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#193490 - 04/05/10 06:15 AM transformer above ceiling?
cgw Offline

Registered: 07/29/04
Posts: 133
Loc: Rochester NY
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?

2014 / 2011 NEC & Related Books and Study Guides
#193502 - 04/05/10 04:10 PM Re: transformer above ceiling? [Re: cgw]
Gregtaylor Offline

Registered: 03/02/05
Posts: 212
Loc: Boise, Idaho, USA
NEC 2008 450.13(B) says, generally for this size and type, you can. The plenum space question is not addressed.

#193506 - 04/05/10 06:40 PM Re: transformer above ceiling? [Re: Gregtaylor]
HotLine1 Offline


Registered: 04/03/02
Posts: 6792
Loc: Brick, NJ USA
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.

#193508 - 04/05/10 07:52 PM Re: transformer above ceiling? [Re: HotLine1]
gfretwell Offline


Registered: 07/20/04
Posts: 9025
Loc: Estero,Fl,usa
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

#193588 - 04/08/10 05:07 PM Re: transformer above ceiling? [Re: gfretwell]
Tesla Offline

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
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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