AFHA & NF Switch

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texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
The label says it must be protected with class J or R fuses if AFC is more than 10K. Below 10K any OCPD is acceptable. If AFC at the breaker is 11.52K do you know what the AFC is at the switch? If the switch is far enough from the breaker maybe the AFC is <10K at the switch.
 
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wbdvt

Senior Member
Location
Rutland, VT, USA
Occupation
Electrical Engineer, PE
First off is why is it not compliant and compliant to what? It seems that the fault current at the non fused disconnect switch may be greater than the rating of the non fused switch which is 10kA. I see that frequently in my studies and if that is the case, it is a violation of NEC and OSHA.

The switch can be replaced with a fused disconnect switch with suitable fuses and that will usually result in the switch being rated at 200kA.
 
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David Castor

Senior Member
Location
Washington, USA
Occupation
Electrical Engineer
George Stolz said:
I have an Arc Flash Hazard Analysis for a customer that is saying that the non-fused switch for a piece of equipment is not compliant, and needs to be changed to a fused disconnect with current-limiting fuses. Does this make any sense? The breaker serving the equipment is within it's AIC rating (11.52 kAIC).

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George Stolz said:
I have an Arc Flash Hazard Analysis for a customer that is saying that the non-fused switch for a piece of equipment is not compliant, and needs to be changed to a fused disconnect with current-limiting fuses. Does this make any sense? The breaker serving the equipment is within it's AIC rating (11.52 kAIC).

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The issue is likely the short circuit rating of the switch. Non-fused disconnect switches have a withstand rating of 10,000 A maximum. If the available fault current exceeds that rating, it is underrated and should be replaced with the fused disconnect.
 
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