3 way switches

[iaov]

I'm sure this is an old topic but I was not able to find it through search. Worked with an electrician today who wires three ways by what he calls dead ending. Has a box with a three way switch in it and 3 conductor wire going to it. Two are travelers and one goes out to the lights. Where he gets the neutral from I'm not sure. I believe this wiring method is a violation of 300.3 (B)... all conductors of same circuit in the same raceway/cable. Am I missing something?

 

[Dennis Alwon]

If the feed is in the light all you need is 2 - 3 wire cables to each 3 way switch from the light. Legal--yes

 

[iwire]

I 'dead end' three ways when I it suits the job.

If the feed is at the fixture all you need is a two wire cable from the fixture to the first three way then a three wire cable to all the other four ways / three way you want.

That is a legal way, it complies with 300.3(B), however there are ways to do it and violate 300.3(B).

 

[EBFD6]

we often dead end 3-ways, you have one box with a 2 wire feed and a 2 wire to the light out of the same end (box) of the three ways, then you run a 3 wire from that box to the dead end.

All you are doing with that three wire is taking your 2 travelers as normal and then splicing your hot for the lights to extend it from the main box to the dead end.

It is the same thing as a standard 3-way setup, just spliced differently. I would imagine this is most likely what he did, and is not a violation.

Hope I explained this ok, I know what I want to say but I'm not sure if I communicated it properly

 

[iaov]

Hey Dennis. I'm not sure if I understand what you mean.

 

[iwire]

we often dead end 3-ways, you have one box with a 2 wire feed and a 2 wire to the light out of the same end (box) of the three ways, then you run a 3 wire from that box to the dead end.

That will also work and comply with 300.3(B). :smile:

 

[iwire]

If the feed is in the light all you need is 2 - 3 wire cables to each 3 way switch from the light. Legal--yes

I have never done that or even thought about it but I agree that would be legal. That is kind of a 'double dead end 3 way'.

That would throw me if I was troubleshooting that circuit.

 

[cadpoint]

210.4(A)

210 , 210.4 & (C) you said lighting, (didn't ya) but if it was equipment,
Table 210.2 Specific-Purpuse branch circuit.

Technically 300.3 seems good enough all by its self....

 

[Dennis Alwon]

I have never done that or even thought about it but I agree that would be legal. That is kind of a 'double dead end 3 way'.

That would throw me if I was troubleshooting that circuit.

I have never done it either but it would work providing you had enough room in the ceiling box.

Hey Dennis. I'm not sure if I understand what you mean.

120 at the light. Neutral stays there. Hot feeds down on a black wire to one 3 way. The other black wire from the 2nd 3 way would feed the light. Red pair and white air from the 3 ways would be spliced respectively.

 

[iaov]

I'm easily confused. When I do three ways I bring powe into the first box with 2/c go out the box with a 3/c . Two travelers (R &B) and white as the neutral. Into the second box with travelers and neutral. Out of that box with a 2/c one of wich goes to switch common and the other carries the neutral. I do this because I thought 300.3 was to prevent inductive heating from running current carrying conductors . The inductive effect being canceled by the opposite polarity always existing in the neutral.

 

[Dennis Alwon]

I'm easily confused. When I do three ways I bring powe into the first box with 2/c go out the box with a 3/c . Two travelers (R &B) and white as the neutral. Into the second box with travelers and neutral. Out of that box with a 2/c one of wich goes to switch common and the other carries the neutral. I do this because I thought 300.3 was to prevent inductive heating from running current carrying conductors . The inductive effect being canceled by the opposite polarity always existing in the neutral.

The wires are just switch legs. Is it any different that most commercial jobs where the feed is at the light and a switch leg is dropped to the switch. Also read 300.3 (B)(3)

 

[iwire]

What you describe I do also, I would call that a feed through 3 way.

It also complies with 300.3(B).

Read carefully 300.3(B) and you will notice that you need not include the neutral if it is not used.

With properly wired switch loops the current going out on one hot is balanced by the current coming back on the other hot. With the current balanced you have no inductive heating issues.

 

[iaov]

What you describe I do also, I would call that a feed through 3 way.

It also complies with 300.3(B).

Read carefully 300.3(B) and you will notice that you need not include the neutral if it is not used.

With properly wired switch loops the current going out on one hot is balanced by the current coming back on the other hot. With the current balanced you have no inductive heating issues.

That makes sense Bob. Thanx to you and Dennis for the help. I guess I'll have to tell the guy he was right tomorrow.:grin:

 

[winnie]

The thing that counters inductive heating of a conduit is _not_ the presence of the neutral, but rather the _equal and balanced_ current flow on all of the conductors contained by the conduit. Imagine a horizontal conduit. As long as all current flowing 'left' in the conduit is balanced by current flowing 'right' in some other conductor, the _net_ current flow will be zero and there will be no current flow induced in the conduit itself.

The most common way to provide this balance is by having all hots and the neutral together in the same conduit. So the presence of the neutral meaningless. If, for example, you were to run the neutral in one conduit and the hot in a separate conduit, both meeting up at a load, then the current flow in each conduot would be unbalanced and you would have a violation of 300.3.

However another situation in which the current flow is properly balanced is if you have a 'switch loop'. In this case, you have an 'unswitched hot' going out to the switch, then the 'switched hot' returning to the load from the switch. Any current flowing _to_ the switch is balanced by current flowing _from_ the switch, so the conductors that make up a switch loop are properly balanced and won't cause inductive heating.

You can similarly design 'three way' circuits where the current flowing on the travellers is balanced by the other 'switched hot' conductor in the cable. This could be a three way switch loop, or the 'double dead ended' approach that Dennis suggested.

-Jon

 

[Ed Carr]

I have run 12/2 to the first 3 way 12/3 through the fixture then to my other
3 way.

 

[Buck Parrish]

I'm sure this is an old topic but I was not able to find it through search. Worked with an electrician today who wires three ways by what he calls dead ending. Has a box with a three way switch in it and 3 conductor wire going to it. Two are travelers and one goes out to the lights. Where he gets the neutral from I'm not sure. I believe this wiring method is a violation of 300.3 (B)... all conductors of same circuit in the same raceway/cable. Am I missing something?

Dead ending a three way is a common practice in electrical work. Be it commercial or residential. Where have you been ?
We do it 'when' it makes it easier en routing cables or wires. Their are a bunch of different ways to wire them and be code compliant.

 

[BackInTheHabit]

Hot to one box. (14/2) Three wire between both boxes. (14/3) Switchleg to light. (14/2)

I never backfeed anymore. Have too many problems with it. I never make junctions in a light box. I only put a switchleg in the lightbox. Make junctions in wall boxes.

 

[c2500]

Don't forget, when wiring a 3-way with just one 3 wire going into the other box, re-identify the white wire as now being a hot wire.

I use this method when necessary. In my own house I had two boxes that backed up to each other. So I used a thin two gang with a plaster ring. I did not have the capacity to have anymore than the 3 wire/ ground/switch in the box.

c2500

 

[stickboy1375]

I have never done that or even thought about it but I agree that would be legal. That is kind of a 'double dead end 3 way'.

That would throw me if I was troubleshooting that circuit.

Why? if the feed isnt at either 3way it pretty much solves the mystery...

 

[BackInTheHabit]

Don't forget, when wiring a 3-way with just one 3 wire going into the other box, re-identify the white wire as now being a hot wire.
c2500

If you are backfeeding (as I call it) you would have to reidentify the neutral as a hot.


The neutral isn't being used as a hot. It is fed through each box by using wirenuts. Black (hot) feeds first 3way. The black and red of the 14/3 are travellers from box to box. Black in second box is switchleg.

NOTE: My way isn't necessarily the best way, it's just the way I prefer it to be done.