# Transformer installations above ceilings



## earshavewalls (Jan 24, 2011)

I have a permit applicant who is proposing installing a 75kVA dry-type transformer (480/208y, 3-phase) above a suspended ceiling.

Article 450.13(B) states that transformers over 50kVA are not permitted in "hollow spaces of buildings not permanently closed in by structure". Does the space above a suspended (acoustic) ceiling fit the definition of "hollow space"?

I have been working with the code since the 70's and never came across this until now (maybe I need to try to read ALL of the Code someday)........I know it's not a new section. Times like this help me to realize how much I still DON'T know.........lol.

Any input is welcome. I don't run into this very often and I wish to be accurate in enforcing the code, but I don't want to put people through the hoops unless it is truly necessary.


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## jar546 (Jan 24, 2011)

The key here is that it is required to be "readily accessible" and when you read the definition of "accessible, ready" in the NEC, you will that it is not.  It would not be "....*in the open* on walls"

I had this issue last year and I am all too familiar with it.


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## chris kennedy (Jan 24, 2011)

earshavewalls said:
			
		

> Does the space above a suspended (acoustic) ceiling fit the definition of "hollow space"?


IMO, yes. From the 08 NECH commentary.



> Section 450.13(B) permits the installation of dry-type transformers rated 600 volts or less and not exceeding 50 kVA in hollow spaces of hung ceiling areas, provided these spaces are fire resistant, ventilated, and accessible. According to 300.22©(2), transformers are permitted to be installed in hollow spaces where the space is used for environmental air, provided the transformer is in a metal enclosure (ventilated or nonventilated) and the transformer is suitable for the ambient air temperature within the hollow space. Of course, the requirement of 450.13(B) applies to transformer installations in “other space used for environmental air” per 300.22©.





			
				earshavewalls said:
			
		

> I have been working with the code since the 70's and never came across this until now (maybe I need to try to read ALL of the Code someday)........I know it's not a new section. Times like this help me to realize how much I still DON'T know.........lol.


Thats why I hang at these boards.


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## earshavewalls (Jan 26, 2011)

Thanks guys!!! I love this profession! It reminds me daily how much I need to keep learning and to keep listening.

No problem with compliance, the designer/contractor agreed and even found a much better location.

Thanks again for the confirmation.


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