NFPA 70E Arc flash labeling requirements

I

Isaiah

Senior Member
Location
Baton Rouge
Occupation
Electrical Inspector
I can certainly understand Arc-Flash labeling for a switchgear MCB, but why would you also need a label for the associated switchgear bus? The bus isn’t really an arcing device.


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The rules have to do with the incident energy that will be created if something causes a fault, not with a device that creates an arc.
 
don_resqcapt19 said:
The rules have to do with the incident energy that will be created if something causes a fault, not with a device that creates an arc.
Click to expand...

Don is it common to see two different incident energy values on the same switchgear? One for the MCB and one for the associated bus?


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Isaiah said:
Don is it common to see two different incident energy values on the same switchgear? One for the MCB and one for the associated bus?
Click to expand...
No. If there are different values, it typically means someone was not following industry conventions/standard practices.

Separate labels would only be applicable if there was appropriate internal compartments as you would find in Medium Voltage and some 600V switchgear.

Different labels should not exist on the majority of equipment like switchboards, panels, and MCCs.
 
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jim dungar said:
No. If there are different values, it typically means someone was not following industry conventions/standard practices.

Separate labels would only be applicable if there was appropriate internal compartments as you would find in Medium Voltage and some 600V switchgear.

Different labels should not exist on the majority of equipment like switchboards, panels, and MCCs.
Click to expand...

Thanks Jim. I figured this would be the case


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Isaiah said:
Don is it common to see two different incident energy values on the same switchgear? One for the MCB and one for the associated bus?


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Click to expand...
Assuming that it is switchgear with compartments, it seems to be common for the main to have one value and the rest to have a lower value. However this is only where the main is separated from the the other compartments on the wiring side. If the feeder and all of the loads can be seen with a single wiring compartment door open, the values should be the same.
 
jim dungar said:
No. If there are different values, it typically means someone was not following industry conventions/standard practices.

Separate labels would only be applicable if there was appropriate internal compartments as you would find in Medium Voltage and some 600V switchgear.

Different labels should not exist on the majority of equipment like switchboards, panels, and MCCs.
Click to expand...
Going to disagree with you here... we have dual labels on a TON of stuff. There's the "normal everyday commercial utility power" set, and a second (much lower) "power company pooped the pan, or maybe we're doing safe-time maintenance, and the energy's coming from Brother Caterpillar" set.
 
ModbusMan said:
Going to disagree with you here... we have dual labels on a TON of stuff. There's the "normal everyday commercial utility power" set, and a second (much lower) "power company pooped the pan, or maybe we're doing safe-time maintenance, and the energy's coming from Brother Caterpillar" set.
Click to expand...
Two different sets of labels because there are two different sources.
I used to do this, but it was to confusing. We suggested only using the worst case on the label and any lower value, from the report, for maintenance and work permits.

Typically, in the hundreds of reports I was responsible for, I found maintenance and generator sources to often have lower available fault currents which meant clearing times were longer and incident energy levels substantially higher. These situations is some of what led the NEC to require energy reduction switches.

But, my point was particularly about labeling the incoming line section different than the other sections.
 
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