Multi-Wire Branch Circuit Shared Neutral in a Kitchen Remodel
A remodel converts a kitchen and adds a 20 A, 120/240 V multi-wire branch circuit (two ungrounded conductors sharing one neutral) to serve the microwave and the disposal. The electrician terminates both ungrounded conductors on a two-pole breaker and lands the shared neutral on the neutral bar. During inspection, the inspector finds the two ungrounded conductors are on a two-pole breaker but the breaker is not a common-trip type that simultaneously disconnects both poles under a single handle. The inspector also notes the circuit serves two separate appliance outlets and that the neutral is not pigtailed at either outlet box-each device is wired with the shared neutral passing through the box unbroken. The inspector must decide whether to approve, red-tag, or require specific corrections, and must document the basis.
1. Evaluate the multi-wire branch circuit arrangement and identify each deficiency with its code basis.
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Two distinct issues:
Simultaneous disconnect. A multi-wire branch circuit must be provided with a means to simultaneously disconnect all ungrounded conductors at the point of origin. A two-pole breaker whose poles are not mechanically tied to trip and open together does not satisfy this. The correction is to install a breaker with a single handle or an approved handle tie that opens both poles together, or a two-pole common-trip breaker.
Neutral continuity / device removal. Where a multi-wire branch circuit supplies devices, the continuity of the grounded conductor must not depend on device connections. The shared neutral must be pigtailed so that removing a device does not open the neutral for the other circuit. Passing the neutral unbroken through the box without a pigtail to each device means removing one device interrupts the neutral return for the other circuit-an unacceptable condition.
The inspector should red-tag with both corrections cited, not approve conditionally.
2. The electrician argues that because the two appliances are on separate outlets, the shared-neutral rules do not apply. How should the inspector respond, and what is the reasoning?
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The argument fails. The multi-wire branch circuit rules apply to the circuit as a whole, regardless of how many outlet boxes or devices it serves. The circuit originates as two ungrounded conductors sharing one neutral; that characteristic-not the number of outlets-triggers the simultaneous-disconnect and neutral-continuity requirements.
The inspector should explain that the requirements exist precisely because a shared neutral can carry current from either circuit, and an open neutral or a single-pole disconnect can create an overvoltage or shock hazard at the other outlet. The inspector documents the correction requirements and re-inspects after the handle tie and pigtails are installed.