Leviton’s 2-pole AFCI circuit breaker is intended to be used on multi-wire circuit (shared neutral) applications. Each Phase is rated at 120V with a common trip. The 2-pole AFCI breaker will monitor and protect two separate circuits that share a neutral.
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 a grounded 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 “prohibits installation 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 it requires 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 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, two-line conductors are used instead of one. Line conductors will be wired from the ‘A’ and ‘B’ phase 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 rated for 240V or 208V applications.
See Figure below.