GROUNDING SEPARATELY DERIVED SYSTEMS

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I am of the camp of installing 480-120/208v transformers with 3 hots & 1 ground on the primary and using 3 hots and 1 neutral for the secondary both installed in fmc. I ground the case of the xfmr with my grounding conductor and ground my neutral at my first means of disconnect, I.E., main circuit breaker panelboard, to building steel, ground rod, etc. I don't use concentric/eccentric ko's for my conduits but punch the holes so i don't use a bonding bushing on my fmc. Am I doing anything wrong?
 

david luchini

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I do believe you are doing something wrong.

I don't see in the description of your installation the Supply-Side Bonding Jumper required by 250.30(A)(2).
 

don_resqcapt19

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In my opinion you need a supply side bonding jumper between the transformer and the first OCPD.
250.30(A)(2) Supply-Side Bonding Jumper. If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supply-side bonding jumper shall be installed with the circuit conductors from t he source enclosure to the first disconnecting means. A supply-side bonding jumper shall not be required to be larger than the derived ungrounded conductors. The supply-side bonding jumper shall be permitted to be of nonflexible metal raceway type or of the wire or bus type as follows:
(a) A supply-side bonding jumper of the wire type shall comply with 250.102(C), based on the size of the derived ungrounded conductors.
(b) A supply-side bonding jumper of the bus type shall have a cross-sectional area not smaller than a supply-side bonding jumper of the wire type as determined in 250.102(C).
 

don_resqcapt19

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DON, I AGREE WITH THE SUPPLY SIZE BONDING JUMPER, BUT I DON'T TIE THIS TO X0 IN THE TRANSFORMER PER THE INSPECTOR, RIGHT?
It ties to the grounded conductor at the same point as the grounding electrode conductor is tied to the grounded conductor. If your grounding electrode conductor connection is at the first disconnect, the supply side bonding jumper connects to the case at the transformer.
 

iwire

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Massachusetts
DON, I AGREE WITH THE SUPPLY SIZE BONDING JUMPER, BUT I DON'T TIE THIS TO X0 IN THE TRANSFORMER PER THE INSPECTOR, RIGHT?

This may help

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