Busway Under a Raised Floor

[cleveland]

Howdy,
Our data management folks are considering installing a busway system beneath the raised floor of their large computer room. This raised floor is 3 foot in height and the room was built to Art 645 requirements. I have a concern about clearances on the overcurrent devices that will be mounted to the busway. I have not seen detailed information on the system but believe it will consist of 225 amp bus with modular circuit breaker/receptacle units installed where required. Seems to me I should have 3 foor clear in front on any O.C. device installed to meet 110.26 (A) as I believe there will be times when "examination, adjustment, or maintenance while energized" might occur. Actually unless the entire busway is shut off, it almost always will occur. Could we satisfy the code if the devices were mounted so they face up? Then when we remove a floor tile we'll have clearance. Of course a bigger question might be: Can the busway be installed at all? I don't see it listed in 645.5 (D) but that seems to be dealing with the branch circuit wiring beneath a raised floor. I see nothing in 368 that would prevent installation of the busway below a raised floor.

Thanks for your time,

Jim

 

[augie47]

That's an excellent question.
Opinion only, but on 1st read, I'd say 368.10(B) would prohibit it.

 

[ron]

I believe that 645 is silent on feeders below the raised floor. The plug-in busway will be the feeder, and the plug positions for the overcurrent protection will be the beginning of the branch circuit. 645.5(D) mentions raceway limitations for branch circuits.

Since 645 is a special equipment section, we go back to the first 4 chapters of the NEC for more information if not specifically modified in 645.

300.22(C)(1) would cover the space below the raised floor, where I believe it specifically prohibits plug-in busway.

I've used the Starline brand busway above the floor several times successfully (and once the Square D version). IMHO, don't put it below the floor. It will block too much airflow anyway.

 

[dbuckley]

I can't comment on the code compliance aspects, but it seems a lousy idea to have electrical distribution switchgear below the floor. It looks like trading reliability for money, and that is seldom a good idea in a data centre.