12kV - 277/480V XFMR Work Clearance Requirement

[djr3203]

All,

I have an existing electrical transformer room with (2) 12kV-277/480V transformers, and I am trying to determine if the room is compliant with NEC 2008. The room is rectangular with a single double door in the middle of the north wall of the room. The transformers sit on either side of the double door with approx. 8' between the two. There is a couple feet of clearance on either end of both transformers. The XFMR are 500KVA and 750KVA.

Would this room require double the work clearance between the two transformers since there is only 1 means of egress? Or is there an exception in Article 450, or elsewhere in the NEC, that would make this installation code compliant?

As always, thanks for the insight.

DJR

 

[djr3203]

No comments?

 

[dpc]

I have not seen the working space requirements in the NEC applied to transformers. Normally it applies to switchboards and panels. Article 450 does not say much about working space. It does mention ventilation requirements and of course, issues related to fire prevention and containment in vaults.

 

[farmape]

FM Global has detailed transformer installation requirements I've used in the past

 

[dpc]

Insurance requirements are generally focused on fire hazards, in my experience.

 

[djr3203]

I thought the work clearances governed any piece of equipment that is energized and in which live parts can be exposed to perform maintenance. Wouldn't this then require a work clearance for the transformer?

P.S. I am a junior engineer so please be patient. Although I am glad I asked this question, because I was under the assumption you needed a work clearance around the transformer.

Thanks for the responses! I thought no one was going to answer.

DJR

 

[HornTootinEE]

This sounds like it might be an NESC (National Electric Safety Code) issue for safe working clearances rather than an NEC issue. I'd find the latest version of the NESC and start there. A large part of it's focus is safe clearances.

 

[dpc]

There are generally no live parts in a transformer that are accessed for maintenance. If maintenance is required on a transformer it is de-energized.

What type of transformers are these? If pad=mounts, you may want consider clearance in front of the terminal cabinet. But I see no reason for applying NEC working space requirements to the other sides of the transformer.

 

[7anoter4]

In this transformer room 2 transformers are located -I think both are dry-type.
If you intend to work on one of two and the second will remain energized then both has to be enclosed or fence has to be provided
according to NESC[as HornTootinEE already said] ch 124. "Guarding live parts."
The fence distance to live parts is stated on Table 124-1 [NESC 2007].
For 12 kV [15 KV] it is 101 mm and for 0.480[0.6 kV] it is 50 mm.
One could work freely outside the fence.
If you intend to work with no energized parts at both transformers then- for inspection only -without room penetration- you have to keep the distance indicated
for unguarded [live] parts [from the entrance with open door].
In any case the medium voltage [12 kV] termination will be near the far wall and a barrier will prevent the access.