NFPA 70E

[hidalgoe]

I would like to know if the various codes affecting arc flash studies require each and every live electrical panel at a site to be considered.

I work at a federal aviation lab center. Thousands of panels exit here. Some "experts" here are of the opinion that existing power panels are "grandfathered" in.

An arc flash study would not be a trivial undertaking.

Thank you.

 

[wbd]

Existing panels are not grandfathered. Some things to consider are that NFPA 70E is refered to in the NEC 2002 by a FPN (Fine Print Note). While FPN's are not technically part of the NEC, they are recommended practices and in my area of the country, if you have an Electrical Work Permit, the electrical inspector requires you to follow NFPA 70E.
OSHA is approaching thru the General Duty clause which states that a place of employment must be free of recognized hazards and arc flash is a recognized hazard. If the hazard can not be eliminated, then the employee must be protected. OSHA is in the process of revising Subpart S to address arc flash using NFPA 70E. In fact, the forward to NFPA 70E states that it is primarily written for OSHA.
Ok, the legal stuff out of the way, on to practical matters. You do not have to do every panel. What I have done is to go as far as 480V power panels and MCC's. For lower voltages, I use the PPE tables in NFPA 70E. Another approach would be to calculate arc flash until you reach a level where below that it is Category 0.

 

[dpc]

NFPA 70E covers electrical safety in the workplace and nothing is "grandfathered" in.

Another reference is IEEE-1584 which covers calculation of arc-flash energy. Per this standards, 208/120V systems smaller than 125 kvA do not require calculation because there is very little chance of an arcing fault occuring. Of course, shock hazards obviously still exist. IEEE-1584 does require calculation of arc-flash energy for all 240V (and higher) systems.

As wbd states, the NFPA 70E is different than the NEC - it does not have the force of law through adoption by states and cities. However, OSHA does consider NFPA 70E a "consensus standard". So if you're not in compliance with NFPA 70E, you'll need your own comparable saftey plan or a good reason you're not following it.

 

[Sebago]

The PPE tables in NFPA 70E are adequate for most applications. Most industrial plants do not have the gobs of money needed to do a full blown flash study, and these tables are written for them. They are quite conservative and tend to err on the "safe side".

 

[dpc]

I would have to disagree that the tables in NFPA 70E are "quite conservative". Sometimes they are and sometimes they are not. It depends on the system and the situation.

The advantage of doing a study is to find the portions of the system that have enormously high arc-flash energy potential so the appropriate safety precautions can be taken.