Sharing Neutrals

16 years ago

We adding an addition, I have a few questions about shared neutral wires: (Every must be up to code since everything will be inspected.)

(1) Are there any exotic rules about what circuit cans share a neutral wire? I plan to run 12/3 (shared neutrals) for the two 20A appliance circuits in my kitchen and 14/3 for the disposal and dishwasher circuits. But can I do the same for say two different lighting circuit in different rooms? Or say the washing machine circuit and the appliance circuit in my laundry room?

(2) Am I required to use double-pole breakers on circuits with shared neutrals, or can I get away with just making sure two single-pole breakers are on different phases at the service panel.

Feel free to point me at previous posts if the answer is already there.

Thanks,

Mitch

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Comments (3)

spencer_electrician
16 years ago
No there are no rules, only things is anything that opens into the bedrooms (smoke alarms, outlets, lights) It is not a good idea to use multi-wire as the circuits require afci breakers and it is expensive/ hard to find double pole afcis. The only thing I've heard about lighting circuits is the fear of the neutral comming loose and sending high voltages up near 240 through the dimmers and lights. In a house with home automation or lutron maestros getting fried, that saving using the multi-wire is lost. I've used 12/3 to laundries in nice homes to have a second iron outlet. Also they do help tidy up kitchen feeds. You do not need double pole as long as the 2 circuits are not on the same outlet. However many suggest to use them for safety. I personally do not, if future people don't get the hint seeing a red wire in the box or volt ticking the box first, that is their problem. Yes they do need to be on seperate phases. I am a fan of this wire saving and cleaner way as most others on here are as well. I do have another post on here that is near the top of the list about my teacher that thinks multi-wire circuits are awful. Everyone disagrees.
Ron Natalie
16 years ago
A shared neutral will play havoc with many dimmers/HA things that are installed on both sides of the neutral.
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I am not a licensed electrician so take everything I say with a grain of salt but the way it reads to me is that you have a 220 run to your kitchen that was split into 110 runs by replacing your double breaker with two single breakers and splitting the powers to run two different circuits. If that is the case you do have some strange wiring as far as I have ever seen. To confirm this do you have you a 12-3 run out of the panel or two 12-2 lines and therefore have one neutral left unattached. I suspect that it is a 12-3 line. If that is the case then the electrician was being cheap and lazy as he is running one instead of two and then probably charging for two lines which would be illegal on top of unethical. At least I have never heard of a code allowing this. Your biggest issue in having two hots and one neutral is load balancing if I remember my electrical courses correctly. It has been ten years since I had them in college so my memory is pretty hazy as it isn't my day job so I won't speculate to much further but I did find this. "A balanced load in an electrical panel means that the current flowing through one leg is equal to the amount of current flowing through the other "hot" leg. The closer these numbers are, the more balanced the load. When the amperage is split up equally, the neutral current is canceled out. But when the current is placed all on one leg, the neutral must carry the entire load." So essentially by doing what they did your panel is unbalanced and you are forcing more current down you neutral lag therefore you neutral leg may potentially be undersized for the current it is carrying.
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I couldn't find them on th eweb page of schneider, thought it was becasue of this: "This document explains why the practice of sharing neutrals in wiring is not a good general wiring practice and why it is incompatible with the use of SQUARE D AFCIs." http://static.schneider-electric.us/docs/Circuit%20Protection/Miniature%20Circuit%20Breakers/Arc%20Fault%20Circuit%20Interrupters-AFCI/0760DB0203R902.pdf I did see a catalog and it had th epart number but the link went to the single pole. I think the 15 amp verison was not available, read a couple of blog where they say it was discontinued. I have 14 AWG cable and the circuit is 15 amp. This is a 20 amp. I did find the 15 amp: http://www.amazon.com/Square-Schneider-Electric-Two-Pole-Circuit/dp/B00KHVM6JU/ref=sr_1_1?s=hi&ie=UTF8&qid=1456718823&sr=1-1&keywords=square+d+afci+two+pole+QO+15+amp I already put the AFCI receptacles on the bedrooms so I think I will be covered, hopefully the inspector will agree. I will ask him about the 2 pole breaker if that would be in code. Thanks again. I have learned a lot about the code in this project.
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michaelpwalton1
16 years ago
One regulation in the Electrical Code regarding common neutrals is that they must be spliced and wire nutted together ahead of the device or circuit that they are feeding. The reason behind this is, If you were to share the neutral by taping into or onto a device, you would break the continuity when and if the device was serviced or removed / replaced and effect the other circuit / load, hence you splice ahead of the devices.

Sharing Neutrals

Comments (3)

spencer_electrician

Ron Natalie

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