Technical question - VERY technical question.

We call 'em closets, electrical rooms, vaults, etc. (Storage rooms )

Building codes have a distinct difference between electrical closets and vaults, but try to find a hard definition of vault and you can run into a stone wall.

Does anyone have a definition, from an authority, of the difference between a vault and an electrical room? I've always held oil filled equipment as the difference, but there is truly no proof of that from NFPA, IEEE, or ANSI that I can find.

Any help is appreciated.

Fire resistance 3hr or greater, direct ventilation etc?
110.31(A) and 450 chapter III
That seems to be the best NEC reference for the definition of a vault I can find. There are also references like 450.2x that say where a vault is necessary.

I consider a vault to be any space that meets NSA/GSA requirements, but I don't think that's what NEC is referring too...

In the 2004 NEC comments, someone made a (rejected) suggestion regarding a definition of "vault". In the commentary, the panel states that the 110.31(A)/450.42 requirements are needed only when containing equipment having a degree of hazard that warrants a vault. Oil filled equipment certainly seems to fit that, but other medium and high voltage equipment might as well.

Thanks guys for the replies. It is one of those thorny points in the code and the first time I had no other issues to influence the outcome.

Sometimes, as we all know, the code is ambiguous in their definitions, not necessarily a bad thing, often what plays in Peoria will make NO sense in DC, New York, or Chicago. A uniform code will not always work.

This situation came down to me calling a meeting between 2 Fire Protection engineers, a Fire Marshal, and myself to come to a conclusion.

FYI, the bone of contention in this particular matter was a 60+ year old cinderblock wall (some solid, some MAYBE not) and a medium voltage vault. We had removed all the oil filled equipment a few months ago. The room was not near any egress path so that was not an issue, and in fact it was really set off by itself, just well hidden.

Anyway, thanks a bunch.