Vault under MCC in existing building

[robgrant3]

I am trying to size a vault to be installed below a double ended 480V switchgear lineup. Do the rules for a traditional pull box apply to sizing the vault? I do not think they do because the vault will be open to the bottom of the MCC.

Any suggestions as to what NEC articles apply to this application, in addition to 450?

The reason for the vault is we have a large quantity of incoming feeds, entering the vault from a concrete encased duct bank, and having the conductors not in conduit saves a ton of room. Let me know what you think.

 

[ericsherman37]

I believe 450 is for transformer vaults specifically, not electrical vaults in general. My code book is AWOL so I couldn't give you a reference on where to find info on regular vaults.

 

[iMuse97]

What I think is that you've got yourself a great idea. I've seen some installs like what you describe.

Do you really need a vault (ie. transformer type enclosure) or are you just going to have the concrete poured in such a way as to create a sort of vault-like space. If you do, you should consider how you will provide for a drain for any moisture that collects there.

And yes, I would size it so that I liked it--and do calcs. based on bending space and wire size.

 

[iMuse97]

you also might want to have a curb around this so that water on the floor doesn't seep right in under your gear.

 

[robgrant3]

I am designing a poured concrete shell, as narrow as possible (27") and (132") long. I do not think bending and space requirments will be an issue. How do you propose I drain it? I did not think about this possibility before....

 

[JWCELECTRIC]

Are these conduits service conduits and feeders to motor loads? Do the loads from MCC go inside the building or outside the building or both? I would run conduits from MCC to 4'x4' concrete handholes outside the electrical room and not woory about the vault. The vault/manhole could get big and you may be subject to 110.70 and confined space.

 

[weressl]

I am designing a poured concrete shell, as narrow as possible (27") and (132") long. I do not think bending and space requirments will be an issue. How do you propose I drain it? I did not think about this possibility before....

How are the electricians will acess the cables to be pulled? The depth of the through needs to accomodate the largest cable's or conductor's bending radius from the uppermost conduit entering the side to the floor level.
Sloope and sump.

 

[iMuse97]

How are the electricians will acess the cables to be pulled? The depth of the through needs to accomodate the largest cable's or conductor's bending radius from the uppermost conduit entering the side to the floor level.
Sloope and sump.

Just got back on after a long day at work. My answer would have been his. You will have major power coming through this area so, as the code says, it must be sized correctly. See 312.6(A) & (B) It's really important that you look at that with reference to where your wire is entering and leaving the space.

 

[iMuse97]

Are these conduits service conduits and feeders to motor loads? Do the loads from MCC go inside the building or outside the building or both? I would run conduits from MCC to 4'x4' concrete handholes outside the electrical room and not woory about the vault. The vault/manhole could get big and you may be subject to 110.70 and confined space.

Wish I thought of that. There's a good solution depending on the situation you face.

 

[iMuse97]

Just thought of another thing: Having pulled wire in configuration such as what you're describing, the design of the working area makes all the difference. It is not always easy to get a rope into the conduits, and then set up a tugger and pull wire without damaging it. You might run your ideas past an experience industrial electrician whose done some of this and get his suggestions as to placement of conduit in relation to breakers, etc.