shared neutral


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Old 11-25-07, 02:03 PM
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shared neutral

Hi Guys,

Easy one I think. I want to put a refig and freezer side by side (2 seperate units) in a new pantry. Can I run a single 12-3 circut with a shared neutral to feed a 2 gang box ? Units are standard household refer and freezer (nothing fancy). 20 amp breaker for each one.

Thanks, George
 
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Old 11-25-07, 02:31 PM
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Yes you can. I would use a double pole breaker. Use a single duplex receptacle and cut the tab on the hot side. That way nothing else can go on the circuits.
 
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Old 11-25-07, 02:32 PM
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Yes you could run a Multi wire circuit.

12/3 feeder to the first outlet with 12/2 between the two.

You would need to use a 20 amp doulbe pole breaker or two 20 amp breakers mechanically interlocked.

They Must however, be on oposite phases, hence the interlocking.
 
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Old 11-25-07, 03:25 PM
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If you use a single duplex receptacle with the brass tab removed, then you MUST use a 20 amp receptacle. and you MUST use a double pole 20 amp breaker.

If you use two separate duplex receptacles then they can be 15 amp receptacles (in the US), and you do not have to use a double pole breaker, although I would.
 
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Old 11-25-07, 04:53 PM
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Hi, Thank you for the responses. Why does it need a dbl pole breaker? Is it because of the shared neutral. I'm not an electrician by any means but would guess that you would want to de energize the "hot" side of any circuit that shares the common neutral and you can accomplish this by default with the dbl pole breaker. I'm more interested in knowing why than how.

Thanks, george
 
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Old 11-25-07, 05:03 PM
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A double pole 240 volt breaker assures that you get both lega of the incoming 240 volts. This is a must for the neutral wire to carry less than 20 amps of current at all times.

A double pole breaker (common trip) is required if you have a single device served by both hot wires. This would be the case if you use a single duplex receptacle, removing the brass tab and feeding it with both hot legs.
 
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Old 11-25-07, 07:59 PM
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With a split wired receptacle you need a means to disconnect simultaneously all ungrounded conductors supplying that yoke. This does not have to be a common trip breaker, but can be. An identified handle tie would be adequate.

As for the rationale, the Code mentions the simple close proximity of the energized wires, not because of the shared neutral.
 
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Old 11-26-07, 08:19 AM
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The upcoming 2008 code cycle will require that all shared neutral circuits use tied breakers whether the hots land on the same yoke or not. That's not exactly relevant to your project since no jurisdictions fall under the 08 code yet, but I thought you may be interested in knowing that's the direction the code is moving in. They also will require that the hots and the shared neutral be loosely grouped together with a wire tie at least one point in the panel.
 
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Old 11-26-07, 08:34 AM
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George,

Much of what has been stated goes into specifics. I was trying to generalize.

It is absolutely necessary that you get both legs of the incoming 240 volts for your circuit to be safe. The easiest way to do this is to use a 240 volt breaker. Doing so means that someone would have to go out of their way to change the setup.

If you use one duplex receptacle with the tab broken, there are several ways to meet the code requirements for the breaker(s), but again the easiest way is to use a 240 volt breaker.

Rather than confuse yourself about what is required when, my recommendation is to use a 240 volt breaker (properly installed) and leave it at that.

As for the receptacle used, either use a duplex 20 amp one (removing the brass tab) or user two duplex 15 or 20 ones (one for each 120 leg of the circuit). If you do go with two separate receptacle, you can use 12-2 to go from the first to the second, but you MUST pigtail the neutral connection.
 
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Old 11-26-07, 08:53 AM
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Although I agree with the advice given above, I would not recommend using a shared neutral circuit for your refrigerator and freezer. If, for some reason, the breaker trips, being a double breaker, both circuits will be de-energise. You will therefore lose the food in both the refrigerator and freezer. Could get expensive. Maybe worth the investment to run two 12/2 cables.
I am not even sure itís allowed by code here in Canada, since a refrigerator must be on a separate circuit, not shared with anything else.
 
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Old 11-26-07, 09:06 AM
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Although the concern express by impeyr is valid, I don't think it's a big worry. If the circuit is serving just these two appliances, the chances of it tripping are extremely small.
 
 

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