6/3 NM cable

[tortuga]

Conductors having the properties of TW are permitted, but not for NM-B

My understanding is UL 719 section 8.1(b) indeed covers 'TW construction' in NM-B with the -B marking it has options 1 and 2.

 

[mark32]

Can residential feeders that are 6/3 NM be protected by 60 Amp O.C. Protection?

55A not a standard size breaker.

Thanks

This comes up often at the HD I work at PT. I am always cutting 6/3 Romex for sub panels. Some guys grab 50 amp breakers and some grab 60 amp breakers. I have a local inspector stop by and talk shop from time to time, and I asked his opinion on this. He said he's cool if someone puts a 60 on 6/3 nm in such an application.

 

[infinity]

I asked his opinion on this. He said he's cool if someone puts a 60 on 6/3 nm in such an application.

As he should be since it's code compliant when the installation qualifies for the next size up rule in 240.4(B).

 

[nizak]

This comes up often at the HD I work at PT. I am always cutting 6/3 Romex for sub panels. Some guys grab 50 amp breakers and some grab 60 amp breakers. I have a local inspector stop by and talk shop from time to time, and I asked his opinion on this. He said he's cool if someone puts a 60 on 6/3 nm in such an application.

I think wire size is often overlooked.

I know in my area for years #2 Al and #4 Cu were always acceptable for use with 100 amp breakers on panels other than main panels providing power to the entire dwelling.

 

[tortuga]

This comes up often at the HD I work at PT. I am always cutting 6/3 Romex for sub panels. Some guys grab 50 amp breakers and some grab 60 amp breakers. I have a local inspector stop by and talk shop from time to time, and I asked his opinion on this. He said he's cool if someone puts a 60 on 6/3 nm in such an application.

Or just make #6 SE widely available and ditch the #6 NM.

Yeah I am starting to think this is the way, it would be cool if HD ordered and stocked spools of 6/3 SE-R copper and 6/2 SE copper instead of 6/2 and 6/-3 NM in its stores, as most of it is going to EVSE's anyway.

 

[suemarkp]

WA state is in process of allowing NM-B to be used at its 75C rating instead of 60C in its state exceptions to the NEC. This will only apply to the larger sizes though, #10 and smaller still get the shaft. The language has been written and proposed, but I don't believe it is approved yet.

 

[don_resqcapt19]

WA state is in process of allowing NM-B to be used at its 75C rating instead of 60C in its state exceptions to the NEC. This will only apply to the larger sizes though, #10 and smaller still get the shaft. The language has been written and proposed, but I don't believe it is approved yet.

But the small conductor rule applies to most circuits so, no matter what the permitted ampacity of the conductor is, you can only protect it at the 60°C ampacity.
However using the 75°C ampacity will provide some relief for loads such as AC equipment and motors, where the small conductor rule does not apply.

 

[infinity]

However using the 75°C ampacity will provide some relief for loads such as AC equipment and motors, where the small conductor rule does not apply.

Which is an excellent reason to just make it a 75° C wiring method like most of the other wiring methods. There is value in simplicity.

 

[tortuga]

While were amending things I would also look at Article 336 in the 2023 NEC. The new Joist Pull Tray cable is nice stuff I'd amend section 336.10(9) and allow the new 'Joist Pull' tray cable type TC-ER-JP tray cable to be used as power cable in any locations permitted in 334.10 for NM, why restrict it to one and two family dwellings?
There is also a good case to allow the JP tray cable to use the 75C ampacity, as the UL standard requires the conductors in tray cable to be actual marked THHN. If its ok for a generator it should be ok for any 75C termination then.

 

[don_resqcapt19]

While were amending things I would also look at Article 336 in the 2023 NEC. The new Joist Pull Tray cable is nice stuff I'd amend section 336.10(9) and allow the new 'Joist Pull' tray cable type TC-ER-JP tray cable to be used as power cable in any locations permitted in 334.10 for NM, why restrict it to one and two family dwellings?
There is also a good case to allow the JP tray cable to use the 75C ampacity, as the UL standard requires the conductors in tray cable to be actual marked THHN. If its ok for a generator it should be ok for any 75C termination then.

Need to also eliminate the part that requires the cable to have control conductors as well as power conductors. This was originally put in by Generac to be used between the ATS and the generator requiring both power and control conductors.

 

[tortuga]

Need to also eliminate the part that requires the cable to have control conductors as well as power conductors. This was originally put in by Generac to be used between the ATS and the generator requiring both power and control conductors.

Yeah agreed thats what I meant about the allow it to be used as 'power' cable part. The cable is no safer if it controls something.

 

[Eddie702]

Don't know about #6 but as everyone knows they make THHN in solid and stranded in the smaller sizes. The thicker strands were like THW which is 75C.

I agree with the above posts that NM-B should be THHN if not allowed in a wet location and get rid of the stupid 60C limitation.

But here is another question. NM-B is used in residential all the time yet with the 60C limitation how can it be used to connect to light fixtures rated for 75C?

Are the conductors actually rated 90C or 75C but since the conductors are not marked it can only be used at a load that will not allow the temp to be over 60C?

So is the cable only rated at 60C or is it rated higher than 60C and only prohibited to use it at a temp with conditions of installation that would allow it to operate over 60C?

 

[don_resqcapt19]

But here is another question. NM-B is used in residential all the time yet with the 60C limitation how can it be used to connect to light fixtures rated for 75C?

The whole reason they went to NM-B was because of that very issue. Both the code and the product standard require that the conductors in NM-B be rated for 90°C.
As far as the 60°C ampacity limitation, I have no idea why it still exists.

 

[Eddie702]

From Southwire:

APPLICATIONS AND FEATURES: Southwire Romex® Brand SIMpull® (nonmetallic-sheathed) Cable may be used for both exposed and concealed work in dry locations with ampacity limited to that for 60°C conductors as specified in the National Electrical Code® (NEC). Individual conductor insulation is rated 90°C as required by the NEC and by the UL product standard (UL 719) for terminations in lighting fixtures. NM-B cable is primarily used in residential wiring as branch circuits for outlets, switches, and other loads. NM-B cable may be run in air voids of masonry block or tile walls where such walls are not wet or damp locations. Voltage rating for NM-B cable is 600 volts. Individual conductors within Type NM-B Cable are not listed or marked as THHN conductors (or any other NEC recognized conductor type) and are not permitted to be installed apart from the complete Type NM-B Cable. Conductors routed inside panelboards and boxes (without the cable jacket) for termination therein are considered part of the complete Type NM-B Cable


So they admit the conductors are 90C although not marked but can't be used at 90 or 75C but it is allowed on 75C fixtures.



Maybe we should buy Canadian Romex. It is allowed to be used at 90C although their max voltage rating is 300v ours is 600v.

We would all give up the voltage rating to be able to run at 75 or 90C


The whole thing is pretty stupid.

 

[don_resqcapt19]

So they admit the conductors are 90C although not marked but can't be used at 90 or 75C but it is allowed on 75C fixtures.

334.112 has required NM cable to be constructed using conductors rate 90°C for at least 20 years.

Maybe we should buy Canadian Romex. It is allowed to be used at 90C although their max voltage rating is 300v ours is 600v.

That would not change the rule in 334.80 that limits conductors in MN to the 60°C ampacity.

 

[Eddie702]

334.112 has required NM cable to be constructed using conductors rate 90°C for at least 20 years.

That would not change the rule in 334.80 that limits conductors in MN to the 60°C ampacity.

Agree. Just pointing out that Canada allows the Canadian NM to be used at 90C per the Southwire website. Southwire also says the US NM is limited to 60C. ours is 600volt. Canada is 300volt.

Southwire Canadian

NM:APPLICATIONS AND FEATURES: Southwire's Romex® SIMpull® NMD90 cables may be used for both exposed work in dry locations or concealed work in dry or damp locations. The maximum allowable conductor temperature is 90°C. The minimum recommended installation temperature is -25°C for two-conductor cables and -10°C for three-conductor cables (with suitable handling procedures). Material should be properly stored above 0°C for 24 hours prior to installation. The maximum voltage rating for all intended applications is 300 volts. Consult the Canadian Electrical Code for further information related to applications


Ampacity of the Canadian wire: Example:

#14 is rated 20 amps @75C
#14 is rated 25 amps @90C

 

[tortuga]

Thats interesting about Canadian NM-D I did not know that.

 

[don_resqcapt19]

Thats interesting about Canadian NM-D I did not know that.

It is not common where CSA has its own standard like they do for NM. Most of the UL standards are for both US and Canada, and some also include Mexico.

 

[kwired]

To me #6 and #8 NM more closely resemble TW, it has those thicker strands that TW has.
It has no resemblance to THWN-2 to me other than the nylon jacket.

It is 7 strand instead of 19 strand There is 7 strand THHN/THWN out there but is not very common.

I kind of like it better for 14-10 AWG, but most of what I have found is in specific cable applications. Center pivot irrigation machine cable (which are only listed for that use) generally has 7 strand conductors and is pretty typical to have 10 AWG power conductors and 14 AWG control cables in it all of which are 7 strand.

 

[kwired]

They do make a #6 SEU cable with 2 hots and a wrapping stranded grounding conductor. This is rated as a 75 C. conductor and if all of your connected terminations are listed for 75C your ampacity is higher.

When ranges were allowed to have the frame bonded to the grounded conductor that is about the only thing we ever used. And of course 70 plus years ago when 60 amp service entrance was more common, NEC at some point said dwellings need minimum of 100 amp service to a dwelling even if load calculation wasn't all that close. I'd guess demand for that product is nearly non existent these days so nobody stocks it.