Sharing Neutral At Receptacle

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bphgravity

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Two 20-ampere dedicated circuits of 12/2 NM cable are run into a single gang box to be used for a switch location. One cable is for the dishwasher, the other is for the diposal. From the box is a single run of 12/3 to supply the receptacle outlet under the sink. In the switch box, one circuit is switched the other passes through. All the whites conductors are tied together.

In result, the loads are sharing the neutral conductor back to the switch box, you then have parallel neutral paths back to the loadcenter. The diswasher operates at about 9.8A and the diposal is at 5.8A.

Any problems with this scenerio?
 
Re: Sharing Neutral At Receptacle

If I read this correctly, you have a paralleled grounded conductor (electrically joined at both ends to form a single conductor)from the supply to the switch box. This installation would be in violation of 310.4
 
Re: Sharing Neutral At Receptacle

Other than the apparent code violation, what hazard is there or could there be due to this arrangement?
 
Re: Sharing Neutral At Receptacle

Are the two 12/2's run next to each other the whole distance or do they seperate?

Roger
 
Re: Sharing Neutral At Receptacle

Lets suppose they are not run together, since I can't see that now. However they may be.


Edit for spelling correction

[ May 27, 2004, 03:18 PM: Message edited by: bphgravity ]
 
Re: Sharing Neutral At Receptacle

If they seperate we will have to think of net current, EMF.

Roger
 
Re: Sharing Neutral At Receptacle

Bryan,
I see no real hazard other than the possibility of an EMF field.
Don
 
Re: Sharing Neutral At Receptacle

What if you lost the neutral on the 12/3 and they are on opposite phases.Somebodys going to the big Orage to buy either a d/w or disposal or both.
 
Re: Sharing Neutral At Receptacle

Allen, WHAT IF a frog had wings? :) :D

Roger
 
Re: Sharing Neutral At Receptacle

Bryan,

Aside from the code violation under 310.4 that volt101 pointed out, I don't believe this scenario presents hazardous condition. Using round numbers if circuit A is drawing 10 amps and circuit B is drawing 6 amps, the draw on the neutral is 4 amps providing that circuits A & B are on different phases.

Now, if somewhere down the line another electrician comes in to do a service upgrade and finds black wires from the two 12/2 rx cables and lands them on the same phase - you are now drawing 16 amps on the neutral. Still OK under this scenario because you're at 80% of the of the rated load for the 12/3 portion of the circuit and you've doubled the neutral capacity of the circuits from the JB to the breaker panel by running two 12/2's.

Roger, I'm sorry to use a "WHAT IF" here but what if the ampacities were 12 amps and 10 amps respectfully. If you ran a 12/3 from JB to the breaker panel, using opposite phases the draw on the neutral is 2 amps but both on the same phase makes it 22 amps and in all probability you'll burn up the neutral.

Phil,
Gold Star Electric
 
Re: Sharing Neutral At Receptacle

I hope that this is a hypothetical situation because only a DIYer would go through those contortions just to feed a dishwasher. Run the 12/2 home run right to the DW and be done with it!

-Hal
 
Re: Sharing Neutral At Receptacle

This is an actual condition I have recently discovered at a clients home. I was there for a completely separate issue and discovered this exact setup.

I feel a reasonable solution is to combine the loads onto one of the circuits and abandon the other. Neither load exceeds the load permitted by 210.23(A) of the circuit ratings. :)
 
Re: Sharing Neutral At Receptacle

Another "WHAT IF".... Homeowner hires a plumber to install a new "Insta-Hot" heater under the sink, uses a plugstrip to the get additional recptacles on the unswitched dishwasher portion of the original receptacle. Now add up the neutral currents......Point is it is a code violation AND there are to many "what-ifs" that you have no control over. I'd have to agree with the above solution, fish a 12/2 to the DW and fix the problem or combine the loads to one circuit and abandon the 2nd 12/2.
 
Re: Sharing Neutral At Receptacle

Phil, although this is not what this thread is about, you sound as though you are scared of a Multi-Wire branch circuit.

Bryan, JMO, I don't know if this would really be a concern, not that it is desirable, but think of all the EMF issues associated with K&T or many NM wired houses.

Of course if I (you in this case) had a gauss meter, I would walk the area with these circuits loaded and make my decision on this. :)

Roger

[ May 28, 2004, 04:33 PM: Message edited by: roger ]
 
Re: Sharing Neutral At Receptacle

Hello Scott, if the 12/2's seperated on the way to the panel, the stray (slang) current would still be present (probably more so) when only one load (dishwasher) was running.


Edit:

Maybe you were talking about combining both on one circuit. :eek:

Roger

[ May 28, 2004, 05:19 PM: Message edited by: roger ]
 
Re: Sharing Neutral At Receptacle

Right. The net current magnetic fields will be greater when only one appliance is drawing.

I once had to deal with the results of this kind of duplex receptacle fed by two home runs. The bonding tab between the hots was removed, but not the tab bonding the neutrals. An electric heater was plugged into one of the receptacle jacks. The magnetic field created when the neutral split and returned on both neutrals (routed separately) was huge, and the circuit passed right behind a sofa where a pregnant woman slept during much of her pregnancy.

Though this is anecdotal, her child was born with several sad birth defects, and the woman had become extremely electrosensitive, with mostly skin burning sensations and rashes. I tested her and found that she could actually tell when a 2 mG (weak) field was present or not (I built a silent test set-up).

Of course this might be coincidence, but I cite it just so electricians reading this might consider that a Code violation that produces high magnetic fields may have other effects besides heat production. So let's not be casual about the Code, OK?

Karl
 
Re: Sharing Neutral At Receptacle

Bryan,

The first thing I would have to do, upon discovering the 12/3 extension from the switch single gang, would be to identify the branch circuit OCPDs, and be certain that they were on opposite electrical sides of the bus.

Next, if the assembly looked clearly new enough, I'd verify the "simultaneous disconnect" of the ungrounded conductors.

Al
 
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