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#217353 - 06/22/16 11:10 PM Outdoor transformer/grounding question
Sparky42 Offline
New Member

Registered: 06/22/16
Posts: 2
Loc: CA
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.

2014 / 2011 NEC & Related Books and Study Guides
#217354 - 06/23/16 12:20 AM Re: Outdoor transformer/grounding question [Re: Sparky42]
gfretwell Offline


Registered: 07/20/04
Posts: 9025
Loc: Estero,Fl,usa
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

#217387 - 06/30/16 09:59 PM Re: Outdoor transformer/grounding question [Re: Sparky42]
Yoopersup Offline

Registered: 03/04/03
Posts: 826
Loc: Michigan
Read 2014 N.E.C. 250.30 (C)

#217393 - 07/04/16 09:09 PM Re: Outdoor transformer/grounding question [Re: Sparky42]
Sparky42 Offline
New Member

Registered: 06/22/16
Posts: 2
Loc: CA
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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