Sub-panel install

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6t9deville

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I had a pool (underground) installed recently, and the contractor installed a subpanel for the lights/pumps. He mounted it next to the main panel, installed a 40A CB (in the main) which feeds two 20A CB in the subpanel. The neutral is isolated from the equipment ground in the sub. I want to use the open "slots" in the subpanel to supply a shed I built a couple of years ago. I bought a two slot panel for the shed and want to wire two 120 branches, using two 15 or 20A breakers. I have a ground rod at the shed. Ok the question(s) is/are, do I isolate the neutral at the shed (since it is isolated at the "pool" subpanel, or bond it with the equipment ground/panel? Also is 10 Ga wire acceptable to use as my feeder wire? Thanks in advance for any/all replies.
 
Re: Sub-panel install

Separate ground and neutral at the shed, this is another sub-panel. Neutral will be isolated from panel and the ground will be bonded to the panel. In regards to wire, #10 will be good for a max 30amp circuit, so this should work fine unless it's a very long run.
 
Re: Sub-panel install

Well I was just told that if I don't include a equipment ground (green) wire with the feeder, then I have to bond the neutral to the panel/ground at the shed. Reason being is that there is no metallic connection between the house and the shed since I am using non-metallic conduit. Is this right???
 
Re: Sub-panel install

Yes.

Originally posted by bphgravity:
You need to review Section 225.30 and 250.32 for proper wiring of a separate structure. :)
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Here's Mike Holt's take on it:
250.32(B)(2) Grounded Neutral Conductor. When an equipment grounding (bonding) conductor is not run to the building or structure disconnecting means, the building or structure disconnecting means can be bonded to a grounded neutral conductor installed with the feeder conductors. This is only permitted where there?s no continuous metallic path between buildings and structures, and ground-fault protection of equipment isn?t installed on the supply side of the feeder.

Where the grounded neutral feeder conductor serves as the effective ground-fault current path, it must be sized no smaller than the larger of:

(1) The maximum unbalanced neutral load in accordance with 220.61.

(2) The available fault current in
accordance with 250.122.

CAUTION: Using the grounded neutral conductor as the effective ground-fault current path poses potentially dangerous consequences and should only be done after careful consideration. Even if the initial installation doesn?t result in dangerous objectionable current on metal parts, there remains the possibility that a future installation of metal piping or cables between the buildings or structures could create unwanted parallel neutral current paths.

Author?s Comment: The preferred practice (or at least my preferred practice) is to not use the grounded neutral conductor as the effective ground-fault current path, but to install an equipment grounding (bonding) conductor with the feeder conductors to the building or structure in accordance with 250.32(B)(1).
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If you do not run an EGC with the feeder, you must bond the neutral to the EGC's in the seperate structure, or there is no path back to the source for opening a circuit breaker during a ground fault.

It would react the same as the open neutral pictured below:
1113855961_4.jpg
 
Re: Sub-panel install

Very informative reply, thanks. I did notice that the drawing did not show the sub-panel being bonded to a grounding electrode? I planned on using one at my shed. Would this eliminate, or at least take the majority of potential danger out of the picture?
 
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