# 25 foot tap rule



## newspark80 (Feb 20, 2011)

Here's what I got:

100 amp 480 breaker feeding a 75 kva xfrmer that feeds a 120/208 panel in an industrial plant. The feed used to got to straight to a 480 panel. They used the old 480 panel as a splice box to feed the new transformer.

What they want:

They are taking most of the loads off the 120/208 panel and want to have more 3ph 480 loads. The plan is to tap off in the old 480 panel to feed a separate 480 panel about 15 feet away. I do not have any of the new loads they are planning to install.

Questions:

Would this be acceptable according to 240.21?
Would this cause problems with the transformer?


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## BBQ (Nov 16, 2010)

newspark80 said:


> Questions:
> 
> Would this be acceptable according to 240.21?


It could be dependent on the specifics.




> Would this cause problems with the transformer?


Not much more so than adding load directly to the panel supplying the transformer circuit. You would be adding a bit of voltage drop to the transformer primary.


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## newspark80 (Feb 20, 2011)

BBQ said:


> It could be dependent on the specifics.
> 
> The new panel is a 100amp
> 
> ...


Could you explain a little more of the effects of this.


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## Bbsound (Dec 16, 2011)

remember 25' is conductor length, not up 8' over 15' down 8' into panel


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## newspark80 (Feb 20, 2011)

Bbsound said:


> remember 25' is conductor length, not up 8' over 15' down 8' into panel


Yep conduit total length is about 15 feet.


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## brian john (Mar 11, 2007)

Bbsound said:


> remember 25' is conductor length, *not up 8' over 15' down 8' into panel*


But about 90% of them are installed this way


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