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Don't know if the title makes sense so I'll explain what I'm doing. I'm trying to wire two adjacent fridges that each require a dedicated 15A circuit. I'm just wondering instead of running two wires if I can run a single 14/3 wire with the black wire powering one fridge, the red wire powering the other but both using white wire as neutral. My instinct says it's not up to code but I thought if ask. Thanks!

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    You should clarify whether you are going to use split-phases, which is the way that this kind of multi-wire circuit usually operates. – Philip Ngai Dec 8 '16 at 23:16
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It is perfectly fine and within code. The only stipulations are that you must splice the neutral, you cannot use the screws on one device to carry the neutral to the other, and that you must use a two-pole or handle-tied breaker.

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    For reference, this is known as a multi-wire branch circuit. – Tester101 May 21 '14 at 20:08
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    +1 It would be interesting and helpful if you could add an explanation about the two-pole breaker and why that prevents the neutral from carrying twice the allowed current. – bib May 22 '14 at 11:30
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    @bib The two pole breaker is used to enforce the use of two counterphase live wires. Each live circuit is rated to the single maximum (15A in this case) and the neutral can support it. However if both live phases are consuming 15A there is no (or only the differential) current in the neutral and it behaves as a single 15A 230V appliance that is neutral referenced at the middle of the load (and supply). – KalleMP Dec 5 '16 at 12:56
  • It is not the two-pole breaker that prevents the neutral from carrying twice the allowed current, it is the fact that the phasors of the two split-phases are always opposite each other. If the current of the two split-phases is equal, the neutral current will be zero. The neutral current will always be the difference of the current in the two split-phases. – Philip Ngai Dec 8 '16 at 23:14
  • With a "you must use a two-pole or handle-tied breaker." does that mean if one fridge causes the trip, the ice cream in both fridges will melt? Risking both desserts certainly must be against some code ;-). – chux Dec 28 '17 at 21:44
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Pay very close attention to that requirement "that you must use a two-pole or handle-tied breaker".

More specifically, this means that these are NOT two breakers on the same phase; this is a split-phase double breaker with the two lines on the opposite phases. You have 120V from each hot (black and red) to the neutral, and 240V across the two hots (which you aren't using in this application).

The shared neutral is allowed because the two phases are flowing in opposite directions, so to speak. As one is flowing one direction, the other is flowing the opposite, so you get some cancellation effect.

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The common will be carrying the current for both fridges, and, therefore, will not provide the same current carrying capability as that expected for the gauge of the wire. This is done in ceiling fans which also have lights on separate wall controls, but they don;t draw as much current as fridges. Make sure you use a gauge of wire that can carry the total current of the two fridges on the common; probably 10 gauge in your case. All that said, if the fridges are on opposite sides of a 220 box, you might get away with it, as explained above.

  • I hope I get away with it because I'm not running all the wires again! Currently everything is 14 gauge on 15 A breakers. Unfortunately none of the appliances (except the microwave) give their power consumption, only that they require a dedicated circuit. – canadianer May 28 '14 at 21:36
  • Usually, a 14/3 with red and black is a multi-wire circuit. If this is the case, the neutral current is the difference of the two ungrounded conductors' current, not the sum. – Philip Ngai Dec 8 '16 at 23:18

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