4 wire cable with 2 circuit breakers

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  #1  
Old 07-28-01, 11:12 PM
BenDRL
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I'm rewiring some stuff in the house, and I found this situation:

A four wire, 12 gauge cable (black, red, white, bare copper wires) goes into the circuit breaker box where the cable is connected to two separate 20A circuit breakers. I persume the black wire is connected to 1 breaker and the red wire is connected to the other breaker. These are two separate breakers -- not the connected type you would use with an electric cooking range or clothes dryer.

On the other end of this 15 feet cable, the wires are split off into two cables. The cables are connected like this:

Black wire connected to black wire in cable #1
Red wire connected to black wire in cable #2
White wire connected to white wires in cables #1 & #2
Bare copper wires connected to bare copper wires in cables
#1 & 2

Is this an OK arrangement or is there a safety issue? I always thought that the white & bare ground wires in different circuits should only be connected in the circuit breaker box.

Thanks for your advice!

-Ben

 
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  #2  
Old 07-29-01, 08:12 AM
I
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This is a shared ground/neutral circuit and all is well, except that breaker is a no-no. A shared neutral circuit MUST be on a two pole breaker to assure that the two hot legs are on opposite buses. That way you have 240 volts between red and black and the neutral currents subtract. If the two hot legs wound up on the same bus the neutral currents would add, possibly to twice the rating of the wire. Change the breaker to a two pole and you're OK.
 
  #3  
Old 07-30-01, 09:58 AM
Guest
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A 2-pole breaker is not required by the NEC if each CB protects a 110 volt circuit. Art.240-20 (b) (1)reads;"individual single-pole CB's shall be permitted as the protection for each un-grounded conductor of multi-wire branch circuits that serve only single-phase line-to-neutral loads". BenDRL simply has to be absolutely sure the Red and Black wires are on juxtaposed CB's.
 
  #4  
Old 07-30-01, 01:08 PM
Wgoodrich
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switchman said it mostly right. A double pole breaker is only required if a multiwire circuit is serving on duplex on the same yoke. This would be a split receptacle with a common neutral and the tab removed making that top half on one breaker and the bottom half on a second breaker. Only then would a double pole breaker be required.

Hope this helps

Wg
 
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