Equipment Withstand Ratings

[ron]

The NEC requires equipment that will be interrupting fault current, have an adequate interrupting rating (110.9).
Is there any code requirement for equipment that doesn't switch, to have an adequate withstand rating.
For example, a #14 THHN conductor has a withstand rating/curve, which represents the conductors ability to withstand fault current for a period of time before failure.
A safety switch has a withstand rating for the same reason.
I am discussing the same concept with a static switch manufacturer, where the switch will not require an interrupting rating, since it doesn't attempt to interrupt a fault, but will be called upon to withstand the fault if it should occur. They feel that a withstand rating is not required by any code. It seems weird to me that there not be a withstand rating.

 

[coulter]

...Is there any code requirement for equipment that doesn't switch, to have an adequate withstand rating. ...

Ron -
How about 110.10, "...the component short-circuit current ratings ..."

It certainly seems the components should stand the available SSC with out catastrophic failure.

carl

 

[cpal]

Additionally the NEC removed the phrase withstand (99 or 02???) from 110.9 and or 10. as I recall the proposal indicated that it was not necessary for the equipment in question to survive the incident. They just to function to clear the event.

OBTW
The withstand rating on conductors is a value of current that it may carry for 5 seconds. Soars book indicates 1 Amp per 42.25 at 75 degrees C No 14 Ga at 4110 CMA / 42.25 = 97.27 A for 5 seconds. then you may have a condition called burn off. Of course as in all things not being equal different eng factions have different values but I believe they are reasonably close.

I would be concerned about a component that was not submitted to a NRTL for testing, is that what the op is implying??

 

[davidr43229]

Ron,
Instead of a Withstand rating, ask for it's SCCR rating, or you may get a I 2 T rating from them, which is hard to compute.

 

[ron]

I received the I^2t rating which doesn't seem to directly relate to the withstand.
They indicate that there is only a SCCR for the input circuit breaker, but is unaffected by the guts of the equipment in the box, which is what I question. The overall unit itself doesn't seem to have a SCCR.

 

[ron]

Carl,
110.10 does not seem to require a component short-circuit current rating, just that it be used to design with.

 

[davidr43229]

Ron,
As you know the I^2 T will look something like 115 X 10^3 for .3 sec, withstand will be represented in RMS values.
The SCCR rating before the CB, I would almost take as the component withstand, excluding any dynamic impedance of the breaker.
Did they specify any manufacturers or part numbers of breakers?

 

[ron]

No model # yet.
It is primarily the dynamic impedance of the equipment, breaker, well heck everything downstream from the service fuses, that make me feel that the equipment needs a withstand (or SCCR) on its own.

 

[davidr43229]

Is there any code requirement for equipment that doesn't switch

UL508A SEPT 05 edition. I have seen equipment using the switch in the buss-plugs, on a dedicated drop.

equipment needs a withstand (or SCCR) on its own

And you're right NEC 409 ?
Just on new stuff manufactured after 2005 or when the state adopts the 2005 NEC..
Just my $.02

 

[ron]

I believe that UL 508A and NEC 409 are for industrial control panels.
The items I'm referring to are unfortunately unrelated to ICP's, although it makes sense the everything else have those similar requirements.