Type MC

[1793]

Would like to here for anyone about using the outer sheathing of MC as a mechanical ground. I have a job that is requiring an Isolated Ground. The cable I have has a ground, green insulated conductor. Can the sheathing act as a "dirty ground"? The run is about 100 feet.

Thanks in advanced

Norb

 

[ryan_618]

Re: Type MC

250.118 Types of Equipment Grounding Conductors.
The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following: (10) Type MC cable where listed and identified for grounding in accordance with the following:
a. The combined metallic sheath and grounding conductor of interlocked metal tape?type MC cable
b. The metallic sheath or the combined metallic sheath and grounding conductors of the smooth or corrugated tube type MC cable.

 

[iwire]

Re: Type MC

Standard MC does not have a armor that you can use as a grounding conductor.

Here are a few options.

1) IG MC, this will come with two insulated grounding conductors, one with a yellow tracer.

2)Hospital grade AC cable, this has an insulated grounding conductor and an armor that is listed for grounding.

3) 3 wire MC remark the red to green, only acceptable in certain occupancies.

 

[rbalex]

Re: Type MC

You will need to look at the specific listing of the cable.

Usually, but not always, where the cable has an integral "green" wire, the cable's sheath is not considered to be an adequate "stand-alone" equipment grounding conductor.

 

[1793]

Re: Type MC

I saw 250.118(B) and that is wat got me thinking. The word OR was the key. According to this rule it appeas that you can, if I read it correctly.

Thanks

Norb

 

[iwire]

Re: Type MC

1793

250.118(11)Type MC cable where listed and identified for grounding in accordance with the following:

a.The combined metallic sheath and grounding conductor of interlocked metal tape?type MC cable

Section (a) covers standard run of the mill MC (interlocking metal tape type) and it requires the combination of the armor and the conductor to make up one total grounding means.

b.The metallic sheath or the combined metallic sheath and grounding conductors of the smooth or corrugated tube type MC cable

Section (b) allows the just the armor to be used as a grounding means.

Unless you specifically ordered it you do not have smooth or corrugated tube type MC cable which are the only types that (b) applies to.

Corrugated tube type MC cable is like a metal flexible straw. It is continuous and watertight.

[ February 21, 2005, 01:46 PM: Message edited by: iwire ]

 

[1793]

Re: Type MC

Iwire:

Thanks you for the explanation of the different types of construction. I will need to get a different cable than the one I have if this job come about.

Thanks again, I do appreciate the information.

Norb