Can two 20A circuits share the same neutral & ground

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Old 02-14-11, 01:45 PM
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Can two 20A circuits share the same neutral & ground

Hi, I'm completely re-doing a bathroom in my house. I'm adding a vent fan/light/heater combo that requires its own 20A circuit. the other lights, towel warmer, GFCI outlet would be on another 20A circuit to meet code. One contractor mentioned running a single 12/3 wire from main panel to the bathroom and using one one hot wire for 20A circuit A, and the other hot for 20A circuit B. this would mean they are sharing the same ground and neutral wires. I would like to do this on a duplex 20A breaker to save space in the main panel. I know I could run two 12/2 wires, one for each breaker, but would one 12/3 work, be safe, etc.?

have 200A main panel so no supply problems, plenty of room in box now but have other upgrades planned in future so want to be judicious with space and would like to use slim breakers where possible.

Thanks for your help
Michael
 
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Old 02-14-11, 01:50 PM
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Mike DIY here, I forgot to mention I'm in San Diego county, California
 
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Old 02-14-11, 01:57 PM
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Originally Posted by MikeDIY View Post
One contractor mentioned running a single 12/3 wire from main panel to the bathroom and using one one hot wire for 20A circuit A, and the other hot for 20A circuit B....but would one 12/3 work, be safe, etc.?
Yes it's okay. It's called a multiwire branch circuit, and when done according to the rules, is perfectly safe. The double-pole breaker is required, as are some details with how the circuit is installed but if you have a licensed electrical contractor these details will be handled no problem.
 
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Old 02-14-11, 01:58 PM
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What you are talking about is a multiwire circuit. By current code it must be on a 2 pole 240 volt breaker. There may or may not be duplex 2 pole breakers available for your panel. Regardless of code it could not be done on a 120v duplex breaker which most duplex breakers are because usually they are on the same hot leg.

Edit: Phrase in blue should be, "240 volt breaker".
 

Last edited by pcboss; 02-17-11 at 06:25 AM. Reason: changed amp to volt
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Old 02-14-11, 04:47 PM
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edited response

Not sure I understand, and not sure I explained accurately. This would require a double pole 240V breaker:?

12/3 wire:
hot wire A
hot wire B
ground
neutral

in the main panel, ground and neutral connect to the appropriate bus bar. hot wire A connects to 20A 120V circuit breaker #1, hot wire B connects to 20A 120V circuit breaker #2

Hot wire A would connect to outlet A, and hot wire B connects to outlet B. ground and neutral are split in a junction box so that they feed outlet A and outlet B.

Thanks for any clarification you can make. If a double pole 240 breaker is needed I would rather run two seperate 12/2 wires connected to seperate breakers.

Michael
 

Last edited by pcboss; 02-17-11 at 06:26 AM. Reason: changed amp to volt
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Old 02-14-11, 05:03 PM
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Yes. It is basically like a a 240v circuit with the 120v derived from the neutral and HA or HB at each outlet. It may save a bit of wire but the cost difference is marginal and using two separate circuits is maybe a bit simpler.
 
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Old 02-15-11, 09:28 AM
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Originally Posted by MikeDIY View Post
If a double pole 240 breaker is needed I would rather run two seperate 12/2 wires connected to seperate breakers.
A double-pole (240V) breaker is mandatory for a multiwire branch circuit.
 
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Old 02-16-11, 06:48 AM
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Originally Posted by MikeDIY View Post
Not sure I understand, and not sure I explained accurately. This would require a double pole 240A breaker:?

12/3 wire:
hot wire A
hot wire B
ground
neutral

in the main panel, ground and neutral connect to the appropriate bus bar. hot wire A connects to 20A 120V circuit breaker #1, hot wire B connects to 20A 120V circuit breaker #2

Hot wire A would connect to outlet A, and hot wire B connects to outlet B. ground and neutral are split in a junction box so that they feed outlet A and outlet B.

Thanks for any clarification you can make. If a double pole 240 breaker is needed I would rather run two seperate 12/2 wires connected to seperate breakers.

Michael
In case you are wondering.....the neutral wire on a multiwire branch circuit only carries the unbalanced load of the two hot feeds. The two hot feeds are on opposite phases so the neutral current from them cancels each other out instead of adding together. The advantage of this type of circuit is that you can save the cost of some copper, but the disadvantage is that in case one circuit trips, the other one trips, too. Or if you have to turn one off, the other one has to be turned off also.
 
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Old 02-16-11, 09:53 AM
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Originally Posted by ray2047 View Post
What you are talking about is a multiwire circuit. By current code it must be on a 2 pole 240 amp breaker. There may or may not be duplex 2 pole breakers available for your panel. Regardless of code it could not be done on a 120v duplex breaker which most duplex breakers are because usually they are on the same hot leg.
I smell a typo. It looks like it may have confused the OP. Pretty sure Ray meant "240 volt breaker". The amp rating would be 20 amps for each side.
 
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Old 02-16-11, 10:06 AM
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Originally Posted by RichA View Post
I smell a typo. It looks like it may have confused the OP. Pretty sure Ray meant "240 volt breaker". The amp rating would be 20 amps for each side.
Yes, definitly a typo. Thanks for the catch.
 
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