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Simplif ied Fault Current
Calculations
Presented by:
Dustin [email protected]
Agenda
Basic electrical distribut ioncomponents & relationship w ith faultlevelsTransformers, conductors, etc.
Overcurrent Protective Devices (OCPD)
Simplified fault calculation example
Relevant NEC requirements
Cooper Bussmann Solutions
Fault Current Basics
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X
54,000A Available
X
X
X
X38,000A Available
31,000A Available
35,000A Available
28,000A Available
Available Faul t Current?
TYPICAL SHORT CIRCUIT
CURRENTS
Home Receptacle - 200 to 500 amps
Home Service - 2,000 to 10,000 amps
Bussmann Headquarters - 70,000 amps
New York City - 202,000 amps
St. Louis, MO - 210,000
Chicago, IL - 215,000
Dallas, TX - 220,000
Tulsa, Oklahoma - 260,000 amps
Short Circuit Calculations
Why short-circuit calculations?
Several sections of the NEC relate to proper
overcurrent protection. Safe and reliable
application of overcurrent protective devices
based on these sections mandate that a short
circuit study and a selective coordination be
conducted.
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Short Circuit Calculations
More on This Later
Sections in the NEC include:
110.9 Interrupting Rating
110.10 Component Protection110.16 Arc-Flash Warning Labels
Art. 240 Overcurrent Protection
409.110 Industrial Control Panels
430.8 Motor Controllers
440.4(B) HVAC Equipment
670.3 Industrial Machinery
Numerous
Articles Selective Coordination
Short Circuit Calculations
Compliance with these code sections can
be accomplished by conducting a short
circuit study. To obtain reliable operation
and assure that system components are
protected from damage, it is necessary to
first calculate the available fault current at
various critical points in the electrical
system.
Short Circuit Calculations
Critical points in the system include:
Service Entrance
Panelboards Industrial Control Panels & Machinery
Motor Control Centers
Motor Starters
Transfer Switches
Load Centers
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Short Circuit Calculations
Once the short circuit levels are
determined, it is possible to specify proper
interrupting rating requirements, selectively
coordinate the system and provide
component protection.
Fault Current Analysis
Simplified method point to point
calculations
More detailed analysis can be done
using commercial software or hand
calculations
Cooper Bussmann short-circui t
calculator
http://www.cooperbussmann.com/7/FreeSoftware.html
MM
MSB
Short Circuit Currents
Vary Depending on Many
Factors
Transformer Size & % Z
Voltage
Conductor Size & Length
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MM
MSB
Short Circuit Currents
Vary Depending on Many
Factors
60,000 A
27,000 A40,000 A
60,000 A
18,000 A
9,000 A
Short Circuit Currents
Vary Depending on Many
Factors
How to Calculate Transformer Secondary(assuming infinite primary)
EPR Page 7 KVA SIZE
VOLTAGE
%Z
500 KVA
480/277V
1
5 % Z
500 KVA
480/277V
1A
2 % Z
1500 KVA
480/277V
2
5% Z
1500 KVA
480/277V
2A
2 % Z
Short Circuit Current Examples #1
1500 KVA
208/120V
3
5% Z
1500 KVA
208/120V
3A
2 % Z
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500 KVA
480/277V
1
5 % Z
500 KVA
480/277V
1A
2 % Z
13,377 A
33,444 A
1500 KVA
480/277V
2
5% Z
1500 KVA
480/277V
2A
2 % Z
40,133 A
100,333 A
1500 KVA
208/120V
3
5% Z
1500 KVA
208/120V
3A
2 % Z
92,533 A
231,333 A
Short Circuit Current Examples #1
How to Calculate Conductor Contribution
EPR Page 7 LENGTH
VOLTAGEC CONSTANT
Isca
208/120V
4
4A
6
6A
480/277V
5
5A
480/277V
40,000 A. 40,000 A.40,000 A.
50 ft # 1 50 ft 250 kcm
Short Circuit Current Examples #2
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208/120V
4
4A
40,000 A.
50 ft # 1
12,181 A.
480/277V
5
5A
40,000 A.
20,104 A.
6
6A
480/277V
40,000 A.
50 ft 250 kcm
27,820 A.
Short Circuit Current Examples #2
Simplif ied Fault Calculation:
EXAMPLE
EPR Page 11 & 12, Number (1)
Simplif ied Fault Calculation:EXAMPLE
ANSWER:
SCA = ~42,000 Amps
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Relevant NEC Requirements
NECAdoption
2002 NEC
1999 NEC
Local Adoption2005 NEC 2008 NEC
LATX
CO
OR
WA
MO
NM
IL
PA
CA
NV
AZ
KS
AR
IA
MN
WI
MI
OK
NE
ND
SD
MT
ID
UT
WY
MSAL GA
FL
TN
IN
KY
OH
WV
SC
NC
VA
NY
ME
CT
MA
NJ
NH
VT
Short Circuit Calculations
Sections in the NEC include:
110.9 Interrupting Rating
110.10 Component Protection
110.16 Arc-Flash Warning Labels
Art. 240 Overcurrent Protection409.110 Industrial Control Panels
430.8 Motor Controllers
440.4(B) HVAC Equipment
670.3 Industrial Machinery
Numerous
Articles Selective Coordination
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IR Exceeded
110.9 Interrupting Rating&
110.10 Component Protection
IR Exceeded
IR Exceeded
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Arc Flash Hazard
110.16 Arc-Flash Warning Labels
Arc Flash Hazard
Fault current effects arc flash hazard level
SCCR
409.110, 430.8, 440.4(B) & 670.3
Equipment Short-Circuit Current Ratings
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What is SCCR?
UL 508A & 2008 NEC
Short-Circuit Current Rating.
The prospective symmetrical
fault current at a nominal
voltage to which an apparatus
or system is able to be
connected without sustaining
damage exceeding defined
acceptance criteria.
What is SCCR?
SCCR is the maximum
current:
a component, assembly or
equipment can safely
withstand
when protected by a
specific overcurrent
protective device, or for a
specified time interval
Simple:
Level of fault current an assembly of components is rated to withstand
X
Motor Controller
Industrial Machinery
HVAC
Industrial Control Panels
54,000A Available
X
X
X
X38,000A Available
31,000A Available
35,000A Available
28,000A Available
What is SCCR?
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What is SCCR?
SCCR markings on equipment labeling
are provided to ensure proper protectionfor assemblies
Equipment SCCR must exceed theavailable short-circuit current at thepoint of installation (NEC 110.10)
Similar to interrupting ratingrequirements found in NEC 110.9
Selective Coordination
517.26, 620.62, 700.27, 701.18, 708.54
Selective Coordination
NEC 2008 Requirements
Emergency Systems 700.27Illumination, ventilation, fire detection, alarm systems, etc.inplaces of assembly, hotels, theaters, and sports arenas
Legally Required Standby Systems 701.18Safety-related systems such as HVAC, communicationsystems, ventilation, and sewage treatment plants
Critical Operati on Power Systems (COPS)
708.54Public safety-related systems that require continuous operationfor like emergency management facilities or business centers
Essential Systems 517.26Emergency, Critical and Equipment branch in Healthcarefacilities (must meet requirements of Article 700)
New in 2005
New in 2005
New in 2008
Increase Systems Reliability Preventing Blackouts
New in 2005
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What is Selective Coordination
For the full range of possibleovercurrents
LINE SIDE
LOAD SIDE
KRP-C-1200SP
LPS-RK-600SP
Only closest upstream OCPDfrom overcurrent opens
Other upstream (larger)overcurrent protective devicesdo not open
Selective Coordination
Ar ticle 100 Defin it ion
Ar ticle 700 Emergency Sys tems
Coordination (Selective)
Localization of an overcurrent condition to restrictoutages to the circuit or equipment affected,accomplished by the choice of overcurrent protectivedevices and their ratings or settings.
700.27 Coordination.
Emergency system(s) overcurrent devices shall beselectively coordinated with all supply side overcurrentprotective devices
(Wording for 701.18 and 708.54 is the similar except for the type system)
Without Selective Coordin ation With Selective Coordi nation
OPENS
NOT AFFECTED
UNNECESSARY
POWER LOSS
OPENS
NOT
AFFECTEDFault Fault
System Prospective
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Circuit Br eaker Instantaneous Trip
Up to where the circuit
breakers cross, it is
interpreted to becoordinated. See
800A
200A
30A
Up to
7600A
Up to
1500AX
X
4
4
5
5
6
6
7
7
8
8
9
9
10
10
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
100
100
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
1000
1000
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10000
10000
2
2
3
3
4
4
5
5
6
6
7
7
.01 .01
.02 .02
.03 .03
.04 .04
.05 .05
.07 .07
.1 .1
.2 .2
.3 .3
.4 .4
.5 .5
.7 .7
1 1
2 2
3 3
4 45 5
7 7
10 10
20 20
30 3040 40
50 50
70 70
100 100
200 200
300 300
400 400500 500
700 700
1000 1000
CURRENT INAMPERESAT 480 VOLTS
CURRENT INAMPERESAT 480 VOLTS
TIMEIN
SECONDS
TIMEIN
SECONDS
1500A 7600A
30A
0.01s
0.1s
800A
IT = 10X
200A
IT = 10X
Reference
IEEE 1015-2006 BLUE BOOK Applying Low-VoltageCircuit Breakers Used in Industrial and CommercialPower Systems
Page 148 5.5.5 Thermal-magnetic MCCBs andinsulated case circuit breakers
It should be noted that if the fault current is above theshort-time rating (instantaneous override), then theICCB will not be selective with downstream devices thatalso have instantaneous trips.
Bussmann Fuse Coordination
No fault levels or plotting required!
LOW-PEAK : LOW-PEAK
2:1 Line:Load RatioLine
Side
Fuse
Load Side Fuse
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Cooper Bussmann Solutions
Quik-Spec Family
Suite of fusible electrical distributionproducts designed to meet Selective
Coordination and other NEC
requirements, providing the numerousbenefits of fused solutions
Cooper Bussmann committed toexpanding our assembly offering,
focused on product differentiation,creating options for fusible solutions
Quik-Spec Family: Coordination Panelboard
Power Module
Safety Switch
One line diagram
With quik spec
products
The New Standard in Fusible Panelboards
SimplifiesSelectiveCoordination
Better Value
SmallerFootprint
Add iti ona lMain Options
Patented FuseRejection,Interlock andIndication
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Quik-Spec Power Module
Fused Elevator
Shunt-Trip Disconnect
Easy to Specify andInstall
UL98 Listed Assembly
Simplifies SelectiveCoordination
Simplifies CodeCompliance
PMP Available formultiple elevatorinstallations
Power
ModuleSwitch
Power
Module
Panel
High IR Protective Devices
Compact Circuit Protector
200kA SCCR
60A 600V
Class J/CC fusing
Smallest fusibledisconnect
available
Finger-safe design
UL98 branch
circuit disconnect
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Summary
NEC contains numerousrequirements related to fault levels
Understanding basics of faultcontribution can simplify efforts withcompliance
Higher wi thstand components maypresent fewer concerns
Fused system selective coordinationthrough 200kA achieved with ampratios
Cooper Tech Center Training
Fusible Design for Bui lding SystemsApril 28, 2009 (Cooper Bussmann)
NEC Emergency Systems, LegallyRequired and OptionalMay 29, 2009 (Mark Hilbert, NH Chief AHJ)
Electrical System MaintenanceAugust 18, 2009 (Jim White, Shermco)
Simplif ied Fault Current
Calculations
QUESTIONS ??
Presented by:
Dustin [email protected]