Circuit Breakers inside Transformer Enclosures?

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flemdog186

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Greetings Forum
I'm a Sr. Electrical engineer and doing "Facilities" related design work for a US govt related organization. Drawings are not reviewed by any local county permitting board. Being the person that will stamp the Electrical drawings, I've been finding a common design and constrution practices that i dont agree with.

We have about a 300-building site and sometimes they mount regular molded case circuit breakers (not ENCLOSED circuit breakers) inside exterior transformer (250-1000 kva range) enclosures to serve various loads. Enclosed circuit breakers are typically too big to fit inside many transformers and non-enclosed circuit breakers are pretty easy to fit in and mount.

Question: Is it code-compliant to mount non-enclosed breakers inside transformer enclosures? :happysad: Is this a common practice? As of now, I dont plan to design this way. IF a secondary breaker/Disconnect switch is required, Ill put it somewhere outside of the transformer enclosure. I havent found anything in the NEC except for the obvious fact that the breaker is being used in an application that it is not designed for..i.e. not code compliant.

Let me know your thoughts
Thanks
 
I don't necessarily know of code issues prohibiting an overcurrent device inside a transformer housing, there could be issues with the listing and instructions for the transformer. If a dry type transformer it could produce cooling air flow problems.

What is the purpose of these overcurrent devices?

If this breaker is intended to be a service disconnect, then I would think this would be a violation of 237.70(A)(1), especially if users don't have access to interior of transformer.

Something else to consider is size of transformer and interrupt rating of the breakers. This location would require higher AIC ratings than for some location away from the transformer.
 
flemdog186 said:
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Let me know your thoughts...
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Welcome :thumbsup:

I have seen manufacturer-supplied transformers with an MMCB mounted inside the transformer enclosure, and the handle accessible from the outside of the enclosure.

Aside from those, I agree with you.
 
We did it all of the time puting a MCCB in the sec ATC of both liquid filled and dry type transformers. The assembly must be listed as UL though. We've even installed load centers and pnlbds in them. As an OEM I also provided breakers to RTE/Cooper for their padmounted transformers.
 
In the 250-1000 kva size transformers you mention I would think there would be an issue with (1) them being readily accessible when required to be so by Code (as kwired mentioned in Post 2), and (b) working clearance as specified in 110.26.
 
weressl said:
None of which is applicable if it is a factory assembled unit with appropriate listing.
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Agree 100%, however, in my sheltered life :D, I have not encountered those (factory assembly transformer with internal C/Bs) in the size transformers the OP mentioned. I *assumed he was speaking of filed installations.

Are factory installed internal breakers common in those size transformers ??
 
augie47 said:
Agree 100%, however, in my sheltered life :D, I have not encountered those (factory assembly transformer with internal C/Bs) in the size transformers the OP mentioned. I *assumed he was speaking of filed installations.

Are factory installed internal breakers common in those size transformers ??
Click to expand...

I have only seen a few. but my exposure is primarily industrial. I would expect those more common in institutional or Government Agencies installations.

I could not imagine in what way could that be field installed. It seems to em that it wold involve the modification of a listed equipment.
 
weressl said:
I have only seen a few. but my exposure is primarily industrial. I would expect those more common in institutional or Government Agencies installations.

I could not imagine in what way could that be field installed. It seems to em that it wold involve the modification of a listed equipment.
Click to expand...

Thanks for the responses. Yes, all the instances I am referring to are field modifications, not factory issued transformers with MCCBs. Currently, in the field I have some breakers installed within transformer enclosures that are not UL listed for this application. However, thanks to the notes, in certain instances I will look into getting a transformer with a factory-installed breaker within the enclosure (UL listed). This appears to be the only safe and acceptable way.

Regards
 
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