Lighting, Light Fixtures, Ceiling and Exhaust Fans - Ceiling fan & Muilti-wire branch circuits
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Dexman1349
02-06-09, 09:27 AM
I am trying to get a ceiling fan installed in my foyer and have come across something I am not very clear on - Muiltiwire branch circuits. It appears I have installed one without knowing and would like some help determing whether it is safe or not (breakers are currently off).
A little background: This is in Colorado (for code purposes). The fan is going in over on open, switch-back stairwell in a tri-level house (livingroom --> 1/2 flight up to kitchen --> 1/2 flight up to bedrooms) which makes for a good spot for circualtion. There is a light switch on each level that controls this light. When I opened up the box for the light in the ceiling, there is just a single cable (white, black, and bare). The fan has it's typical 4 wire system: white-common neutral, black-fan hot, blue-light hot, & green-ground.
My goal was to wire this so that the fan would run continuously and the lights would be operated by the switches. Obviously, I would need an additional hot wire to do this. Unfortunately the circuit this light is connected to is in the living room and is not an easy place to run a parallel line from. So instead, I spliced into the master bedroom circuit to provide the hot for the fan. This is where I created the multi-wire branch circuit (two seperate hot wires with a single common neutral.
I know MWBC's can be very useful if done correctly, but can be very dangerous if not. The livingroom circuit (hot for the light) provides power for things like the entertainment center (42" TV, DVD player, Cable box, etc), two lights, and a couple outlets. The bedroom circuit (hot for the fan) provides power for a ceiling fan/light, and 4 outlets (including a switch controlled outlet for a second light). The one thing I have read at multiple sources (including Electriciansparadise -- Multiwire Branch Circuits (http://www.electriciansparadise.com/articles.html)) states that a MWBC can be done if the two circuits are on different phases.
My questions then are:
1) is this correct?
1a) if yes, how do I tell if the circuits are on different phases
2) would I just be better off seperating the common neutral on the fan/light and wiring them completely seperately?
A little background: This is in Colorado (for code purposes). The fan is going in over on open, switch-back stairwell in a tri-level house (livingroom --> 1/2 flight up to kitchen --> 1/2 flight up to bedrooms) which makes for a good spot for circualtion. There is a light switch on each level that controls this light. When I opened up the box for the light in the ceiling, there is just a single cable (white, black, and bare). The fan has it's typical 4 wire system: white-common neutral, black-fan hot, blue-light hot, & green-ground.
My goal was to wire this so that the fan would run continuously and the lights would be operated by the switches. Obviously, I would need an additional hot wire to do this. Unfortunately the circuit this light is connected to is in the living room and is not an easy place to run a parallel line from. So instead, I spliced into the master bedroom circuit to provide the hot for the fan. This is where I created the multi-wire branch circuit (two seperate hot wires with a single common neutral.
I know MWBC's can be very useful if done correctly, but can be very dangerous if not. The livingroom circuit (hot for the light) provides power for things like the entertainment center (42" TV, DVD player, Cable box, etc), two lights, and a couple outlets. The bedroom circuit (hot for the fan) provides power for a ceiling fan/light, and 4 outlets (including a switch controlled outlet for a second light). The one thing I have read at multiple sources (including Electriciansparadise -- Multiwire Branch Circuits (http://www.electriciansparadise.com/articles.html)) states that a MWBC can be done if the two circuits are on different phases.
My questions then are:
1) is this correct?
1a) if yes, how do I tell if the circuits are on different phases
2) would I just be better off seperating the common neutral on the fan/light and wiring them completely seperately?
wirenut1110
02-06-09, 07:05 PM
One way to tell if they're on different legs is that you would have 240 volts measured across the hots.
To make a long story short, an MWBC breakers need to be handle tied (double pole breaker) so unless these breakers for this circuit are next to each other in the panel (top/bottom) this isn't legal. Just use one circuit for the fan/light.
If you use 2 circuits for this, the breaker handles HAVE to be tied together.
Hope this doesn't sound confusing.
To make a long story short, an MWBC breakers need to be handle tied (double pole breaker) so unless these breakers for this circuit are next to each other in the panel (top/bottom) this isn't legal. Just use one circuit for the fan/light.
If you use 2 circuits for this, the breaker handles HAVE to be tied together.
Hope this doesn't sound confusing.