CM and CMG - What is the difference?

[cfarrally]

The only difference I can discern is that the G in CMG stands for general purpose. However, as the code is concerned (NEC 2008), they are both only for use as general purpose cables in commercial or residential applications. What is the difference? Thanks in advance.

 

[augie47]

I'm sorry, but I'm completely lost as to what you are referencing.

 

[cfarrally]

I apologize, I should have posted the location. I am referring to communications cable types CM and CMG, as defined in Section 800.179 (C) and (D).

 

[nhfire77]

I'm sorry, but I'm completely lost as to what you are referencing.

There is no difference between the two. I cannot back that up with a code reference but I see CM or CMG on the same cable from time to time.

Augie

CMR is a riser cable CMP is a plenum cable CMG or just CM is a non plenum, non riser cable just like FPL, not FPLR (riser) or FPLP (plenum)

 

[cfarrally]

Thanks for that answer. The question stems from an academic and redundancy standpoint...why is there one recognized type of cable for Riser (CMR), Plenum(CMP), and Residential(CMX), but two for general purpose? Wouldn't it behoove the industry to eliminate one of the two if their purpose is the same? The point of the NEC is to simplify, yes? I was curious if there was a reason behind it or if it's just something that takes up an extra 6 lines of space, and nobody's thought to change it. Thank you again.

 

[hbiss]

You can add MP to that also. In my opinion all the LV articles need to be rewritten. Notice that a CMX cable larger than .25" can't be used in residences? There is no reason all communications cable shouldn't be either CMR or CMP with a CL2 or CL3 dual listing if applicable. Oh yeah, while they are at it make the coax manufacturers put CMR or CATVR on all their cable. Right now you have to order it as a different part number if for some reason you want that put on the jacket for the inspector to see.

-Hal