||12-26-2010 12:36 PM
Originally Posted by sparks1up
It is also important when using tandem breakers that both wires attached are on the same phase! If you mix phases (attach 2 wires from opposite phases that share a neutral) you can overload the neutral!
Also, new code changes, which may be applicable to the new work you are doing, do not allow for 2 circuits sharing a neutral to be supplied via single pole breakers. You must now use a 2-pole breaker to feed 2-circuits sharing a neutral or run separate neutrals for each circuit. In addition to that for new work you must also use a AFCI circuit breaker for all household circuits unless they are supplying power to an appliance. This does not necessarily apply to existing work, but it definitely applies to new work!
If the work you are doing is permitted you may want to ask your local electrical inspector or AHJ prior to completing this work!
You can share a single neutral between two opposite hot legs from a double-breaker. Four-wire appliance circuits (dryers and electric ranges) use this approach to power the 120V components of those appliances.
share a neutral between two circuits connected to a tandem breaker. Each circuit must be individually bonded to the neutral bus (as well as grounded individually to the grounding bus). A tandem breaker by design can only draw from a single hot leg in a service panel.
Not to confuse the OP here, but if you want to share a single neutral between two circuits in a multi-wire branch circuit (MWBC), you must use a double-pole breaker with tie-bar. This will draw from opposite hot legs in the service panel, which prevents the possibility of overload on the shared neutral and also ensures that if one side of the MWBC trips, both sides will be cut off simultaneously.
Depending on what the OP is trying to do, a tandem breaker may be the correct approach, or maybe she needs an MWBC. If she needs an MWBC, then a tandem breaker will not be appropriate and there are some special considerations concerning the neutral connection which must be taken.