Flash Protection Boundary

[dakota1sparks]

When we open a disconnect on a 480 VAC panel and open the door, the power is off in the panel below the disconnect. There is still power on the line side of the disconnect. Do we still have to wear the PPE required within the flash protection boundary because we are within a foot or two of the line side voltage? If so, is there anything besides shutting the line side down we can do so we don't have to have this level of PPE on.

 

[petersonra]

Re: Flash Protection Boundary

Is there any chance of being exposed to the line side voltage with the disconnect open? The answer to that question should tell you a lot.

 

[don_resqcapt19]

Re: Flash Protection Boundary

The panel is still energized and PPE for the available incident energy is required. Wear the PPE or kill the supply side. Rememeber that after you kill the power, the PPE is required when you do a voltage test to prove the power is off.
Don

 

[rbalex]

Re: Flash Protection Boundary

One of the most significant changes to the 2002 NEC occurred with a subtle redefinition:

1999 and before:

Live Parts. Electric conductors, buses, terminals, or components that are uninsulated or exposed and a shock hazard exists.

2002 and after

Live Parts. Energized conductive components.

That simple change has been taken by the 70E Technical Committee to mean all that Don said - and more, like various formal Hazard Analyses since it affects a broad number of NEC and 70E topics. The person who made the proposed NEC change attended the 70E-2004 cycle meetings, so the TC was fairly confident what it meant. Actually, that was partly why it was delayed a year. Certain accommodations needed to be made for very low energy systems.

 

[dakota1sparks]

Re: Flash Protection Boundary

Thanks for the help. What about touch safe disconnects where personnel are protected by the barrier on the disconnect?

 

[bphgravity]

Re: Flash Protection Boundary

Originally posted by dakota1sparks:
...What about touch safe disconnects where personnel are protected by the barrier on the disconnect?

They may be protected from shock exposure, but I don't think those barriers qualify for arc flash and certainly not arc blast events.

 

[rbalex]

Re: Flash Protection Boundary

Again, here Bryan is right. The various required hazards analyses MAY indicate minimal or reduced PPE is appropriate; however, the 70E TC wants management (not just supervision) to recognize their responsibilities in specifically analyzing hazards.

The "outcomes" of the required analyses cannot be adequately derived on this forum. It takes knowledgeable investigation of a broad range of criteria. At this point, referring to NFPA 70E as the starting point is the best "general" information that can be given.

Edit Add: A specific question to a specific NEC or 70E Section can usually be dealt with here, but a question about your specific operations will still likely only result in a general "philosophical" answer.

[ March 15, 2005, 10:30 AM: Message edited by: rbalex ]

 

[petersonra]

Re: Flash Protection Boundary

Originally posted by dakota1sparks:
Thanks for the help. What about touch safe disconnects where personnel are protected by the barrier on the disconnect?

Look at it this way. You open the disconenct and go in to test the load side of the disconnect for power. No voltage. You might think - it is now safe to take off my arc flahs suit and work inside the cabinet.

Keep in mind that a single failure could still cause an arc flash. What happens if while you are working inside the cabinet you accidently snip the wires feeding the disconnect? Even though the disconnect terminals are not accessible, you could still create an arc flash. Or what if one of the line side wires is loose and while working on the cabinet it falls off the terminal?

If you want to work without the arc flash PPE, the only "safe" way to do so is to remove all sources of power coming into the cabinet that might create an arc flash. This means an external disconnect of some kind.