AIC or SCCR

[BJSIM]

There is a Lighting control panel that has 10kA AIC(Amps interrupting capacity) on its Breakers, but 100KA SCCR(Short Circuit Current Rating)on the entire dimming module due in part to the dimming coils and interworking parts. Which does the NEC Require under 110.9 and 110.10?
In this application the available fault current at the panel is 23KA.

 

[ryan_618]

Re: AIC or SCCR

It sounds like 110.9 has been violated.

 

[jim dungar]

Re: AIC or SCCR

In your case:
AIC is a short circuit rating for a device that interrupts a fault.

SCCR is a short circuit rating for a device that does not open a fault.

As Ryan said there is a violation, the circuit breaker is being misapplied.

 

[BJSIM]

Re: AIC or SCCR

Thank you,
I have been arguing that same point. Glad to see someone agrees.
The Supplier is trying to get me to buy off on this one. But I can make him supply a new panel with the proper AIC to feed each dimmer module.

Thanks again

[ December 22, 2005, 10:11 AM: Message edited by: BJSIM ]

 

[pierre]

Re: AIC or SCCR

Actually this may not be a violation. If this is installed in a circuit that is not rated higher than 10,000 AIC, it is not a violation. It is permitted to install (manufacturer) 10kAIC devices along with 100,000 SCCR equipment as long as the smallest rated portion is not exceeded by the circuit rating.

 

[BJSIM]

Re: AIC or SCCR

If this is installed in a circuit that is not rated higher than 10,000 AIC, it is not a violation.

What defines this circuit rating. The calculated fault current is slightly below 23KA.

Is it feasible that in a worst case scenario is the breaker melts closing the circuit. Then all grounded conductors and conduit on the system would be Hot at 277/480 Volts?

 

[jim dungar]

Re: AIC or SCCR

BJSIM,

All of the installed components must have a rating higher than the available 23kA fault current.

The problem is not one of the breaker melting on closing, but rather violently failing (think explosions and shrapnel) when opening a short circuit.

 

[pierre]

Re: AIC or SCCR

"The calculated fault current is slightly below 23KA."

That is an issue that has to be addressed, I did not read that in your first post...

 

[bphgravity]

Re: AIC or SCCR

If the 23KA fault current is available at the line side terminals of the panelboard, that means each of the branch circuit breakers must be at least 23KA rated? Assuming the OCD ahead of the panel protecting the panel and feeder is rated at least 23KA.

 

[augie47]

Re: AIC or SCCR

I don't believe anyone has mentioned series-ratings. BJSIM, if the panel has a main, check with the supplier, your 10k branch breakers may be "series rated".

 

[ed downey]

Re: AIC or SCCR

I am kind of fuzzy on how this works but could you simply add a fused disconnect switch ahead of the panel that is rated for something larger than 23kA AIC?
-Ed

 

[jim dungar]

Re: AIC or SCCR

No.
Well maybe. It is up to the manufacturer.

Series rating must be individually tested they can not be calculated (expect for very extreme situations, see 240.86(A)). Every major manufacturer has a published combination of breaker-breaker and fuse-breaker ratings that meet 240.86(B).

 

[BJSIM]

Re: AIC or SCCR

Series Rating was an initial thought however, there are 4 large roof top units on this job with a total of 346 FLA connected to the same distribution panel that feeds this dimming panel.
By my limited understanding of art 240.86(C) of the 2005 NEC? which prohibits the use of series rated combinations when the sum of the full load current of the motors exceeds 1% of the interrupting rating marked on the
LOAD SIDE circuit breaker. I don't think that is a viable option.