NM-B vs NM-D

[kbsparky]

Over the past holidays, I found myself in Canada in the electrical aisle in one of the home-horror stores.

I was intrigued that the "romex" wire looked a bit different, and was called type NMD. On the surface, it appeared to be the same thing as our NM-B, except that it did not have any of the paper fillers we are used to dealing with.

I bought some of the 12-2, to bring home for close comparison.

After I stripped the end, it became apparent there was another major difference: The bare ground conductor is undersized -- a #14!!

I remember in the old days (pre-1971 NEC) that we utilized an undersized EGC -- I think that #12 used a #16 way back then.

On a side note, it was a bit more expensive, too.

 

[jwjrw]

Over the past holidays, I found myself in Canada in the electrical aisle in one of the home-horror stores.

I was intrigued that the "romex" wire looked a bit different, and was called type NMD. On the surface, it appeared to be the same thing as our NM-B, except that it did not have any of the paper fillers we are used to dealing with.

I bought some of the 12-2, to bring home for close comparison.

After I stripped the end, it became apparent there was another major difference: The bare ground conductor is undersized -- a #14!!

I remember in the old days (pre-1971 NEC) that we utilized an undersized EGC -- I think that #12 used a #16 way back then.

On a side note, it was a bit more expensive, too.

I heard a guy on here call it non metallic DRY on here the other day. I wouldnt think it would be legal in the nec.

 

[George Stolz]

That's weird - I always thought the CEC was a touch more restrictive than the NEC.

 

[LarryFine]

Maybe they thought their first NM's EGC was better than ours, because it was only one gauge lower than ours, and decided it was still big enough when we raised ours.



Maybe not.

 

[kbsparky]

I think they call it "loomex" up there? Any Canadian members care to comment?

 

[cpal]

Not sure what the D indicates in Canada but in the NEC there is this reference.

310.11 (C) Suffixes to Designate Number of Conductors. A type letter or letters used alone shall indicate a single insulated conductor. The letter suffixes shall be indicated as follows:
(1) D ? For two insulated conductors laid parallel within an outer nonmetallic covering

 

[tortuga]

Canada goes to a #8 ECG at 60 amps where as the NEC will allow a #10 to be the ECG on a 90A breaker.
There is nothing that prevents you from using NM-D that I can see. It is listed and made in the USA at the same southwire factory as NM-B
You can buy red 10-2 NM-D that has a red and a black and use it on a 20A 240V heater circuit for voltage drop.
Or you can use 12-2 on a 120V 15A circuit for voltage drop.
I wonder if T250.122 has poor engineering at 15 - 30A loads?
I posted on this some time ago. It seems like a reasonable run of 12-2 is no more than 150 feet before your voltage drop goes above 5% total. At that a 75 foot run of #14 is in my opinion sufficient size to trip a standard inverse time breaker. I see no reason for the ECG being #12 AWG on a 20A.
and it makes no sense to have a #10 wire try to trip a 90A breaker.

You can also buy Federal Pacific Arc Fault breakers from Home Depot Canada made by the same people whom make Square D.
Cheers

 

[kbsparky]

....
You can buy red 10-2 NM-D that has a red and a black and use it on a 20A 240V heater circuit for voltage drop.
Or you can use 12-2 on a 120V 15A circuit for voltage drop....

How do you reconcile the requirements in 250.122(B) ?

You are required to upsize the EGC when upsizing circuit conductors ...

I believe my roll of 12-2 NM-D is useless for installations in the US.

 

[tortuga]

Ahh yes 250.122 (B)!

This has inspired me to get out the engineering text books and run the numbers.
I am really unsure what formula T250.122 is based upon.