kwired
Electron manager
- Location
- NE Nebraska
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- EC
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.
California 3-way...
- Thread starter xformer
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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.
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
Senior Member
- Location
- Minnesota
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- Electrical Contractor, Electrical Consultant, Electrical Engineer
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.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
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):
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
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
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
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
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.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
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
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Well, let's look at how 300.3(B) and 300.3(B)(3) interlink.
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
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
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.
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
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
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.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
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
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
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
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
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.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Welcome to the Forum, patbet.
Your question goes to one of the fuzzier aspects of various threeway setups. The nomenclature is not precise.
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.
Your question goes to one of the fuzzier aspects of various threeway setups. The nomenclature is not precise.
I think that xformer actually answers your question, himself, while he is clarifying his opening post (OP) way back in post four .
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.
tunnel switch
tunnel switch
Too bad this violates NEC by making the screw shell hot and switching neutrals.
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
Senior Member
- Location
- Portage, Indiana NEC: 2008
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.
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Here is the one I have had on my site for years
http://home.comcast.net/~ronaldrc/wsb/light_circuits.htm
http://home.comcast.net/~ronaldrc/wsb/light_circuits.htm
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
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:
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