California 3-way...

[kwired]

Submit a proposal to change the wording of 310.4 to allow conductors to be installed in parallel if each conductor is rated according to the OCPD. Until the code definition is changed, then it is as Al and Dennis say: an extremely small misinstalled parallel conductor.

Bear in mind, 300.3(B) already puts some constraints on this principle.

The language already exists. It just doesn't allow it for supplying receptacles and luminaires.

Make the switching circuit control a relay or contactor that controls the lighting outlet and you are OK. Make it low voltage control and you can do a lot of things differently.

 

[jap]

Submit a proposal to change the wording of 310.4 to allow conductors to be installed in parallel if each conductor is rated according to the OCPD. Until the code definition is changed, then it is as Al and Dennis say: an extremely small misinstalled parallel conductor.

Bear in mind, 300.3(B) already puts some constraints on this principle.

So it's the wording and a small amount of magnetic field that makes this an unacceptable install.

Thanks for the information.
JAP.

 

[al hildenbrand]

So it's the wording and a small amount of magnetic field that makes this an unacceptable install.

Actually, if this is installed in non-ferrous wiring method, the NEC is silent about the magnetic field. Look at 300.3(B)(3) for this.

So, really, it's just the wording of 300.3(B)(1) and 310.4

The post it sketch showing a California Threeway wired only with 14/2 (or 12/2) creates a situation common in Knob & Tube installations. In certain parts of the circuit the actual current carrying conductors will be physically separated and, depending upon the installer's labor saving efforts, may easily allow a person to stand, sit or sleep in the middle, between them.

 

[jap]

interesting and enlightening.

Thanks,

 

[kwired]

Actually, if this is installed in non-ferrous wiring method, the NEC is silent about the magnetic field. Look at 300.3(B)(3) for this.

So, really, it's just the wording of 300.3(B)(1) and 310.4

The post it sketch showing a California Threeway wired only with 14/2 (or 12/2) creates a situation common in Knob & Tube installations. In certain parts of the circuit the actual current carrying conductors will be physically separated and, depending upon the installer's labor saving efforts, may easily allow a person to stand, sit or sleep in the middle, between them.

I do not agree with that.

300.3(B) does not limit the conductors of a circuit that are required to be run together to ferrous raceway installations.

300.3(B):

(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).

Even if you disregard effects of EMF's it is a good idea to run the conductors together because there will be lower impedance during short circuit events which will result in higher fault current and faster operation of overcurrent protection.

 

[al hildenbrand]

300.3(B) does not limit the conductors of a circuit that are required to be run together to ferrous raceway installations.

Yes, you are correct. However, that's not what I was posting about. In this post it sketch:

. . . is a California Threeway wired with NM, we have a non ferrous wiring method. 300.3(B)(3), therefore, allows the conductors to be run separate from each other.

My statement in my post above is saying that the only thing that makes the threeway switch setup illustrated non-Code is the conductors being smaller than 1/0, as stated in rule 310.4.

 

[kwired]

Yes, you are correct. However, that's not what I was posting about. In this post it sketch:

. . . is a California Threeway wired with NM, we have a non ferrous wiring method. 300.3(B)(3), therefore, allows the conductors to be run separate from each other.

My statement in my post above is saying that the only thing that makes the threeway switch setup illustrated non-Code is the conductors being smaller than 1/0, as stated in rule 310.4.

I still disagree that the installation is allowed outside of 310.4 unless all conductors are in the same raceway or cable.

300.3(B)(3) gives us some addtional requirements when single conductors are permitted to be in individual raceways or cables it does not give any permissions to use single conductors in raceways or cables.

I think about the only way this is allowed is for existing knob and tube wiring. All other conditions of 300.3 still require all conductors of a circuit to be in close proximity of each other if they are allowed to be in separate raceways or cables. They are not allowed in ferrous raceways - period.

 

[Dennis Alwon]

Kwire, are you saying that I cannot feed both sides of a three way and use the ungrounded conductor on one end and the neutral at the other end? This has been done for years with NM and although I find it a bad method , do to EMF's, I cannot find anything in the NEC that doesn't allow it.

 

[al hildenbrand]

300.3(B)(3) gives us some additional requirements when single conductors are permitted to be in individual raceways or cables it does not give any permissions to use single conductors in raceways or cables.

Well, let's look at how 300.3(B) and 300.3(B)(3) interlink.

2008 NEC
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).

As I read this, the key is that "unless otherwise permitted in accordance with 300.3(B)(3)" is part of the only sentence that is 300.3(B).

Paraphrasing that one sentence of 300.3(B) for the NM install in the post it sketch, "Conductors shall be in the same cable, but if the cable is nonferrous, and where ferrous boxes are installed to the conditions of 300.20(B), the conductors may be run in different cables."

 

[kwired]

I had been taught that 3003(B) means all circuit conductors in any given circuit or portion of a circuit need to be run in close proximity to each other to minimize magnetic effects both on the conductor itself and surrounding items.

I see that the NEC does not specifically say this but you can see that it is implied in a few places. In places where you are allowed to run individual conductors or parallel conductors with each phase in its own non metallic raceway you still are required to place all phases plus grounded and grounding conductors in close proximity to each other.

Conductors will have less impedance - especially during a short circuit event if they are in close proximity of the other conductor(s) that are carrying current in opposite direction at the same time.

 

[kwired]

Kwire, are you saying that I cannot feed both sides of a three way and use the ungrounded conductor on one end and the neutral at the other end? This has been done for years with NM and although I find it a bad method , do to EMF's, I cannot find anything in the NEC that doesn't allow it.

I don't quite follow what you are asking.

May be code compliant. Could still be poor design choice however.

If you can clamp an ammeter around any NM cable (not an individual conductor) and get a current reading I would say at the very least is a poor design choice. There is increased EMF's in this situation and conductors will have higher impedance - especially during short circuits and ground faults when a low impedance is important for faster operation of overcurrent devices.

A cable that is a switch loop or part of a switching loop may not need a neutral conductor (2011 code may need one even if it is not used but that is a different issue) but should have a feed and a return, or multiple returns with current equaling what is coming in on the feed. The net magnetic field on the whole cable should be zero.

 

[Dennis Alwon]

I was questioning your statement about all the circuit conductor being run together. I was giving a common example where ec's run a two wire between the 3 ways and feed both ends. You seemed to be saying it was not compliant and I am saying it is compliant-- I would not install it that way but it is compliant.

 

[al hildenbrand]

I see that the NEC does not specifically say this but you can see that it is implied in a few places.

You are correct that the Code does not specifically state a closed, immutable, all conductors must be in the same cable, raceway, etc.

The Code specifically says, in 300.3(B), "unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4)".

That's very specific, and trumps, IMO, implications or inferences.

 

[al hildenbrand]

I also agree that, from the standpoint of the effects of EMF, especially biologically, that the permission in 300.3(B)(3) results in poor design.

 

[patbet]

california 3 way

california 3 way

Are you referring to the "carter system"? Google it.

 

[al hildenbrand]

Welcome to the Forum, patbet.

Your question goes to one of the fuzzier aspects of various threeway setups. The nomenclature is not precise.

Are you referring to the "carter system"?

I think that xformer actually answers your question, himself, while he is clarifying his opening post (OP) way back in post four .

no, that is not what I am describing. What I am describing is the use of two 3-way switches in a circuit used to control a light while the rest of the circuit continues downstream to feed an additional load.

Perhaps you missed that? Or, better yet, what is it about the Carter System that you are thinking of when you ask your question?

In a nutshell, I'd say the heart of the Carter is that the lampholder polarity changes, depending upon the switch positions.

The heart of the switching asked about in the OP rests in the path of the unswitched hot conductor for the circuit passing along one traveler between threeway switches, and the switched load being connected to the other traveler.

 

[edmoon]

tunnel switch

tunnel switch

Here's what I was always told was a travling buss three way/ tunnel switch?
Flip the first switch and first light comes on, flip the second switch and first light goes out and second light comes on and so on, flip the last switch and last light goes out.

Too bad this violates NEC by making the screw shell hot and switching neutrals.

 

[hurk27]

Too bad this violates NEC by making the screw shell hot and switching neutrals.

I would say that if non-screw shell type fixtures are used would it still be a violation? there are many fixtures that could be used that would not cause a danger if the hot and neutral was swapped.

I have only seen one of these in operation in an old barn, what was neat was if one of the end 3-ways was on hot, and the other was on neutral you could put the two middle switch toggle handles in the middle so they don't make any contact and all three lights would be in series and burn very dimly, you can have two or more like this depending upon how many switch's you put the handles in the middle, they have to be toggle type as decora wont stay in the middle.

 

[ronaldrc]

Here is the one I have had on my site for years

http://home.comcast.net/~ronaldrc/wsb/light_circuits.htm

 

[hurk27]

Here is the one I have had on my site for years

http://home.comcast.net/~ronaldrc/wsb/light_circuits.htm

With that one only one person or group of people can go through the tunnel at a time and would have to return back before another could go through, and if a person was to come in from the right side, they would not have any power if no one has gone through from the left.

I still love the animation:thumbsup: