Three-Way Wiring

[Mike01]

Is it code compliant to run two runs of 12/2 and combine it at the switchbox for use on a three-way switch I thought for some reason this was a code violation to run two branches for a single three-way and that all the conductors had to be in the same conduit or piece of mc.

 

[winnie]

The general requirement is that all conductors of the same circuit have to be in the same raceway or cable assembly. However there are exceptions to this general rule.

Relevant to your question is the exception for 'non-metallic' wiring methods. You _cannot_ use two runs of 12-2 MC as a substitute for a single run of 12-3 or 12-4 MC for three way wiring. However you _can_ use two runs of 12-2 NM in place of 12-3 or 12-4 NM. If you have metal junction boxes, then both runs have to enter through the same hole.

Additionally, if the two runs are separated in space, you will generate 'EMF's and you will increase the inductive impedance of the circuit. Code doesn't address these two issues, however I would recommend that if you use two runs of 12-2 in place of one run of 12-3, that the two cables be run side by side.

-Jon

 

[Mike01]

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Relevant to your question is the exception for 'non-metallic' wiring methods. You _cannot_ use two runs of 12-2 MC as a substitute for a single run of 12-3 or 12-4 MC for three way wiring. However you _can_ use two runs of 12-2 NM in place of 12-3 or 12-4 NM. If you have metal junction boxes, then both runs have to enter through the same hole. -Jon

I don not get this so it would be acceptable if NM was used but not MC?

 

[SEO]

Nm could be acceptable, not mc. Take a look at section 300.3 (B)(1) through (B)(4).

 

[benaround]

Alum. mc cable could be used.

 

[don_resqcapt19]

Alum. mc cable could be used.

While electrically that statement it correct, it would not be code compliant. The section in question uses the term "nonmetallic" and not the term "nonferrous".

 

[benaround]

While electrically that statement it correct, it would not be code compliant. The section in question uses the term "nonmetallic" and not the term "nonferrous".

thank you Don, I will remember that.

 

[al hildenbrand]

While electrically that statement it correct, it would not be code compliant. The section in question uses the term "nonmetallic" and not the term "nonferrous".

"The section" means 300.3(B)(3), right. Here's the section:

2008 NEC
300.3 Conductors.
(B) Conductors of the Same Circuit.
(3) Nonferrous Wiring Methods. Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with the provisions of 300.20(B). Conductors in single-conductor Type MI cable with a nonmagnetic sheath shall comply with the provisions of 332.31. Conductors of single-conductor Type MC cable with a nonmagnetic sheath shall comply with the provisions of 330.31, 330.116, and 300.20(B).

 

[benaround]

"The section" means 300.3(B)(3), right. Here's the section:

thank you Al, I will remember this also !

 

[don_resqcapt19]

thank you Al, I will remember this also !

Sorry, I need to learn to read the sections before I post.

 

[hillbilly]

Additionally, if the two runs are separated in space, you will generate 'EMF's and you will increase the inductive impedance of the circuit. Code doesn't address these two issues, however I would recommend that if you use two runs of 12-2 in place of one run of 12-3, that the two cables be run side by side.

I generally use this set-up (2, #12/2's) for HLV's in residential bathrooms.
I measure the length, cut the cables, tape them together at a few intervals, and run it as a single cable.
I only use the neutral and ground from one of the cables, and cut the other off flush.

I know.....I'm wasting time, but that's how I do it.:roll:

steve

 

[480sparky]

I generally use this set-up (2, #12/2's) for HLV's in residential bathrooms.
I measure the length, cut the cables, tape them together at a few intervals, and run it as a single cable.
I only use the neutral and ground from one of the cables, and cut the other off flush.

I know.....I'm wasting time, but that's how I do it.:roll:

steve

Try getting a roll of 12/4.

 

[hillbilly]

Try getting a roll of 12/4.

Around here, you can buy two rolls of 12/2 cheaper than one roll of 12/4.

I know, I know, the labor.....:roll:

steve

 

[LarryFine]

I generally use this set-up (2, #12/2's) for HLV's in residential bathrooms.
I measure the length, cut the cables, tape them together at a few intervals, and run it as a single cable.
I only use the neutral and ground from one of the cables, and cut the other off flush.

So, that gives you one white, one bare, and two blacks. Why not use a 12/3? That gives you two hots. Now, if you need three hots, then use a 12/2 and a 12/3.

If I use two cables, I connect both EGC's, but I'm not shy: I'll recolor one of the whites if I need that many colors. I use blue so I have fewer duplicate colors.

 

[hillbilly]

So, that gives you one white, one bare, and two blacks. Why not use a 12/3? That gives you two hots. Now, if you need three hots, then use a 12/2 and a 12/3.

If I use two cables, I connect both EGC's, but I'm not shy: I'll recolor one of the whites if I need that many colors. I use blue so I have fewer duplicate colors.

I mis-spoke in my post.
I use one of the whites for a hot conductor...re-identified of course.

steve