75 kVA xfmr located above ceiling- permitted?

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greenspark1

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New England
I have an existing office space with a 75 kVA 480-208/120V dry type transformer located above the drop ceiling. Per 450.13(B) I don't see this being allowed by the letter of the code. However there is plenty of free space, air movement, the transformer is well supported, and you can access it via ladder after removing ceiling tiles. The HVAC units are all ducted so it's not in a plenum either.

I'm having trouble explaining to the client & electricians what is wrong with this scenario. They are pulling a permit to renovate the space and I expect to run into a Code issue. What is the reasoning to limiting this type of install to 50 kVA? What's so different about this and the exception for all kVA sizes for dry types per 450.13(A)?
 
I agree that the Code limits this situation to 50 kVA. As electrical professionals I like to have an understanding of the Code, not just an ability to cite it. Especially when conversing with the public, citing the Code without a reasonable explanation does not build trust of the Code. Nothing is more frustrating to an owner than not understanding why something isn't permitted.
 
Can you check the handbook?
Sometimes there is a code rule that goes far back that no one today knows the why.
 
How about this for an answer
"Code is Code. We don't like the rules we don't agree with. Its OK as long as it does not cost us time and money" Mike Holt
 
tom baker said:
Can you check the handbook?
Sometimes there is a code rule that goes far back that no one today knows the why.
Click to expand...

Yea, nothing in the handbook unfortunately.

I can imagine they didn't want a 225 kVA hung in a ceiling somewhere due to heat/access issues, but don't see any appreciable difference between a 50 and 75 kVA.
 
You have to draw the line somewhere, and that line is 50 kva. I would think it has to do with more than just heat buildup, but that would be the primary concern. Perhaps weight was a concern as well. Bottom line, the 75 kva is a no go.
 
zbang said:
50%?

This might just be one of those arbitrary rules that we have to follow. (BTW, I took a quick look in the 1984 book- 450.13 doesn't exist and I didn't see anything readily comparable.)
Click to expand...

In the 1984 and earlier versions of the NEC a similar restriction was in section 450-2(Exception #2).
 
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