Arc Flash Reduction Maintenance Switch

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steve66

steve66

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Illinois
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240.87 of the 2017 code requires a method of reducing the clearing time for breakers 1200A and larger. One option is an energy reducing maintenance switch.

Say for example, a 2000 Amp main breaker supplies a 1200 Amp breaker. Are both required to have the arc flash reduction switch, or does having a switch on the larger breaker count for also reducing the arc flash energy at the downstream breaker?
 
The wording seems to apply to the individual device, so we put an ERMS switch on each breaker or each piece of equipment which then applies the switch to each breaker in the enclosure.
 
We have been having lengthy discussions on 240.87 lately and still have more questions than answers. If a facility has an absolute rule against working on (servicing adjusting,l etc) any energized equipment would the provisions of 240.87 be required ? We have an senior engineer from Eaton who indicates it only applies for arc flash reduction where such work might be performed.
 
Gus, my answer will contradict the Eaton representative. 240.87 does not include the (admittedly vague) phrase, "likely to require" that appears in 110.26(A). I think the only way one can avoid applying one of the energy reduction options provided in 240.87(B) to a breaker that can be set at or above 1200 amps is to keep that breaker on the shelf as a spare for future use. Of course, when you install that (no longer a) spare breaker, the energy reduction rule comes back into play.
 
augie47 said:
... only applies for arc flash reduction where such work might be performed.
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The arc flash reduction, for both breakers and fuses, must exist even if you do not work on energized equipment. The NEC does not contain any exceptions like it does for Ground Fault protection.

If your company policy is to always work deenergized, how do you accomplish that without making a voltage check. during the voltage check it certainly would be nice to have the potential incident energy lowered.

One thing I don't like about the new wording is that it does not point out that an ERMS switch cannot protect the device it is connected to. ERMS protection is always for the downstream locations.
 
steve66 said:
Say for example, a 2000 Amp main breaker supplies a 1200 Amp breaker. Are both required to have the arc flash reduction switch, or does having a switch on the larger breaker count for also reducing the arc flash energy at the downstream breaker?
Click to expand...
A switch on the larger breaker alone would not suffice, and you would not want to do that anyway. When the use of the switch disables the delay on the instantaneous trip feature, it will reduce the incident energy from a fault. But it will also disable selective coordination. So if you are working on the panel fed from the 1200 amp breaker, and something shorts out, you want the 1200 amp breaker to trip, and not the 2000 amp breaker. For that to happen, the intentional delay on the 2000 amp breaker's instantaneous trip mechanism must be in operation.
 
jim dungar said:
One thing I don't like about the new wording is that it does not point out that an ERMS switch cannot protect the device it is connected to. ERMS protection is always for the downstream locations.
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I am not sure I follow this, Jim. If you are working on the 2000 amp main panel mentioned in Post #1, putting its 2000 amp breaker into Energy Reduction mode will, in fact, reduce the available incident energy at that panel. In other words, the panel is "the downstream location" from the breaker.

If you were saying that the ERMS will not have an impact on a fault that occurs in the 2000 amp breaker itself, then I would suppose it depends on the exact location within the breaker the fault occurred (i.e., upstream or downstream from the location of the current sensor).
 
A basic tenet of arc flash mitigation is that a device can not mitigate itself (e.g. the fault envelopes both the line and load side terminals thereby preventing the device from clearing the fault). Most people performing arc flash studies consider that a main breaker will be involved in the arcing event unless there is sufficient isolation or separation from the downstream equipment.

A service entrance switchboard that has an integral 2000A main breaker with no barriers between it and the feeder breakers is usually evaluated based on the incident energy at the line side of the breaker. However if that main breaker is separated by some amount of cable and conduit then the switchboard is evaluated based on the incident energy let through by that breaker.
 
Hi Guys,

I had a clarification question on this Code that I am struggling to wrap my brain around. Is there a Voltage requirement for this Switch? I have some contractors that say it's only required on a 480v service and that a 120/208v service is exempt no matter what the Amperage is.

My personal take from what I have read in the codebook is ANYTHING 1200a or larger regardless of the voltage requires this switch in the new code.

Are there any exceptions?

Thank you for any help clarifying you may have.
 
DSG JASON said:
I had a clarification question on this Code that I am struggling to wrap my brain around. Is there a Voltage requirement for this Switch? I have some contractors that say it's only required on a 480v service and that a 120/208v service is exempt no matter what the Amperage is.

My personal take from what I have read in the codebook is ANYTHING 1200a or larger regardless of the voltage requires this switch in the new code.

Are there any exceptions?
Click to expand...
None that I saw
 
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