Arc Flash Hazard Work Interpetation

[JimCrowell]

Hi.
I've searched the forums and cannot find this question addressed clear enough for several persons involved in the evaluations and decision making, hope you can help.
We're looking for guidance or discussion for arc flash hazards when changing fuses in fused switches in a switchboard. The switchboard is energized, the fused switch is in the off position, the switchboard is energized. One group is claiming the fused switch does not have energized components present or otherwise provides a reduction in hazard below that of OCPD supplying power to the supply side of the fused switch. Another group claims that since the line side of the switch is energized the arc flash hazard is that of the supply to the switch.
Other information that seems important - 1) the fused switch is not locked out, 2) voltage measurements to verify the fuses at the supply side would have the incident energy rating of the OCPD supplying the switch, 3) the fused switch compartment has the supply connectors energized, and 4) the arc flash PPE requirements are based on the severity and not the relative likelyhood of an arc flash occuring.
Thanks in advance,
Jim Crowell

 

[zog]

Not really sure what you are asking, I think you are asking if this is considered energized work, and yes it is, it is very clearly defined in the definitions section of the 2009 70E (It was less clear in the 2004 70E). Any work inside the LAB is energized work, plus the part you are working on is still considered energized until it has been placed in an electricially safe working condition per 70E (Cant remmember the article off the top of my head, 120 or 140?).

 

[JimCrowell]

Thanks. If the OCPD at the switchboard bus limits arc flash to HRC4. The claim by some is that the fused switch compartment or fused switch itself reduces the arc flash hazard to either "none" or significantly below that of the HRC4 of the OCPD protecting the line side of the fused switch. Does anyone know of any data or analysis that provides a reduction for the presence of the switch or switch cubicle.

 

[rcwilson]

Jim - IMHO - your first interpretation is correct.

When we open up the fused switch to check or change the fuses, the line side of that disconnect is still hot. While those terminals are behind some type of a barrier, the arc flash level is only limited by the upstream protective device. That insulating barrier is not designed to stop or mitigate the arc flash.