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Old 11-18-2009, 12:06 AM   #1
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feeding 4-wire grd sub off old panel


Need to tie into an old panel that is 3-phase (2-110 legs & 1 240 leg & neutral-ground) to a new sub- panel feeding boathouse 3 wire single phase w/grd . Anything special to watch out for? Plan on running 2- 110 legs and neutral #8 thwn w/# 12 solid ground wire. The old panel already has some new wiring in it w/neutral and ground tied to the same bar in panel. Would this be right if I did the same or should I drive a ground rod at new subpanel? Thanks for any help

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Old 11-18-2009, 08:09 AM   #2
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feeding 4-wire grd sub off old panel


I believe you are confused.... by your description I would say you have a 120/240V SINGLE PHASE panel, not a 3 phase panel.
You plan to run a new subpanel to the boathouse that will also be a 120/240V SINGLE PHASE panel. If you use #8 THHN/THWN wire for the two hots and neutral, the ground will need to be at least #10. These wires will need to be run in conduit, at the subpanel the ground and neutral will need to be separated, the neutral isolated from the enclosure, and a grounding electrode will need to be installed (assuming it is a detached building).

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Old 11-18-2009, 06:15 PM   #3
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feeding 4-wire grd sub off old panel


You also didnt state the amount of amps at what given voltage you are wanting at the boat house and the distance from the feeder panel.
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Old 11-18-2009, 06:21 PM   #4
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feeding 4-wire grd sub off old panel


Quote:
I believe you are confused.... by your description I would say you have a 120/240V SINGLE PHASE panel, not a 3 phase panel.

Do the math.


Quote:
(2-110 legs & 1 240 leg & neutral-ground)
3 phase delta (one high leg, 208V to ground)


If you are running 8's for the hot conductors, you must run an 8 for the neutral and a 10 for the ground. Add 2 ground rods at the sub and keep the neutral bus isolated.

I think I'd put a boathouse sub on a GFCI breaker. .

A boathouse is by the water...right? Sounds dangerous

Last edited by 220/221; 11-18-2009 at 06:24 PM.
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Old 11-18-2009, 07:59 PM   #5
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feeding 4-wire grd sub off old panel


Quote:
Originally Posted by HouseHelper View Post
I believe you are confused.... by your description I would say you have a 120/240V SINGLE PHASE panel, not a 3 phase panel.
You plan to run a new subpanel to the boathouse that will also be a 120/240V SINGLE PHASE panel. If you use #8 THHN/THWN wire for the two hots and neutral, the ground will need to be at least #10. These wires will need to be run in conduit, at the subpanel the ground and neutral will need to be separated, the neutral isolated from the enclosure, and a grounding electrode will need to be installed (assuming it is a detached building).
Another important point. If there is a cutoff switch between the meter and the panel, then the Neutral and Ground terminals (grid/s) must be separated even in the existing panel. At the risk of sounding like a broken record, or CD I will repeat my advice to beginner DIY'ers. Please pick up a book on Residential wiring projects at any home center. That will give you a basic understanding about the workings of Electrical wiring in the house. It will also facilitate the highly dedicated and experienced members on this forum to assist you to the best of their abilities. (No matter what) Don't Drink and Drive, Ever!!!
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