transformer clearance

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pdmtn

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Thanks up front for your help. I have a 15kva / 480 Dry type transformer in a large concrete room with no other equipment in the room. My question is... why does Art 110 0r Art.450 not clearly address the number of entrance doors or how much working spaces is needed..Both articles are clear as MUD concerning this..... Thanks
 
You are only required on entrance to this space.

110.26(C)(2) is only for large electrical equipmnet rated 1200 amperes or more that contains overcurrent devices, switching devices or controle devices.

As far as working space clearance, unless the transformer is likely to require examination, adjustment, serviceing, or maintenance while energized Table 110.26(A)(1) would not apply.

The general requirement in 110.26 requires sufficent working space about all electrical equipment to permit ready and safe operation and maintenance of the equipment but does not specify and actual distances.

450.9 does require proper ventilation of the transformer. The distance required for this ventilation should be marked on the transformer.

Chris
 
Chris,
I've been to the job in question (by pdmtn) and, if I may correct a typo, it's a 15kv/480 (4000 kva) transformer. Would this change your answer any ?
 
It would not change my answer, and I agree with Chris. I do not reserve the 110.26 working space around transformers. For larger transformers, such as is described here, the more important issue is leaving room to remove and replace the coils, should a transformer fail while in service. That sometimes winds up leaving more room than 110.26 would have required, if it applied (which as I say, I believe it does not).
 
guys, if I may. This is also a resin filled transformer, which I believe is "dry".
Am I correct that the only "room" requirement is that listed in 450.21(B) and that costruction is base on the transformer Class ?
This would not be subject to any of the "vault" requirements listed in Section II (430.41 ,etc), would it ?
 
augie47 said:
guys, if I may. This is also a resin filled transformer, which I believe is "dry".
Am I correct that the only "room" requirement is that listed in 450.21(B) and that costruction is base on the transformer Class ?
This would not be subject to any of the "vault" requirements listed in Section II (430.41 ,etc), would it ?
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I would say yes, and since this is a commercial application, your room would probably be one hour by default (5/8 + 2x4 + 5/8).

You mean 450.41, I would say no, I would consider a vault to be in ground.
 
Pierre C Belarge said:
What about the clearance required at Table 110.34, and entrance requirements at 110.33?
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Those are questions which caused me to add to the post. As far as 110.34, the consensus of opinion seems to be the transformers are "NOT likely to be serviced while energized", and 110.33 specifically mentions switchboards and control panels so I was hesitant to apply it to transformers only.
Not saying my thinking is correct, thats why I'm looking for opinions and yours is appreciated.
David (pdmtn) and I will discuss it futher, I'm sure.
 
I was called to a job this past weekend. There are issues of voltages flucuating.
The electrician pulled the cover off and tested the transformer while it was energized to discern the actual readings from the transformer itself.


I am sure this is not a procedure that is rare. I just do not understand how some can say that transformers are not likely to require examination, etc... while energized.:confused:
 
On a preliminary I showed 41-5/8" of working clearance for a 45kVA, 480:208/120 transformer and I tried arguing the case. No luck.

"Many feel ... yada yada yada."
 
while that may be a de facto practice, it is often unsafe, especially when measurements can often be taken at the next splice/switch/device down the line.
 
Pierre C Belarge said:
I was called to a job this past weekend. There are issues of voltages flucuating.
The electrician pulled the cover off and tested the transformer while it was energized to discern the actual readings from the transformer itself.


I am sure this is not a procedure that is rare. I just do not understand how some can say that transformers are not likely to require examination, etc... while energized.:confused:
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I think that awhile back everyone was on the same page when someone asked if they should open a resi panel while it was energized and people were saying no. I sure don't think you should be opening a transformer that large.:)
 
cowboyjwc said:
I think that awhile back everyone was on the same page when someone asked if they should open a resi panel while it was energized and people were saying no. I sure don't think you should be opening a transformer that large.:)
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OSHA and NFPA70E have rules about not working on live circuits. One of the exceptions is for testing purposes, as long as the proper training and PPE is provided.
 
Originally Posted by Pierre C Belarge
OSHA and NFPA70E have rules about not working on live circuits. One of the exceptions is for testing purposes, as long as the proper training and PPE is provided.
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Which we both know..........
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Yes we all know John, but what can be done about it? If you have a facility that's done arc flash studies and all the equipment is labeled with the available arc levels then it's the idiot's fault for not wearing PPE while working on energized equips. This is a real problem that some electricians just don't want to understand. While NFPA70E and IEEE std. 1584 present different calculation methods it's at least nice to see some people care about this issue a bit more recently.
 
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