Do we have to bond the insulated grounding wire of MC cable to a metal box? Isn't the metal jacket enough? If so, what do you do in the case of an Isolated grounding receptacle? Mike
The jacket of standard sriral wound MC cable is not sufficient to provide grounding without supplemental grounding conductors.
As far as your installation, there is an assortment of special MC cables available. This includes those that have additional grounding conductors.
If you have a handbook, the commentary following 330.108 explains this situation.
[This message has been edited by Redsy (edited 09-17-2002).]
The NEC does not allow the device (receptacle) to bond the box. Since the MC sheath is not rated for grounding, you must ground the green wire to the box. Here we use a green wire pigtail that comes with a #10 screw available a most any supply house. This screws to the tapped ground screw hole in the box. We use a special green wirenut with a hole in it that allows the green wire to be stripped out bare long enough to reach the receptacle after it leaves the wirenut.
As for as using MC for IG installations, you can order MC cable with both a solid green conductor and a green/yellow stripe conductor. It's not really cost effective to use that cable. You might as well use conduit. MC comes in about any configuration you want. I believe you can get it in large feeder sizes as well. I am bidding a job that calls for weatherproof (pvc jacketed) #8 MC to run on the bottom of sewage treatment ponds to aereator motors!