Arc Flash and Clearances around electrical equipment

[a10jp]

Recently I was running into increasing the size in the electrical room and trying to account for all NEC clearances around the equipment, when a thought hit me. The equipment I was dealing are low voltage, from 208V to 480V as the highest. The thought was what about arc flash. I was merely using the 3-foot clearances when perhaps the arc flash calculation might necessitate a larger clearance than the 3-ft, depending on the category of the equipment. I have not done a thorough calc yet, but has anyone come across this?

 

[Zogzog]

Your arc flash boundaries will have no impact on where you place your gear, seeing AFB's in excess of 20 feet is not that uncommon.

 

[PHovnanian]

You've got to think about the logic behind an arc flash boundary. Basically, this is the distance within which one must utilize personal protective equipment. A three foot boundary (or a 20 foot boundary) suggests that persons staying outside of this boundary won't be doing work on the equipment in question (under conditions with an arc flash hazard like the panel being opened up, etc.). Exceptions are for equipment operated/maintained with hot sticks. But with 208 or 480V systems, this is quite rare.

So the question you have to ask yourself is: Is there any reason to design an electrical room with clearances sufficient to accommodate occupants not doing work on the equipment under hazard conditions? Off the top of my head, I can't think of any, but your situation might be different. If not, additional space is just wasted.