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Basic question - if I have a long run of flexible mc, 12/2 with a green equipment ground wire inside, am I limited in my overall length of this run as long as I meet the support requirements? I see conflicting statements online about 6’ limits unless I provide another dedicated equipment ground line.

I have a garage with finished walls, and want to add a circuit to provide a few additional outlets for the garage and for the outside walls of the garage on the exterior.

The service panel is in the 2 car garage on one far exterior wall, and I need to make a run from the panel to the closest one side of garage door 1 for an outlet, up and over the door and down to put an outlet between the doors, up and over the second door to put an outlet on the side of door #2, and then transition through the wall to put an outlet on the exterior outside.

The runs up and over the doors will be about 30’.

If I tie the box/outlets together with the green wire inside the fmc, will this suffice to provide proper grounding?

  • Are you talking about a metal-clad cable that came with wires in it from the factory, or a flexible metal conduit that you installed then pulled separate wires through? – ThreePhaseEel Sep 14 '19 at 18:00
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    Metal clad cable, has three wires inside, black, white, green. Bought a 250’ roll of it. – Adam Toth Sep 16 '19 at 4:37
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I am confused as to whether you are using FMC or MC cable.

Flexible Metal Conduit

This is empty conduit (a pipe) in which you add your own wires. The metal shell of FMC can be used as a grounding path provided it is less than 6 feet and terminated into metal boxes with cable clamps listed for FMC. But I don't consider it a best practice.

You add as many THWN-2 (aka THHN) individual wires as you please. For circuits >20A, you can run currents out of the 75C column of 310.15B16, so in this case #8 is ok for 50A.

Some people have only ever seen Romex style cable in their whole lives, and have never conceived of the idea of individual wires. Those people believe when you use conduit, you must then chicken-choke the very stiff Romex down the conduit. However, since Romex comes with a bare ground wire, I doubt you'd be asking about grounds in that case.

I recommend you run a ground wire in FMC regardless. If you don't want to buy yet another color, then simply strip the insulation off; bare is an acceptable ground color.

MC Cable

MC cable has all its wires pre-packed inside the MC cable. The shell may not be used as ground, period. Proof of this is that they provide a green or bare wire for the specific purpose of being a ground...

...which begs the question "Why would you need shell as ground?" If the answer is "Because I plan to use green as a conductor", nope. You cannot re-task or re-mark a green wire to be anything but a ground. For that, run 12/3 MC; or run FMC conduit and any wires you please.

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MC or metal clad comes with a grounding wire there is no length limit on this cable, it requires support or anchoring per NEC 330.30.B Within a foot of the box then every 6’ horizontally or 10’ vertically.

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You can exceed the 6' limit on FMC if you run a ground it it. You mentioned that you're running 12/2 and a separate ground. That leads me to believe you're running 12/2 romex and adding a ground. When running cable, all the conductors, including the ground, have to be in the cable so 12/2 with ground... but why run romex in FMC?. If you're running 2#12 and a #12 ground, then you're ok. Fishing through FMC can be difficult depending on the fish you're using so you might want to lay out the FMC and run the wires before securing it to the walls and boxes.

Securing the boxes and outlets to the ground will make everyone happy. Don't forget that the outlets in the garage and outside have to be GFCI protected so you might want to install a GFCI breaker in the panel instead of the first outlet and feeding the rest from it. Good luck

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