Lighting Contactors Withstand of 5kA

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lizzie14

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I am working on a job with 5kA withstand rating for the lighting contactors. I performed the short circuit calculation from the panel feeding coil down to contactor. It is less than 5kA so it was ok. The inspector wants to know if the AIC from the loads served (lighting circuits) by the contactor are also under 5kA. I've never heard of this. Any ideas?
 
Actually, it's only the loads that count, not the control circuit. You need to look at the available fault current (AFC) at the terminals and plot that against the let-through chart of whatever breaker is feeding the contactor. If it ends up higher than 5kA, you're screwed. Your only choices will be to limit the fault current with either current limiting fuses or maybe a CL breaker, or replace both the breaker and the contactor with a pair that have a coordinated SCCR rating greater than what your AFC is.
 
lizzie14 said:
I am working on a job with 5kA withstand rating for the lighting contactors. I performed the short circuit calculation from the panel feeding coil down to contactor. It is less than 5kA so it was ok. The inspector wants to know if the AIC from the loads served (lighting circuits) by the contactor are also under 5kA. I've never heard of this. Any ideas?
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AIC means Amps Interrupting Capacity, it applys only to devices that open/break short citcuti currents therefor it is not applicable to loads.

The common term for things that do not breaker fault currents (like appliances and control panels) is Short Circuit Current Rating (SCCR).
 
A universally common mistake to be sure.

I gave a seminar last year where I discussed all these issues with plant electricians at a local factory. One of them piped up in the background;

"I couldn't even spell AIC, how do you expect me to spell SCCR now?" :D
 
Wasn't there an old thread about this a a year or so ago? One lighting controller manufacturer required a minimum of X feet of conductor between the breaker and the contactor. Anyone remember that one?
 
infinity said:
Wasn't there an old thread about this a a year or so ago? One lighting controller manufacturer required a minimum of X feet of conductor between the breaker and the contactor. Anyone remember that one?
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Yes, I think it was 20' of wire would bring it down to less than 5K. I think the wire size was no more than #10 though.
 
Jraef said:
If it ends up higher than 5kA, you're screwed. Your only choices will be to limit the fault current with either current limiting fuses or maybe a CL breaker, or replace both the breaker and the contactor with a pair that have a coordinated SCCR rating greater than what your AFC is.
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Or longer run of wire between the breaker and contactor?
 
Don't confuse kaic with withstand.
This is my understanding:
Withstand is the components ability to withstand a given fault without being damaged.
KAIC is the ability to interupt a given fault, that is it's ability to open automatically in response to and clear a fault.
Component listed UR contactors and starters must have a 5ka withstand by default which is the minimum rating. But when combined as a listed enclosed combination starter that has been tested with the OCPD there will be a label on the side of the enclosure that stated its interupting rating.
 
templdl said:
Don't confuse kaic with withstand.
This is my understanding:
Withstand is the components ability to withstand a given fault without being damaged.
Click to expand...

This sounds correct.

KAIC is the ability to interupt a given fault, that is it's ability to open automatically in response to and clear a fault.
Click to expand...

This is where my understanding differs. KAIC (my understanding) is the fault current available.

Component listed UR contactors and starters must have a 5ka withstand by default which is the minimum rating. But when combined as a listed enclosed combination starter that has been tested with the OCPD there will be a label on the side of the enclosure that stated its interupting rating.
Click to expand...

Indeed a series rated/tested assembly may have a higher rating than the "withstand" rating of a single component.
 
hardworkingstiff said:
KAIC (my understanding) is the fault current available.
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No, SCA is commonly used for Short Circuit Available. Although I know of no official acronym.

AIC is definitely Amps Interuppting Capacity.
 
Trevor,

Yes, I do remember that one. I don't know how to do that click 'here' trick

but if you go to Benaround profile and then 'all threads started by' then click

" Slave for life" that should be the one.
 
Yes, AIC (Amps Interrupting Capacity) can only be applied to something that interrupts, such as a circuit breaker or fuse. Everything else has a "withstand rating", usually expressed in kA, which is related but not the same. Lately because of the changes to Article 409, they now use the term "SCCR" for Short Circuit Current Rating, which is basically the same thing, but as mentioned before, the SCCR can be diferent for series tested combinations. 5kA is just the courtesy rating given to un-tested or legacy components.

Here's an example:
Siemens SCCR white paper link If you scroll down to page 9 you can see that in the example they give, the breaker is rated 25kAIC, the contactor and OL relay are only 5kA short circuit withstand, but the combination has been tested together at 100kA SCCR.

This link gets you to examples of all of their SCCR listed combinations. Several other control equipment manufacturers have similar resources available now.
Siemens SCCR web site, but be forewarned; if the component combinations are not very specifically on one of these lists, you default back to the 5kA un-tested.
 
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