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Joined: Feb 2006
Posts: 78
i have a old 480 3 ph open delta service no neutral and i am adding a 3ph 480/120/240 trans. to run a 240 pump and a dust to dawn lite. i took 3ph and a ground from a 480 disconnect to the trans. in pvc, and a neutral, ground and 3 phases to the 120/240 panel in pvc. bonding to be done in trans.and split in 120/240 panel which is in the same room. do i just connect the 480 side ground to the trans. case, and the net. and ground from the 240v side to xo with a ground jumper from the trans. case to xo.

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Joined: Mar 2003
Posts: 849
I take it if I;m reading you correctly . You have a 480 volt ungrounded Delta.
Your adding a 120/240 v high leg Delta via a transformer.
Hope I;m right so far.
Question Case & (Net)??
Load side I;d say XO to lug on case , also XO sized by 250.66 . To grounding electrode as required by 250.30.
Ground & Neutral seperate as you stated in 120/240 volt panel.
I usually tie the Equipment ground coming in on the 480 side to the same bar or lug( on the case) as XO's tied to in the Transformer.
Thats the way I see it.

Joined: Feb 2006
Posts: 78
The grounding electrode is a mat of rebar that was tied together, base plate bolts tied to the rebar, then the rebar incased in concrete, then a steel structure with conveyors built on the concrete slab the grounding electrode conductor 3/0 is in pvc underground from the structure to a wood frame building detached from the structure about 50' away and comes up into the mcc panel. Can I tap the grounding electrode conductor inside the mcc panel for the transformer, or do I have to go back to the steel structure.

Joined: Mar 2003
Posts: 849
Read 250.32 N.E.C. 2005 . You;ll have to use an existing grounding Electroid system if ones there.(In the second building).
If ones not there you must add one. You cannot use the equipment grounding conductor run with the feeders.As your bonding XO in the transformer the grounding electroide conductor well be required to terminate there and not in the panel.
I hope I;m reading you right.

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