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Two 3-way switches on two seperate circuits in ONE double switch box

Two 3-way switches on two seperate circuits in ONE double switch box

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  #1  
Old 01-13-11, 10:38 AM
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Two 3-way switches on two seperate circuits in ONE double switch box

I am looking to educate myself on an electrical problem I have seen multiple times. I am an investor and invest in row homes built in the late 60's. Currently, I own 5 of these properties, all in the same development, and I have seen this issue in all 5 of these homes.

At the bottom of the basement stairs are TWO 3 way switches in the same double switch box.

Switch #1 is a 3-way with the switch at the top of the stairs, and controls the main room of the basement and is on Circuit A.

Switch #2 is a 3-way with a switch at the back of the laundry room, and controls the laundry room light and is on Circuit B.

In all of these cases, when all of the breakers are in the ON position, all switches and lights work as they should.

HOWEVER, when I turn off Circuit A (which should ONLY control Switch #1 and it's partner), and then operate Switch #2, the light in the main room of the basement go on VERY DIMLY based on the positions of Switch #2. Remember that the light in the main room SHOULD NOT go on at all since Circuit A is in the OFF position.

Further investigation has revealed that, even though there are two seperate circuits going into the double switch box, there is only ONE "TRUE" Neutral (contuinity tested to go back to the CB panel). In this double switch box, the whites are all tied together, which I know is not the correct way to wire this situation. However, wired in this way, the lights and switches do work as would be expected.

In my mind, what seems to me to be happening, is that, when Circuit B is left on, but Circuit A is turned off, power going through Circuit B is "backfeeding" into the white wire for Circuit A and providing power (albeit reduced power) to the light fixture on Circuit A, and therefore Circuit A's light fixture lights up dimly. This would be due to the fact that the TRUE NEUTRAL for Circuit B is tied to a white wire for Circuit A that is not a TRUE neutral.

Is my theory correct? Do any of you know a website where I might be able to play with wire configurations to test my theory?

Thanks in advance.
 
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  #2  
Old 01-13-11, 11:26 AM
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I haven't wrapped my head around exactly what is going on yet but I can tell you that you have a multiwire circuit. Two circuits on opposite phases sharing one neutral. The two circuits in the panel, (if breakers) are they one on top of the other? (IE circuits 1 & 3, or 2 & 4)
 
  #3  
Old 01-13-11, 11:38 AM
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Honestly, I am not sure if they are on the same phase or not. If memory serves me, I believe they are in position 2 and position 4 on the CB panel, which would make them on the same phase (correct???) but I cannot swear to that. Since there is a tenant int he property, I would prefer not to go there and bother them for this unless it is a fire hazard, which I do not believe it is.

I am just trying to understand what is going on, so that, on my next property that is wired this way, I can correct the problem.

If I were to call the "supply" switch (the switch where the hot black goes to the common terminal of that switch) the MASTER, and the other 3-way of that pair (where the black wire goes from the common on the switch to the black wire of the fixture) and call that the "SLAVE", I think I could make my explanation more clear. If you understand my "Master" & "Slave" wording, it seems to me that they miswired one of the circuits such that the Master Switch (which should be the first switch on the path from the CB panel) goes directly to the light fixture, rather than to the other switch. As a result, at the SLAVE switch, there is no TRUE NEUTRAL. Therefore, they stole the neutral from the other circuit, which is, in fact, wired correctly. I hope this does not confuse you more!!!

Thanks for your help.
 
  #4  
Old 01-13-11, 12:39 PM
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To clarify... when I say positions 2 and 4, I mean that they are both on the right half of the panel, with one of the breakers being the second one down from the top, and the other breaker being the 4th one down from the top.

Also, I have done some research on what is meant by a "Multiwire" circuit. I understand the concept of running one piece of 14/3 rather than two pieces of 14/2. As I understand it, a multiwire circuit would require a double pole breaker (handles tied together) so that this would ensure that the two circuits are on opposite phases. However, this would also mean that there would be RED wires somewhere, which is NOT the case in my situation. Even where I would normally use 14/3 (ie. between the two 3-way switches), they used two pieces of 14/2 and capped one of the wires.
 
  #5  
Old 01-13-11, 12:39 PM
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Do you have a cable with red and black connected to the breakers in the Main panel? Is the voltage between the red and black 240v? It should be. If it isn't chances are you have a dangerously miswired multi-wire circuit.

Another problem that comes to mind is you have two 2-conductor circuits and they tied the neutrals together. If you have two cables, each with black and white wires, bringing power in the whites can not be connected. Only the grounds are tied together.

Final problem I ran into once was insulation breaking down allowing bleed through from one circuit to another. No visible damage to the wire insulation. It is rare and I wouldn't expect it but just thought I'd mention it.
 
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Old 01-13-11, 12:43 PM
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Even where I would normally use 14/3 (ie. between the two 3-way switches), they used two pieces of 14/2 and capped one of the wires.
This is not permitted. All conductors must be in the same sheath.

Our posts crosed and I see you say no 3-conductor cable at the breaker box so probably ignore my first paragraph.
 
  #7  
Old 01-13-11, 12:50 PM
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Ray:
Your post, and my clarification were posted almost at the same time.

To answer you... there are NO red wires anywhere in the house. I routinely change out evvery switch, and every receptacle and every light fixture in these properties, so I have been in every box. I also run new circuits, and at the CB panel, I have not seen any red wires. This is true in all 5 properties.

Yes, I ABSOLUTELY do have TWO two wire circuits. As I stated in the original post, one pair of 3 way's are controlled by circuit breaker A, and the other pair of 3-ways are controlled by circuit breaker B. For me to have no hot wires in the double switch box, I have to turn off BOTH Circuit breaker A and Circuit breaker B. As I see it, the problem is that there is no neutral where one is needed for the second circuit, so they simply "stole" or "jumped onto" the neutral for the other circuit. To me, that means that even though one breaker is turned off, the other breaker (which remains on) is "backfeeding" power through the jumped white back through the OTHER circuit, and that is why the light goes on, but DIMLY.

Does my theory make sense to you?

Thanks.
 
  #8  
Old 01-13-11, 12:58 PM
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Ray:
Was it code correct back inthe 60's to use two pieces of 14/2 rather than one piece of 14/3? I ask because I have seen many instances of this in these homes, even though it makes no sense logically or economically.
 
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Old 01-13-11, 02:18 PM
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Originally Posted by JMattero View Post
Ray:
Was it code correct back inthe 60's to use two pieces of 14/2 rather than one piece of 14/3? I ask because I have seen many instances of this in these homes, even though it makes no sense logically or economically.
The old pros will have to answer that.
 
  #10  
Old 01-13-11, 02:20 PM
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I do not believe it would have ever been acceptable. All circuit conductors must travel in the same raceway. Separate cables are separate raceways.
 
  #11  
Old 01-13-11, 02:24 PM
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Ray:
Do you know of any websites that would allow me to play around with animated wires and switches to re-create the situation I am asking about? I remember back in high school science classes where the teacher would have a piece of plywood with switches and wires on it as well as a light fixture, to show how these worked. I am contemplating doing the same thing when I have some time to build one, but, in the meantime, I am wondering if there is a website where I could play around "virtually" with some animated wires and switches.

Thanks
 
  #12  
Old 01-13-11, 02:27 PM
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I guess they simply didn't have any 3 wire on the truck when they were wiring these homes!!! Thanks.
 
  #13  
Old 01-13-11, 04:40 PM
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Couple things to mention:

1) Handle ties (as on 2 pole breakers) were not required on multiwire circuits until 2008 code.

2) If your breakers are on the same side (IE 2 & 4) then then are on opposite phases. Phases go 1/2=A 3/4=B 5/6=A 7/8=B etc.

What wiring method are we talking about here? NM (Romex)? BX/AC/MC? EMT? Flex conduit/Greenfield?

I know of no web sites to play with wiring but you could do this with a table, switches and some short pieces of wire.
 
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Old 01-13-11, 07:39 PM
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Originally Posted by JMattero View Post
Ray:
Was it code correct back inthe 60's to use two pieces of 14/2 rather than one piece of 14/3? I ask because I have seen many instances of this in these homes, even though it makes no sense logically or economically.
As far as I know, that was never allowed by code, as ibpooks has already mentioned. You have to understand that in the '60s, many builders did their own wiring and plumbing and when they finished, it usually worked. But, just becasue it works doesn't mean it's right! Today there are still some areas where builders can wire their homes.
 
  #15  
Old 01-14-11, 04:27 AM
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Tolyn:
We are talking about NM (Romex) wire here.

Also, as far a position/phase is concerned, these two breakers are, as I recall, on the right side of the panel, with one unrelated breaker in between them. That is why I think they are on the same phase.

Thanks for your help.
 
  #16  
Old 01-14-11, 08:44 AM
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Originally Posted by JMattero View Post
Tolyn:
We are talking about NM (Romex) wire here.

Also, as far a position/phase is concerned, these two breakers are, as I recall, on the right side of the panel, with one unrelated breaker in between them. That is why I think they are on the same phase.


Thanks for your help.
Tolyn:
If these two circuits ARE on the same phase,, my reading has indicated that it would be possible for the shared neutral to actually be carrying twice as much current as it should. Am I reading that correctly? If so, and since the neutral is 14 gauge wire, should I put these breakers on opposite phases so that the current over the shared neutral is cancelled, rather than additive?
 
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Old 01-14-11, 09:41 AM
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You have written that there are no cables with red at the breaker box. You have written they used two 2-conductor cables for three way wiring instead of one 3-conductor. I can not come up with any rational reason why they would do it but is it possible they ran a multi-wire using two 2-conductor cables and capped off the white on both ends?
 
  #18  
Old 01-14-11, 10:21 AM
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Originally Posted by ray2047 View Post
You have written that there are no cables with red at the breaker box. You have written they used two 2-conductor cables for three way wiring instead of one 3-conductor. I can not come up with any rational reason why they would do it but is it possible they ran a multi-wire using two 2-conductor cables and capped off the white on both ends?
Ray:
I believe that what they did was run 2 two wire cables, but used two pieces of 14/2 between the switches, rather than one piece of 14/3, and simply capped the extra white on both ends.
 
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Old 01-14-11, 08:40 PM
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Originally Posted by JMattero View Post
Tolyn:
If these two circuits ARE on the same phase,, my reading has indicated that it would be possible for the shared neutral to actually be carrying twice as much current as it should. Am I reading that correctly? If so, and since the neutral is 14 gauge wire, should I put these breakers on opposite phases so that the current over the shared neutral is cancelled, rather than additive?
Yes you are correct. With both breakers on the same phase, as you describe, the neutral could carry twice the current. However, are we sure they are sharing the same neutral? Earlier you mentioned there was no red wires which are found in 3 wire cable (12/3 or 14/3) If you only have two wire cables in the panel (not counting 240 volt circuits) then each circuit has it own neutral and it is not an issue.

One thing the popped into my head is that maybe the installer got some neutrals crossed up someplace. Not sure why the odd circuit lights glow, but just tossing it out there.
 
  #20  
Old 01-22-11, 10:47 AM
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Tolyn, Suppose that the neutral for CIRCUIT #1 went unused (just capped off), and the neutral for CIRCUIT #2 was being used as the neutral for circuit #1. As I see it, with this hookup (which I know is not correctly connected), when circuit #1 was turned off in the breaker panel, but circuit #2 was left on, and a light that is on circuit #2 was turned on by the switch, wouldn't some of the power that is going through circuit #2 "backfeed" into circuit #1 and explain the glowing of the lights on circuit #1?
 
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