Grounding question...having a brain fart

Jokarva · #1 02/11/12, 02:35 AM

I'm hanging a new light fixture in the powder room, the old one has no junction box because there's a stud right there...the romex is just poking out of the wall next to it. So I bought a metal pancake box to surface mount, it will fit behind the fixture I'm using.

I'm having the brain fart with wiring the ground...on a metal box I need to wrap the romex copper and the fixture ground around the green screw - is that right? It's not enough to just tie them together. And it doesn't matter which wraps around the screw...either the house wire or the fixture wire, as long as the wire ends up wrapped around the screw and then tied together? I've wired fixtures before, but it's been a few years and we always had plastic boxes.

Thanks for any help and I hope this makes sense...it's late, I'm tired and I think I'll finish this in the morning

Alice In TX/MO · #2 02/11/12, 04:53 AM

I don't understand this...

on a metal box I need to wrap the romex copper and the fixture ground around the green screw - is that right? It's not enough to just tie them together. And it doesn't matter which wraps around the screw...either the house wire or the fixture wire, as long as the wire ends up wrapped around the screw and then tied together?

idigbeets · #3 02/11/12, 05:45 AM

If I understand it right, you're asking if the romex ground and the light fixtures ground wire both need to be bonded to the junction box you just purchased....

You can wire nut the ground wire from light fixture to the romex ground wire. (I would double check that it is too grounded at the electrical panel box).

If there were no ground wire from the romex present, you would bond the light fixture to your junction box you purchased or sometimes there is a little mounting bar that comes w/ light fixtures that you can bond too as well.

OkieDavid · #4 02/11/12, 07:16 AM

Yes. Romex bare copper and light fixture green go to the green nut on the metal box. The most important thing is that the bare copper Romex ultimately connects back to the service panel grounding bar.

Harry Chickpea · #5 02/11/12, 11:08 AM

OkieDavid is right. However... I question the use of a surface mount metal box in this situation. I'd feel more comfortable if that circuit had a GFCI breaker on it. 99.9% of the time it could be fine, but there is potential for shocks. If it was a bedroom or living area, I'd be less concerned.

#6 02/11/12, 11:30 AM

I assume you are going to screw the pancake box to the stud . If so I would wrap the bare romex ground wire around one of these screws before tightening & leave a few inches after wrapping to wirenut the fixtures ground wire to .

cfabe · #7 02/11/12, 03:24 PM

In this situation I have always wrapped the romex ground around the green ground screw, leaving at least 6" tail out of the box. Then wire nut the fixture ground to the end of the romex ground.

Oldcountryboy · #8 02/11/12, 04:14 PM

Having been a electrician for many years I would most always wrap the ground wire coming from the light fixture on the green screw of the outlet box and tighten down first. This way I could let go of the fixture and it would hang there while I use two free hands to make all my splices.

Jokarva · #9 02/11/12, 07:03 PM

Quote:

Originally Posted by Oldcountryboy

Having been a electrician for many years I would most always wrap the ground wire coming from the light fixture on the green screw of the outlet box and tighten down first. This way I could let go of the fixture and it would hang there while I use two free hands to make all my splices.

Thanks guys, the fixture is up and working and this is how I ended up doing it. Logistically just didn't have the length I needed on the romex copper...and the fixture ground wire was easier to wrap anyway. Everything is wirenutted tight and tucked in clean.

Harry, I couldn't think of any other way to get a box up there but the pancake box. There is a GFCI outlet in the powder room and the wires are all on the same breaker - does that give me GFI protection at that fixture?

And, since I have several more fixtures to change out and don't figure the wiring is any better in the rest of them, how would I know for sure that the romex bare copper connects back to the service panel? Is there an easy, beginner's way of checking that? And doesn't wiring to the bracket ground it thru the house (I think)?

Thanks again for all your help! I am sincerely trying not to burn the house down...

OkieDavid · #10 02/11/12, 07:34 PM

The good news is that the Gfci can be tested by turning the light circuit on and tripping the test button. If the light goes out, that gfci circuit protects the light as well. The bad news is that unless the breaker itself is a GFCI breaker, the light fixture is probably not protected. Most often, a GFCI recepticle only protects that outlet. Occasionally I see them wired in series where current is fed through a gfci recepticle and on to several other recepticles thus protecting them all.

As to the question about grounds, I am not sure but I would start by verifying that the number of bare ground wires in the panel box should equal the number of circuits.

#11 02/11/12, 08:02 PM

To check which outlets and fixtures are protected by the GFI outlet, push the test button on the GFI outlet. The outlet will not work nor will any protected outlets and fixtures. Push the button again to turn them back on.

If the wire comming out of the wall at the fixture is a romex with ground and all the wires coming into the breaker box are romex with ground and all the grounds are hooked up to the ground bar inside the breaker box, the chances are good that the ground wire at the fixture is grounded. If you want to invest in a multimeter you can check for impedence (ohms) between the ground wire at the fixture and a radiator or plumbing pipe (assuming that your plumbing pipes are metal). Zero impedence means the wire is grounded. Large impedence means no ground.

If you are confident enough, you can set the multimeter for AC volts, make sure none of the wires at the fixture are touching anything else, turn on the circuit breaker, and test for current flow from the hot (usually black) wire to the ground. A low voltage reading means no ground. A reading of 110 to 130 volts means good ground. Be sure to turn the circuit breaker off before you do more work on the circuit.

Make sure that the romex can't touch the the metal of the pancake box. I once got shocked while removing a switch plate cover. Turns out the pancake box for the fixture was connected to the box for the switch with flexible metal conduit but this wasn't grounded. The romex coming into the pancake box rubbed on the sharp edge of the box until the hot wire was touching. This electrified the box, the metal conduit, and the switch box.

francismilker · #12 02/11/12, 10:10 PM

Back to the OP. You asked about the need to have the romex grounded to the junction box. The green ground screw was only intended to be a "safety" or "equipment" ground to keep you, the user, safe in the event of a fault or ground. It's very important to have all metal surfaces involved in an electrical system tied to ground to help get static or fault to ground asap so a breaker will trip.

There's no need to install a ground screw in a plastic box. (As you already know I'm sure.) Simply connecting the two wires together is adequate.

Oldcountryboy · #13 02/11/12, 10:44 PM

Quote:

Originally Posted by Nimrod

If you are confident enough, you can set the multimeter for AC volts, make sure none of the wires at the fixture are touching anything else, turn on the circuit breaker, and test for current flow from the hot (usually black) wire to the ground. A low voltage reading means no ground. A reading of 110 to 130 volts means good ground. Be sure to turn the circuit breaker off before you do more work on the circuit..

Ditto!

Harry Chickpea · #14 02/11/12, 11:07 PM

"Harry, I couldn't think of any other way to get a box up there but the pancake box. There is a GFCI outlet in the powder room and the wires are all on the same breaker - does that give me GFI protection at that fixture?"

You have already had good responses, but in direct answer, stuff wired in DOWNSTREAM of the GFCI outlet can be protected. If the light is upstream (closer to the breaker box), sport for a new breaker to be safe. Take Nimrod's experience to heart as well.

You are very smart to be asking the questions and doing it right. Much of home wiring can be done easily and safely if proper care is taken and you understand what you are doing. Sometimes you do have to do stuff you would rather not, like the exposed pancake box in a damp area, but you make accommodations.