1 W K4 W K7 W

E B-1 E C-1 E D-1 To open rear access doors K-4, K-5 and K-6
A-1 E B-1 E C-1 E
1. Open breaker B.
T T T 2. Turn key B-1 in L-O interlock on breaker B to lock open.
Key B-1 is now free.
3. Open breaker C.
A B C D 4. Turn key C-1 in L-O interlock on breaker C to lock
E E E E
open. Key C-1 is now free.
A1 A B1 B C1 C D1 D 5. Insert key B-1 and C-1 in transfer interlock.
6. Turn key B-1 in transfer interlock. Keys K-4, K-5, and K-
6 are now free. Keys B-1 and C-1 are now held.
7. Insert keys K-4, K-5, and K-6 in their respective rear
E F G
access door interlocks and turn to unlock. Keys K-4,
K-5, and K-6 are now held.
E E E 8. Open the rear access doors.
A-1 B-1 C-1
B-1 C-1 D-1
L-O L-O L-O Reverse sequence to restore service.

M N P R To open rear access doors K-7, K-8 and K-9

1. Open breaker C.
2. Turn key C-1 in L-O interlock on breaker C to lock
open. Key C-1 is now free.
3. Open breaker D.
4. Turn key D-1 in L-O interlock on breaker D to lock
open. Key D-1 is now free.
Breakers A, B, C, and D are closed to supply their respective 5. Insert key C-1 and D-1 in transfer interlock.
loads. Keys A-1, B-1, C-1, and D-1 are held in L-O interlocks of 6. Turn key C-1 in transfer interlock. Keys K-7, K-8, and K-
breakers A, B, C, and D. Tie-Breakers E, F, and G are locked 9 are now free. Keys C-1 and D-1 are now held.
open. Breaker E interlock has an apartment lock and can be 7. Insert keys K-7, K-8, and K-9 in their respective rear
unlocked for operation with either key A-1 or B-1. Breaker F access door interlocks and turn to unlock. Keys K-7,
interlock has an apartment lock and can be unlocked for K-8, and K-9 are now held.
operation with either key B-1 or C-1. Breaker G interlock has an 8. Open the rear access doors.
apartment lock and can be unlocked for operation with either
key C-1 or D-1. All rear access doors are locked closed. All Reverse sequence to restore service.
keys for rear access doors (K-1 through K-9) are held in transfer
interlocks.
Scheme 18 Scheme 19
To prevent paralleling of lines A, B, and C. Three loads, fed from any To prevent paralleling lines A, B, C, and D. Four loads fed from any source
source (three tie-breakers). (four tie-breakers).
A B C D
A B C

A1 A B1 B C1 C D1 D
A1 A B1 B C1 C

B-1
C-1

L-O
D E
E F G
N
A-1 C-1
A-1 B-1 A-1
B-1 D-1
B-1 C-1 L-O
D-1
L-O
L-O L-O L-O

A-1 E H
C-1
L-O M N P R

A E B
Breaker A is closed to supply load M.
F Breaker B is closed to supply load N.
H F
Breaker C is closed to supply load P.
M P Breaker D is closed to supply load R. D C
G

Breaker A is closed to supply load M. Breaker B is closed to supply load Keys A-1, B-1, C-1, and D-1 are held in L-O interlocks of breakers A, B, C, and
N. Breaker C is closed to supply load P. Keys A-1, B-1, and C-1 are held D. Tie breakers E, F, G, and H are locked open. Breaker E interlock has a
master or apartment lock and can be unlocked with either key A-1 or B-1.
in L-O interlocks on breakers A, B and C. Tie-breakers D, E, and F are Breaker F interlock has a master or apartment lock and can be unlocked
locked open. Master or apartment lock interlocks are mounted on tie- with either key B-1 or C-1. Breaker G interlock has a master or apartment lock
breakers D, E, and F, and can be unlocked for operation with either and can be unlocked with either key C-1 or D-1. Breaker H interlock has a
keys A-1 or B-1, B-1 or C-1, and A-1 or C-1, respectively. master or apartment lock and can be unlocked with either key A-1 or D-1.

To transfer load M from breaker A to breaker B:

A
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A-1 is
D F now free.
3. Insert key A-1 in L-O interlock on tie-breaker E and turn to unlock.
Key A-1 is now held.
C

E
B

4. Close tie-breaker E.
To transfer load M from breaker A to breaker B: Reverse sequence to restore service through breaker A.
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A- To transfer load M and N from breaker A and B to breaker C:
1 is now free. 1. Close tie-breaker E as above.
3. Insert key A-1 in L-O interlock on tie-breaker D and turn to 2. Open breaker B.
3. Turn key B-1 in L-O interlock on breaker B to lock open. Key B-1 is
unlock. Key A-1 is now held. now free.
4. Close tie-breaker D. 4. Insert key B-1 in L-O interlock on tie-breaker F and turn to unlock.
Reverse sequence to restore service through breaker A. Key B-1 is now held.
5. Close tie-breaker F.
To transfer load M and N from breakers A and B to breaker C: Reverse sequence to restore service (M and N) through breakers A and B.
1. Close tie-breaker D as above.
2. Open breaker B. To transfer load R from breaker D to breaker C:
3. Turn key B-1 in L-O interlock on breaker B to lock open. Key B- 1. Open breaker D.
1 is now free. 2. Turn key D-1 in L-O interlock on breaker D to lock open. Key D-1 is
now free.
4. Insert key B-1 in L-O interlock on tie-breaker E and turn to
3. Insert key D-1 in L-O interlock on tie-breaker G and turn to unlock.
unlock. Key B-1 is now held. Key D-1 is now held.
5. Close tie-breaker E. 4. Close tie-breaker G.
Reverse sequence to restore service (loads M and N) through breakers Reverse sequence to restore service through breaker D.
A and B.
To transfer load M from breaker A to breaker D:
To transfer load P from breaker C to breaker A: 1. Open breaker A.
1. Open breaker C. 2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A-1 is
2. Turn key C-1 in L-O interlock on breaker C to lock open. Key now free.
3. Insert key A-1 in L-O interlock on tie-breaker H and turn to unlock.
C-1 is now free. Key A-1 is now held.
3. Insert key C-1 in L-O interlock on tie breaker F and turn to 4. Close tie-breaker H.
unlock. Key C-1 is now held. Reverse sequence to restore service through breaker A.
4. Close tie-breaker F. Any of the loads M, N, P, or R can be transferred from its own supply to any
Reverse sequence to restore service through breaker C. adjacent supply.
Scheme 20
To prevent paralleling three power sources through a common tie bus not Breakers A, B, and C are normally closed. Breakers D, E, and F are normally
normally in service. To permit feeding any load bus from a second power open. Under normal conditions keys A-1 and A-5 are held in breaker A
source through the tie bus. To permit one power source to supply all three interlock, keys A-2 and A-5 are held in breaker B interlock, and keys A-3 and
load busses through the tie bus. A-5 are held in breaker C interlock.

To transfer load from line No. 1 to line No. 2 or line No. 3 through the tie
bus, proceed as follows:

Line 1 Line 2 Line 3 1. Open breaker A.

2. Turn key A-1 in L-O interlock on breaker A to lock breaker open.
Keys A-1 and A-5 are now free.
3. Insert key A-1 in L-O interlock on breaker D and turn to unlock.
Key A-1 is now held.
4. Close breaker D.
5. Insert key A-5 in L-O interlock on either breaker E or F and turn to
A A5 B A5 C A5
unlock. Key A-5 is now held.
A1 A2 A3
6. Close breaker E or F (whichever is selected).

L-O L-O L-O Reverse sequence to restore load to line No. 1.

Load Bus Load Bus Load Bus To transfer load from lines No. 1 and No. 2 to line No. 3 through tie bus,
proceed as follows:

1. Close breaker D as per steps 1 to 4 above.

D A-1 E A-2 F A-3 2. Open breaker B.
A-5 A-5 A-5 3. Turn key A-2 in L-O interlock on breaker B to lock breaker open.
Keys A-2 and A-5 are now free.
L-O L-O L-O
4. Insert key A-2 in L-O interlock on breaker E and turn to unlock.
Key A-2 is now held.
5. Close breaker E.
6. Insert one of the A-5 keys from either breaker A or B in L-O
Tie Bus interlock on breaker F and turn to unlock. Key A-5 is now held.
7. Close breaker F.

Reverse sequence to restore load to lines No. 1 and No. 2.

Scheme 21
To prevent paralleling three power sources through a common tie bus not Breakers A, B, and C are normally closed. Breakers D, E, and F are normally
normally in service. To permit feeding any load bus from a second power open. Under normal conditions key A-1 is held in breaker A interlock, key A-2
source through the tie bus only when authorized by supervisor. To permit is held in breaker B interlock, and key A-3 is held in breaker C interlock. Key
one power source to supply all three load busses through the tie bus only A-5 is retained by supervisor.
when authorized by supervisor.
To transfer load from line No. 1 to line No. 2 or line No. 3 through tie bus,
proceed as follows:
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock breaker open.
Line 1 Line 2 Line 3
Key A-1 is now free.
3. Insert key A-1 in L-O interlock on breaker D and turn to unlock.
Key A-1 is now held.
4. Close breaker D.
5. Insert supervisor's key A-5 (only one A-5 is available) in L-O
interlock on either breaker E or F and turn to unlock. Key A-5 is
A A1
B A2
C A3
now held.
6. Close breaker E or F (whichever is selected).

Reverse sequence to restore load to line No. 1.

Load Bus Load Bus Load Bus

To transfer load from lines No. 1 and No. 2 to line No. 3 through tie bus,
proceed as follows:
A-1 A-2 A-3 1. Close breaker D as per steps 1 to 4 above.
D E F 2. Open breaker B.
A-5 A-5 A-5
3. Turn key A-2 in L-O interlock on breaker B to lock breaker open.
L-O L-O L-O Key A-2 is now free.
4. Insert key A-2 in L-O interlock on breaker E and turn to unlock. Key
A-2 is now held.
5. Close breaker E.
6. Insert supervisor's key A-5 in L-O interlock on breaker F and turn to
Tie Bus unlock. Key A-5 is now held.
A 5
7. Close breaker F.
SUPERVISORY
KEY
Reverse sequence to restore load to lines No. 1 and No. 2.
Scheme 22 Scheme 23 (Continued)
To prevent paralleling incoming primary sources, lines 1 and 2, through
primary tie bus disconnect. To prevent operation (open or closed) of the Line 1 Line 2
disconnects under load. Permits one power source to supply both loads
through tie bus.

Line 1 Line 2
D E
A2 A4 A4 A2

C D L-O A-1 A1 A-4 A-3 L-O

A2 A4 A4 A2
L-C A3 A-2 L-C

L-O A-1 A1 A-4 A-3 L-O

L-C L-O
L-C A3 A-2 L-C

L-C L-O
T

T
A5 A C B A5

A1 A3
A B A3 A-5
L-O L-O

L-O L-O L-O

Load 1 Load 2
Load 1 Load 2

Under normal conditions breakers A and B are closed, disconnects C and

Under normal conditions breakers A and B are closed, breaker C is locked
D are locked closed, and tie bus disconnect T is locked open. Keys A-1 are
open, disconnects D and E are locked closed, and tie disconnect T is
held in L-O interlock on breaker A and L-C interlock on tie bus disconnect T.
locked open. Keys A-1 are held in L-O interlock on breaker A and L-C
Keys A-2 are held in L-O interlock on disconnects C and D. Keys A-3 are
interlock on primary tie bus disconnect T. Keys A-2 are held in L-O interlocks
held in L-O interlock on breaker B and L-C interlock on tie bus disconnect T.
on disconnects D and E. Keys A-3 are held in L-O interlock on breaker B and
Keys A-4 (free keys) are shown removably held in the L-C interlocks on
L-C interlock on primary tie bus disconnect T. Keys A-4 (free keys) are shown
disconnects C and D.
removably held in the L-C interlocks on disconnects D and E. Keys A-5 are
held in L-O interlocks on breakers A and B.
To transfer load No. 1 from line 1 to line 2 through bus tie disconnect T,
proceed as follows:
To transfer load No. 1 from line 1 to line 2 through primary bus tie disconnect
1. Open breaker A.
T, proceed as follows:
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A-1 is
1. Open breaker A.
now free.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Keys A-1
3. Insert key A-1 in L-C interlock on disconnect C and turn to unlock.
and A-5 are now free.
Keys A-1 and A-4 are now held.
3. Insert key A-1 and free key A-4 in L-C interlock on disconnect D
4. Open disconnect C.
and turn to unlock. Keys A-1 and A-4 are now held.
5. Turn key A-2 in L-O interlock on disconnect C to lock open. Key A-
4. Open disconnect D.
2 is now free.
5. Turn key A-2 in L-O interlock on disconnect D to lock open. Key A-
6. Insert keys A-2 and free key A-4 (from L-C interlock on disconnect
2 is now free.
D) in L-O interlock on bus tie disconnect T and turn to unlock.
6. Insert key A-2 and free key A-4 (from L-C interlock on disconnect
Keys A-2 and A-4 are now held.
E) in L-O interlock on primary bus tie disconnect T and turn to
7. Close tie bus disconnect T.
unlock. Keys A-2 and A-4 are now held.
8. Turn key A-3 in L-C interlock on disconnect T to lock closed. Keys
7. Close bus tie disconnect T.
A-1 and A-3 are now free.
8. Turn key A-3 in L-C interlock on bus tie disconnect T to lock closed.
9. Insert key A-1 in L-O interlock on breaker A and turn to unlock. Key
Keys A-1 and A-3 are now removable.
A-1 is now held.
9. Insert key A-1 in L-O interlock on breaker A and turn to unlock. Key
10. Close breaker A.
A-1 is now held.
Reverse sequence to restore load No. 1 to line 1. To transfer load No. 2
10. Close breaker A.
from line 2 to line 1 through bus tie disconnect T, proceed in a similar
Reverse procedure to restore service to line 1. Load No. 2 can be supplied
manner.
from No. 1 through the primary bus tie in a similar manner.

To transfer load No. 1 from line 1 to line 2 through the secondary tie breaker
C, proceed as follows:
1. Open breaker A.
Scheme 23 2. Turn key A-1 in L-O interlock on breaker A to lock open. Keys A-1
and A-5 are now removable.
To prevent paralleling incoming primary sources, lines 1 and 2, through the 3. Insert key A-5 in L-O interlock on tie breaker C and turn to unlock.
primary tie bus disconnect or the secondary tie bus breaker. To prevent Key A-5 is now held.
operation (open or closed) of the disconnects under load. Permits one 4. Close tie breaker C.
power source to supply both loads through either the primary or secondary Reverse procedure to restore service on line 1. Load No. 2 can be supplied
tie bus. from line No. 1 through the secondary tie breaker C in a similar manner.
Scheme 24
To prevent paralleling incoming primary sources, lines 1 and 2. To To transfer load No. 1 from line 1 to line 2 through bus tie disconnect T,
prevent operation (open or closed) of the disconnects under load. proceed as follows:
(Permits transformer primary disconnects K & L to open and close the
transformer magnetizing current.*) Permits isolating breakers for 1. Open breaker A.
servicing. Permits one power source to supply both loads through tie 2. Turn key A-2 in L-O interlock on breaker A to lock open. Key
bus. A-2 is now free.
3. Open breaker C.
4. Turn key A-4 in L-O interlock breaker C to lock open. Keys A-1
and A-4 are now free.
Line 1 Line 2 5. Insert key A-2 from L-O interlock on breaker A and key A-1
from L-O interlock on breaker C in L-C interlock on
disconnect F and turn to unlock. Keys A-1 and A-2 are now
held.
E G 6. Open disconnect F.
A-3 A2 B2 B-3
7. Turn key A-3 in L-O interlock on disconnect F to lock open.
Keys A-3 and T-1 are now free.
L-C L-O L-O L-C 8. Insert key T-1 in L-O interlock on bus tie disconnect T and turn
to unlock. Key T-1 is now held.
9. Close bus tie disconnect T.
A B 10. Turn key B-1 in L-C interlock on bus tie disconnect T to lock
A2 B2 closed. Keys A-1 and B-1 are now free.
11. Insert key A-1 in L-O interlock on breaker C and turn to
L-O L-O unlock. Keys A-1 and A-4 are now held.
12. Close breaker C.
F H Reverse sequence to restore load No. 1 to line 1. To transfer load No.
T1 A-1 A1 B-1 T1
2 from line 2 to line 1, proceed in a similar manner.
A3 A-2 B1 T-1 B-2 B3
To isolate breaker A for servicing, proceed as follows:
L-O L-C L-C L-O L-C L-O
1. Proceed from normal position with operations as in 1
through 7 above.
2. Insert key A-3 in L-C interlock on disconnect E and turn to
T unlock. Key A-3 is now held.
3. Open disconnect E.
K L 4. Turn key A-2 in L-O interlock on disconnect E to lock open.
A-4 B-4
Key A-2 is now free.
5. Return key A-2 to breaker A and unlock for operation during
L-O-C L-O-C servicing.

Reverse sequence to restore service. To isolate breaker B for servicing,

proceed in a similar manner.

A1 C D B1 To isolate breaker C for servicing, proceed as follows:

A4 B4
1. Open breaker C.
L-O L-O
2. Turn key A-4 in L-O interlock on breaker C to lock breaker
open. Keys A-1 and A-4 are now free.
Load 1 Load 2
3. Insert key A-4 in L-O-C interlock on disconnect K and turn to
unlock. Key A-4 is now held.
4. Open disconnect K.
5. Turn key A-4 in L-O-C interlock on disconnect K to lock open.
Under normal conditions breakers A, B, C, and D are closed, Key A-4 is now free.
disconnects E, F, G, H, K, and L are locked closed, and bus tie 6. Return key A-4 to breaker C and unlock for operation during
disconnect T is locked open. Keys A-1 are held in L-O interlock on servicing.
breaker C and L-C interlock on bus tie disconnect T. Keys A-2 are held
in L-O interlocks on breaker A and disconnect E. Key A-3 is held in L-O Reverse sequence to restore service. To isolate breaker D for servicing,
interlock on disconnect F. Key A-4 is held in L-O interlock on breaker C. proceed in a similar manner.
Keys B-1 are held in L-O interlock on breaker D and L-C interlock on bus
tie disconnect T. Keys B-2 are held in L-O interlocks on breaker B and * To prevent primary disconnects K and L from opening magnetizing
disconnect G. Key B-3 is held in L-O interlock on disconnect H. Key B-4 current only, additional interlocks should be provided for disconnect K
is held in L-O interlock on breaker D. Keys T-1 are held in L-O interlock and L.
on disconnects F and H.
Scheme 25 Scheme 27
To prevent opening fuse compartment door when the interrupter switch To prevent operation (open or closed) of interrupter switch A when
A is closed. To prevent closing interrupter switch until fuse compartment breaker is closed. To prevent opening fuse compartment door when
door is locked closed. the interrupter switch A is closed. To prevent closing interrupter switch
until fuse compartment door is locked closed. Permits the breaker to be
serviced and operated while the interrupter is locked open.
A

A
E E
A 1 A-1

L-O L-C E E E E
A 1 A-1 A 2 A-2

Fuse compartment door and interrupter are shown in closed position. L-O L-O-C L-O L-C
Key A-1 is held in interrupter interlock.

1. Open interrupter.
2. Turn key A-1 in L-O interlock on interrupter switch to lock open.
Key A-1 is now free.
3. Insert key A-1 in L-C interlock on fuse compartment door and A
turn to unlock. Key A-1 is now held.
4. Open fuse compartment door.

Reverse sequence to restore service.

E E E E
A 1 A-2 A 2 A-1
Scheme 26
L-O L-C L-O L-O-C

To prevent operation (open or closed) of interrupter switch A when

breaker is closed. Permits the breaker to be serviced and operated
while the interrupter switch is locked open.

Breaker, fuse compartment door and interrupter are shown in closed

A position. Key A-1 is held in breaker interlock and key A-2 is held in
interrupter interlock.

To service breaker, proceed as follows:

1. Open breaker.
E E
2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
A 1 A-1 is now free.
3. Insert key A-1 in L-O-C interlock on interrupter and turn to
L-O L-O-C unlock. Key A-1 is now held.
4. Open interrupter.
5. Turn key A-1 in L-O-C interlock on interrupter to lock open. Key
Interrupter and breaker are shown in closed position. Key A-1 is held in
A-1 is now free.
breaker interlock.
6. Return key A-1 to breaker interlock and unlock for operation
of breaker during servicing.
1. Open breaker.
2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
Reverse sequence to restore service.
is now free.
3. Insert key A-1 in L-O-C interlock on interrupter and turn to
To open fuse compartment door, proceed as follows:
unlock. Key A-1 is now held.
4. Open interrupter.
1. Proceed from normal position with operations as in 1 through
5. Turn key A-1 in L-O-C interlock on interrupter to lock open. Key
4 above.
A-1 is now free.
2. Turn key A-2 in L-O interlock on interrupter switch to lock open.
6. Return key A-1 to breaker interlock and unlock for operation
Key A-2 is now free.
of breaker during servicing.
3. Insert key A-2 in L-C interlock on fuse compartment door and
turn to unlock. Key A-2 is now held.
Reverse sequence to restore service.
4. Open fuse compartment door.

Reverse sequence to restore service.

Scheme 28
To prevent dropping load when shifting from one source to the other. Interrupter switch A is shown closed and interrupter switch B is shown
To prevent opening both interrupter switches A and B at the same open. Key A-1 is held in interrupter B interlock.
time. Permits both interrupter switches to be closed at the same time.

1. Close interrupter B.
2. Turn key A-1 in L-C interlock on interrupter B to lock closed.
Key A-1 is now free.
A B 3. Insert key A-1 in L-C interlock on interrupter A and turn to
E E
A-1
unlock. Key A-1 is now held.
A 1
4. Open interrupter A.
L-C L-C

Reverse sequence to restore service through interrupter B.

Scheme 29
To prevent paralleling lines A and B requires dropping load when Interrupter switch A is shown closed and interrupter switch B is shown
shifting from one source to the other. To prevent closing both interrupter open. Key A-1 is held in interrupter switch A interlock.
switches A and B at the same time. Permits both interrupter switches to
be opened at the same time. 1. Open interrupter A.
2. Turn key A-1 in L-O interlock on interrupter A to lock open. Key
A-1 is now free.
3. Insert key A-1 in L-O interlock on interrupter B and turn to
A unlock. Key A-1 is now held.
B 4. Close interrupter B.
E E
A 1 A-1
Reverse sequence to restore service through interrupter A.
L-O L-O

Scheme 30
To prevent paralleling lines A and B requires dropping load when To service breaker, proceed as follows:
shifting from one source to the other. To prevent closing both interrupter
switches A and B at the same time. Permits both interrupter switches to 1. Open breaker.
be opened at the same time. To prevent operation (open or closed) of 2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
either interrupter switch when breaker is closed. Permits breaker to be is now free.
serviced and operated while both interrupter switches are locked 3. Insert key A-1 in L-O-C interlock on interrupter A and turn to
open. unlock. Key A-1 is now held.
4. Open interrupter A.
5. Turn key A-1 in L-O-C interlock on interrupter A to lock open.
Key A-1 is now free.
A B 6. Return key A-1 to breaker interlock and unlock for operation
E E E E of breaker during servicing.
A 2 A-1 A-2 A-1 Reverse sequence to restore service.
L-O L-O-C L-O L-O-C To transfer load from interrupter A to interrupter B:

1. Proceed from normal positions with operations as in 1

through 4 above.
2. Turn key A-1 in L-O-C interlock and key A-2 in L-O interlock on
interrupter A to lock open. Keys A-1 and A-2 are now free.
3. Insert key A-1 in L-O-C interlock and key A-2 in L-O interlock
A 1
on interrupter B and turn to unlock. Keys A-1 and A-2 are now
L-O
held.
4. Close interrupter B.
5. Turn key A-1 in L-O-C interlock on interrupter B to lock closed.
Key A-1 is free and key A-2 is held.
6. Insert key A-1 in L-O interlock on breaker and turn to unlock.
Breaker and interrupter A are shown in closed position. Interrupter B is Key A-1 is now held.
shown in open position. Key A-1 is held in breaker interlock. Key A-2 is 7. Close breaker.
held in interrupter A interlock. Reverse sequence to restore service through interrupter A.
Scheme 31 Scheme 32 (Continued)
To prevent operation (closed, open, or closed) of interrupter switch
when breaker is closed. Permits the breaker to be serviced and
operated while the interrupter switch is locked open.
A B
A B

E E
A2 A-1

E
L-O L-C-O-C
A-1

E
L-C-O-C
A-2

L-C

E
A 1

L-O
E

Breaker and interrupter are shown in closed position, connected to line A 1

B. Key A-1 is held in breaker interlock.
L-O
To service breaker, proceed as follows:

1. Open breaker. Breaker, fuse compartment door, and interrupter are shown in closed
2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1 position, connected to line B. Key A-1 is held in breaker interlock and
is now free. key A-2 is held in interrupter interlock.
3. Insert key A-1 in L-C-O-C interlock on interrupter and turn to
unlock. Key A-1 is now held. To service breaker, proceed as follows:
4. Open interrupter.
5. Turn key A-1 in L-C-O-C interlock on interrupter to lock open. 1. Open breaker.
Key A-1 is now free. 2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
6. Return key A-1 to breaker interlock and unlock for operation is now free.
of breaker during servicing. 3. Insert key A-1 in L-C-O-C interlock on interrupter and turn to
unlock. Key A-1 is now held.
Reverse sequence to restore service through either line A or line B. 4. Open interrupter.
5. Turn key A-1 in L-C-O-C interlock on interrupter to lock open.
To transfer interrupter from line B to line A: Key A-1 is now free.
6. Return key A-1 to breaker interlock and unlock for operation of
1. Proceed from normal position with operations as in steps 1 breaker during servicing.
through 3 above. Reverse sequence to restore service through either line A or line B.
2. Open interrupter switch from line B and connect to line A.
3. Turn key A-1 in L-C-O-C interlock on interrupter to lock closed. To open fuse compartment door:
Key A-1 is now free.
4. Insert key A-1 in L-O interlock on breaker and turn to unlock. 1. Proceed from normal position with operations 1 through 4
Key A-1 is now held. above.
5. Close breaker. 2. Turn key A-2 in L-O interlock on interrupter to lock open. Key A-
2 is now free.
Reverse sequence to restore service through line B. 3. Insert key A-2 in L-C interlock on fuse compartment door and
turn to unlock. Key A-2 is now held.
4. Open fuse compartment door.
Reverse sequence to restore service.

To transfer interrupter from line B to line A:

Scheme 32
1. Proceed from normal position with operations as in steps 1
To prevent operation (closed, open, or closed) of interrupter switch through 3 above.
when breaker is closed. To prevent opening fuse compartment door 2. Open interrupter switch from line B and connect to line A.
when the interrupter switch A is closed. To prevent closing interrupter 3. Turn key A-1 in L-C-O-C interlock on interrupter to lock closed.
switch until fuse compartment door is locked closed. Permits the Key A-1 is now free.
breaker to be serviced and operated while the interrupter switch is 4. Insert key A-1 in L-O interlock on breaker and turn to unlock.
locked open. Key A-1 is now held.
5. Close breaker.

Reverse sequence to restore service through line B.

Scheme 33

To prevent opening of guard B with motor circuit closed. TO OPERATOR

Starting switch normally closed. Key A-1 is held in starting switch

E
interlock. Guard B (or door) is locked closed by means of type D SWITCH A 1
(detachable) interlock.
L-O W
1. Open starting switch. A2
2. Turn key A-1 in L-O interlock on switch to lock open. Key A-1 is
now free. E
A-1
3. Insert key A-1 in L-C interlock (type D) on guard B and turn to
unlock. Key A-1 is now held.
L-C
4. Open guard. Service person can remove key A-2 and hold
until the service is complete. Thereby ensuring that the key
sequence cannot be reversed until the guard is locked
closed again.
GUARD B
Reverse sequence to restore service.

Scheme 34

To prevent opening of guard B for a pre-determined time after TIME DELAY KEY RELEASE UNIT
removal of power.
SIGNAL LIGHT

Starting switch normally closed. Key A-1 is held in starting switch A 2 A-1
interlock. Guard B (or door) is locked closed by means of type D
(detachable) interlock.

1. Open starting switch. TO OPERATOR

2. Turn key A-1 in L-O interlock on switch to lock open. Key A-1 is E
now free. SWITCH A 1
3. Insert key A-1 in time delay key release unit (type TDKRU) and
L-O W
rotate to start the time delay action. A3
4. Signal light energized and key A-2 can be removed after the
prescribed time elapses. Key A-1 is now held. E
A-2
5. Insert key A-2 in L-C interlock (type D) on guard B and turn to
unlock. Key A-2 is now held. L-C
6. Open guard. Service person can remove key A-3 and hold
until the service is complete. Thereby ensuring that the key
sequence cannot be reversed until the service is complete
and the guard is locked closed again. GUARD B

Reverse sequence to restore service.

Scheme 35 Scheme 36

To prevent paralleling of any sources while allowing switching of the To prevent paralleling of any sources while allowing switching of the
loads to alternate sources. loads to alternate sources.

GENERATOR A B GENERATOR

A B GENERATOR
A-1
B-1
A-1
H L-O
B-1 A-1 A1 A B B1 G B-1

L-O
A1 A B B1 G B-1

C M N

Breaker A is closed to supply load M. Breaker B is closed to supply load

M N N. Tie-Breaker C and generator breakers G and H are locked open.
Key A-1 is held in the L-O interlock on breaker A. Key B-1 is held in the L-
Breaker A is closed to supply load M. Breaker B is closed to supply load O interlock on breaker B. Tie-Breaker C cannot be closed unless either
N. Tie-Breaker C and generator breaker G are locked open. Key A-1 is breaker A or breaker B is locked open. Generator breaker G cannot
held in the L-O interlock on breaker A. Key B-1 is held in the L-O be closed unless breaker B is locked open. Generator breaker H
interlock on breaker B. Tie-Breaker C cannot be closed unless either cannot be closed unless breaker A is locked open. Tie-Breaker C
breaker A or B is locked open. Generator breaker G cannot be closed interlock has an apartment lock and can be unlocked for operation
unless breaker B is locked open. Tie-Breaker C interlock has an with either key A-1 or B-1. Generator G breaker interlock can be
apartment lock and can be unlocked for operation with either key A-1 unlocked for operation with key B-1 only. Generator H breaker interlock
or B-1. Generator breaker G interlock can be unlocked for operation can be unlocked for operation with Key A-1 only.
with key B-1 only.
To transfer load N to breaker A, proceed as follows:
To transfer load N to breaker A, proceed as follows: 1. Open breaker B.
1. Open breaker B. 2. Turn key B-1 in L-O interlock on breaker B to lock open.
2. Turn key B-1 in L-O interlock on breaker B to lock open. Key B- Key B-1 is now free.
1 is now free. 3. Insert Key B-1 in L-O interlock on tie-breaker C and turn
3. Insert Key B-1 in L-O interlock on tie-breaker C and turn to to unlock. Key B-1 is now held.
unlock. Key B-1 is now held. 4. Close tie-breaker C.
4. Close tie-breaker C. Reverse sequence to restore service through breaker B. Load M can
be supplied through breaker B in a similar manner.
Reverse sequence to restore service through breaker B. Load M can
be supplied through breaker B in a similar manner. To transfer load M to generator H, proceed as follows:
1. Open breaker A.
To transfer load N to the generator, proceed as follows: 2. Turn key A-1 in L-O interlock on breaker A to lock open.
1. Open breaker B. Key A-1 is now free.
2. Turn key B-1 in L-O interlock on breaker B to lock open. Key B- 3. Insert key A-1 in L-O interlock on generator breaker H
1 is now free. and turn to unlock. Key A-1 is now held.
3. Insert key B-1 in L-O interlock on generator breaker G and 4. Close generator breaker H.
turn to unlock. Key B-1 is now held. Reverse sequence to restore service through breaker A.
4. Close generator breaker G. Load N can be transferred to generator G using the B-1 key in a similar
manner.
Reverse sequence to restore service through breaker B.
To transfer loads M and N to generator H, proceed as follows:
To transfer loads M and N to the generator, proceed as follows: 1. Open breaker A.
1. Open breaker A. 2. Turn key A-1 in L-O interlock on breaker A to lock open.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key Key A-1 is now free.
A-1 is now free. 3. Open breaker B.
3. Open breaker B. 4. Turn key B-1 in L-O interlock on breaker B to lock open.
4. Turn key B-1 in L-O interlock on breaker B to lock open. Key B- Key B-1 is now free.
1 is now free. 5. Insert key B-1 in L-O interlock on tie-breaker C and turn
5. Insert key A-1 in L-O interlock on tie-breaker C and turn to to unlock. Key B-1 is now held.
unlock. Key A-1 is now held. 6. Close tie-breaker C.
6. Close tie-breaker C. 7. Insert key A-1 in L-O interlock on generator breaker H
7. Insert key B-1 in L-O interlock on generator breaker G and and turn to unlock. Key A-1 is now held.
turn to unlock. Key B-1 is now held. 8. Close generator breaker H.
8. Close generator breaker G. Reverse sequence to restore service through breakers A and B.
Loads M and N can be transferred to generator G in a similar manner.
Reverse sequence to restore service through breakers A and B. Open breakers A & B, then utilize the A-1 key to unlock tie-breaker C
and utilize the B-1 key to unlock generator breaker G.
Scheme 37

To prevent closing ground switch B under load and to enable To gain access to capacitor bank enclosure, proceed as
access to the capacitor bank enclosure only after the follows:
capacitor bank has been grounded and discharged.
1. Open breaker A.
CAPACITOR BANK 2. Turn key A-1 in L-O interlock on breaker A to lock
ENCLOSURE
open. Key A-1 is now free.
3. Insert key A-1 in L-O interlock on ground switch B and
turn to unlock. Close ground switch B. Key A-1 is now

ACCESS
#2
A E held.
A-3
4. Turn key A-2 in L-C interlock on ground switch B to
ACCESS L-C lock closed. Key A-2 is now free.
#1
5. Insert key A-2 in L-C interlock (Type M2D) on capacitor
E E E
B bank enclosure access door #1 and turn to unlock.
A1 A-1 A2 W
A3 Key A-2 is now held and key A-3 is now free.
L-O L-O L-C
A-2
E 6. Open access door #1 to enter capacitor bank
L-C
enclosure.
7. Insert key A-3 in L-C interlock (Type D) on access door
#2 and turn to unlock. Key A-3 is now held.
Capacitor bank scheme without time delay. 8. Open access door #2 to enter capacitor bank
enclosure.
Breaker A is closed. Ground switch B is locked open. All
capacitor bank enclosure doors are locked closed. Key A-1 is Reverse sequence to restore service.
held in L-O interlock on breaker A. Key A-2 is held in L-C
interlock on ground switch B. Key A-3 is held in L-C interlock
(Type M2D) on access door #1.

Scheme 38

To prevent closing ground switch B under load and to enable To gain access to capacitor bank enclosure, proceed as follows:
access to the capacitor bank enclosure only after the capacitor
bank has been grounded and discharged.
1. Open breaker A.
CAPACITOR BANK
2. Turn key A-1 in L-O interlock on breaker A to lock open.
ENCLOSURE Key A-1 is now free.
3. Insert Key A-1 in initiating lock on TDKRU. Turn key to start
ACCESS

time delay action.

#2

A E
A-4 4. Signal light energized and key A-2 can be removed
after the prescribed time period. Key A-1 is now held.
L-C
E E E
B ACCESS
#1 5. Insert key A-2 in L-O interlock on ground switch B and turn
A1 A-2 A3
to unlock. Close ground switch B. Key A-2 is now held.
L-O L-O L-C A4
W 6. Turn key A-3 in L-C interlock on ground switch B to lock
E
closed. Key A-3 is now free.
A-3 7. Insert key A-3 in L-C interlock (Type M2D) on capacitor
SIGNAL LIGHT L-C
bank enclosure access door #1 and turn to unlock. Key
A 2 A-1
A-3 is now held and key A-4 is now free.
TIME DELAY KEY RELEASE UNIT 8. Open access door #1 to enter capacitor bank
enclosure.
9. Insert key A-4 in L-C interlock (Type D) on access door #2
Capacitor bank scheme with time delay. and turn to unlock. Key A-4 is now held.
10. Open access door #2 to enter capacitor bank
Breaker A is closed. Ground switch B is locked open. All capacitor enclosure.
bank enclosure doors are locked closed. Key A-1 is held in L-O
interlock on breaker A. Key A-2 is held in Time Delay Key Release Reverse sequence to restore service.
Unit (TDKRU). Key A-3 is held in L-C interlock on ground switch B.
Key A-4 is held in L-C interlock (Type M2D) on access door #1.
Scheme 39 Scheme 40
To prevent improper maintenance bypass of Uninterruptible To prevent improper maintenance bypass of Uninterruptible
Power Supply. Power Supply.

SKRU
SKRU

KIRK

KIRK A1

A1 E
B-1
UPS SYSTEM MAINTENANCE UPS SYSTEM MAINTENANCE
OUTPUT
E BYPASS OUTPUT BYPASS
BREAKER BREAKER BREAKER BREAKER
(NC) (NO) (NC) A A1 A-1 B (NO)
A B1 A-1 B B-1 B1
W W

CRITICAL LOAD CRITICAL LOAD

Solenoid Key Release Unit (SKRU) shown with A-1 Key held Solenoid Key Release Unit (SKRU) shown with A-1 Key held
captive. UPS output breaker A is closed supplying the critical captive. UPS output breaker A is closed supplying the critical
load through the UPS. Key B-1 is held captive in the L-O load through the UPS. A second key A-1 is held captive in the
interlock on breaker A. Maintenance bypass breaker B cannot L-O interlock on breaker A. Key B-1 is held captive in L-O
be closed until the UPS is placed in bypass mode, sending a interlock on maintenance bypass breaker B. Maintenance
signal to the SKRU allowing release of key A-1. The SKRU has an bypass breaker B cannot be closed until the UPS is placed in
apartment lock that will accept either key A-1 or B-1. bypass mode, sending a signal to the SKRU allowing release of
SKRU key A-1.
To supply critical load through the maintenance bypass
breaker, proceed as follows: To supply critical load through the maintenance bypass
1. Place the UPS in bypass mode. breaker, proceed as follows:
2. Upon receipt of the proper signal, key A-1 in SKRU can 1. Place the UPS in bypass mode.
be turned changing status of SKRU internal contacts 2. Upon receipt of the proper signal, key A-1 in SKRU can
and releasing key A-1. be turned changing status of SKRU internal contacts
3. Insert key A-1 in L-O interlock on maintenance bypass and releasing key A-1.
breaker B and turn to unlock. 3. Insert key A-1 in L-O interlock on maintenance bypass
4. Close maintenance bypass breaker B. Key A-1 is now breaker B and turn to unlock.
held. 4. Close maintenance bypass breaker B. Key A-1 is now
5. Open UPS output breaker A. held. Key B-1 is now free.
6. Turn key B-1 in interlock on UPS output breaker A to 5. Open UPS output breaker A.
lock open. Key B-1 is now free. 6. Insert key B-1 in interlock on UPS output breaker A and
7. Insert key B-1 in SKRU and turn to return the SKRU turn to lock open. Key B-1 is now held. Key A-1 is now
internal contacts to the original position. Key B-1 is free.
now held in the SKRU. 7. Insert key A-1 in SKRU and turn returning the SKRU
internal contacts to the original position. Key A-1 is
Reverse sequence to restore equipment to original condition. now held in the SKRU.

Note: Refer to UPS manufacturer's operation and maintenance Reverse sequence to restore equipment to original condition.
manual for instructions regarding transferring the load to the
UPS maintenance bypass source. Persons not familiar with the Note: Refer to UPS manufacturer's operation and maintenance
operation of the UPS system should not attempt to change the manual for instructions regarding transferring the load to the
position the above devices. UPS maintenance bypass source. Persons not familiar with the
operation of the UPS system should not attempt to change the
position the above devices.
Scheme 41

To prevent opening any access doors of a precipitator until all power supplies are de-energized and properly grounded.

CONTROL CIRCUIT BREAKERS

E E
A1 A2 A2

L-O L-O L-C

TRANSFER PANEL

SINGLE SINGLE
G-1 G-2 G-3 G-4 INSERTION OF
T/R SWITCH T/R SWITCH
ALL GROUND
SWITCH KEYS
G-6 G-7 G-8 G-9 REQUIRED
E E TO RELEASE
HV A-1 HV A-2 ANY ACCESS
POSITION POSITION D1 D1 D1 DOOR KEYS.
L-C L-O

TR TR D1 D1 D1 D1

E
GROUND E
GROUND
G1 A1
POSITION POSITION D1 D1 D 1 ACCESS DOOR

L-C L-O KEYS NORMALLY

HELD IN
D1 D1 TRANSFER PANEL.

E E
D-1 D-1 D-1 ACCESS DOOR KEYS ARE
RETAINED WHEN DOOR/HATCH
L-C L-C L-C IS IN THE OPEN POSITION.

ACCESS DOORS

Precipitator scheme with single output transformer rectifiers.

The scheme above represents basic guidelines regarding the proper interlock sequence for an Electro-Static Precipitator. The equipment that
comprises an E.S.P., Scrubber, or Baghouse can vary depending upon the manufacturer and age of the equipment. Let us know your specific needs
and we will be glad to provide a free proposal without obligation.
Scheme 42

To prevent opening any access doors of a precipitator until all power supplies are de-energized and properly grounded.

CONTROL CIRCUIT BREAKERS

E E
A1 A2 A3
E E
A1 A2 A3
L-O L-O L-C

TO
REENERGIZE
ONE SIDE
DUAL OUTPUT ONLY DUAL OUTPUT
T/R SWITCH T/R SWITCH TRANSFER PANEL

E E E
HV A-1 A-1 HV HV A-2 G-1 G-1 G-2 G-2
POSITION INSERTION OF
W POSITION POSITION
L-C A1 L-C L-O
ALL GROUND
G-6 G-6 G-7
SWITCH KEYS
TR G-1
E

TR TR
G-7
REQUIRED
TO RELEASE
ANY ACCESS
GROUND E TRANSFER E
GROUND GROUND E
D1 D1 D1 DOOR KEYS.
G1 G1 A1
POSITION POSITION POSITION
L-C L-C L-O
D1 D1 D1 D1

ACCESS DOOR
D1 D1 D 1 KEYS NORMALLY
HELD IN
TRANSFER PANEL.
D1 D1

E E
D-1 D-1 D-1

L-C L-C ACCESS DOOR KEYS ARE

L-C
RETAINED WHEN DOOR/HATCH
IS IN THE OPEN POSITION.
ACCESS DOORS

Precipitator scheme with dual output transformer rectifiers.

The scheme above represents basic guidelines regarding the proper interlock sequence for an Electro-Static Precipitator. The equipment that
comprises an E.S.P., Scrubber, or Baghouse can vary depending upon the manufacturer and age of the equipment. Let us know your specific needs
and we will be glad to provide a free proposal without obligation.
When appropriately applied, Kirk Key Interlock systems ensure that a pre-determined sequence of
operation is followed. Kirk Key Interlock systems can prevent expensive machinery and electrical
equipment from being damaged due to operator error. On high-voltage switchgear, the proper use
of Kirk Key interlocks could ultimately save someone’s life.

Most manufacturers provide key interlock provisions on their equipment. With Kirk Key's wide range of
components, it is possible to quickly design and supply an interlock system that is custom designed
for your specific physical requirements. If you need one key, one lock, or a whole interlock system -
Kirk Key is ready to help.

Interlocking is accepted by safety, insurance, and standards authorities throughout the world as the
most reliable and cost effective way of guarding against operator error. If you are concerned about
preserving safety in your sequential operations, let Kirk Key Interlock Company fulfill your needs with a
customized interlocking system for your particular project or operation.

Kirk Key Interlock Company

“The key that ends costly mistakes”

For more information concerning any schemes in this book, or for help in configuring a custom interlock system, please feel free
to contact any one of our Product Coordinators. Kirk Key’s wide range of components makes it possible to quickly design and
supply an interlock system that is custom designed to your specific physical requirements.

1-800-438-2442
www.kirkkey.com

KIRK KEY DOCUMENT SB2003