# Are two circuits allowed to have a common neutral?

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!

• You should clarify whether you are going to use split-phases, which is the way that this kind of multi-wire circuit usually operates. Commented Dec 8, 2016 at 23:16

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.

• For reference, this is known as a multi-wire branch circuit. Commented May 21, 2014 at 20:08
• +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
Commented May 22, 2014 at 11:30
• @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). Commented Dec 5, 2016 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. Commented Dec 8, 2016 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 ;-). Commented Dec 28, 2017 at 21:44

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.

Note the stipulation that a shared neutral MUST be for two circuits fed from a two-pole, common-trip breaker. This ensures that the neutral current never exceeds the Ampacity of one of the two phases feeding the circuits.

• Does not need to be common-trip. Just needs to be common shutoff. From a practical standpoint, a common trip double breaker is the easy and safe way to do this. But, particularly if you already have two single breakers and they are just not connected to each other, a listed handle tie is adequate to connect them - common trip is not required. Commented Nov 28, 2022 at 0:49