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Can (2) 1-pole CAFI, AFI, GFI, DF, AFGF or EPD breakers be used to feed (2) 120V single-pole circuits that share a common neutral? (shared neutral)
Product Line:
Circuit Breakers
Environment:
Applies to 1p QO, QOB, and HOM breakers with suffix CAFI, AFI, GFI, DF or EPD
Resolution:
For 120V circuits that are fed by 1p CAFI, AFI, GFI, DF or EPD breakers, the neutral MUST NOT be shared between two circuits. Doing so will cause both breakers to nuisance trip. The circuits must be wired in such a way that each 120V circuit has its own neutral.
If existing wiring already uses shared neutrals between two 120V circuits, and re-wiring is not an option, consider using one 2p breaker in place of the two 1p breakers (if local electrical code allows). The following 2p breakers types are available:
2p CAFI (use on 120/240V system; not for use on 208Y/120V system)
2p GFI (use on 120/240V as well as 208Y/120V systems)
2p EPD (use on 120/240V as well as 208Y/120V systems)
NOTE: The reason for needing a 2p breaker for a shared neutral circuit when using a breaker with these suffixes is that they will trip if there is a net current flow in either direction in their ground-fault detection zero-sequence CT. With two breakers there are two CTs; one will have the neutral and with neutral current for both circuits flowing through it, there will be a net current flow back to the load. The other will have no neutral current flow to balance the load current, Both will trip.
A 2p breaker has one CT for both legs of the shared neutral circuit and can therefore properly sense net current flow.
Circuit Breakers
Environment:
Applies to 1p QO, QOB, and HOM breakers with suffix CAFI, AFI, GFI, DF or EPD
Resolution:
For 120V circuits that are fed by 1p CAFI, AFI, GFI, DF or EPD breakers, the neutral MUST NOT be shared between two circuits. Doing so will cause both breakers to nuisance trip. The circuits must be wired in such a way that each 120V circuit has its own neutral.
If existing wiring already uses shared neutrals between two 120V circuits, and re-wiring is not an option, consider using one 2p breaker in place of the two 1p breakers (if local electrical code allows). The following 2p breakers types are available:
2p CAFI (use on 120/240V system; not for use on 208Y/120V system)
2p GFI (use on 120/240V as well as 208Y/120V systems)
2p EPD (use on 120/240V as well as 208Y/120V systems)
NOTE: The reason for needing a 2p breaker for a shared neutral circuit when using a breaker with these suffixes is that they will trip if there is a net current flow in either direction in their ground-fault detection zero-sequence CT. With two breakers there are two CTs; one will have the neutral and with neutral current for both circuits flowing through it, there will be a net current flow back to the load. The other will have no neutral current flow to balance the load current, Both will trip.
A 2p breaker has one CT for both legs of the shared neutral circuit and can therefore properly sense net current flow.
Released for:Schneider Electric Canada
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