Equipment Short-Circuit Current Rating and Available Fault Current - SW IAEI.243212239

8/12/2019 Equipment Short-Circuit Current Rating and Available Fault Current - SW IAEI.243212239

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2013 Eaton. All rights reserved.

Equipment Short-Circuit CurrentRating and Available Fault Current

Dan Neeser Field Application Engineer

Eatons Bussmann Business

[email protected]

2 2013 Eaton. All rights reserved.

Agenda

Interrupting Rating & Series Rating

Short-Circuit Current Ratings

Maximum Fault Current Marking

Fault Current Calculations

UL 508A Industrial Control Panels

Supplement SB - SCCR


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Interrupting Rating

NECArticle 100 Definition Highest current an OVERCURRENT DEVICE

(fuse or circuit breaker) is rated to safely interrupt.

Self protection rating only

NEC 110.9 Interrupting Rating.

Requires the overcurrent device to have an

interrupting rating not less than the maximum

available fault current.

The maximum fault current must be calculated and

varies based on system size/location.

Similar Requirements in OSHA 1910.303(b)(4)


Interrupting Rating NEC 110.9: Device interrupting rating MUST

be equal to or greater than the maximum

available fault current.

Chapter 1 Video Clips - Interrupting Rating


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1st

Determine available short-circuit

current (Isca) at lineside

terminals of each OCPD.

2nd

Apply OCPDs with adequate

Interrupting Rating.

Isca 3

MM

MSB

Isca 1

Isca 4 Isca 5

Isca 6

Isca 2

Interrupting Rating - Proper Application


Must select circuit breaker with interrupting rating adequate for

point of application varies by voltage and circuit breaker type.

Interrupting Rating - Proper Application


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High Interrupting rating of current-limiting fuses at full voltage reduces

concerns about proper interrupting rating at point of application

I.R. - Proper Application


A combination of:

- Circuit breakers / circuit breakers

OR

- Fuses / circuit breakers

that can be applied at available fault levelsabove the interrupting rating of the load side

circuit breaker, but not above that of the mainor line side device.

Downstream device will ALWAYS be a circuit breaker

Series Rated Systems


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Series Rated

Combination

65,000 A.I.R.200A Circuit Breaker

65,000 A.I.R.

ISC=65,000 A

20A Circuit Breaker

ISC=65,000 A

10,000 A.I.R.

Series Rated Systems: CB-CB


Series Rated

Combination

200,000 A.I.R.

ISC=200,000 A

20A Circuit Breaker

ISC=300,000 A

10,000 A.I.R.

Series Rated Systems: Fuse-CB

LPJ 400 SP

300,000 A.I.R.


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NEC 240.86(A) Selected Under EngineeringSupervision in Existing Installations The series rated combination devices must be selected

by licensed, professional engineer.

Requires Documentation and Stamp.

Series combination rating and upstream device must befield marked on end use equipment.

Downstream circuit breaker must remain passive.

NEC 240.86(B) Tested Combinations

The combination of line side and load side devices mustbe tested and marked on the end-use equipment(panelboards & switchboards).



Additional Limitations and Requirements

Labeling Requirements

Manufacturer NEC 240.86(B)

Field Marking NEC 110.22(B)&(C)

Motor Contribution Limitations

NEC 240.86(C)

Motor FLA cannot exceed 1% of IR of protected CB.

Lack of Selective Coordination


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Current Limitation

A current limiting

fuse will clear a

fault within one

half of a cycle. Thermal energy is

proportionate to thesquare of RMScurrent multiplied bythe time (Irms2t)

Mechanical stressesare proportionate to

the square of peakcurrent multiplied bythe time (Ip2t)


Current Limitation

Conductor protection for fault of 45kA/480V (26kA with

conductor) with non-current-limiting device (1 cycle) vs.

current-limiting device (>1/2 cycle)


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Short-Circuit Current Ratings

NECArticle 100 Definition

The highest current EQUIPMENT can withstand without extensive

damage (fire or shock hazard).

Also known as component protection

May be based on a specific type of overcurrent device

NEC 110.10 Circuit Impedance, Short-Circuit Current Ratings,

and Other Characteristics.

Requires the equipment to have a short circuit current rating

not less than the maximum available fault current.

The maximum fault current must be calculated and varies

based on system size/location. Similar Requirements in OSHA 1910.303(b)(5)


Motor Starter - SCCR High Fault Test: starter

protected by an instantaneoustrip circuit breaker (MCP) thatonly provides Type 1 protection

High Fault Test: starterprotected by Low-Peak fusesthat provides Type 2 (NoDamage) protection

Fault

480V - 22,000A

Fault

480V - 22,000A


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430.8 Marked on motor controllers

440.4(B) Marked on HVAC equipment

409.110(3) Marked on industrial control panels 409.22 Fault current cannot exceed marked SCCR

670.3(A)(4) Marked on industrial machinerycontrol panel 670.5 Fault current cannot exceed marked SCCR

UL 508A, Supplement SB is an approved methodto determine SCCR forindustrial control panelsand industrial machinery control panels

SCCR Marking Requirements


Fault Current Marking Requirement

110.24 Available Fault Current.

(A) Service equipment must be marked with

the maximum available fault current and

date of calculation

(B) If fault current increases due to system

modification, the marking must be updated.


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How to Comply?

Service Equipment

Isc = 60,142 A

Isc = 27,532 AIsc = 42,153 A

Max Avail. Fault Curr ent = 58,524 A

Date Determined/Calculated: 9/2010

Isc = 18,752 AIsc = 38,525 A

Required per NEC 110.24

Motor Controller

SCCR = 25kAIndustrial Control Panel

SCCR = 30kA

Industrial Machinery Panel

SCCR = 65kA

HVAC

SCCR = 40kA

All equipment must comply with:

NEC 110.9 (IR) &110.10 (SCCR)

Engineer Calculate

Contractor Label


IR/SCCR Inspection Check-List


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Fault Current Calculations

To determine the fault current:

Draw the one-line diagram

Identify sources of short-circuit current (utility,

generation, motors)

Include system component information

(tranformers, conductors, busway, overcurrent

devices are not considered)

Use calculation method (ohmic, per unit, point-to-

point, software)

Use typical fault current values as a reference

only.


Typical Short-Circuit Current Values

Short-Circuit Current at service entrance equipmentvaries by type/size of system: Small residential systems (100A to 200A) 10,000A to

15,000A or less

Small commercial building systems (400A to 800A) 20,000A to 30,000A

Larger commercial and manufacturing building systems(2,000A to 3,000A) - 50,000A to 65,000A

Higher short-circuit currents are possible where lowimpedance (energy-efficient) transformers are used (orwhere larger transformers (kVA) feed multiple services.

Commercial buildings directly connected to utility gridsystem 200,000A or greater


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Short-Circuit Current Factors

Typicallyhighest atservice point

Decreases indownstreamequipment(due toimpedance oftransformers

andconductors)


Calculation Example

480V/3000A Service supplied from 2500 kVA

Transformer

Find Isc at Transformer Secondary & Service

Equipment480V, 3000A Service Equipment

Service Transformer

2500 kVA

13.2kV 480V

5% Impedance

7 600 Cu kcmil/phase

25 Feet in PVC

Isc = 60,142 A

Isc = 58,524A


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IFLA =KVA X 1000

EL-L X 1.732

KVA = KVA of TransformerEL-L = Secondary Phase to Phase voltage

Calculation Example

Step One: Calculate Secondary FLA of

Transformer (3 phase)


2500 KVA Transformer

13.2kV - 480V, 3 Phase

Z = 5%

ISC

IFLA =2500 X 1000

480 X 1.732

IFLA = 3007 A

Calculation Example


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480V

Switchgear


25 Feet in PVCISC = 60,140A

Calculation Example

Calculate Short Circuit Current at 480V

Switchgear


ISC 480V SWGR = ISC X Mult

Calculation Example

Isc known from previous calculation

Calculate multiplier for Cable

Step One: Calculate f value


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f =1.732 X L X ISC

C X EL-L

L = Length of conductor

ISC = Short-circuit current at beginning of circuit

C = C Value Constant for Cable

From Table. Multiply by # of runs

EL-L = Phase to Phase Voltage

Calculation Example

Step One: Calculate f value


Calculation Example

C Value 600 kcmil, CU, PVC = 28,033


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f =

1.732 X 25 X 60,140

7 X 28,033 X 480= 0.0276

Calculation Example

Step One: Calculate f Value

L = 25 Feet

ISC = 60,140 A

C = 7 X 28,033 - See C Value Table

EL-L = 480V


Mult =1

1 + f

Step Two: Use Calculated f Value

Calculate Multiplier

Calculation Example

Mult = = 0.973111 + 0.0276


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ISC 480V SWGR = ISC X Mult

ISC 480V SWGR = 60,140 X .9731

ISC 480V SWGR = 58,522 A*

* Add motor contribution if present

Calculation Example

Calculate Short Circuit Current at 480V

Switchgear


What if the System Changes?

480V, 4000A Service EquipmentService Transformer

3000 kVA

13.2kV 480V

5% Impedance


25 Feet in PVC

Isc = 72,171 A

Isc = 70,587A

480V, 3000A Service EquipmentService Transformer

2500 kVA

13.2kV 480V4% Impedance


25 Feet in PVC

Isc = 75,178 A

Isc = 72,667A


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Cooper Bussmann Short-Circuit Calculator

New version

Apple or Android Apps

Web (run from homepage)

Old version

Download for Window XP


Choosethreephaseor

singlephasesystem

Calculating available fault current and creating 110.24 labels has never been easier!

1 2 3

ClickonAddtomy

System

Selectacomponent

youwanttoadd

Create a System


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SelectAdd

Transformer


1 2 3

Ifyou

have

aknown

primary

fault

currentyoucanaddithere. Ifnot,

selectassumeinfinite

Entervalues

into

the

appropriatefields

Add a Transformer


AfteraddingaTransformer,

youwillbeaskedifyouwant

toaddmotorcontribution


1 2 3

Youcancompleteaquickcalculation

byselectinga%ofyour

transformersFLAoradditmanually

Addthese

calculationstoyour

system

Add Motor Contribution


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SelectAdd

To

MySystem


1 2 3

AddConductor

RunorBussRun

Addthecorrectvalues

andAddToSystem

Add Other Components


Viewsystemoneline

diagram


1 2 3

Emailoneline

diagram

Selectaspecificfaultto

createalabel

System Summary


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Selectafaultandclick

onCreateLabel


1 2

Entertheemailaddress, projectname,

faultname,andlabelsize,thenSendLabel

Create a Label


TaponFuse

SizingDiagram

Sizing fuses for mains , feeders, and branch ci rcuits has never been easier!

1 2 3

Taponthecircuit

toprotect

Review eachsectionandthefuse

suggestionsfortheselectedlocation

Fuse Sizing


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TheUserguide

providesuseful

informationaboutFC2

Thereisauserguide

selectionatthebottom

ifeachpage

Basedonwhereyou

areintheapp,youwill

beprovidedaspecific

overviewofFC2s

functionality

WhiletheFC2isvery

intuitive,theremaybe

additionalquestions

ThereisaContactUs

selectionatthe

bottomofeachpage

Fromthislocation,

youcanselecttosend

anemailfortechnical

assistanceor

customerservice

support

User Guide & Contact Us


Cooper Bussmann FC2 Web Version - Example


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How to Determine SCCR?

Short-Circuit Current Rating (SCCR)

Can be established by testing during the listing

and labeling process

OR

Can be determined using an approved

(calculation) method

UL 508A Supplement SB is an approved method

(industrial control panels and industrial machinery

control panel)

AHJ Approved Method

NRTL field evaluation can also be used.


Industrial Control Panel SCCR

Industrial Control Panel.

An assembly of two or more components consisting of one of the

following:

1)power circuit components only, such as motor controllers,

overload relays, fused disconnect switches, and circuit breakers;

2)control circuit components only, such as push buttons, pilot

lights, selector switches, timers, switches, and control relays;

3)a combination of power and control circuit components. These

components, with associated wiring and terminals, are mounted

on, or contained within, an enclosure or mounted on a subpanel.The industrial control panel does not include the controlled

equipment.

48


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UL 508A Supplement SB

What Needs to be Analyzed per UL 508A,

Supplement SB?

All power circuit components (SB 4.1)

Feeder and branch circuit components that supply power to

loads (motors, lighting, heating and appliances)

Includes disconnect switches, fuses, circuit breakers, load

controllers, overload relays, power distribution/terminal

blocks, bus bars, etc.

Control circuit components are not required to be

analyzed Pushbuttons, pilot lights, selector switches, timers, control

relays, etc.


Power vs. Control Circuits

Control circuit components

dont have to be analyzed

Power

Transformer

Control Transformer

*

*Control Circuit, but

affects SCCR


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How to Determine Component SCCR (SB4.2.2)? The SCCR marked on the component or on instructions.

The SCCR determined by the voltage rating of thecomponent and the assumed short circuit current fromTable SB4.1.

or

The SCCR for a load controller, motor overload relay, orcombination motor controller that has been investigatedin accordance with the performance requirements,including short circuit test requirements for standard faultcurrents or high fault currents specified in the Standardfor Industrial Control Equipment, UL 508, and describedin the manufacturers procedure.



What are the Rules (Sweep 1)?

Lowest component SCCR limits

assembly SCCR unless:

Combination ratings can be used to

increase branch circuit component ratings

(SB 4.2.2)

Component with marked/specified OCPD

Check with component manufacturer for

combination ratings


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Combination Ratings - Branch

Use combination

ratings with

specified/marked

OCPD to fix low rated

branch components

Component SCCR OCPD I.R.

Combination ratings of overcurrent protective devices and components can be used

Nameplate

480

SCCR:

Voltage:

100kA


Combination Ratings - Contactor


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Combination Ratings - MMP

OL Protection Only

Fuse or Circuit Breaker Required for

SC Protection

Suitable for Group Installations

Straight Ratings (480V)


Combination Ratings Type E/F

Combination Motor Controller

SC & OL Protection

Line Side Adapters Required

Slash Ratings (480/277V)


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Combination Ratings - ASD

200kA with Class CC/J/T Fuse

Suitable for Group Installations

65kA with Type E CMC (480/277V)


Combination Ratings - Feeder

Use UL Listed powerdistribution block with highSCCR when used withspecified fuses or circuitbreakers and required loadside conductors

Must have feeder circuitspacing (Listed PDB) if infeeder circuit

Nameplate

480

SCCR:

Voltage:

100kA


Combination ratings of PDBs is cost effective fix


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59 2013 Eaton. All rights reserved.59

Combination Ratings - PDBs

PDBFS220 (4 14 Load Side

Conductors) 100kA with 175A

Class J fuse or less




Lowest component SCCR limits assembly

SCCR unless:

Feeder components are used that limit the short-

circuit current reducing the need for higher branch

circuit component SCCR (SB 4.3)

Current limiting overcurrent protective devices

Transformers rated 10kVA or less


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Feeder Circuit

Branch

Circuit

Branch

Circuit

Feeder vs. Branch Circuits


Use of CL Devices - OCPD

CL Device must be in the feeder circuit

For CL Fuses or Circuit Breakers Use PEAK Let-through, Not RMS Let-Through (more

conservative)

Fuses - cannot use manufacturer specific fuse data only tables based on performance requirements fromUL 248 (more conservative - apply to allmanufacturers)

Circuit Breakers - must be Listed and marked current-limiting and use published let-thru curves (most circuit

breakers are not CL) Can only raise downstream BRANCH circuit

components (not overcurrent protective devices fuses/circuit breaker IR or Combination motorcontrollers SCCR)


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Fuse LT UL vs Manufacturer

LPJ-100SP

UL Limits 50kA = 12kA

100kA = 14kA

200kA = 20kA

Manufacturer LetThrough Curves Ip LT:

50kA = 9kA

100kA = 12kA

200kA = 14kA

Irms LT: 50kA = 4kA

100kA = 5kA

200kA = 6kA


Current limitingfeeder OCPDcan be used to

increase branchcomponentSCCR.


Use of CL OCPD can only fix components

F

B

Use of CL Devices - OCPD

Nameplate

480

SCCR:

Voltage:

14kA


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Use of CL Devices - Transformers

CL Device must be in the feeder circuit

For Transformers If 10kVA with secondary devices (components and

overcurrent devices) of 5kA or higher, apply the IRof the primary overcurrent protective device

If 5kVA (120V Secondary) with secondary devices(Components and overcurrent devices) of 2kA orhigher, apply the IR of the primary overcurrent

protective device



10 kVA

Use of CL Devices - Transformers

Transformers can be used tolimit the short-circuit currentavailable

If 10kVA & sec comp = 5kA+ If 5kVA/120V & sec comp = 2kA+ Then assign entire circuit I.R. of

primary overcurrent device

Use of Small Transformers (10kVA or less) can increase secondary component/OCPD ratings

Nameplate

480

SCCR:

Voltage:

200kA


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Lowest overcurrent protective device interrupting

rating (or SCCR for some devices) always limits

assembly SCCR

All Feeder and branch circuit overcurrent devices

Tested series combination ratings or series ratings

(fuse-circuit breaker or circuit breaker-circuit breaker)

are NOT allowed.

Branch circuit overcurrent devices tapped from the feeder

circuit supplying a control circuit. Supplemental protective devices protecting the control

circuit transformer in a motor branch circuit.


Overcurrent Protection Devices

Branch Circuit Protective Devices

Fuses

Circuit Breakers

Application Limited Devices

Supplemental Protectors/Fuses

Not suitable for branch circuitprotection (protecting a load)

Can only be used in control circuits


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Why High SCCR?

NEC & Equipment standards only require the

SCCR to be marked

NEC requires the marked value to be adequate

for the maximum available fault current

Although not required, high SCCR is often

preferred

Flexibility of application

Multiple installations

Fault current unknown

Insufficient SCCR can delay installation


Fix It - Solutions

High I.R. Protective

Devices

Class R

Class J

Class J Drive Fuse

Class T

Class CC

CubeFuse

High Speed

High IR/CL CBs

Equipment Short-Circuit Current Rating and Available Fault Current - SW IAEI.243212239

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