# Penetrating transformers



## amxfan (May 7, 2011)

It has been a long time "over 10 years" since I have worked in the electrical construction field. With this amount of time going by I find myself thumbing through the code book trying to find information that I used to know the exact location of. My question is this, on air cooled transformers, or any transformer for that matter, if I am not mistaken, the code states that no penetrations of the transformer can be made above the XO. For the life of me though, I can not find this in the code. Not being able to find it in the code, I am beginning to doubt my memory. Can somebody please enlighten me before I pull out what is left of my hair?

Note: 
I am talking standard NEC and not any supplemental code.


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## BBQ (Nov 16, 2010)

amxfan said:


> It has been a long time "over 10 years" since I have worked in the electrical construction field. With this amount of time going by I find myself thumbing through the code book trying to find information that I used to know the exact location of. My question is this, on air cooled transformers, or any transformer for that matter, if I am not mistaken, the code states that no penetrations of the transformer can be made above the XO. For the life of me though, I can not find this in the code. Not being able to find it in the code, I am beginning to doubt my memory. Can somebody please enlighten me before I pull out what is left of my hair?
> 
> Note:
> I am talking standard NEC and not any supplemental code.


Not in the NEC at all, it is often a manufactures label requirement and at that point NEC 110.3(B) tells us we have to follow the listing and labeling.


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## brian john (Mar 11, 2007)

And recently I have installed some transformers where the termination bar was even with the top of the coils. Unusual IMO.


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## amxfan (May 7, 2011)

Thank you both for your reply.

I guess I have been away from it a little to long. Trying to remember what I learned in my apprenticeship and always doing it one way, people forget why they do it that way. They just know it is the right way.

Thanks Again

@brian john
Virginia... I worked many of day in Maryland, D.C. and Virginia. Did my apprenticeship @ 6220 back in the 80's.


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## piperunner (Aug 22, 2009)

Well the factory tells us with instructions were to drill were to enter transformer but as another post has said and let me add this .

GE is getting bad every year plastic holding up 500 mcm and larger conductors and when the cover goes on there less room each year to close it up metal to lugs getting closer each year and these are factory lug kits .

Sometimes you think the tightening of the bolts to the transformer tap buss when installing lugs that they will break off due to design of the cheap low cost way they make these now today attached with plastic .

The transformer has a instruction on it and it will say no conductors above this line meaning dont drill out a hole above this line .

We come in the front sides below the coils or bottom underground most of the time we never use the top or back of a transformer ever you dont do that .

We only stack two high in a room or hang it from the ceiling with 6 inches of clear space all sides and back its common practice to do this .

And its writen on the front cover by factory .

We never run soilid conduit into a transformer ive seen this done on this forum but i dont do that its flex or sealtite around here .

We use bonding bushings on everything even the grounds and BS CW GR 
just a habbit i guess .

And we install rubber vibration pads on every transformer even if they come with vibration pads .

Rule of thumb drill or stub 1/4 distance from front of transformer left or right side or bottom center underground thats pretty much how its done .

Hope this helps ya !


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## amxfan (May 7, 2011)

@piperunner

Thanks.

I did not state this in my first post but what brought this conversation on was I did a walk through of a new school building. When I walked into the shop area two transformers jumped out at me. Both of these transformers are Square D and on both of them the contractor punched the holes on the top side right under the top lid at the same height as the front and rear vent. I looked closer and on one of them the seal-tight that went from the conduit to the transformer was 6' long. 
What really got my gut in all of this was this building has already been inspected and passed. So I had to check my memory and make sure I'm not loosing it.

In my walk though I noticed a bunch of things, but these two were the straw the broke the camels back. On one hand I'm glad I did not have anything to do with the wiring of this building. On the other hand I wish I did.


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## BBQ (Nov 16, 2010)

Just keep in mind not all transformers prohibit top feed, and flex is an option not a requirement.


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## MDShunk (Jan 7, 2007)

BBQ said:


> Just keep in mind not all transformers prohibit top feed, and flex is an option not a requirement.


:laughing::laughing:That's one that wouldn't have crossed my mind. I've typically went with Square D catalog nomenclature when they get that big, and call them 'unit substations'. As you rightly point out, they're just transformers, when it comes right down to it.


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