Electrical Question – 2 circuits on 12-3 w ground oK?
Waters
| Posted in Construction Techniques on
Greetings,
I’m working on a house right now that has several circuits, kitchen and bath, run where the electrician has used 12-3 with ground to two separate 20Amp breakers to create two circuits, the red on one, the black on the other with the single ground and neutral coming back to the box as normal.
Is this Kosher? Or is it dangerous because it could potentially overload the neutral, that is basically serving two circuits at the same time?
Thank you.
Replies
So long as the two circuits are on opposite sides of the 240V line there's no problem -- the neutral will actually carry less current when both circuits are loaded.
It is best if twin breakers are used, vs two individual breakers (to assure that circuits are on opposite legs, and to disable both when one is worked on), and some inspectors may require this. But it's been claimed here that that's not required by code.
Thanks Dan,
What's the reasoning there with the breakers being on opposite legs?
I think that's the case with this box anyway, because the legs alternate sides as you travel down the breaker bars anyway. Cutler hammer with the brown tabs.
To to my understanding then, less current on the neutral because during load the appliance is using the current?
Cheers,
pat
If the breakers were not on opposite legs you would indeed get double current in the neutral when both circuits were loaded. But if opposite legs are used then when one side is "pushing" the other side is "pulling" and so you get the DIFFERENCE between the two currents in the neutral, vs the SUM.
potential problem
If the neutral wire does not have a GOOD connection at the Panel you can have a higher voltage running thru the wiring , 220 volts less what the load causes for voltagae drop It can damage electronic equipment.
If you'd like to continue my lesson...
'Pushing' vs 'pulling'
This is Alternating Current?
Yep
Alternating current. It's a little hard to visualize, but think of the two "sides" of a 240V line as being, say, two long channels or troughs containing water that is moving up and down in waves. In the middle is a 3rd trough that contains still water -- the neutral. "Work" is done by letting water flow from one of the "wavy" troughs into the middle one, or vice versa. (Imagine that power is extracted using a tiny water wheel that can get energy out of the flowing water while moving in either direction.)
"Voltage" is the (instantaneous) difference in height between the two troughs. When the trough on the left is "up" the trough on the right is "down", so while the peak difference between either and the (still) middle trough is 120V, the difference between the two outer troughs is 240V.
"Current" is the amount of water flowing between troughs. (Remember, this is instantaneous -- the water is flowing back and forth 60 times a second.) When water flows into the center trough on the left side, it flows out on the right side, if there are connections on both sides. So having two "circuits" actually reduces the current flow through the neutral.
Good analogy Dan.
I think he is talking about wtao 120V circuits with a shared neutral.
For 240V circuite the Nec does indeed reguire that the double breaker feeding it msut have a tie bar across both toggles, or be a single toggle that trips both legs simultaneously.
If it were a 240V circuite he would not need the neutral unless it was serving an appliance with that also had 120V circuits in it.
But you know all that stuff.
You mentioned a kitched and bath so probably GFI breakers, not a problem around here with shared neutals. As mentioned earlier, if you place the breakers on oposide legs they will be 180 degrees out of phase so the neutral would theoretically never see 2X current.
If for some reason you needed to put AFCI breakers in, you would have an issue with the shared neutral.
You would use a GFCI device after the multi wire split into separate circuits and use a regular 2 pole breaker ... or you could buy a $$$$ 2 pole GFCI.
AFCIs are tougher and you are probably precluded from using multiwire circuits, simply by the ridiculous cost of the 2 pole AFCI.
The subject of GFI's has come up as these circuits are kitch and bath.
I was planning to use GFI devices at the point of use, so, running the single 3 conductor wire to a j box, and splitting from there to run, say the GFI over a vanity, feeding a fan/can light to protect it over the shower, or a just a receptacle downstream.
OR
same scenario and splitting from there to run a GFI receptacle alone to plug the disposal into.
Problems?
That will work but you really don't need a GFCI on the disposal circuit if it is just going there. You only need GFCIs on receptacles serving the kitchen countertop and on all receptacles in the bath, not the light and fan in tub space unless the manufacturer requires it. (I bet most do tho)
My understanding is that a GFCI is required on a light/fan if it can be touched from the tub -- there's a distance rule.
Only in a trailer 552.54(B)
"(B) Shower Luminaires. If a luminaire is provided over a bathtub or in a shower stall, it shall be of the enclosed and gasketed type and listed for the type of installation, and it shall be ground-fault circuit-interrupter protected."
In a regular dwelling it only has tobe wet location listed, unless the manufacturer requires it in the installation instructions. Most do.
This is the commentary frm, the handbook
"The last sentence of 410.10(D) clarifies that securely fastened luminaires installed in or on the ceiling or wall are permitted to be located in the bathtub or shower area. Where they are subject to shower spray, the luminaires must be listed for a wet location. Luminaires installed in the tub or shower zone and not subject to shower spray are required to be listed for use in a damp location. GFCI protection is required only where specified in the installation instructions for the luminaire."