INSTALLATION AND

MAINTENACE MANUAL

FOR

GROUND MONITOR
GM-200

Patent #4153923

Copyright 1979
American Mine Research, Inc.

Manual Part Number 180-0009

Revised: June, 1993

 LIST OF FIGURES

1. WIRING SCHEMATIC FOR SINGLE MONITOR……………………..5

2. WIRING SCHEMATIC FOR MULTIPLE MASTER MONITORS…….5
3. WIRING SCHEMATIC FOR MASTER AND SLAVE MONITORS…..8
4. LINE POWER CUT OUT………………………………………………...8
5. ENSIGN CUT OUT……………………………………………………….8
6. COVER FOR GM-200……………………………………………………9
7. BACK OF GM-200………………………………………………………..9
8. GM-200 PILOT WIRE MONITOR – TUNED FILTER PAIR………...13
9. GM-200 PILOT WIRE MONITOR – NO TUNING……………………14
 TABLE OF CONTENTS
TITLE PAGE
I. General Description…………………………………………………….………..…1
I.A. Introduction……………………………………………………………….1
I.B. Circuit……………………………………………………………………..1
I.C. Operation…………………………………………………………………1
II. Installation and checkout procedure……………………………………………..3
II.A. General installation directions…………………………………………3
II.B. Installation instructions for low voltage
Pilotless system…………………………………………………………3
II.C. Installation of main monitor enclosure………………………………...7
II.D. Transmitter connection………………………………………………..11
II.E. Installation of three-phase filters on
Equipment being monitored………………………………………….12
II.F. Installation instructions for low voltage
Pilot wire system………………………………………………………..12

III. Trouble Shooting………………………………………………………………….15

Step 1. Determine location of problem……………………………………..15
Step 2. Location of problem within power center………………………….16
Step 3. Location of problem in the trailing cable
Or on the machine……………………………………………………18
Step 4. Calibration…………………………………………………………….19

WARRANTY……………………………………………………………………………21
1. GENERAL DESCRIPTION

I.A. INTRODUCITON

The AMR AC Frame Ground Monitor is a solid state frequency

controlled system whose purpose is to monitor the continuity of
the AC frame ground conductor on three phase equipment. It is a
continuity monitor system that has a maximum allowable trip
resistance of 75 ohms. The monitor can be operated pilotless, or
with a pilotwire.
The GM-200 system is a single circuit monitor that was specif-
ically designed for monitoring on modular output panels of
today’s modern power distribution equipment. The unit is very
versatile in that it allows the operator many options to provide
the most reliable and economical ground monitoring system
available. The GM-200 contains all the features found on other
AMR ground monitors that reduce nuisance tripping due to low
voltage or intermittent conditions in the cable. The circuit
description and installation instructions are given in the
following pages.

I.B. CIRCUIT

The AMR ground check monitor is composed of the following

basic functional components:

• Power supply
• Transmitter
• Receiver
• Current Transformer
• Two three-phase filters or one set of pilot wire filters

I.C. OPERATION

The AMR Ground Monitor system utilizes an audio frequency

signal to monitor the continuity of the ground conductor. An

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audio signal is generated by the transmitter section. This signal
is coupled onto the three phase power conductors going to the
equipment being monitored by one of the three phase filters. The
signal then travels up the three conductors to the monitored piece
of equipment. The signal is then coupled from the three phase
lines to the ground conductor by the second three phase filter.
The audio signal travels back to the power center through the
ground conductor and passes through the current transformer to
frame ground and the common side of the transmitter output.
The current transformer couples the audio signal from the ground
line to the receiver. The receiver then detects this signal and
closes a relay which is part of the hold-in circuit for the three
phase circuit breaker feeding the monitored equipment. If the
audio signal is lost for any reason due to a broken ground
conductor or any open in the above transmissions circuit, the
relay is released and power is shut off to the machine being
monitored.

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II. INSTALLATION AND CHECKOUT PROCEDURE

II.A. GENERAL INSTALLATION DIRECTIONS

• All installation wiring shall be performed according to

applicable codes.
• All hookup wiring should be at least 18 AWG, type,
THNN, or Equivalent insulations, except the transmitter
output lead, which should be at lease 14 AWG. It may be
preferable to use a larger size wire for mechanical
strength reasons.
• All terminations and connections shall be made using
approved termination and splice connectors.
• The MAIN AC power and the MAIN DC power should
be visibly disconnected, locked and tagged out before and
during installation of this equipment.

II.B. INSTALLATION INSTRUCTION FOR LOW VOLTAGE

PILOTLESS SYSTEM

The installation of the AMR GM-200 Ground Monitoring

System consists mainly of the mounting and wiring of the
following pieces of equipment:

• Master monitor enclosure

• A receiver current transformer on the ground line of the
AC outlet to be monitored.
• One three phase filter on the piece of equipment to be
monitored

The wiring schematic for the GM-200 single unit monitor is

shown in Figure 1. Figure 2 and 3 are wiring schematics for
installations with more than on monitor. These schematics
should be referred to while installing the GM-200 units.

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II.C. INSTALLATION OF MAIN MONITOR ENCLOSURE

The first step of the installation process is to determine where

the GM-200 main enclosure will be mounted. The unit is de-
signed to be panel mounted in either the standard Line Power
Inc. cutout (Figure 4) or the standard Ensign cutout (Figure 5). If
a standard mounting cutout is not already available, the six 1/4”
holes should be drilled in the panel as indicated in Figure 4, and
the proper cutout should be made.

Once a panel is properly prepared, remove the front cover from

the monitor chassis by removing the tow cover mounting screws
as shown in Figure 6. The cover can then be completely
disconnected by unplugging it from the main chassis circuit
board. Once the cover is removed, you will see four 8/32
machine screws that should be removed from the monitor frame
and used for mounting the GM-200 to the output panel. Mount
the main frame of the monitor to the back side of the panel by
screwing the 8/32 screws through the panel into the main frame
of the monitor. Once the monitor frame is securely mounted, the
cover can be plugged back into the main frame and screwed in
place. This completes the mechanical mounting of the monitor
main assembly.

The wiring connections for the GM-200 series monitor are

made on the terminal strip at the rear of the unit. This is shown
in Figure 7. The top two terminals on the GM-200 are for
supplying the unit with 120 VAC. Locate a point on the power
center where 120 VAC is available. On most modern equipment,
120 VAC control voltage should already be available on the
output panels.

The GM-200 system provides a pilot interlock feature that will

satisfy the MSHA Regulations requiring the circuit breaker to
open if the machine plug is accidentally removed while under
load. This disconnect feature of the GM-200 does not contain
the 250 millisecond time delay that is allowed in the approved
monitor circuitry. This pilot interlock gives an immediate trip
upon removal of the three phase machine plug. If the pilot
interlock feature is desired, connect a wire from the terminal
marked Pilot Interlock to the pilot pin on the back of the power
receptacle. This connection is shown in Figure 1. Each three
phase plug that is used in any of the monitored outlets must

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Figure 4, Line Power Cut Out

Figure 5, Ensign Cut Out

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Figure 6, Cover for GM-200

Figure 7, Back of GM-200

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contain a jumper wire that connects the pilot in the plug to the
ground pin. This connection allows the pilot interlock to flow
into the frame ground of the power center.

If it is not desirable to use the pilot interlock feature, a jumper

will have to be run from the pilot interlock terminal to the frame
ground lug on the GM-200 frame as shown in Figure 7.

The next connection made is from the contacts of the monitor’s

tripping relay to the Under-voltage Release or Shunt Trip in the
AC breaker to be monitored. Locate the two wires coming out of
the breaker that carry its Shunt Trip or Under-Voltage current.
When the correct wires have been found, cut one of the wires and
strip the insulation off both open ends. A wire must be
connected to each of these ends, and then each wire must be
routed to the Main Monitor Enclosure. The terminal strip on the
rear of the GM-200 contains both the Normally Open and
Normally Closed contacts of the relay. The Normally Closed
contacts would be used for breakers with Shunt tripping and the
Normally Open contacts would be used for the Under-voltage
trip devices. Connect one wire to the terminal marked (C) for
common and the other lead to the correct Normally Open or
Normally Closed contact. This will complete the hookup of the
tripping circuit.

One receiver CT will have to be installed on the ground line of

each AC outlet that is to be monitored. The ground conductor
should be disconnected form the frame ground of the power
center and pushed through the current transformer immediately
after it enters the power center through the receptacle. Ii is
NECESSARY that the ground conductor not be connected to
frame ground in any way before the point at which it passes
through the current transformer. It is best to test this while the
ground line is disconnected with an ohm meter set to the lowest
resistance scale. This test can be made by grounding one of the
test leads of the ohm meter to the frame of the power center and
touching the other lead to the end of the disconnected ground
line. If a very low resistance is indicated (less than 10 ohms), the
ground line is most likely not isolated from the plug or recep-
tacle. An insulating sleeve must be obtained from the manu-
facturer of the plug and installed before the monitor will operate
properly. Once the CT is properly installed, the ground should

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be connected back to the frame of the power center.

Two pieces of wire should be cut that are long enough to get
from the CT lead to the GM-200 enclosure. Each wire should be
crimped to the CT output leads with the terminals that are
already installed on the leads. The wire should then be neatly
routed and tied down through the power center to the GM-200
enclosure. One wire should be connected to the terminal marked
input, and the other lead should be connected to the frame
ground bolt below the terminal strip on the back of the unit.
Since the CT is not polarized, each wire can be connected to
either the terminal strip “input” or the Frame Ground lug.

Three high voltage terminals can be seen in the bottom of

Figure 7. A wire should be run from each of ht terminals to the
plug receptacle. The three phase connections must be connected
on the machine side of the breaker so that monitoring can
continue when the machine does not have power unit. This
completes wiring of ht Main Enclosure except for the transmitter,
which will be covered in the next section.

II.D. TRANSMITTER CONNECTION

The GM-200 can be installed with one transmitter supplying all

the circuits of the Power Center, or with a transmitter on each
individual circuit. There are advantages and disadvantages to
both system which should be carefully evaluated before deciding
which method is best for you application. Figure 3 shows all
connections that need to be made for a three circuit application
using only one transmitter. The unit that contains the transmitter
is labeled the Master Unit and the other two monitors that
contain receivers only are labeled Slave Units.

To connect the units for this type of application, a wire would

have to be connected from the terminal marked “Trans. Gnd” on
the Master unit only to frame ground of the power center. A
second wire would run from the terminal marked “Trans In/Out”
on the Master unit to the “Trans In/Out” on all the Slave units.
This connects the Master unit’s transmitter to the phase filter in
each of the slave units.

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 The circuit of Figure 2 shows three GM-200 monitors
connected as individual circuit monitors. Each unit has its own
transmitter and requires an Arc Trap or Blocking Inductor in the
ground line of each circuit t reduce cross talk between the
individual transmitters. If only one monitor was to be used, then
the Arc Trap could be eliminated.

To connect the monitor for this type of operation, connect a

wire from the terminal marked “Trans Gnd” to the ground bolt
on the back of the power receptacle. The “Trans In/Out”
terminal would not have any wires connected to it for this type of
operation.

II.E. INSTALLATION OF THREE-PHASE FILTERS ON

EQUIPMENT BEING MONITORED

The three-phase filer should be installed inside the electrical

box on the equipment being monitored. The unit should be
securely mounted to the piece of equipment using large wire ties.
The green wire of the phase filter should be connected to frame
ground of the equipment. The three Black wires should be
connected to the power phase lines as shown in Figure 1. It is
necessary for this connection to be made at a point on the line
side of the equipment disconnect device, so that the monitor will
be able to continue monitoring when the equipment is shut down.
One three-phase filter must be installed on each piece of equip-
ment being monitored.

II.F. INSTALLATION INSTRUCTIONS FOR LOW

VOLTAGE PILOT WIRE SYSTEM

The installation and checkout procedures described in pilotless

installation will apply to pilot wire installations. The major dif-
ferences are explained in the following section.

The GM-200 can monitor trailing cable grounds using a pilot

wire. Two methods are accepted at present.

The first method involves the use of a tuned filter pair (see
Figure 8). The transmitter output is connected to a power center
filter (PF-162-A, AMR P/N 270-0024A). No polarity needs to
be observed in the filter hookup. The other lead of this filter is

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 connected to the pilot pin. The machine filter (PF162-B, AMR
P/N 270-0025B) is connected between the pilot wire and frame
ground. Again, this filter is not polarized. These two filters in
series create a tuned circuit having a low impedance to the
monitor frequency while reducing induced 60 cycle current.
This approach is preferred, since it is able to detect pilot-to-
ground shorts in the cable.

If there is not sufficient room to mount to a machine filter

(such as in pumps), the second approach is to simply run the
monitor signal through the pilot wire directly to ground at the
machine (see Figure 9). A 1000 VAC phase filter (PF160, AMR
P/N 270-0002) is placed in series with the pilot wire to reduce 60
cycle induced currents and to protect the ground monitor. This
method is unable to detect pilot-to ground shorts, as is the case
with many impedance type monitors. When no filter pair is used,
and monitor is used on non-cable reel equipment with cables
shorter than 250 ft., a 10 ohm resistor (RK-1, AMR P/N 270-
0008) is inserted in series as in Figure 9.

Figure 8, GM-200 Pilot Wire Monitor – Tuned Filter Pair

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Figure 9, GM-200 pilot Wire Monitor – No Tuning

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III. TROUBLE SHOOTING

Experience indicates that the most common problems en-

countered are faulty wiring connections, broken or intermittent
connections in the trailing cable or ground wires not isolated from
the frame before passing through the receiver CT. Before going
into the detailed Trouble Shooting Procedures outlined below, all
wiring should be verified to the correct according to the electrical
schematics, and examined to insure proper electrical and
mechanical integrity.

The Trouble Shooting Procedure for the AMR Ground

Monitoring System is a simple process of elimination. The idea
is to eliminate as quickly as possible the different components of
the system to pinpoint the problem area. The following
procedure should quickly lead to the source of the trouble.

Step 1. Determine Location of Problem

A. Remove power from the circuit under test by opening

the circuit breaker at the power center feeding that piece of
equipment.
B. Remove the machine cable plug from the power center.
C. Verify that the power has been removed by using a
volt-ohm meter (VOM).
D. Connect the three phase conductors to the ground
conductor at the receptacle outlet on the power center. This
can be done by using the phase filter found in the TK-150
Test Kit or a piece of bare wire that can be bent

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 to connect the three phase terminals to the ground
terminal of the receptacle. If the pilot interlock feature
is being used. It will also be necessary to connect a
jumper from the pilot pin to the ground pin.
E. If the red trip indicator light for this circuit now stays
out when the reset button is pressed, this indicates that all
the monitor equipment in the power center is working and
the problem is limited to the following areas:
o In the trailing cable or on the machine being
monitored. (see Step #3 in this section).
o The monitor is out of calibration. (see Step #4 in
this Section).
F. If the red trip indicator light can not be reset after the
jumpers are installed, this indicates the problem is within
the power center and you should proceed with Step #2.

Step 2. Location of Problem within the Power Center

A. Remove power from the power center and visually

check all wiring connections from the ground monitor to
the phase filter, current transformer (CT), and to the phase,
ground, and pilot connections. If any wiring errors are
suspected, the following checks can be made with a volt-
ohm meter to verify correct wiring.

o With the volt-ohm meter set to the lowest resistance

scale, place one probe on the pilot interlock terminal
on the back of the GM-200 and the other probe on the
pilot to ground jumper that is plugged into the power
receptacle for this circuit, the resistance read should
not be more than one or two ohms. If a higher
resistance is read, this indicates that the Pilot
Interlock circuit is not wired correctly, or that the
monitor is not properly grounded.
o With the Volt-ohm meter still set on the lowest
resistance scale, place one probe on the transmitter
ground terminal and the other probe on the frame of
the power center. The meter should indicate a low
value of resistance if the transmitter is properly
grounded.

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 o With the volt-ohm meter still set for the lowest
resistance scale, place one probe on the input terminal
and one probe on the ground bolt of the back of the
GM-200. If a low resistance is indicated (less than 5
ohms), then the receiver current transformer can be
assumed to be good.
o Set the Volt-ohm meter on a scale sufficient to
measure the tripping voltage (117 VAC for most
Under-voltage trip Circuits) and then place one probe
on each of the two wires coming to the monitor’s trip
contacts. If the correct voltage is not found, trace the
wiring to the correct breaker to identify the problem.
B. To determine if the transmitter is operating, check the
cover of the Master unit to see if the yellow “Trans On”
light is on. If this light is not on, remove the access cover
on the side of the monitor by its one screw. If all lights are
out on the monitor, depress the red reset button on the small
circuit breaker to the left of the large power transformer.
Press this button several times to insure that the breaker has
been reset. If service has not been restored, check the 2
amp glass fuse on the transmitter board to see if it’s blown.
If it is, replace it with a comparable 2 amp SLOW_BLO
fuse. After replacement, again check to see if the “Trans
On” light is now on. If it is not on, remove and replace the
larger transmitter PC board with the spare board found in
the TK-200 trouble shooting kit. If the “Trans On”
indicator now lights, the old transmitter board has failed
and it should be returned to AMR for repair.

C. If the “Trans On” light was found to be on, but the monitor
will not pick up, replace the receiver board with the spare
found in the TK-200 shooting kit. This board can be identified
by the calibration control that is facing out. If the monitor now
picks up, the receiver board should be returned to AMR for
repair.

D. If none of the above measures work, return the GM-200 for

service, the entire unit should be removed and replaced. The
defective unit should then be returned to AMR for repair.

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Step 3. Location of Problem in the Trailing Cable or on
Machine

A. Remove all power from the machine and leave the

cable plug disconnected from the power center so as to have
visual disconnect.

B. With an ohm meter set to the lowest ohms scale, check to

see if the ground pin is isolated from the frame of the plug.
This can be done by placing the probe on the ground pin and
the other on the frame of the plug. Move the cable at the strain
relief as much as possible and if the meter indicates a low
resistance (less than 10 ohms), the plug must be taken apart and
the ground wires isolated from the cable plug frame. If the
pilot interlock feature is being used, pace one probe on the
ground pin and one probe on the pilot pin of the plug. There
should be a low resistance short in this circuit (less than 2
ohms) indicating that the correct jumper has been installed in
the plug between pilot and ground. On the newer pieces of
distribution equipment, the entire power receptacle may be
isolated from the frame of the equipment by mounting the
receptacle on an insulated board. If this is the case with the
unit you are working on, it will not be necessary or advisable to
isolate the ground through the plug and the receptacle.

C. Visually inspect the cable for cuts or bad splices. The

probability is high that the problem will be in the cable.

D. Remove the cover from the control box on the piece

of equipment and visually check all connections.

E. Leaving one person to observe the red trip indicator

light on the monitor, go up and short the four terminals of
the phase filter on the machine.

F. Return the cable plug t the power center and lock out
the circuit breaker so that power can not be placed on the
machine.

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 G. If the red trip indicator light now goes out, when the
reset button is pushed, this indicates that the machine filter
is bad and should be replaced.

H. If the red trip indicator light stays on when reset, this

indicates that the problem is in the cable or the associated
wiring on the machine.

I. The cable or machine wiring can be checked by using a

jumper to short one phase to ground at the three phase filter on
the machine. Place the probe of a volt-ohm meter, set to the
lowest resistance scale, on the ground pin of the machine cable
plug at the power center end of the cable. With the other
probe, find the phase pin in the plug which contains the short.
This resistance should be less than 4 to 5 ohms on machines
that do not have cable take-up reels. If the machine does have
a take-up reel, hold the ohm meter on the phase and ground
pins while another person slowly pulls the cable off the reel.
This resistance should not exceed 5-35 ohms. If a higher
resistance is measured, the cable reel brushes should be
serviced. All three phases should be checked in this manner to
further isolate the problem.

Step 4. CALIBRATION

A. The calibration of the GM-200 Ground Monitoring System

can easily be checked by using the Test Button found on the
cover of the Master unit. The following procedure will
determine if the monitor is correctly set at its maximum trip
resistance setting.

B. Remove all machine plugs from the Power Center. On the

receptacle of the circuit that you wish to calibrate, short the
three phase pins to the ground pin. If the pilot interlock feature
is being used, it will also be necessary to short the pilot pin of
the receptacle to ground.

C. After the monitor has had at least 15 minutes to warm up,

remove the access cover from the side of the unit by its one
screw. Located the sensitivity control that is on the top of the
receiver board.

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D. Press the test button on the Master unit and hold it in. This
button places a 75 ohm test resistor in the output of the
transmitter and monitor should now trip and turn the trip
indicator light on. You should also be able to observe the relay
for the circuit under test opening. With a small screwdriver
adjust the sensitivity control on the receiver card counter-
clockwise to increase the trip resistance of the receiver.
Continue to hold the test button in and turn the sensitivity
control till either the relay picks up or you reach the maximum
sensitivity position of the receiver board. If the relay picks up,
slowly turn the sensitivity control back in the clockwise
direction until the relay drops back out. If the relay did pick up
when the receiver was turned to its maximum position, replace
the receiver card return the defective one to AMR for repair.

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 WARRANTY

American Mine Research Inc., warrants that each product manufactured by

it is free from defects in material and workmanship under normal usage and
service. The obligation under this warranty shall be limited to the repair or
exchange of any part or demonstrated to be defective; provided, such part or
parts is returned to American Mine Research, Inc.’s plant or to an author-
ized agent of American Mine Research, Inc., within ninety (90) days after
delivery of the product to the original purchaser; such return to be made at
the sole expense of the original purchaser.

THE WARRANTY IS EXPRESSLY IN LIEU OF ANY AND ALL

OTHER WARRANTIES, INCLUDING THE WARRANTIES OF MER-
CHANTABILITY AND FITNESS FOR PARTICULAR PURPOSE, AND
OF ANY AND ALL OTHER OBLIGATIONS OR LIABILITIES ON THE
PART OF AMERICAN MINE RESEARCH, INC. AMERICAN MINE
RESEARCH, INC. NEITHER ASSUMES NOR AUTHORIZES ANY
OTHER PERSON TO ASSUME FOR IT ANY LIABILITY OTHER
THAN THIS WARRANTY IN CONNECTION WITH THE SALE OF ITS
PRODUCTS OR ANY PART OR PARTS THEREOF.

THIS WARRANTY SHALL NOT APPLY TO ANY PRODUCT OR

ANY PART THEREOF WHICH HAS BEEN SUBJECT TO ACCIDENT,
NEGLIGENCE, ALTERATION, ABUSE, OR MISUSE, INCLUDING
ANY PRODUCT OR ANY PART THEREOF ON WHICK THE SERIAL
NUMBER HAS BEEN ALTERED, DEFACED, OR REMOVED.

THIS WARRANTY SHALL FURTHER NOT APPLY TO ANY PROD-

UCT OR ANY PART THEREOF WHICH HAS BEEN CONNECTED, IN-
STALLED, OR ADJUSTED OTHERWISE THAN IN ACCORDANCE
WITH AMERICAN MINE RESEARCH INC.’S INSTRUCTIONS
AND/OR SPECIFICATIONS.

American Mine Research, Inc. reserves the right to discontinue any

product model at any time or with MSHA approval to change specifications
or designs at any time without prior notice and without incurring any oblige-
tions thereby.

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