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Old 07-15-2012, 01:10 PM   #1
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Shared Neutral


I'm not fully understanding what's allowed for a shared neutral and ground. I have 10/3 UF running underground from the garage to a pool outlet and also a shed. The red wire isn't being used. The circuit is on a timer, so I can't use the shed unless the pool pump is running.

Can I make the red wire the shed's power, the black wire the pool's outlet, and share the neutral and ground between them? My understanding is this would be allowed only if each circuit was protected at 15 amps, so the neutral would never exceed 30 amps.

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Old 07-15-2012, 01:28 PM   #2
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Shared Neutral


I believe you would have to have the wires on seperate legs in the panel. This would make it so the unbalanced load flows back on the neutral and would never exceed 15a not 30a.

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Old 07-15-2012, 01:34 PM   #3
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Shared Neutral


Pool pumps cannot be wired with UF due to the requirement of an insulated ground.
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Old 07-15-2012, 05:08 PM   #4
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Shared Neutral


When you have red, black, white (and ground) in a cable you can share the neutral (white) when red and black are on opposite sides of a 120/240 volt circuit (240 volts between the two) and then for 10 gauge wire you can have 30 amps on each. This produces two allotments of 120 volts at 30 amps or one allotment of 240 volts at 30 amps or some combination in between. The actual current on the neutral will range from 0 to 30 amps as the difference between the amperes on the red and on the black.

Should red and black of a cable with one white wire be on the same side of the 120/240 volt line they must both be on the same circuit, i.e. on the same single breaker supplying 120 volts (up to 30 amps for 10 gauge). This latter might be the case if black is unswitched and red is switched at a box downstream of the panel (a cable without the red wire goes between the switch box and the panel). Note that the maximum amperage allowed to reach ordinary switches and receptacles and light fixtures is 20 amps. A (10 gauge) circuit actually breakered at 30 amps must go to a subpanel first before any of the aforementioned devices can be wired (downstream of 15 or 20 amp "sub-branch circuit" breakers).

Ten gauge may be used (and needed) for a 20 amp circuit if the distance from main panel to receptacle is great, say more than about 150 feet.
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Last edited by AllanJ; 07-15-2012 at 05:24 PM.
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Old 07-16-2012, 05:52 AM   #5
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Shared Neutral


So as long as I put the 2 separate breakers on top of each other on the panel, they can be split?
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Old 07-16-2012, 05:55 AM   #6
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Shared Neutral


Quote:
Originally Posted by matt151617 View Post
So as long as I put the 2 separate breakers on top of each other on the panel, they can be split?
Yes, but the maximum breaker you could use is a 20 amp.
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Old 07-16-2012, 06:35 AM   #7
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Originally Posted by stickboy1375 View Post
Yes, but the maximum breaker you could use is a 20 amp.
The 20 amp breaker limit occurs because of the wire size (not relevnt in the OP's original question) or there are/will be devices intended for circuits with no more than 20 amps with no subpanel breaker in between.

Not because the neutral is shared.

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