Arc Flash Reduction Switch

[timm333]

NEC-2014 section 240.87(B)(3) requires an arc flash reduction switch for breakers 1200A or higher. This means that when the main breaker of a local panel is 1200A or higher, we put an arc flash maintenance switch for maintenance.

What if the distribution panel does not have main breaker, and the main breaker is located in the upstream switchgear; in this case shall the arc flash maintenance switch be required in the local panel or in the upstream switchgear? Thanks

 

[jim dungar]

NEC-2014 section 240.87(B)(3) requires an arc flash reduction switch for breakers 1200A or higher...

Not really.

The NEC requires some method for tripping the >1200A breaker 'instantly', an AMS is only one of the possible methods listed.

The requirement is not applicable to equipment that is not a breaker.

 

[timm333]

Thanks. Yes AMS (arc flash maintenance switch) is 1 of 5 options given in NEC 240.87(B); however it looks that AMS is the one which is most commonly used. I think the idea is that when persons are performing maintenance on a panel, they should turn the AMS to "on" so that the breaker trips without delay and the arc flash incident energy is reduced. And when the maintenance work is finished, they turn the AMS back to "off".

My question is about the outgoing feeders. When the outgoing feeder is 1200 A, the workers working on the downstream local panel are in danger even though the breaker is located in upstream panel and not in the local panel.

So if the outgoing feeder in the upstream panel is 1200 A, what will the workers do in case they need to perform maintenance on the downstream local panel? Will it be Ok that a policy is made that the workers first come to the upstream panel and turn the AMS to "on"; then perform maintenance on the downstream local panel, and finally come back to the 1200 A breaker in the upstream panel and turn the AMS back to "off"?

 

[jim dungar]

So if the outgoing feeder in the upstream panel is 1200 A, what will the workers do in case they need to perform maintenance on the downstream local panel? Will it be Ok that a policy is made that the workers first come to the upstream panel and turn the AMS to "on"; then perform maintenance on the downstream local panel, and finally come back to the 1200 A breaker in the upstream panel and turn the AMS back to "off"?

The breaker itself is not the danger. The issue is how long it takes to clear the fault and the resultant Arc Flash Incident Energy (AFIE).

Doesn't it make more sense to put the 'switch' at the location where you want the reduced AFIE rather than at the breaker?

 

[timm333]

Yes absolutely it makes sense to put the switch at the local panel where the reduced arc flash energy is required. The only problem is that the switch has to be placed on a breaker. And if we want to place the switch at the local panel where reduced arc flash energy is required, then we will also have to put another 1200 A main breaker in the local panel on the incoming feeder; this does not make sense because the incoming feeder already has a 1200 A breaker in the upstream panel.

 

[iwire]

The switch does not have to be on the breaker.

 

[jim dungar]

The switch does not have to be on the breaker.

I agree, the NEC is silent on the location of the switch.
I also acknowledge that many people have a "git it over with' attitude when it comes to AMS therefore they let equipment manufacturers control the application. Imagine if all motor start-stop switches could only be in the MCC because 'it costs more' to but them where they are used in the field.

 

[big john]

I guess I don't understand why you're concerned about the location of the maintenance switch?

We always put it adjacent to the breaker that it actually controls. The style we install has RJ45 jacks, so it would be simple to make a piece of longer cable to locate it wherever the customer requested. But in an environment with multiple maintenance switches this would run the risk of a person enabling protection on the wrong circuit, and obviously it would make installation far more labor intensive.