# Transformer Supply Side Bonding Jumper



## jar546 (Aug 7, 2019)

If you had a 480/277v to 208/120v wye-type transformer where the primary side of the transformer (xfmr) was fed from an MDP after the service, what table would you use to size the supply-side bonding jumper on the secondary side of the transformer if the xfmr was supplying power to a panelboard for an office?

Remember that the primary side feeding the transformer from the MDP would be sized per Table 250.122 as it is an equipment grounding conductor.


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## Rick18071 (Aug 8, 2019)

table 250.102(C)(1)


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## jar546 (Aug 8, 2019)

Rick18071 said:


> table 250.102(C)(1)



I like that answer because it is correct.


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## steveray (Aug 9, 2019)

Pics of said MBJ? Or MBJ vs. EGC.......? Helpful for the non-sparkys


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## Rick18071 (Aug 9, 2019)

But I don't see any difference between table 250.102(C)(1) and table 250.66 Grounding Electrode Conductor for Alternating-Current System except in the notes.


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## chris kennedy (Aug 9, 2019)

Yup
I always use T250.66 for the OP’s application because I have a tab on that page.


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## jar546 (Aug 9, 2019)

chris kennedy said:


> Yup
> I always use T250.66 for the OP’s application because I have a tab on that page.


You are on fire today.  Is it beer-thirty yet?


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