Bundling Romex and Derating

[Jimmy7]

You’re supposed to derate romex if you bundle it more than 24”, correct? Does this apply if you’re stapling two romex cables on the flat down to a receptacle box? Isn’t two romex cables carrying 120 volts each actually four current carrying conductors? Or does this not apply to cables stapled down a stud?

 

[infinity]

Yes IMO two cables stapled together on top of each other would be bundled and would require derating. Two 2-wire cables would be 4 CCC's so derating would apply but for #14 or #12 conductors the standard 15 and 20 amp ampacity wouldn't be affected until you reached 9 CCC's.

 

[Jimmy7]

Yes IMO two cables stapled together on top of each other would be bundled and would require derating. Two 2-wire cables would be 4 CCC's so derating would apply but for #14 or #12 conductors the standard 15 and 20 amp ampacity wouldn't be affected until you reached 9 CCC's.

Two questions on this.
1. Would you continue, or do you still staple two 14-2’s, or two 12-2’s for receptacles?
2. How come 9 CCC’s? I’m just curious

 

[infinity]

1) Yes
2) NM cable has 90° C conductors so you can use the 90° C ampacity as the basis for your derating. Even with 9 CCC's #12 would be still good on a 20 amp OCPD. 30*70%=21 amps.

 

[acrwc10]

1) Yes
2) NM cable has 90° C conductors so you can use the 90° C ampacity as the basis for your derating. Even with 9 CCC's #12 would be still good on a 20 amp OCPD. 30*70%=21 amps.

in most cases, when you run through all the possible combinations you will always be able to put 4 NM cables together ( if they are #10 or smaller) and not exceed the rating.

 

[LarryFine]

Then there are these:

 

[AC\DC]

There only making bundling when at the staple there air gaps after staple if we’re getting this picky then we need to find some really safety issue to improve

 

[tom baker]

Why 9 CCCs? More creates heat. In a raceway, the heat is trapped.
But why 9 and not 10? Likely where the CMP drew the line.

 

[retirede]

Why 9 CCCs? More creates heat. In a raceway, the heat is trapped.
But why 9 and not 10? Likely where the CMP drew the line.

Comes out even for 3 full boats, 3 phase?

 

[nizak]

in most cases, when you run through all the possible combinations you will always be able to put 4 NM cables together ( if they are #10 or smaller) and not exceed the rating.

With the exception of them being 3 wire NM cables.

 

[infinity]

With the exception of them being 3 wire NM cables.

Can you give an example? I'm thinking of four 3-wire cables with MWBC's would still be only 8 CCC's. 3-wire cable with two switch legs?

 

[wwhitney]

Can you give an example? I'm thinking of four 3-wire cables with MWBC's would still be only 8 CCC's. 3-wire cable with two switch legs?

Maybe an apartment served by 2 of 3 phases from a 208Y/120V system? Then the MWBCs would be 3 CCCs each.

Cheers, Wayne

 

[AC\DC]

They should have allowance based on load. Those circuits are never max capacity so no max heat. The fact a home and commercial building has same de ration is nuts
My kit circuit vs my commerical kit no comparison

 

[garbo]

They should have allowance based on load. Those circuits are never max capacity so no max heat. The fact a home and commercial building has same de ration is nuts
My kit circuit vs my commerical kit no comparison

True to a point. You never know what changes will be made in the future greatly adding a load to a few circuits. I have a modest size house with natural gas for everything and a newer efficient central Air conditioning sling with low e windows and extra insulation. Have 38 circuit breakers in the service panel and 6 in my garage subpanel on a 100 amp service. Never open my windows until end of October and run the central AC from April to October and doing by my electric bill heaviest month electric usage is less then 2 KW a hour. While working in some old homes they had the washer machine on same 15 amp fuse as the living & dining rooms. Years later they added a gas dryer and a coffee maker on same circuit overloading a circuit that was sufficient for over 40 years. Going to be interesting when homes are wired with 16 guage copper NM cable that's only approved for LED luminares and on a 10 amp circuit breaker. Johnnie homeowner surely will run a NM cable from some wall switch boxes to feed the receptacles that he installed. Johnnie will save money at big box stored purchasing 16 guage NM cable for a kitchen counter top receptacle that he is installing.

 

[nizak]

Can you give an example? I'm thinking of four 3-wire cables with MWBC's would still be only 8 CCC's. 3-wire cable with two switch legs

Can you give an example? I'm thinking of four 3-wire cables with MWBC's would still be only 8 CCC's. 3-wire cable with two switch legs?

3- 14/3 nm cables through a penetration would be the max allowed . 9- CCC

Am I incorrect in saying that?

 

[don_resqcapt19]

3- 14/3 nm cables through a penetration would be the max allowed . 9- CCC

Am I incorrect in saying that?

In most cases that would only be 6 current carrying conductors for the purposes of ampacity adjustment.

 

[nizak]

In most cases that would only be 6 current carrying conductors for the purposes of ampacity adjustment.

Say the scenario is 4- 14/3 nm cables through a single hole in a 2x4 top plate leading down to switch box.
These cables all supply 3 way switching. A common ( hot) and two travelers.

I would think this would need to be de rated at 50%

 

[infinity]

Say the scenario is 4- 14/3 nm cables through a single hole in a 2x4 top plate leading down to switch box.
These cables all supply 3 way switching. A common ( hot) and two travelers.

I would think this would need to be de rated at 50%

Since only one traveler is energized at a time that's only 8 CCC's which is 70 % ampacity derating. I'm assuming that you're thinking that the hole is filled. If the hole is unfilled then no derating applies.

 

[Little Bill]

Say the scenario is 4- 14/3 nm cables through a single hole in a 2x4 top plate leading down to switch box.
These cables all supply 3 way switching. A common ( hot) and two travelers.

I would think this would need to be de rated at 50%

No, the travelers both don't carry current at the same time.

 

[nizak]

Since only one traveler is energized at a time that's only 8 CCC's which is 70 % ampacity derating. I'm assuming that you're thinking that the hole is filled. If the hole is unfilled then no derating applies.

Since only one traveler is energized at a time that's only 8 CCC's which is 70 % ampacity derating. I'm assuming that you're thinking that the hole is filled. If the hole is unfilled then no derating applies.

Thank you.