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Old 02-24-2009, 06:44 PM   #1
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Confused wiring


Hi -

Wonder if anyone can help me with a "strange" circuit situation in my 1970-built single family home (in NY, USA).

Broadly, I have: 120V/60Hz suppy, BX cable w/ hot(black)-1neutral(white), generally 14AWG, ground via metal boxes&armor. I am in process of replacing (probably original) switches and receptacles, and pig-tailing mid-runs (they are currently poorly back-stabbed), and am trying to isolate frequent tripping. Overall I would guess that the overall condition of the electrical system is not great but does not warrant a full scale replacement. To my issue:

Schematically, I have room A (in its original state) on circuit 1 and room B (I have isolated/opened the incoming hot) on circuit 2. If 2 is off (and all others on), a reading on the incoming bare black wire in B is around 20V, but (I think) the circuit is not powered in the sense that a reading across a 400Ohm/0F/0H resistor to ground or return gives 0V. I am assuming this could be a "capacitive coupling" situation between 1 and 2, though I'm definitely no expert. There is no shock to be had with circuit 2 off.

The odd behavior is: with 1 off and 2 (and all others) on, both rooms A and B are not powered. Room B has strictly 0V even with high impedance multimeter. With 1 on and 2 off, A is powered, but not B (as it should be, but see caveat above). With 1 and 2 on, B's incoming has 123V. Overloading room B causes circuit 1 to blow, not 2.

I am not sure how this can happen. Is there a problem with the return? Or are 1 and 2's hot wires in contact somewhere? Perhaps I'm optimistic in my capacitive coupling "analysis," and there is true, somewhat resistive coupling of 1 and 2 upstream. I don't get this, though, since even if 1 is off, B should still get power from 2 (even if there is hidden contact with 1's hot somewhere).

BTW1: Wiring the incoming hot in room B to its downstream receptacles causes 1 (not 2) to blow, so a downstream hot in room B certainly seems to be (partially) grounded. With 1&2 on, the incoming room-B hot registers 120V wrt the other blacks in the box, not just the returns and ground.

BTW2: Rooms A (circuit 1) and D (circuit 4) in their original state have the same issue, in the sense that D is not powered if either 4 or 1 are off - so it's not something I inadvertently might have done to room B.

BTW3: The tripping on 1 began when it got really cold. With circuitry in room B offline (and 2 off, of course), the tripping has stopped. This lends credence to the idea that there is an inadvertent 1-to-2 (and 1-to-4) coupling somewhere, which finally deteriorated when the temperatures changed drastically.

BTW4: Sometimes I am finding wires in boxes are nicked down to bare copper - not sure why. Do rodents or carpenter ants chow down on insulation?? I cannot imagine an electrician being so careless. Currently there is no evidence of rodents, though I know they were around before I purchased the house.

Any help/insight is very much appreciated! Sorry for long exposition, chalk it up to not knowing what is relevant....

Tyro

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Old 02-24-2009, 08:01 PM   #2
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Confused wiring


First thing you said was you isolated the incoming hot to room B. You must isolate hot and the neutral.
What are measuring voltage against. It takes two points. You should be using the hot and the neutral.
The 20v is phantom voltage. It is really zero.
You lost me with all the rest. Too confusing

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Last edited by joed; 02-25-2009 at 03:09 PM.
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Old 02-24-2009, 08:35 PM   #3
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Confused wiring


Thanks for the reply. You're right - my post is as confusing as my wiring problems!

Yes, I meant to say I opened all hots and all neutrals. They are all bare and on their own. The voltages I quoted are between the incoming hot wire and any neutral or ground. Additionally, there is 80-120V between the incoming hot and the separate outgoing hot, indicating (?) that the outgoing hot is compromised/grounded. (note that there is no recognizable completed circuit on the outgoing blacks - all receptacles have been removed)

My basic problem is that circuit 2 is not independent of circuit 1 - as it should be. Room B has no power when its controlling circuit (2) is on, but 1 (should be a separate circuit) is off. I get only a phantom voltage in room B when 1 is on, but 2 is off - though, as you say, this might not be an issue.

To run room B, circuits 1 and 2 both need to be on. I'm not clear how this can arise.

Cheers,
Tyro

Last edited by Tyro; 02-24-2009 at 08:39 PM.
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Old 02-24-2009, 08:39 PM   #4
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Confused wiring


I'm no expert but your wiring is not the only thing that is confused. I think I am more confused than your wiring. You may want to break down your explanation a bit and try to explain your situation better and some of the pros in here will be able to help you out. If I dare to try to understand what you are saying it sound like you have one breaker for room 1 and 2 and another breaker for room 2. This can't be good.

Last edited by Bocolo; 02-24-2009 at 08:42 PM.
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Old 02-24-2009, 08:51 PM   #5
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Confused wiring


Hi Bocolo - Agreed re confused writing, it's not you. Does my reply to joed help?

Your last sentence is right: I think A should be on 1, B on 2. But B is only on if 1 and 2 are both on. A is powered when 1 is on and 2 off.

Cheers
Tyro (aptly named)
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Old 02-24-2009, 09:00 PM   #6
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You said you "isolated". How did you "isolate"? Did you run a complete new line to a new breaker? The only bare wire you should have is a ground wire which you should not have if you are using BX. Be careful, none of this sounds good. If you have hots and neutrals that are bare you definitely have a short somewhere and not to scare you but possibly a fire hazard. Again, I am no expert and if you hold tight some of the pros here will give you more solid responses.
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Old 02-24-2009, 09:15 PM   #7
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Thanks Bocolo!

I completely removed all receptacles and switches in room B. One of the boxes has 3 neutrals, three blacks and a single, short ground to the metal box (3 B+W BX cables plus one grounding wire for receptacle). By isolated I meant that all seven wires are stripped back 3/4inch and the ends are all several inches apart (not connected, not touching etc); I did not run a separate line.

One of the blacks is hot (wrt neutral or ground) when circuits 1 and 2 are on, but not if either 1 or 2 are off. The other two B-W cables are two branches that run off to the light switch (which controls a receptacle, not a fixture) and receptacles. They are dead regardless, so we can ignore them for now? (called branch circuits?) Though I do have a secondary problem (for later LOL) that their blacks might be grounded somewhere (see my "mouse" problem in the OP).

Cheers,
Tyro

Last edited by Tyro; 02-24-2009 at 09:19 PM.
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Old 02-24-2009, 09:26 PM   #8
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Confused wiring


Im sorry Tyro I am still not quite following you. What prompted you to do what you have done? When you test the switch cable you say is dead regardless of what you do, is the switch in the on position? I am trying to get you to provide more information so that others may help you out. I have some knowledge but it is a bit limited. Thanks.
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Old 02-24-2009, 09:50 PM   #9
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Hi Bocolo - thanks for your patience.

The issue first started when I could not map out the circuitry in the house (1 controls room A, 2 controls B, etc) because some rooms (like B) are off when 1 is off or "X" (like 2 in the posting) is off. I left this task for another day.....

More recently, though, circuit 1 started blowing for no apparent reason, but when 2 was off, this behavior stopped. So I figured I'd start by inspecting room B and removed all receptacles and switches (I want to replace them anyway). Power comes into room B on one of the BX-cables and leaves on two others. These other two are currently disconnected from the power-in-cable (and each other), and are never hot wrt any neutral or ground (just dead, unconnected wiring in the walls).

It seems I have two problems -

(1) room B's cables (branch (?) circuits) are compromised leading to a ground fault somewhere. This problem will need addressing later, but for the moment it's not an issue (since B's incoming cable has been disconnected from B's branch circuits).

(2), which I am trying to solve first, is why do 1 and 2 both have to be on to power room B? I am unable to conceive of how this can be, unless it's some weird connection (upstream from room B) that is broken if either 1 or 2 are powered off. Is something like this "commonly" seen?

Thanks
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Old 02-24-2009, 10:26 PM   #10
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It sounds like the two cables that have no power are just cables going downstream to where you disconnected them so they will not have any power or readings. Your other issue the only thing I can think would be that somewhere you have one wire from circuit A touching one wire from circuit B. When you turn them both on the circuit trips if only one is on none of the circuits trip. Not sure how you would find the issue though. I don't know why the two breakers need to be on to power room B. How are the wires tied in the main panel? There should be a black to each breaker and a white to the neutral bus. If you have never opened a panel before I would not recommend it, there are cables in there that are always live. They should be wired correctly though since this problem started recently. Anything you did before the problem arose? Any new connections, switches, lights, etc.
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Old 02-24-2009, 10:27 PM   #11
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Confused wiring


Quote:
Originally Posted by Tyro View Post
Overall I would guess that the overall condition of the electrical system is not great
I agree.

Quote:
Originally Posted by Tyro View Post
but does not warrant a full scale replacement.
Maybe not full scale, but it's time to replace this dicey wiring before someone gets fried. I've been reading the conversation and you have a mess. It's time to start replacing the wiring.

Jamie
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Old 02-24-2009, 10:45 PM   #12
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Quote:
you have a mess. It's time to start replacing the wiring.
Jamie is right you know. Sooner or later you will have to. Better sooner.
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Old 02-24-2009, 10:54 PM   #13
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Thanks for the posts!

Quote:
Originally Posted by Bocolo View Post
It sounds like the two cables that have no power are just cables going downstream to where you disconnected them so they will not have any power or readings.
Yes

Quote:
Originally Posted by Bocolo View Post
How are the wires tied in the main panel? There should be a black to each breaker and a white to the neutral bus. If you have never opened a panel before I would not recommend it, there are cables in there that are always live. They should be wired correctly though since this problem started recently. Anything you did before the problem arose? Any new connections, switches, lights, etc.
The panel is correctly wired (alternate blacks and reds to breakers, whites to bus, wires in good shape) and I did no work prior to the tripping that started recently. I have only had the house for a year or so, though, and do not know what sins the previous owner may have committed.

Jamie - I agree, in particular for the wiring inside room B, but how is it possible that 1 and 2 are both needed to get power room B in the first place? Bocolo's explanation dovetails with why the tripping started in the first place (since room B is "bad"), but not why two sources are needed to power one incoming wire...

Cheers
Tyro
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Old 02-24-2009, 11:13 PM   #14
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Quote:
alternate blacks and reds to breakers
You said you had BX cable (black and white) where did the "reds" come from?
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Old 02-24-2009, 11:27 PM   #15
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A picture is worth a thousand words! So far you owe us 9 pictures!

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