fire pump short circuit and wic considerations

Short Circuit (WIC) Testing and Parameters.

- for -

F.M. Approvals- by -

James S. Nasby

Columbia Engineering

C.E. F.M. Approvals 2

Topics to be Covered High Current Effects Medium Current Effects Breaking the Circuit (Clearing the Fault) Effects and Construction Components Design Parameters Testing Safety (Arc Flash & PPE Requirements)


Definitions Ip = Peak Current AttainedI2t = Total "Energy" (amp2-seconds)

I2 x R = P (Power in watts) & P x t = E (Energy in watt-seconds or joules), but R is a constant so I2t ~ Energy

P.F. Power Factor = Cosine of Phase Angle between the voltage and current

Higher Current Circuits Tend to be More Inductive Hence Lower Power Factor Lower Power Factor Current Flow is Harder to Interrupt

since The Current is Still Flowing at Voltage Zero Crossings, -

and- The Voltage is Non-Zero at Current Zero Crossings


More Definitions Current Limiting = Fuses or Breakers (or Blow Apart Isolating Switches) which Completely Clear (Interrupt Current Flow) Prior to the First Half Line Cycle (8.33 mSec @ 60Hz or 10 mSec @ 50 Hz)Inductive Circuit - Circuit where the Current Lags the Voltage. In Capacitive Circuits it Leads instead.Blow Apart Design = Current Flows in a "U" Shape Path which Creates Opposing Magnetic Force at High Currents. When said Force Exceeds Spring Force, Contacts Begin to Separate.


Yet More Definitions IEC Type 1 Protection = Basically the U.L. Criteria, Namely that Equipment:

Won't Start a Fire Won't Become a Shock Hazard Will Contain the Event (Parts Stay Inside) Equipment May (and usually is) Damaged Beyond Use

or Safe Operation

IEC Type 2 Protection = Basically the U.L. Criteria, Namely that Equipment:

Meets all of Type 1 Protection -and- Equipment is Largely Undamaged E.g.: Still Functional; although some repair may be

needed.


Still More Definitions First Half Cycle Offset Occurs in Inductive A.C. Circuits Maximum when Circuit is Closed at a Voltage

Zero Crossing Minimized when Circuit is Closed at a Voltage

Peak This is Because Inductive Component of

Current Lags the Voltage by 90 Degrees

This also affects Motor Starting Inrush Current Max Theoretical Peak Current = 17 x FLA Max "Practical" = Approx. 13 x FLA


First Half Cycle Offset Waveforms

2.83 x LRA = 6 x 2.83 x FLA = 17.0 x FLA Maximum Theortical This curve shows starting a motor

which still has BACK EMF (voltage) present.


Parametric Considerations

Higher Ip Results in Magnetic Effects which Tends to Pull Conductors out of Lugs, especially on Parallel Runs

Higher I2t causes Greater Arcing, Overpressure, Heating Damage and Arc Flash Energies Higher Can Come from:

Higher Available S.C. (Fault) Current Higher Power Circuits More Direct (Lower Impedance) Short Circuit


Type of Faults (Shorts)

Fault to Ground Line to Line (Phase to Phase) Bolted (Solidly) Fault Medium Current Faults (Impedance Faults) Arcing Fault Lower Level Faults


Higher Level Faults

May Create Higher Overpressure May Create Higher Arc Fault Energy May be Easier to Clear than Lower Level Faults Causes Breakers to Begin to Open Faster Causes Fuses to Melt and Begin Arcing Sooner

Usually Create Higher Ip Peak Currents May Result in Lower I2t Energy (and resulting Overpressure)


Lower (Medium) Level Faults

May Create Higher Overpressure May Create Higher Arc Vault Energy May be Harder to Clear than Lower Level Faults Causes Breakers to Begin to Open Later Causes Fuses to Melt and Begin Arcing Later

Usually Create Lower Ip Peak Currents May Result in Higher or Lower I2t Energy (and resulting Overpressure)


Low Level and Arcing Faults

Arcing Faults Tend to Be Low Level; but, May Be Medium Level Current Limiting Usually Won't Occur Clearing May Depend on Long Time

Characteristics May take Seconds or Longer to Clear

Overpressure May Be Low However, Significant Damage Will Occur


Breaking the Fault OCP Device Must Wait for a Zero Crossing of Voltage and Current (or as Close to same as possible) -or- Restive (1.0 PF) Circuits are Easiest to Clear Lower Inductance Circuits (Higher PF) are next

easiest Lowest PF (Most Inductive) Circuits are Hardest

Or Must Limit the Current, Usually while the Current is Still Rising


Power Factor WaveformsA.C. Voltage & Current Waveforms

Resistive with Power

0 90 180 270 360 450 540 630 720

Time in Electrical Degrees

Current Power - E x I x Cos(theta) Voltage


Power Factor WaveformsA.C. Voltage & Current Waveforms

Reactive with Power

0 90 180 270 360 450 540 630 720

Time in Electrical Degrees

Current Power - E x I x Cos(theta) Voltage


Typical Fire Pump Controller Breaker Curve

EC Series - "F" Frame Breaker Trip Curve

0.001

0.01

0.1

1

10

100

1000

10000

1 10 100 1,000 10,000

Multiples of Range Setting

Tri

p T

ime

(Sec

onds

)

Notes:

1) “F” Frame = 250 Amp Frame Rating.

(260 x 250A = ~ 65 Kamp)

2) Typically two devices are used in series (I/S + C/B) to achieve ratings up to 100 Kamp.

3) Ratings to 200 Kamp are available

4) Curve shown is different for Current Limiting Breakers


Typical EFPC Ratings Nameplates

Note


NFPA Required WIC RatingWIC = Short Circuit

Withstand

and Interrupting Capacity Rating Controller WIC Rating

Must Equal or Exceed the Available Short Circuit Current from the Power Source.

Note: Some controllers now being sold with WIC’s below 100 Kamp. This doubles need to check available fault (S.C.) current.


What’s Wrong with This Picture?


Main Reason for Bolted Fault Short Circuits…

…and for Motor Junction Box Explosion.

Note that Workmanship is Vital.


Cause for Overpressure


Cause – cont’d


Clearing the Fault(Safely Breaking the Circuit)

Single Phase Arcs are interrupted 120 times per second, although inductive loads obviate this to at least some degree.Three Phase Arcs are Continuous (No Zero Crossing). They Rotate Around the Three Poles of Whatever is Arcing.


Testing UL-218 & FM-1321/23

Short Circuit Test: Parameters Criteria Dielectric Voltage - Withstand

Test Shock Hazard



Short Circuit Test - Fault Currents From 10,000* Amperes test current to

a maximum of 200,000 Amperes. Tested at 100 - 105% of rated voltage. Power factor range from 0.80 through

0.20 depending on test current.

* = Minimum Allowed for 400 Hp



Short Circuit Test. No parts discharge from the enclosure. No damage to a conductor or terminal

connector. No breakage of insulating bases which

would compromise mounting integrity. Door must remain closed only by the

intended latch mechanism, no major deformation.

Circuit breaker must remain operable.



Short Circuit Test: Closing Test (UUT Closes on Fault) Withstand Test (Voltage Applied to UUT with

current path already closed)

Must not Blow 30 Amp Ground Fuse (or wire link)After Testing: Dielectric Voltage - Withstand Test Door Wiring Flexing Test Circuit breaker must remain operable.



Dielectric Voltage - Withstand Test Tested at twice the rated voltage but

no less than 900 Volts Between line and load terminals of C.B.

and I.S. in open position. Between terminals of opposite polarity

on C.B. and I.S. in open position Between live parts and enclosure with

C.B. and I.S. both opened and closed



This is to assure that the unit has Not Become a Shock Hazard or a Fire Hazard, and Can Be Deenergized.The UUT May be otherwise Destroyed Type 1 Criteria = Non-Functional After a

Short Unless Type 2 Criteria is verified



Allowed to Change Components Between Tests Never Needed for M.C.S. for Full Service Should Not be needed for IEC Type "2" Commonly Needed Otherwise

Paper Coordination Requires Test Data (I2t and Ip) for

Component I/S and/or C/B: Let Thru Less Than Controller Withstood.

Controller (WIC): How Much Withstood or How Much Delivered

Other Components: (Contactors, Xfer Switches, Etc.) Withstand more than Controller will Deliver?


Arc Flash and PPE Requirements

NFPA 70E (Workplace Safety) requires that Equipment be marked where installed. This requires a specific Short Curcuit Available (Available Fault Current) study along with the environment (Indoors, Outdoors, Room Layout, No. of Doors, etc.)The Arc Energy is then calculated which then yields the PPE level of protective clothing required.


PPE Levels Defined - NFPA-70E

Table 130.7(C)(11) Protective Clothing CharacteristicsTypical Protective Clothing Systems

Required Minimum Hazard/Risk Clothing Description Arc Rating of PPE Category (Typical number of clothing layers is given in parentheses)

[J/cm2(cal/cm2)]0 Non-melting, flammable materials (i.e., untreated cotton, wool,

rayon, or silk, or blends of these materials) with a fabric weightat least 4.5 oz/yd2 (1) N/A

1 FR shirt and FR pants or FR coverall (1) 16.74 (4)

2 Cotton underwear — conventional short sleeve and brief/shorts,plus FR shirt and FR pants (1 or 2) 33.47 (8)

3 Cotton underwear plus FR shirt and FR pants plus FR coverall, orcotton underwear plus two FR coveralls (2 or 3) 104.6 (25)

4 Cotton underwear plus FR shirt and FR pants plus multilayerflash suit (3 or more) 167.36 (40)

Note: Arc rating is defined in Article 100 and can be either ATPV or EBT. ATPV is defined in ASTM F 1959-99 as the incident energy on a fabricor material that results in sufficient heat transfer through the fabric or material to cause the onset of a second-degree burn based on the Stoll

curve.EBT is defined in ASTM F 1959-99 as the average of the five highest incident energy exposure values below the Stoll curve where the specimensdo not exhibit breakopen. EBT is reported when ATPV cannot be measured due to FR fabric breakopen.

Note: See Also: Table 130.7(C)(10) Protective Clothing and Personal Protective Equipment (PPE) Matrix


Selective Coordination

NFPA-70 (NEC®) §700.27 & 400.18 require Selective Coordination. It is Important to Note that the Fire Pump is Usually the Largest Load on the Emergency System, and that it Can, and Does Create a Bolted Fault on the System.Selective Coordination prevents the Fire Pump from taking out Other (All Other) Emergency Loads, and vice versa.


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fire pump short circuit and wic considerations

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