Arc Fault @ Existing Panelboards

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Sparky2791

Sparky2791

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Northeast, PA
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Electrical Design
Hello!
I have a reno project of a building that was constructed in the 1990’s. We had an arc flash hazard analysis study performed on the entire electrical system (new and existing) which has resulted in 3 existing panelboards failing.
These are in a section of the building not being renovated. The arc fault current at the panel is shown to be higher than the panelboards rating which is of course based on the AIC of the circuit breakers installed.

From a safety standpoint I know the proper thing to do is to correct this. We have requested a change order from the contractor to add fused switches ahead of each of the panels to reduce the AIC @ the panelboard.

Does the NEC address this in anyway? 110.16 is not specific to that. I suppose it falls under maintenance while the NEC is regarding new installation.

This is for a 100A,200A & 400A branch circuit panelboard.

Thanks for your comments
 
Unless it is a tested combination, the fuses ahead of the panelboard will not change the panelboard's required AIC rating. Replacing the panel's breakers or looking at a series rating are the typical ways to correct this issue.
 
Agree with dOnut; you can't just arbitrarily add a fused disconnect. 240.86 gives a bit more detail.
 
As communicated, it's 240.86 (A) Engrng Sup'vsn in Existing Systems, or (B) Tested Combinations.
Using (B) Determine the part number for the main breaker in the underrated panel and use the (Bussman?) Fuse Series Ratings Charts to determine the correct fuse to use, which will carry an increased short-circuit rating and be series-rated with the breaker in the panel for an overall increase.
 
d0nut said:
Unless it is a tested combination, the fuses ahead of the panelboard will not change the panelboard's required AIC rating. Replacing the panel's breakers or looking at a series rating are the typical ways to correct this issue.
Click to expand...
The intension is to do exactly what mayanees indicates in their reply
 
mayanees said:
As communicated, it's 240.86 (A) Engrng Sup'vsn in Existing Systems, or (B) Tested Combinations.
Using (B) Determine the part number for the main breaker in the underrated panel and use the (Bussman?) Fuse Series Ratings Charts to determine the correct fuse to use, which will carry an increased short-circuit rating and be series-rated with the breaker in the panel for an overall increase.
Click to expand...
As I read this again your response also makes me think 240.86 A would apply to as well since it is an engineer performing the analysis.

I am not a protection engineer and do not perform the study but we do require one as part our specifications and our systems (New work) are designed with proper protection (and coordination where it applies) in mind. It always seems to be where we do renovations and the building never had an arc flash study done where we run into issues. Thanks for the response!
 
The manufacturer should have a series-rating chart available. I know that Square D and Eaton do; I used them both last week. For 2-tier series ratings as you describe they’ll list the specific fuse class & breaker combination and what rating you will get.


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