# 330.2 Type MC what is the "smooth metallic" type MC?



## Abeyta87 (Mar 10, 2013)

Hello. 

I was recently troubleshooting in a 30+ year old commercial building and up in the ceiling I noticed the 2x2 troffers were wired with a cable assembly (factory installed 12/2 with insulated ground) that had to have been a tad bigger than 1/4 and smaller than 3/8 inch aluminum looking conduit. It was non-corrugated and non-interlocking type cable. It was just smooth, metallic (probably aluminum) and flexible handling it. I dont have a fancy phone or else I would have taken a picture..

I looked in the 2014 NEC 330.2 'Type MC' definition: "A factory assembly of one or more insulated circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape, or a smooth or corrugated metallic sheath."

My question is did I just encounter the 'smooth metallic' type MC they are talking about? Or am I way off.. nobody I work with seems to know what it is either.


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## Black Dog (Oct 16, 2011)

Abeyta87 said:


> Hello.
> 
> I was recently troubleshooting in a 30+ year old commercial building and up in the ceiling I noticed the 2x2 troffers were wired with a cable assembly (factory installed 12/2 with insulated ground) that had to have been a tad bigger than 1/4 and smaller than 3/8 inch aluminum looking conduit. It was non-corrugated and non-interlocking type cable. It was just smooth, metallic (probably aluminum) and flexible handling it. I dont have a fancy phone or else I would have taken a picture..
> 
> ...


Hello Abeyta87;

Sounds like you have type MI cable

332.2 Definition.
Mineral-Insulated, Metal-Sheathed Cable, Type MI. A factory assembly of one or more conductors insulated with a highly compressed refractory mineral insulation and enclosed in a liquidtight and gastight continuous copper or alloy steel sheath.


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## telsa (May 22, 2015)

Abeyta87 said:


> Hello.
> 
> I was recently troubleshooting in a 30+ year old commercial building and up in the ceiling I noticed the 2x2 troffers were wired with a cable assembly (factory installed 12/2 with insulated ground) that had to have been a tad bigger than 1/4 and smaller than 3/8 inch aluminum looking conduit. It was non-corrugated and non-interlocking type cable. It was just smooth, metallic (probably aluminum) and flexible handling it. I dont have a fancy phone or else I would have taken a picture..
> 
> ...



MC was originally made in three different 'wraps.' Raw economics has driven everyone over to the one design we now all know and love. 

[ Interlocking metal tape ]

The smooth and corrugated metallic sheath MC types faded in the market place. The winding machines that lay on the interlocking metal tape were so much quicker at producing MC that they stole the market. ( They can also shift from one wire group// size to another with virtually no set-up headaches. )



As you might imagine, there was a hope at one time that the other styles would have some niche applications -- say food processing. It did not transpire. ( Dang if Sealtite didn't steal that niche. Today's PVC coated MC is a prospective solution for such an application. )



Also: watch out for factory assemblies such as Re-Loc that are constructed to Listed specifications -- but which cannot be ordered by us for field wiring.

You might be looking at master-slave whips that were dimensioned according to engineered specifications. Hence, their weird non-standard diameters. These could well have been manufactured to the early MC 'smooth' standard.


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## Abeyta87 (Mar 10, 2013)

Thanks for the quick replies! Those give me something to report to the guys tomorrow as we were all curious.


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