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jnahman 07-09-2012 12:07 PM

Wiring and using a common ground
 
Hello to all. I am new so bear with me.

I have a 220v panel in the garage. Currently romex feeds the plugs and lights.
What I would like to do is to put in a switch box that would turn on a pair of lights in the front of the garage, a separate switch to the lights in the back of the garage, and have a separate line (always on) that had drops from three boxes to a plug so I can plug in a vacuum or tool. It is my intention to run the plugs off of a dedicated 20a breaker (for tools) and the lights off of a separate 20a.
breaker.

My question is this, should I run a black (hot) and white to each line or can I use a common white (neutral) for the plugs and lights? I am assuming I can run a bare copper for the ground and pigtail off of it rather than running three separate grounds. All is being run in EMT and 12 guage.

All comment are welcomed and thank you in advance.

AllanJ 07-09-2012 12:38 PM

You may not use a common neutral shared between two independent circuits with separate breakers.

Wherever you tap off or branch off or pigtail off of a line you need to have a junction box inside of which you make the connections.

Provided that the box is large enough it can have the branchings and also hold a receptacle or a switch.

Typical setup with one conduit feeding a box with a receptacle and two other conduits going off in different directions elswhere (all metal conduit): Have one set of black and white wires for the power feed, another set of black and white wires going out one of the branch off conduits, and yet another set of black and white wires going out the other branch conduit. Add a white pigtail for the receptacle and connect together all the whites (4). Add a black pigtail for the receptacle and connect together all the blacks (4). Use a bare pigtail or a clip sold separately for that purpose to bond the receptacle to the box. Add more black (or red or blue) wires as needed to carry switched power in addition to unswitched power. A white wire (for neutral) must go down to every switch box even if nothing continues beyond.

Slightly more complicated setup with two circuits sharing the same conduit, for example one circuit for the receptacles and one circuit for the lights: have two sets of black and white coming up the conduit from the panel. Do not combine either the white (neutral) or the black (hot) of one circuit with those of the other circuit. Here you would have in the junction box two bundles of white wires held together with wire nuts, and two bundles of black wires.

For plastic conduit with bare ground wires running inside, only one ground wire has to come up and continue on even if you have two or more circuits (separate black.white pairs). For flexible metal conduit with a grounding strip, the strip does not have to be long enough to come out and be wire nutted to anything.

With conduit, wires not being tapped off or pigtailed off of in a box can enter and leave the box without being cut and wire nutted back together, although stringing them through that way can be tricky.

jnahman 07-09-2012 04:27 PM

Hi AllanJ,

Thank you very much. The part that was most concerning was whether two circuits from two different breakers could share a common. Your response certainly cleared that up and the rest of the narrative is very useful. Again, thank you for your assistance.

jaime

jnahman 07-09-2012 06:18 PM

romex vs emt
 
one last question. With the subpanel in the garage (wall), would you run romex to the junction box or use EMT? The romex would run up the wall and then across the garage rafters. I have had a couple of mice on occasion, and a rat once or twice (the problem when one forgets to close the garage door). There is already romex from the original wiring (not mine) and there hasn't been any damage to it. I guess I'm mixed about romex, which is why I am asking.

AltaSparky 07-09-2012 06:34 PM

Quote:

Originally Posted by jnahman (Post 961773)
one last question. With the subpanel in the garage (wall), would you run romex to the junction box or use EMT? The romex would run up the wall and then across the garage rafters. I have had a couple of mice on occasion, and a rat once or twice (the problem when one forgets to close the garage door). There is already romex from the original wiring (not mine) and there hasn't been any damage to it. I guess I'm mixed about romex, which is why I am asking.

IF you have wood studs I would use romex. If your concerned about damage consider BX (called MC cable in the US).

EMT is cosmetically nicer if you know how to bend it and make it look nice. The other main advantage is that if you have room in the pipe you can add wires in it in the future.

andrew79 07-09-2012 07:00 PM

if your in canada and i assume you are by the fact you called it bx you can't have lighting loads on 20A breakers, 15Amax
30-104 Protection (see Appendix B)
Luminaires, lampholders, and lighting track shall not be connected to a branch circuit protected by overcurrent
devices rated or set at more than
(a) 15 A in dwelling units;
(b) 15 A in other than dwelling units, where the input voltage exceeds 347 V nominal;
(c) 20 A in other than dwelling units, where the input voltage does not exceed 347 V nominal; or
(d) 40 A in other than dwelling units, where the load is from
(i) luminaires with lampholders of the incandescent mogul base type;
(ii) high-intensity discharge (HID) luminaires, with or without auxiliary lighting systems, where the input
voltage does not exceed 120 V nominal;

edit:nm that wasn't original poster that said that, i'll leave it up anyways just in case

jnahman 07-09-2012 08:57 PM

re Romex vs emt
 
Actually I am in Los Angeles, does that negate the restriction on using romex for lightling? The lights are going to be flourescents. Thanks to both of you for your input.

andrew79 07-09-2012 09:26 PM

I'm not exactly sure what the rule is from the nec. I think ours is the same though. Basically you can run romex anywhere where there's no chance it will get damaged. I would say it's a no go in your case unless you get it into a wall if they're drywalled. EMT is definately nicer but metal sheath cable looks good too if it's clipped nicely.

gailquilter2 07-09-2012 09:48 PM

romex or conduit
 
I was told some time back romex is for inside the walls where it cannot get chewed on etc. Conduit for where you see it or if it could be chewed on.
Your building inspector should know

jnahman 07-09-2012 09:53 PM

Again....thank you for your help....greatly appreciated. Guess now I have to get to work.


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