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Outdoor transformer/grounding question #217353 06/23/16 02:10 AM
Joined: Jun 2016
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Sparky42 Offline OP
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Application is an outdoor 30kVA, 480V/400V step down delta-wye transformer to be located within 10 feet of a building panel breaker box. The box has three phase 480V fused power and an input ground wire tied to the breaker box via a screw lug. The output is a 3P4W IEC-309 receptacle, the ground pin of the receptacle has a wire that screws into the breaker box. My question is: Can I use the receptacle ground wire to be the ground for the transformer chassis and X0 of the secondary (via a terminal bar inside and bonded to the transformer enclosure)? Or will I have to run a ground wire independent of the receptacle so that ground is always made regardless of if the plug is in the receptacle. I could not find this detail in NEC.

2017 / 2014 NEC & Related Books and Study Guides
Re: Outdoor transformer/grounding question [Re: Sparky42] #217354 06/23/16 03:20 AM
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gfretwell Offline
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I suppose you need to back up and see if that transformer is listed for cord and plug connection. If that is OK, I suppose the pin in the plug is sufficient to establish the ground.
Those 309 plugs are designed so the ground makes before the ungrounded pins.


Greg Fretwell
Re: Outdoor transformer/grounding question [Re: Sparky42] #217387 07/01/16 12:59 AM
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Yoopersup Offline
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Read 2014 N.E.C. 250.30 (C)

Re: Outdoor transformer/grounding question [Re: Sparky42] #217393 07/05/16 12:09 AM
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Sparky42 Offline OP
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Hmmm, the breaker box is mounted on a metal building. Can I consider the breaker box as the source location? In that case there is a ground wire connected to the breaker box itself (and it comes out via the IEC-309 connector). This is not a permanent installation it will only be active for a month or so.


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