Article 404.2(A) Three Way and Four Way Switches

[AMD57]

Question: Would a switch loop be considered a set of travelers with a switch leg to a three-way or 2 sets of travelers going to and from a four-way switch where a return wire must accompany a hot in absence of a neutral?

Code Article: Three-way and four-way switches shall be wired so that all switching is done only in the ungrounded circuit conductor. Where in metal raceways or metal-armored cables, wiring between switches and outlets shall be in accordance with 300.20(A). Exception: Switch loops shall not require a grounded conductor.

 

[George Stolz]

Question: Would a switch loop be considered a set of travelers with a switch leg to a three-way or 2 sets of travelers going to and from a four-way switch where a return wire must accompany a hot in absence of a neutral?

Yes, hence the exception to that section.

 

[Receptive]

Hence, this would prohibit the use of 2-wire travelers in NM right?

 

[Receptive]

Just looked at the 05 handbook and it says that "The NEC does not specifically prohibit the use of two 2-conductor nonmetallic-sheathed cables instead of a single 3-conductor cable for wiring three-way and 4-way switches."

Since there isn't a specific prohibition does that mean the Code actually condones it? To me, it seems like the code has a flavor that would prohibit the use of 2-conductor NM. I know this has been beat like a dead whatever. Sorry to hijack you thread.

 

[Dennis Alwon]

I wish the NEC would outlaw this much too common practice. Here is the article that gives it an okay for nm. This is code compliant but it will cause high unwanted electromagnetic fields.

300.3 Conductors.
(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

(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).

 

[Receptive]

I see... The FPN under 300.20(B) adds that the code recognizes that metals that might not heat up will have currents induced upon them in this situation (appearantly not enough to present a hazard). Yet I also notice that it does not specifically address the problems with EMF's. Seems like it would just put the issue to rest if they would just require a three conductor as the travelers for a 3-way wiring system.

 

[LarryFine]

Hence, this would prohibit the use of 2-wire travelers in NM right?

That's incorrect, and it's still easy enough to run more than one cable together, which eliminates the EMF concern.

I've often run two 2-conductor cables together as a 4-conductor cable hot/neutral/travelers and for 4-way switches.

 

[Mikboo]

That's incorrect, and it's still easy enough to run more than one cable together, which eliminates the EMF concern.

I've often run two 2-conductor cables together as a 4-conductor cable hot/neutral/travelers and for 4-way switches.

So you're saying running two 2 wires is legal? Our inspectors say it is not due to heat.

I am new here and thank you for a reply.

Mike

 

[Dennis Alwon]

So you're saying running two 2 wires is legal? Our inspectors say it is not due to heat.

I am new here and thank you for a reply.

Mike

Hey Mike welcome to the forum. You have pulled up a thread that is a few months old and Larry is probably sleeping now so I'll try and answer it.

Yes with NM cable, not ferrous (metallic) wiring methods, you may run 2 wires. This creates unwanted electromagnetic fields (EMF) that is why Larry stated he would run a hot and neutral conductor in another cable but right next to the traveller pair. This will eliminate the EMF.

They make 14/2/2 nm which has two pairs of conductors in the cable. It is always better to keep the hot conductor running with the neutral to cancel any potential EMF's.

 

[Dennis Alwon]

BTW, read art. 300.3 esp. (B)(3)

 

[Mikboo]

Thanks Dennis!

 

[LarryFine]

You have pulled up a thread that is a few months old and Larry is probably sleeping now so I'll try and answer it.

*yawn* Oh, is it morning already? :grin:

It is always better to keep the hot conductor running with the neutral to cancel any potential EMF's.

Not the neutral, necessarily, but along with whichever conductor carries the current back the other way in the given cable run.


Here's the basics of what I'm talking about: In a house with several rooms on the main floor, say the kicthen, dining room, hallway, etc., where each room has 3-ways, I'll run a hot and neutral from switch box to switch box, hitting both boxes in each room.

In addition, I'll run a second 2-conductor between the pair of switch boxes for each room, parallel with the feeds. Now, I can run the switch leg from whichever box I like, and pick up the hot in the companion box. No 3-wire cable needed, and no EMF concerns.

I don't always do it like this; I do often use 3-wire, but it's about 2x 2-wire per foot. This works well when you have several rooms that are more-or-less arranged end-to-end, and especially if you have 2-gang boxes with two 3-ways where the switched zones meet.