Selective Coordination

Essential Electrical Systems In Healthcare Facilities, Emergency Systems and Legally

Required Standby Systems
In recent history, there has been an increasing demand for reliability of New Article 100 Definition
electrical power for buildings spanning the entire spectrum from single-family Coordination (Selective). Localization of an overcurrent condition to restrict
residences to places of assembly to industrial facilities. Many building outages to the circuit or equipment affected, accomplished by the choice of
systems have gone to the extent of installing emergency back-up or standby overcurrent protective devices and their ratings or settings.
systems to ensure maximum possible reliability and continuity of their
NEC® 700.27 (Emergency Systems) and 701.18 (Legally Required Standby
electrical system. There are some types of buildings that require an emer-
Systems) have added selective coordination of overcurrent protective devices
gency system or legally required standby system such as hotels, theatres,
to help ensure life safety. Examples of circuits that require selective
sports arenas, healthcare facilities and many more similar institutions. These
coordination would be emergency and egress lighting for the safe evacuation
life safety electrical systems are used to ensure electrical power in the case of
from a building and to assist in crowd and panic control. Also, in many cases,
power loss due to an outside source (utility loss) or an inside source
some elevators and ventilation equipment may be classified as an emergency
(overcurrent condition). Very important loads must remain energized as long
or legally required standby system by the “Authority Having Jurisdiction” (AHJ)
as possible during times of normal power outage and emergencies that may
or the locally adopted building code. Also, 527.26 requires the essential
be caused by equipment failures, nature or man. However, simply installing a
electrical systems of healthcare facilities have overcurrent protective devices
back-up system is not the entire solution, the electrical system must be
that are selectively coordinated.
designed to maximize power to these important loads and minimize outages
even under physical catastrophes. It is very important to analyze the The New NEC® Requirements
characteristics of the overcurrent protective devices (OCPDs) of these life 517.26 Application of Other Articles. The essential electrical
safety systems to ensure they will perform as desired. system shall meet the requirements of Article 700, except as
The NEC® has special requirements for these life safety electrical systems. amended by Article 517.
These include several requirements that are based upon providing a system 700.27 Coordination. Emergency system(s) overcurrent devices
with reliable operation, reducing the probability of faults, and minimizing the shall be selectively coordinated with all supply side overcurrent
effects of an outage to the smallest portion of the system as possible. Below protective devices.
are a few of these sections: 701.18 Coordination. Legally required standby system(s)
• 700.4 maintenance and testing requirements overcurrent devices shall be selectively coordinated with all supply
• 700.9(B) emergency circuits separated from normal supply circuits side overcurrent protective devices.
• 700.9(C) wiring specifically located to minimize system hazards System Requirement
• 700.16 failure of one component must not result in a condition where a As stated in the NEC® requirements above, selective coordination is not just
means of egress will be in total darkness. between the branch circuit and feeder. It is the entire circuit path from the
The objective of these requirements is to ensure system uptime with the goal main overcurrent protective device to the branch circuit device. See figure
of safety of human life during emergencies or for essential health care below.
functions.
The 2005 NEC® has adapted to this demand and has modified a few articles
to address the issue of selective coordination and to ensure by design and
installation that the intended life safety electrical systems will stay in service
for the longest possible period of time.
The installation of a back-up system could easily be negated by the use of
overcurrent protective devices that are not selectively coordinated. Selective
coordination helps ensure by design and installation that some life safety
electrical systems will stay in service for the longest possible period of time.
There has been a requirement for selective coordination in the NEC® for many
years. NEC® 620.62 has had a selective coordination requirement for multiple
elevators in a building. This requirement is crucial for a few specific reasons
such as not stranding passengers for normal operation and for emergency
egress as well as keeping elevators in use for emergency firefighting
operations. The 2005 NEC® selective coordination requirements have been
expanded and a definition Coordination (Selective) has been added to Article
100:

100 ©2005 Cooper Bussmann

 Selective Coordination
Essential Electrical Systems In Healthcare Facilities, Emergency Systems and Legally
Required Standby Systems
A given emergency branch circuit load has a circuit path up through to the 3. A coordination study should fully investigate, interpret, and present the
main on the normal source and another circuit path up through to the main on level of coordination achieved for the full system and for the determined
the emergency source. The requirement for selective coordination means that amount of available short-circuit currents. This requires a person qualified for
all the overcurrent protective devices must be selectively coordinated with this task. Too often, coordination studies are performed where the deliverable is
just time current curve plots with no interpretation or discussion on the level of
each other, from each emergency branch circuit up through to the main of the
coordination achieved (or sacrificed). Also, the studies should be performed in the
normal power supply and up through to the main on the emergency power design phase so that if the study results prompt a change, the change can be
supply. See following example: without major ramifications.

Fusible Systems
Cooper Bussmann makes it easy to design fusible systems that are selectively
coordinated. For the modern current-limiting fuses, selectivity ratios are
published (see Fuse Selectivity Ratio Guide section). It is not necessary to plot
time current curves or do a short-circuit current analysis; all that is necessary
is to make sure the fuse types and ampere rating ratios for the mains, feeders
and branch circuit meet or exceed the selectivity ratio. These selectivity ratios
are for all levels of overcurrent up to the interrupting ratings of the respective
fuses. The ratios are valid even for fuse opening times less than 0.01
seconds. This means with current-limiting fuses, it is not necessary to do any
analysis for less than 0.01 seconds when the fuse types and ampere rating
ratios adhere to the selectivity ratios. The industry standard for publishing fuse
time current curves is to plot the times from 0.01 seconds and longer. The
following example illustrates all that is necessary to achieve selective
coordination with a fusible system.

How Can Selective Coordination Be Achieved?

Selective coordination of the overcurrent protective devices for these life
safety systems for both the normal power source path and the alternate power
source path can be achieved with either modern current-limiting fuse
technology or modern circuit breaker technology. However, not all fuse types
or circuit breaker types can be used in any and all situations to ensure
selective coordination. The ability to achieve selective coordination depends
on the specific circuit parameters (short-circuit currents available at various
points in the system) and the fuse or circuit breaker opening characteristics
and possible setting options. Proper overcurrent protective device choice and
selective coordination analysis is absolutely necessary. However, if the proper
choices and analysis are not made so that selective coordination is ensured,
the system may be built with deficiencies that may negatively impact life
safety.

Other Important Considerations

1. Either a system has overcurrent protective devices that are selectively
coordinated or the system does not. There is no middle ground. When terms
such as “enhancing” coordination, “optimizing” coordination, coordination "to the
best degree possible," or similar terms are used, it generally means the
overcurrent protective devices are not selectively coordinated over the full range
of short-circuit currents that are available in the application.
2. Selective coordination is for the full range of overcurrents available at all
mains, feeders and branch circuits. It is not acceptable to arbitrarily consider
selective coordination is applicable only above certain times such as 0.01, 0.1, or
1.0 seconds. The coverage of selective coordination in the sections on Selective
Coordination for Fuses and Circuit Breakers of this SPD publication explains how
to assess fuses and circuit breakers for the full range of overcurrents irrespective
of the times. Also, these preceding sections provide some easy, quick methods to
assess selective coordination for both fuse and circuit breaker systems.

©2005 Cooper Bussmann 101

 Selective Coordination
Essential Electrical Systems In Healthcare Facilities, Emergency Systems and Legally
Required Standby Systems
Frequently Asked Questions: Fuse System
Q. How about when two different current-limiting fuses are plotted on a time
current curve and there is a space between the lower ampere fuse total clear
curve and the larger ampere fuse minimum melt curve – does this ensure
selective coordination (if the selectivity ratio is not known)?
A. In this case, without knowing the selectivity ratio and having only time
current curves, selective coordination can only be ensured for the level of
overcurrent up to the point where the larger fuse curve crosses 0.01 seconds.
For times where the fuse opening time is less than 0.01 seconds, selectivity
ratios are necessary. It is not necessary to plot fuse time current curves; just
adhere to the selectivity ratios.
Q. What about lighting branch circuits? There has not been a commercially
available fusible lighting panelboards, so how can selective coordination be
achieved for the 20A panelboard circuits?
A. In order to achieve a selectively coordinated fusible system, Cooper
Bussmann has the Coordination Module™, which is a fusible branch circuit
panelboard. So now it is easy to achieve selective coordination from main to
branch circuit with an all fusible system, including branch circuit lighting
panelboards, by adhering to the simple selectivity ratios. Information on
Coordination Module on www.cooperbussmann.com data sheet 3115.

Selectivity Ratio Guide For Coordination Module

Load-Side Fuse
LP-CC
FNQ-R
KTK-R
Line-Side Fuse

LPJ_SP 2:1
LPN-RK_SP 2:1
LPS-RK_SP 2:1
FRN-R 2:1
FRS-R 2:1
Ratios only apply to Cooper Bussmann Fuses. When fuses are in the same case size, consult
Cooper Bussmann.

102 ©2005 Cooper Bussmann

 Selective Coordination
Essential Electrical Systems In Healthcare Facilities, Emergency Systems and Legally
Required Standby Systems
Circuit Breaker Systems New Requirement Compliance
As stated earlier, if a designer wants to use circuit breakers, it may be possible Achieving overcurrent protective device selective coordination for a system
to achieve a selectively coordinated system. There are a host of circuit requires the proper engineering, specification and installation of the required
breaker alternatives in the form of circuit breaker types, optional features, and devices, and in addition, knowledgeable plan review and inspection to ensure
possible settings. See Circuit Breaker Coordination section in this publication compliance. The designer, contractor, and plan review/inspector each have
for more in-depth discussion on some of the options and tradeoffs. The their role in compliance to selective coordination in order to ensure safety to
designer must understand the characteristics, setting options and override human life.
particulars for each circuit breaker considered and in some cases, factor in the
specific circuit parameters such as the available short-circuit currents at each Role of Designers
point in the system. For these vital systems, the designer must select, specify, and document
If circuit breakers are considered, typically the following become important: overcurrent protective devices that achieve selective coordination for the full
range of possible overcurrents and for faults at all possible points in the
1. A short-circuit current study with a coordination study (interpreted properly) is system (faults can occur in the branch circuits, sub-feeders, and feeders). The
necessary to determine if selective coordination is achieved for each circuit and
designer should provide the plan reviewer a stamped analysis verifying that
for the entire circuit path. It is necessary to have the available short-circuit
currents and circuit breakers’ characteristics and settings. Depending on the
selective coordination is achieved as designed for the required electrical
circumstances, the designer may have to use different type circuit breakers or systems. Documentation of the basis should be included. Also, this information
options in order to achieve selective coordination. is necessary so that the contractor quotes and installs the overcurrent
protective devices as designed.
2. Typically the designer will have to utilize circuit breakers with short-time delays
and possibly larger frame sizes. This may increase the cost and equipment size. Role of Plan Review/Inspectors
3. Tradeoffs in system protection: These decisions that may improve the level of The plan review process is a critical phase. If a non-compliant design does not
coordination may negatively impact the level of component protection. get caught and corrected in the plan review, it could get red tagged in the
4. Arc flash hazard level: These decisions that may improve the level of coordination inspection phase, which may require a very expensive gear change out.
may negatively impact the arc flash hazard level. During the plan review process, the engineer must provide the stamped
5. In many cases, the circuit breaker solution may only be selectively coordinated for substantiation in the form of documentation that his design achieves selective
the exact designed system (for specific circuit breaker settings and available short coordination for these vital circuits. The plan reviewer should not have to
circuit currents of a specific system). Most systems get upgraded or change at prove or disprove that selective coordination is achieved. The engineer’s
some point in time and this can significantly increase the available short-circuit documentation should be clear enough to demonstrate that the design work
currents. This may negate the selective coordination for some circuit breaker included the proper selective coordination analysis and that the plans and
systems that may have originally been selectively coordinated. specifications clearly articulate the required details on type of overcurrent
6. Testing and maintenance: periodic exercising and testing are important for circuit protective devices, ampere ratings, and settings (if circuit breakers). The
breakers to ensure they operate as intended. If circuit breakers are found not to engineer’s documentation should clearly state that the plans specify
operate as specified, maintenance or replacement of these circuit breakers is overcurrent protective devices that achieve selective coordination for these
necessary. For instance, if a feeder circuit breaker fails to operate or operates vital systems.
slower than as specified, it may cause the main circuit breaker to open due to a
During the inspection process, prior to energizing the system, the field
feeder fault. The result would be a much larger portion of these critical system
inspection should include verifying that the overcurrent protective devices
loads being without power.
have been installed as specified. If circuit breakers are used, the settings
System with Mixture of Fuses and Circuit Breakers should be verified as per plan.
Fuses and circuit breakers operate in totally different ways. Fuses are thermal Role of Contractors
devices that have encased fusible elements that operate under overcurrent
Contractors must install the system as designed to ensure selective
conditions by melting or vaporizing at some points of the element, arcing, and
coordination for the system. If a fusible system, install the fuse types and
clearing the circuit. All circuit breakers have three operating functions to clear
ampere ratings as called for in the design. If a circuit breaker system,
a circuit: (1) overcurrent sensing, (2) unlatching, and (3) parting the contacts,
install the circuit breaker types with the specified settings.
arcing, and clearing. There are numerous technologies used for circuit breaker
overcurrent sensing. If the contractor opts to suggest a value engineering option for these vital
systems, it is critical that the engineer evaluates and approves of any changes
For downstream fuse and upstream circuit breaker, it is not a simple matter to
as well as the plan reviewer.
determine if a fuse and circuit breaker will be selectively coordinated. Even if
the plot of the time current curves for a downstream fuse and an upstream
circuit breaker show that the curves do not cross, selective coordination may
not be possible.
If a fuse is upstream and a circuit breaker is downstream, at some point the
fuse time current characteristic crosses the circuit breaker time current
characteristic. For short-circuit currents at that point and higher, the upstream
fuse is not coordinated with the down stream circuit breaker.

©2005 Cooper Bussmann 103

 Ground Fault Protection
Coordination Considerations

This fact is commonly overlooked when applying ground fault relays. The system above illustrates the typical problem concerning this point. The
Generally, the short-time-delay on the ground fault relay is thought to provide main ground fault relay is set at 1200A, 18 cycle delay and the feeder ground
coordination for higher magnitude feeder ground faults. However, as shown by fault relay is set at 100A, six cycle delay. These ground fault relay settings
this example the main circuit breaker operates to cause an unnecessary could mistakenly be interpreted to mean that feeder ground faults would be
blackout. cleared by only the feeder ground fault relay opening the feeder
Note: Circuit breakers with short-time-delay trip settings were not considered disconnect. But the analysis must also include the phase overcurrent device
in this section. The reason is that a short-time-delay on a circuit breaker characteristics since these devices also respond to current.
defeats the original purpose of protection. Short-circuit currents and high 1,000
magnitude ground fault currents, when intentionally permitted to flow for 800
600
several cycles, dramatically increase the burn time and damage to the system
400
as well as increasing the arc-flash hazards to personnel.
300
Electrical systems are not designed to withstand, for long periods, the torturous 200
forces that fault currents produce. Circuit breaker short-time-delay trip settings
with typical delays of 6, 18, 24, or 30 cycles can greatly exceed the short circuit 100
MAIN GFR
withstandability of system components. According to industry standards, the 80
duration for equipment short-circuit current testing is three cycles for 60 FDR GFR
switchboard bus (UL891) and three cycles for busway (BU1-1999). The short- 40
1200A CB
30
circuit current withstandability for insulated conductors decreases as the over-
current device operating time increases (reference Insulated Cable Engineers 20
200A CB
TIME IN SECONDS

Association Publication P-32-382, “Short-Circuit Characteristics of Cable”).

Short-circuit currents and high magnitude ground fault currents must be 10
8
interrupted as rapidly as possible (preferably with current-limiting devices) to 6
minimize equipment damage. 4

Whenever insulated case and molded case circuit breakers have a short-time- 3

delay feature they also have an instantaneous override This requires the 2

sensing mechanism to override the short-time-delay feature for high ground

fault or line-line faults. The result is a lack of coordination with the feeder 1
.8
breakers for any fault current above the instantaneous override setting. .6
Selective coordination is therefore very difficult to achieve. .4
.3
B. Two Step Ground Fault Relaying
.2
Two step ground fault relaying includes ground fault relays on the main service
and feeders. BLACKOUT
.1 AREA
In many instances, this procedure can provide a higher degree of ground fault .08
.06
coordination to prevent unnecessary service blackouts. Yet it is mistakenly
.04
believed by many that two step ground fault relays assure ground fault
.03
coordination. For complete selective coordination of all ground faults, the
.02
conventional overcurrent protective devices must be selectively coordinated as
well as the ground fault relays. The fact is that even with this two step relay
.01
provision, ground fault coordination is not assured on many systems designed
000,1

000,2

000,3
000,4

000,6
000,8
000,01

000,02

000,03
000,04

000,06
000,08
000,001
008
001

002

003
004

006
008

with mechanical overcurrent protective devices which incorporate

CURRENT IN AMPS
instantaneous unlatching mechanisms.
The two step ground fault relays give a false sense of security. The graph
RESULT: BLACKOUT above illustrates that the ground fault relays are coordinated, but overcurrent
devices are not coordinated for feeder or branch circuit ground faults above
11,000 amps. This is indicated as the BLACKOUT AREA on the curve. In this
case the main overcurrent device and the feeder overcurrent device both open
1200A CB Main
G.F. Relay on a feeder circuit fault. Thus the entire system is blacked out; even though
Circuit 1200A two step ground fault relays are provided.
Breaker Opens 18 Cycle Delay
Circuit WARNING!
Breaker Opens
For Health Care Facilities: Section 517.17 requires the main and feeders to
200A CB Feeder be 100% selectively coordinated for all magnitudes of ground fault current -
G.F. Relay
100A including low, medium, and high ground fault currents.
6 Cycle Delay

Ground Fault
11,000A
or Greater

112 ©2005 Cooper Bussmann

 Ground Fault Protection
Coordination Considerations

In many cases two step relays do provide a higher degree of ground fault
1,000
coordination. When properly selected, the main fuse can be selectively 800
coordinated with the feeder fuses. Thus on all feeder ground faults or short 600
circuits the feeder fuse will always open before the main fuse. When 400
selectively coordinated main and feeder fuses are combined with selectively 300
coordinated main and feeder ground fault relays, ground fault coordination 200
between the main and feeder is predictable. LPS-RK 200SP
100
80 MAIN GFR
60 FDR GFR
40
KRP-C1200SP
Main 30
G.F. Relay
KRP-C1200SP 20
1200A

TIME IN SECONDS
18 Cycle Delay
Does Not 10
Open 8
6

4
Feeder 3
G.F. Relay 2
LPS-RK200SP 100A
6 Cycle Delay
1
Only Feeder
.8
Disrupted
.6
Any Level Ground
Fault Current .4

.3

.2
The above figure illustrates a selectively coordinated main and feeder for all
levels of ground faults, overloads and short circuits. Any fault on the feeder will .1

not disrupt the main service. .08

.06
This system offers full selective coordination for all levels of ground faults or
.04
short circuits.
.03

1. The feeder ground fault relay is set at a lower time band than the main ground
.02
fault relay, therefore the relays are coordinated.
2. The feeder fuses are selectively coordinated with the main fuses for all ground .01
000,2

000,3
000,4

000,6
000,8

000,001
000,01

000,02

000,03
000,04

000,06
000,08
000,1
08
001

002

003
004

006
008

faults, short circuits, or overloads on the load side of the feeder. The feeder fuses
would clear the fault before the main fuses open.
CURRENT IN AMPS
Conclusion: This system is completely selective for all levels of ground faults
and short circuits. This system meets the intent of NEC® 517.17 for 100%
selectivity.

Complete Ground Fault Selective Coordination Is

Necessary To Prevent Blackouts!
To assure complete selective coordination for all ground faults, it is essential
that the conventional overcurrent protective devices be selectively coordinated
as well as the ground fault relays’ requirement. The intent of 517.17 is to
achieve “100 percent selectivity” for all magnitudes of ground fault current.

©2005 Cooper Bussmann 113

 Selective Coordination Now Required

Selective Coordination Now Required For

Emergency Systems,
Legally Required Standby Systems, and
Essential Electrical Systems in Health Care Facilities

BLACKOUT

Background coordination of overcurrent devices fits well with the other

requirements such as:
Selective coordination is now required for increased system
reliability, which is vital for these critical systems. Selective • 700.4 maintenance and testing requirements
coordination can be defined as isolating an overloaded or • 700.9(B) emergency circuits separated from normal
faulted circuit from the remainder of the electrical system by supply circuits
having only the nearest upstream overcurrent protective • 700.9(C) wiring specifically located to minimize system
device open. The following was added to NEC® 2005 hazards
• 700.16 failure of one component must not result in a
condition where a means of egress will be in total
Article 100 Definitions: Coordination (Selective). darkness
Localization of an overcurrent condition to restrict outages
to the circuit or equipment affected, accomplished by the
choice of overcurrent protective devices and their ratings
Ensuring Compliance
or settings.
Achieving the proper overcurrent protective device selective
coordination requires proper engineering, specification and
The one-line diagrams in Figure 1 and Figure 2 demonstrate installation of the required devices.
the concept of selective coordination.
During the plan review process, it is the design engineer’s
Selective coordination is an important new NEC® 2005 responsibility to provide documentation that verifies the
requirement that is consistent with the critical need to keep overcurrent devices are selectively coordinated for the full
these loads powered even with the loss of normal power. range of overcurrents that can occur in the system. And the
Article 700, Emergency Systems, and Article 701, site inspection should verify the overcurrent protective
Legally Required Standby Systems have several devices are installed as specified to achieve selective
requirements that are based upon providing a system with coordination.
reliable operation, reduction in the probability of faults and
minimizing the effects of an outage to the smallest portion of It is possible for both fusible and circuit breaker systems to
the system as possible. Article 517, Health Care be selectively coordinated with proper analysis and selection.
Facilities, requires essential electrical systems to Selective coordination is easy with Bussmann® fuses by
meet the requirements of Article 700 except as amended in using the published fuse selective coordination ratios; a full
Article 517. The objective of these requirements is to ensure short-circuit and coordination study is not necessary to verify
system uptime with the goal of safety of human life during selective coordination. Selective coordination with circuit
emergencies or for essential health care functions. Selective breakers depends on their characteristics and settings as
well as the circuit parameters for the specific application. It

©2005 Cooper Bussmann 5

 Selective Coordination Now Required

is generally difficult to achieve selective coordination with New Requirements

common circuit breakers that incorporate instantaneous trip
settings. Typically circuit breakers with short-time delay
2005 NEC®
settings or zone selective interlock features may be
700.27 Coordination. Emergency system(s)
necessary, which can add to the cost and may create other
overcurrent devices shall be selectively coordinated with
system issues. If using zone selective interlocking
all supply side overcurrent protective devices.
options, molded case and insulated case circuit breakers
still have an instantaneous trip that overrides the
701.18. Coordination. Legally required standby
zone selective tripping feature. This is necessary to
system(s) overcurrent devices shall be selectively
protect the circuit breaker from severe damage.
coordinated with all supply side overcurrent protective
Consequently blackouts can occur even with this zone selec-
devices.
tive interlocking feature. If circuit breakers are to be consid-
ered, a full short-circuit current and coordination study must
517.26 Application of Other Articles. The
be done with proper analysis and interpretation. See simple
essential electrical system shall meet the requirements of
fuse and circuit breaker examples are on page 8.
Article 700, except as amended by Article 517.
Example (See Figures 1 & 2)
Notes:
If overcurrent protective devices in the emergency system 1. Article 517 has no amendment to the selective
are not selectively coordinated, a fault at X1 on the branch coordination requirement, therefore selective coordination
circuit may unnecessarily open the sub-feeder; or even is required.
worse the feeder or possibly even the main. In this case, 2. Selective coordination is required for both the normal
emergency circuits are unnecessarily blacked out. With supply path and the emergency system path.
selective coordination as a requirement for emergency,
legally required standby, and essential electrical systems,
when a fault occurs at X1 only the nearest upstream fuse or
circuit breaker supplying just that circuit would open. Other
emergency loads would remain powered.

Figure 1 - Normal Source Power to Emergency Circuits

6 ©2005 Cooper Bussmann

 Selective Coordination Now Required

Figure 2 - Emergency Service Power to Emergency Circuits

©2005 Cooper Bussmann 7

 Selective Coordination Now Required

The Cooper Bussmann SPD Selecting Protective evaluation rules for coordination of instantaneous trip circuit
Devices publication (download from www.bussmann.com) breakers, and illustration of short-time delay circuit breakers.
has an in-depth discussion on selective coordination analysis Go to www.bussmann.com for Bussmann® Fuse Selectivity
with the published fuse selectivity ratios, some simple Ratios Interactive Guide under Application Info/Software.

® Lineside KRP-C-800SP to Loadside LPJ-100SP

800/100=8:1 Table shows only 2:1 needed
Therefore Selective Coordination achieved

Lineside LPJ-1000SP to Loadside LPS-RK-20SP

100/20=5:1 Table shows only 2:1 needed
Therefore Selective Coordination achieved

1. If circuit breakers are not maintained, extended clearing times or nuisance operation may compromise coordination.
2. If using zone selective interlocking option, molded case and insulated case circuit breakers still have an instantaneous trip that
overrides the zone selective tripping feature. Blackouts still can occur since selective coordination can not be achieved.

Other Information normal source. Legally required standby systems typically

serve loads in heating and refrigeration, communication
Emergency systems are considered in places of assembly systems, ventilation and smoke removal systems, sewage
where artificial illumination is required and for areas where disposal, lighting systems, and industrial processes where
panic control is needed such as hotels, theaters, sports interruption could cause severe human safety hazards.
arenas, health care facilities, and similar institutions.
Emergency systems also provide power to functions for Essential electrical systems in healthcare facilities are
ventilation, fire detection and alarm systems, elevators, fire portions of the electrical system designed to ensure
pumps, public safety communications, or industrial processes continuity of lighting and power to designated areas/functions
where interruption could cause severe human safety during normal source power disruptions or disruptions within
hazards. the internal wiring system. Essential electrical systems can
include the critical branch, life safety branch, and equipment
Legally required standby systems are intended to systems which are essential for life safety and orderly
supply power to selected loads in the event of failure of the cessation of procedures during normal power disruptions.

8 ©2005 Cooper Bussmann