Grounding when using Flexible Metal Conduit

[John Hines]

Ok, I've been following the Grounding with Armored Cable (BX) thread with interest. So I've got the following situation, and questioning on how it should be handled.

I'm remodeling the kitchen/bath wet wall, and I ran 3/4" emt over from the breaker box to a good sized box, to which I'm running 3 or maybe 4 flexible metal runs, like a spider.

What is the code for running the grounding conductor, do I have to pull a single ground wire all the way back to the panel box ground bar for each remote outlet?

Or can I run a single wire back to the junction box, spliced to a single (heavier?) ground wire running back to the panel box, similar to what I'd do if everything was on a single power wire?

Or can I just attach the ground wire to the metal junction boxes at either side of the flex run that I'm providing the grounding run for.

All metal is required by local code. TIA

[SQLit]

The NEC in the USA does not require a ground wire in metal conduit. It does in Flexible conduit. You need to run a conductor the same size as your circuit conductors, unless your circuits are over 40 amps. Then you are allowed to lower the size of the ground. As an example I have your junction box with 5 20 amp circuits feeding the loads. I fed the junction box with 10 #12 conductors. This would be a code violation, because after the second current conductor in a single phase panel you have to start de-rating the conductors because of heating. To serve the 20 amp loads you would need to run #10 wire or de-rate the circuit to 15 amps. I would run at least a #10 ground in the feeder conduit and then get a ground bar install it in the junction box and tie all of my other circuits to the ground bar. I always run a ground in everything I do. It does not cost that much more. I have seen both set screw and compression connectors and couplings pulled apart in ceilings. The circuits they were feeding had no ground. Just the way I do it. Your house up to you if you want to exceed the minimum standard which is the NEC.

[John Hines]

Double the circuit rating (ie someone reconfigures two circuits on a single mini twin breaker) is the worst over current situation I can think of, here in the US of A, anything more would make an impromptu 220 circuit.

Good idea.

That is why I'm running it by the crowd here. The combo of metal conduit and separate ground conductor is a bit unusual to me, in connecting it up.

[zxcvbob]

I did something similar recently, with NM cable rather than conduit. A 15A lighting circuit, with a #12 cable feeding into a rather deep 4 11/16" box and about 4 or five #14 cables spidering out all over the place -- some of them are switch loops and some go to light fixtures. I gathered all the ground wires together and clamped them with a big split bolt connector. It's one of the few things the inspector liked about my project.

You could something similar; bring all the ground wires in the junction box and join them with an appropriately large connector. (when you are figuring how many conductor you can legally pack in the J-box, you only have to count one of the ground wires)

Best regards, Bob

[me]

Run a green wire thru the flex, attach it to the junction box. That's all. Providing of course that the steel conduit goes all the way to the breaker panel. You COULD run a strand of the green wire back to the main panel (same gauge as youe other wires), but it's not required, at least not by the national code. Your local code could differ.

[volts500]

Installing the equipment grounding conductor (EGC) inside all metal conduits and pigtailing the EGC to a green ground screw in each box provides a low impedance ground-fault return path and is the preferred wiring method. Steel couplings and connectors, while more expensive than zinc die-cast fittings, are a much more dependable fitting for conducting fault current.

[John Hines]

Makes sense, I was getting the EGC mixed up with the ground rod to main box run, which can not be spliced. EGC is more like just another conductor to the outlets.

D'oh, (as the light bulb goes on), oh yeah they would be a lot better as well.

[Chris Lewis]

According to :

Generally, by CEC (Canadian) code, you ignore the fact that the conduit is metal, and wire it just as if it was NMD (ground wire from panel to junction connected to ground wires in all cables to outlets (and the boxes)).

Which means, in conduit, you have to add the green wire.