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#193490 04/05/10 08:15 AM
Joined: Jul 2004
Posts: 136
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cgw Offline OP
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30KVA dry type transformer (480 X 120/208)
Can it be located above a suspended accessible ceiling (say in a medical office building)?
Can it be located above this ceiling if the ceiling space is a return air plenum?

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Joined: Mar 2005
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NEC 2008 450.13(B) says, generally for this size and type, you can. The plenum space question is not addressed.

Joined: Apr 2002
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300.22 (c)(2) should be read, and then I suggest you speak to the local AHJ for his/her interp. Under 50 KVA is no issue, BUT...the air handling ceiling needs to be addressed. Also, you may want to have a cut sheet for the exact xfr you intend to install.



John
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I think this is probably legal, depending on the transformer but it might be a questionable design choice. If that transformer smokes it will share the joy with the rest of the building pretty fast, at least that HVAC zone anyway.


Greg Fretwell
Joined: Jun 2004
Posts: 1,273
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If the Life Safety System ( Fire Alarm ) is up to snuff a duct detector is going to shut things down well enough in time.

Not quite the same set-up...

But I rigged a 45kVA XFRMR, dry-type, above a grid to give isolated power to data loads. Upon the detection of fire, within this space only, a shunt-trip killed total power - with a time delay of seconds so that the data state could be frozen/ preserved. Subsequently the dry fire system would be flooded into the now unpowered space.

So the question of plenum return air really would seem to be a life safety question not to be answered within our Code.


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