2-pole AFCI breakers are needed for multi-wire branch circuits, also known as “shared neutrals” or “Edison circuits”. The definition of a multi-wire branch circuit provided by NEC 210.4 is circuits that “consist of two or more ungrounded conductors that have voltage between them, and agrounded conductor that has equal voltage between it and each ungrounded conductor of the circuit, and that is connected to the neutral or grounded conductor of the system”. Another important point from this section of Code, is that all conductors for a multi-wire branch circuit must originate from the same panel. The NEC made a change in 2011, in section 200.4, that “prohibitsinstallation of ungrounded conductors on the same phase, to share a neutral”, essentially ending this practice.

Shared neutrals were quite common in the past so when upgrading a panel or replacing breakers you may see shared neutrals. To meet the latest version of the NEC, if AFCI protection is required on the shared neutral circuits being wired, you will be unable to use a 1-pole AFCI breaker, because in order for the 1-pole AFCI to function properly, you need a dedicated conductor for the line and neutral.

When wiring a dedicated circuit with AFCI protection, the line conductor is wired from the ‘A’phase lug of the breaker that feeds a dedicated load device and the neutral return is wired back to the neutral lug for that same breaker. For a multi-wire branch circuit with a shared neutral, the difference is two-line conductors are used. Line conductors will be wired from phase ‘A’ and ‘B’lugs of the breaker that feeds load devices and the neutral return will be shared with one conductor landing on the neutral lug ‘C’ for the same breaker. 2-pole AFCIs are NOT 240V rated. See Figure below.