Current on a 12 gauge wire

[downsizingnow48]

Thx B&D less heat is a functional advantage that could be important in some circumstances.

I missed the water and electric in one conduit. May not be illegal strictly speaking but dumb and dangerous. No reason to do that anywhere.

 

[ultrarunner]

Agreed... it's just in my line of work I have to be careful when I say illegal... as there are distinctions and when I make the call I also need to cite the applicable law, statute or code...

It would be illegal to install a 30 amp dryer circuit in my city with 10 Gauge wire as code requires 8 Gauge... or the next city over state no plastic pipe above ground... so no plastic P-traps, Ice Maker Lines, Water Lines, or DWV... yet 10 minutes away these are all legal...

 

[mbohuntr]

Whats it matter if the circuit is heavily loaded or not? Electricity is hazardous if you dont know what you are doing. Thus why only qualified people should mess with it. A competent electrician would have no issues with a MWBC. ITs basically the same way the power enters your house. Two lines at 120v each (240v line to line), with a shared neutral. Thats all thats being done on a MWBC. The only "hazard" is you can have the potential between two of the lines to be 240v. So if you take a switch or recep. out of a workbox and touch the wrong two wires, you have a 240v shock instead of a 120v shock. But again, no different than working in the breaker panel.

Ok, So you are telling me that 28 amps is ok for a #12 wire, and you are telling me that since you are sharing that load between two independent breakers, that one couldn't inadvertently break open the wire nut neutral connection and create an arc because you thought there was only one load on it and you shut it off??? Sorry, I am an industrial electrician, and I run with one neutral per circuit because the next guy might not know any better...

 

[RNeumann]

We are building a home in the country and there are no building inspections or code requirements in this area. I've told the builder that we want to at least meet all the code requirements even though there will not be any official inspections. So, here's the question: There are (2) romex 12/3 wire with ground running thru conduit (with water pipes) to the kitchen island. Supposedly there are (2) single pole 20 amp breakers tied into these wires somehow. I suspect the black wire is tied to one breaker and the red is tied to the other breaker. The primary current loads are:
- Dishwasher - calls for it's own 15 amp breaker
- 2 gallon hot water heater under the sink - probably a 1500 watt heating element (~12 amps)
- small appliance outlets - about 1500 watts for an electric skillet or waffle iron.
1st, I don't see how (2) 20 amp circuits can carry that load. I talked to the electrician and he says "not to worry, it's fine". (I've seen 12 gauge wire on a 30 amp breaker around here and I know that is NOT "fine".) It seems to me that the electrician is using a single 12 gauge neutral to carry the current from (2) 20 amp hot wires and the electrician tells me that 12 gauge can do that. :shocked: Nor do I understand how he's going to provide for the 3 circuits with 2 circuit breakers. I suppose that if we sequence the usage "properly" everything will work.

Am I behind the times? or am I missing something? I'm getting ready to tell the builder to stop work until this is fixed, but don't want to do that unless I'm right. Any thoughts?

(2) 12/3 Romex wires is up to 4 circuits. A kitchen would typically have a dedicated DW circuit, and 2 circuits for the plugs (maybe one on the island and the other on the other cabinets). I'm guessing (if it's not what is noted below) he ran (1) 12/3 for the DW and plugs and the second is either for other plugs and the WH or the WH is a little 240v.

Note- usually the DW is next to the sink. The sink usually has a disposer. It is very common to run a 14/3 or 12/3 for the DW and disposer. You just break the little bar that provides power between the top and bottom of the plug.

If the electrician does it for a living every day I'd bet a few bucks the 12/3 makes it back to the panel. The odds he ran out of wire and or did something else are slim. One possibility would be a junction box that was placed before the slab was poured. He can add the breaker tie later if it doesn't make it in. Why would the breakers be in before the plugs and switches are set anyway? Are they really all in?

I'm sure it will work fine. The fact that you didn't understand about the shared neutral has me thinking you are looking at stuff you don't fully understand. With that, you have worried yourself into thinking the worst. You hired the contractor after much research because you trust him and like him. Continue to do so!

 

[dstig1]

Electrical threads always bring out 10+ pages of comments...

A couple points on what would be considered "code" and/or good practice were you subject to it for your kitchen:
- Microwave on it's own 20A circuit
- DW on it's own circuit (I'd do 20, but 15 may be OK depending on equipment...which is why i would do 20...)
- Your water heater needs its own circuit, 20A would be wise
- Fridge should be on it's own circuit (yeah, it's not required but it is a good idea)
- Code requires your countertops to have 2x 20A circuits, GFI protected serving them. There are a variety of restrictions on what can and cannot be covered by these.
- A disposal might be able to tap into your water heater circuit, especially if it is not heavily used

Many posters have explained about the common neutral already, so you just need to make sure he either uses double breakers or handle ties to have them trip together. A double breaker is by far the easier way, IMO.


One other point...

I strongly disagree that 14ga/15A circuits are a bad idea, and here is why: Lights. Have you ever tried to wire a light with a 12ga wire? The fixture wires are so tiny - often 16 or 18ga that you cannot get a good solid connection with a 12ga wire. I prefer to run all outlets at 20A and all lights at 15A, unless there is a special reason to do otherwise. And yes, I tend to separate those types of circuits, again, unless there is a special reason. To my knowledge, there is no overall code restriction saying lighting and outlets cannot be mixed. This is just what I have developed as my own best practice.

 

[LD1]

Ok, So you are telling me that 28 amps is ok for a #12 wire, and you are telling me that since you are sharing that load between two independent breakers, that one couldn't inadvertently break open the wire nut neutral connection and create an arc because you thought there was only one load on it and you shut it off??? Sorry, I am an industrial electrician, and I run with one neutral per circuit because the next guy might not know any better...

Where in my post did I say 28a was okay for 12ga?

And, as has already been discussed, you either use a double breaker or handle ties on a MWBC. That way you CANNOT inadvertently "break open a neutral connection" on a live circuit. You open the breaker for the MWBC and BOTH line 1 AND line 2 become de-energized. Thus no current on the neutral.

This is a classic case of people only like what they are familiar with and all else is taboo. There is absolutely nothing wrong with a MWBC, and poses no greater risk than a standard circuit. Any good electrician can quickly identify a MWBC and would have no issues working on/around that circuit.

As to the benefits, I think its all been covered. Less wire, less knockouts, less drilling holes in studs to make the runs, less heat generated in the circuit with fewer current carrying conductors, etc. No, it dont sound like much on a short run, but lets say you are wiring the bedrooms at the far end of the house. And ~150' of wire required to make the run. And you want two circuits in each bedroom. So, do you pull 150' of 12/2 FOUR times, or 12/3 twice? Lots of labor saved, lots of time saved, lots of material saved. And works just the same as if each had their own neutral.

 

[LD1]

I've looked at the electrical installation in more detail - the distance from the main breaker panel is about 30'. There are NO bonded 20 amp breakers in the main panel (no 240v 20a) The 12/3 wire goes somewhere but the red wire never shows up in the main breaker panel so now I'm wondering if there are other things on the circuit as well. I also found a 10 gauge wire on a 240v 40a breaker. I'm going to have to have a serious discussion with the builder (not the electrician) after this weekend!

10ga should not be on that 40a breaker. What is that powering?

As to the 12/3 not showing back up at the breaker box.....try to follow that wire. At first I though since it didnt show up, possibly the red wire was being used as the traveller between a pair of 3-way light switches. But you said that wire is feeding one of the outlets for the kitchen island....so ......without first hand eyes on and following the wire to see where things go....hard to say just what you have going on.

 

[ray66v]

Have you ever tried to wire a light with a 12ga wire? The fixture wires are so tiny - often 16 or 18ga that you cannot get a good solid connection with a 12ga wire.

Yes, I never have a problem.

Use this method: Insert the stranded, smaller wire all the way into the wire nut first. Then, put them both over the solid wire(s), and turn.

Using this trick, the smaller wire cannot be pushed out, when tightening the nut.

 

[3Ts]

I appreciate all the input. I like the builder, still do. I believe that the builder will make sure everything is correct, the builder is aware of this and doesn't fully understand what the electrician is doing either. The electrician works full time at something during the week - maybe electrician for a company, I just don't know. He wires houses for builders on the weekends. The reason this came up in the first place has to do with low voltage wiring for ethernet cables. The electrical plan shows where all the 240v, 120v, switches, outlets, lights, telephone, TV outlets, and low voltage cat6 cable outlets go. (Some of the cables will go to POE cameras under the soffit.) When he said he was done, I asked where the rest of the cat6 cables were - he said he doesn't do cameras. (??? I'm not asking for him to do cameras, just to run cable from point A to point B like the drawings specify.) So, then I started looking at the rest of his work and found outlets and switches missing that are in the plan. And there are other things like the main breaker panel requires a stool to reach the top breakers, pvc electrical conduit is not glued, etc. There's a whole lot of little things that by themselves are not a big deal, but after accumulating them all, I'm beginning to wonder what his qualifications are.

Everything on the island (DW, disposer, 2 gal hot water heater, outlets and lights) are all 120v, so I was not expecting to see a 240v line, especially when there is no indication of one in the breaker panel. I do not know where the wires go since they are covered with spray foam.

And I am not a licensed electrician, but some things just seem wrong. Here's an example of the low voltage wire and the 120v wiring.

 

[RNeumann]

I appreciate all the input. I like the builder, still do. I believe that the builder will make sure everything is correct, the builder is aware of this and doesn't fully understand what the electrician is doing either. The electrician works full time at something during the week - maybe electrician for a company, I just don't know. He wires houses for builders on the weekends. The reason this came up in the first place has to do with low voltage wiring for ethernet cables. The electrical plan shows where all the 240v, 120v, switches, outlets, lights, telephone, TV outlets, and low voltage cat6 cable outlets go. (Some of the cables will go to POE cameras under the soffit.) When he said he was done, I asked where the rest of the cat6 cables were - he said he doesn't do cameras. (??? I'm not asking for him to do cameras, just to run cable from point A to point B like the drawings specify.) So, then I started looking at the rest of his work and found outlets and switches missing that are in the plan. And there are other things like the main breaker panel requires a stool to reach the top breakers, pvc electrical conduit is not glued, etc. There's a whole lot of little things that by themselves are not a big deal, but after accumulating them all, I'm beginning to wonder what his qualifications are.

Everything on the island (DW, disposer, 2 gal hot water heater, outlets and lights) are all 120v, so I was not expecting to see a 240v line, especially when there is no indication of one in the breaker panel. I do not know where the wires go since they are covered with spray foam.

And I am not a licensed electrician, but some things just seem wrong. Here's an example of the low voltage wire and the 120v wiring.
View attachment 511015

Yes that photo it wrong. You shouldn't run cat5/6 with the romex. The inductive field around the romex can cause all kinds of issues with the cat5/6.

Based on your story I'm more concerned about the "electrician." Ask your builder to bring a full time electrician in to verify everything. If it's all good it was $80 spent for piece of mind. If it's a mess at least it will get fixed before drywall and or you are living with stuff you don't want.

Btw it is understandable that an electrician wouldn't do the low voltage. A lot of them don't do it anymore because it has become such a specialty.