Underfloor Raceway - 390.2 (A) & (C)

[831]

I want to install a trench duct 18"w x 24"D w/ a removeable steel cover. The first part of 390.2 (A) seems to indicate that I can do this and (C) states that I need a cover (will be removeable) that will withstand pressures mechanically.

Am I missing something???

 

[infinity]

Did you really mean 24" deep?

The cover needs to be strong enough to support a very heavy chair+person rolling over it among other things.

The covers provided by the duct manufacturer should be strong enough for use in this application.

 

[831]

I'm talking about a trech that I build w/ a steel plate cover - it would never know a chair was even on it. Trench duct was the wrong term - sorry.

My initial subject actually has (2) parts. Let me be a little more specific about the second...

I'm trying to design a trench that can hold a "bunch" of conductors from an MCC to a room w/ some furnaces, etc. The MCC is a 2000 unit and there are many circuits. There is also a provision for a second 2000A MCC. I'm not trying to cheat the code, but I don't want to derate any more than I need to. Running 2000A of conductors @ 50% derating gets expensive. Running 4000A @ 50% get's even more $ive.

 

[cleveland]

Constructing a trench 24" deep in not inexpensive in itself. I'm not sure I see much advantage of this over running PVC conduits below the floor (assuming we are on grade). A trench, even with a good plated cover, is always open to contamination from spilled liquids, etc. I remember watching an electrician about 25 years ago standing in a trench on top of numerous cables trying to figure out just which cable he needed to remove........ "Yikes" I said...... and have stayed away from trenches ever since! We've got a very few with MV cables in them. They are no ones favorite place to work in.