Is Wall Mounting a Transformer no longer Code Compliant?

M

msilva94

Member
Location
PA, USA
Occupation
Electrical Engineer
A coworker said it’s illegal to mount a transformer high up on a wall since it’s not directly next to its panel or disconnect and isn’t easily accessible for maintenance. I disagreed, since I’ve seen and designed plenty of setups where a transformer is wall-mounted, with the panel or disconnect nearby and accessible.
Example setup:
480/277V Panel -> 150kVA Wall-Mounted Transformer (offset from panels, hosted 6'+ AFF to reduce space consumption) -> 208/120V Panel
I reviewed NEC 450.13, which restricts transformers over 112.5 kVA from being installed in ceilings, floors, or hollow spaces in combustible buildings unless:
-It’s rated 600V or less
-It’s in a vault per 450.41
-It meets ventilation requirements in 450.9

and
450.14 Disconnecting Means. Transformers, other than Class
2 or Class 3 transformers, shall have a disconnecting means located either in sight of the transformer or in a remote location.
Where located in a remote location, the disconnecting means shall be lockable in accordance with 110.25, and its location shall be field marked on the transformer.

In this case, the transformer is under 600V and in an open area and as long as the disconnect is accessible and clearly associated, I believe that satisfies code.
A side note: I assume the same exceptions would apply if this equipment/setup was mounted on any structure (i.e. - uni-strut)?

Thoughts?
 
The primary disconnect can be anywhere there is no distance or withing sight rule. If the primary disconnect is not within sight, the transformer must be marked with the location of the primary disconnect.
The only restriction on the secondary would be the secondary conductor protection rules in 240.21(C) that will, in general, limit the distance to 25' wire feet.
 
msilva94 said:
A coworker said it’s illegal to mount a transformer high up on a wall since it’s not directly next to its panel or disconnect and isn’t easily accessible for maintenance
Click to expand...
I tend to ignore co-workers unless they can cite a specific code section. In this case your co-worker is incorrect. Transformers are hung everyday. Just take a look the next time you're at a big box store.
 
Many people view dry type transformers as not needing any more regular service than any a typical motor. They can typically be mounted just about any place you can get to.

As youhave noticed, it is the primary and secondary disconnects that have access and distance requirements.
 
Thank you all for the information. This confirms my understanding that the code requirement applies to the disconnect source, rather than the transformer itself.
infinity said:
I tend to ignore co-workers unless they can cite a specific code section. In this case your co-worker is incorrect...
Click to expand...
In this case I agree, ears are closed off!
 
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