MC cable for health care

[darkov]

Question: Does the aluminum egc on the outside of MC cable has to be connected to MCI-A fitting, or it could be cut back behind the fitting?
I know it has to be cut flush at the end of MC as per manufacturer, but many times I see it wrapped around cable and about inch or two back from the fitting ( not touching the fitting).

 

[tom baker]

You are referring to Smart MC cable…
The aluminum wire is not an EGC, it serves to short out the spirals of the armor. Cut it off at the end of the sheath
By the way red heads are not required for MC cable.

 

[winnie]

My understanding is slightly different.

The 'normal' way of installing this sort of cable is as described in post #2.

An alternative way of installing this sort of cable is to run the Al wire into the box and splice it with other EGCs. There probably isn't ever a good reason to do this; it is extra work, uses box space, and requires the use of Al rated splicing hardware. But it is an explicitly allowed alternative.

Spiraling the Al wire back around the cable so that it gets clamped by the fitting is _not_ an approved alternative installation. It might work just fine, it might even work better than cutting the wire flush. But is is not described in the installation instructions, and was probably not tested. And it might interfere with the function of the fitting.

See note 2 of https://www.afcweb.com/installation/mc-stat-cable-installation/

-Jon

 

[darkov]

Question was, does it has to be in touch with the MCI-A fitting, or it could be cut back further away from the fitting?

 

[LarryFine]

Question was, does it has to be in touch with the MCI-A fitting, or it could be cut back further away from the fitting?

It does not. It is not an EGC, it merely shorts each wrap of the spiral housing to make sure it doesn't behave like an inductor (which increases impedance and OCPD reaction time) when subject to fault currents.

 

[darkov]

Thank you

 

[darkov]

It is EGC according to NEC 250.118 (10) b
Thank you all.

 

[RWC/NC.]

That last paragraph in posting #3 (and thank you posting link)..Little history, I started in this craft many years ago in a town nicknamed "The City of Medicine".. And I can't begin explaining the amount of medical clinical establishments (and area Hospitals) having worked on though those many years. Back then, we were taught to spiral the AL couple times around the AC cable's outer sheath, cutting off excess, then installing (tighten) the cable connector. Guessing some of us were doing it incorrectly, those many years ago.. wow..

 

[LarryFine]

It is EGC according to NEC 250.118 (10) b

I was referring to the bonding wire itself. You're correct that the assembly qualifies as an EGC; the wire is why.

 

[winnie]

It does not. It is not an EGC, it merely shorts each wrap of the spiral housing to make sure it doesn't behave like an inductor

What you are describing is the function of the bonding strip in AC cable. This strip is much smaller than the required EGC, and functions in concert with the spiral sheath to form the EGC.

In this MC cable, the bare Al wire provides the same functionality, forming the EGC when combined with the sheath. But it is also on its own large enough to be an EGC.

Jon