Old House, Curious Wiring


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Old 02-17-07, 07:33 PM
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Old House, Curious Wiring

Hello all,

Right next to my front door (on the outside wall of my house), there is a metal plate covering what I assume used to be an electrical fixture. I opened it up and took a look and found some pretty old-looking wiring.

Now, I'll preface this all by saying I got it pretty much down on some basics - basics being, if I open a box and there's the white and black - I know one is the "hot", one is not, and there might even be a ground in there, too. I've hung and wired a whole bunch of ceiling fans and light fixtures.

What this box had, however, was not so simple. There were three openings - I'll call the A, B, and C.

One thick dark cable came out of B and disappeared into A. Another thick, dark one came out of B and disappeared into C. Figured that is electricity coming and going throughout the house, right?

Then things get interesting.

1) Two cables came out of A (one of the old-looking thick dark kind along with a newer, thinner, white wire)

2) One thick, dark cable came out of C.

These three wires met with and were joined by a wire nut.

So what's going on here? All the cables are dark (except for the white one I mentioned). I assume I can hook up a light to this box, just not sure what is what. I'm especially confused because as I understand things...there needs to be a hot and neutral wire to get the fixture going. And, if there ARE hot and neutral wires in that box - they appear to be joined together! And I know that's bad.

Any help would be appreciated!

Confused In Los Angeles
aka Homewrecker
 
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Old 02-17-07, 08:14 PM
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With out seeing it, I think your looking at old knob & tube wireing. Someone added to it. With out knowledge or the proper testing tools... Cover it back up and start a new.

Probably not the answer you want, But the best route. You could create all kinds of issues inside if you mess with this.
 
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Old 02-17-07, 08:26 PM
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HomeWrecker, do you know in what year the house was built?
 
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Old 02-17-07, 09:18 PM
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Originally Posted by John Nelson
HomeWrecker, do you know in what year the house was built?
I do. 1939. Also, to update something...I believe one of the wires that comes in from one of the little inlets and disappears again might be red (but not a new red, an old thick red wire). I can open the box up again if that's relevant and check.

Thanks!
 
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Old 02-19-07, 09:40 PM
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Originally Posted by lectriclee
With out seeing it, I think your looking at old knob & tube wireing. Someone added to it. With out knowledge or the proper testing tools... Cover it back up and start a new.

Probably not the answer you want, But the best route. You could create all kinds of issues inside if you mess with this.
I do have testing tools. Just not sure where to start testing. There aren't any typical positive or negatives to gauge a voltage potential across that I can see. As for knob and tube wiring...would I be seeing that inside a metal junction box?
 
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Old 02-19-07, 10:01 PM
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Wink

Have you tried with a small meter and see what you read there. On any one too another or find a ground some where and then see what you read wire by wire?
 
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Old 02-19-07, 10:16 PM
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Originally Posted by Ed Imeduc
Have you tried with a small meter and see what you read there. On any one too another or find a ground some where and then see what you read wire by wire?
Thanks. I'll give that a try and write back.

(and idea why the quotes aren't working?)
 
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Old 02-20-07, 07:01 AM
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Quotes don't work because vb Code is turned off. If you are quoting the entire previous post, it's unnecessary to quote and just a waste of bandwidth anyway. I'd generally prefer you to just use the Post Reply button rather than the Quote button.
 
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Old 02-20-07, 11:00 AM
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"1) Two cables came out of A (one of the old-looking thick dark kind along with a newer, thinner, white wire)

2) One thick, dark cable came out of C.

These three wires met with and were joined by a wire nut."

This part of your post is confusing, amd makes me think you are using the word "cable" when you mean "wire". When used in the context of residential wiring, "cable" usually means more than one insulated wire wrapped inside an outer protective sheath, such as Romex. "Wire" means a single conductor, insulated or not, such as a ground wire. If your house was built in 1939, I doubt there's any K&T wiring, but I suppose its possible.

My house was built about this time, and the original wiring was done using two insulated conductors inside rigid metalic conduit, which looks much like ordinary water pipe. Each end of the conduit is threaded, and is fastened into each junction box with threaded collars. Inside this junction box, where the wires enter, can you see what look like pipe fittings, with the wires entering through the middle of them?

The box obviously originally housed some type of outside light fixture, which was taken out of service. It could have been wired in any one of several different ways. The line from the fuse panel may have come to the junction box first, with another line to the switch. Or the power may have gone directly from the fuse panel to the switch, and then to the llight. And the electrician may have then used this box as a convenient place from which to extend power to, say, utility baseboard outlets. And it sounds like someone may have routed wiring through the box as part of a later electrical update/expansion.

And even if you do have conduit, it is possible that someone pulled some Romex through it, as an alternative to fishing it through walls. My understanding is that this is not the preferred method of running Romex, but is often the most practical approach in an old house.

It is certainly possible that different wires in the box are on different circuits. You could test this by shutting off (unfusing) circuits one-by-one and testing the wires for power. But the cables that "pass through" could not be tested unless you expose the conductor, which I would not do just to test.

Unless there is some compelling reason to know, I 'm not sure it's worth the trouble it will take to sort out what each wire is.
 
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Old 02-21-07, 03:08 PM
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Thanks for the reply....

For starters:

"This part of your post is confusing, amd makes me think you are using the word "cable" when you mean "wire"."

Yep. I was using the interchangeably. I would have to check again, but I believe they were ALL wires.

"The box obviously originally housed some type of outside light fixture, which was taken out of service"

Definitely. My hope is that the cables are still there and can be used, though.

"But the cables that "pass through" could not be tested unless you expose the conductor, which I would not do just to test."

That is good to know - thank you. I assume the ones that "pass through" were not part of the fixture that was there. Sound right?

That leaves me with what I described earlier:

"1) Two cables came out of A (one of the old-looking thick dark kind along with a newer, thinner, white wire)
2) One thick, dark cable came out of C.
These three wires met with and were joined by a wire nut."

To clarify based on proper wire/cable terminology, I believe two WIRES come out of A (one of the old-looking thick dark kind and a newer, thinner, white wire). Also, one thick, old WIRE came out of C. All three were joined by a wire nut.

Putting aside the scenarios you laid out about how they were wired (which were also very helpful, thank you), I'm guess that the two dark wires were attached to the lighting fixture. Where it is swtiched I don't know - there actually IS no switch anyway. But I have a feeling that a timer in the attic which controls another nearby newly light might also control this.

In any case, I'm guessing the two dark wires "fed" one fixture (sound right?) and the newer white wire fed the aforementioned new light.

Could that be right? It seesm so. But if so, what confuses me is - these two wires fed into a fixture, right? Then how can the fixture be removed...and the two wires just attached to each other? Isn't that a short-circuit?
 
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Old 02-22-07, 12:23 PM
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[quote]"But the cables that "pass through" could not be tested unless you expose the conductor, which I would not do just to test."

[Edit] The reason I would not disturb old wiring without cause is that sometimes old insulation can be a bit, errrr.....fragile. I've installed a new light fixture in an old ceiling box, and had several inches of the insulation just flake off, leaving me a much shorter piece of insulated conductor than I was happy with. [End Edit]

That is good to know - thank you. I assume the ones that "pass through" were not part of the fixture that was there. Sound right?[quote]

No way for me to tell. Consider how a household circuit is physically laid out with conduit. Conduit with wire inside is run from the panel to, lets say, a light fixture. A switch loop is carried inside conduit to an accessible spot beside a door. Now suppose that you need some baseboard outlets along that wall. Are you gonna run ANOTHER piece of conduit alongside the first, from the light fixture down to the first outlet? No way, not if you can run the wire in the conduit that carries the switch loop, saving 10-15' feet of conduit and, more importantly, the time to install it. So when you look in the junction box where the switch is, you'll see that the wire set for the baseboards "passes through". Will it be clearly labeled so you can tell what it is? I doubt it. It would take time, and pay the installer nothing. Same situation with your box. Someone found it in a useful place to save time. Whether that was the originall work or later additon is hard to tell. If the wire used looks like a match for other original wiring, then it's a good bet it was original work, but not a sure thing.

The logic above applies to cable also, but to a lesser extent because cable is so much easier to run.

[Edit] And if later additions were made to your house, you may well have both conduit and cable. My house does. Some of it I put in myself. [End Edit]

[quote]To clarify based on proper wire/cable terminology, I believe two WIRES come out of A (one of the old-looking thick dark kind and a newer, thinner, white wire). Also, one thick, old WIRE came out of C. All three were joined by a wire nut.[quote]

Based on what I know about household wiring (admittedly a limited knowledge to be sure) I believe it is exceedingly strange that any TWO wires coming out of a single conduit would be wirenutted together. Ordinarily one would carry current to the destination (box, receptacle fixture, whatever) in ONE wire, and then split the service there. This kind of makes me wonder if the wires in question are the individual conductors in Romex cable. Often two such cables enter a junction box through a single cable clamp. For two wires to then be connected would be routine. Look closely where the wires enter throug "A". Can you see part of a sort of 'pinch-clamp" holding the wire in place? That would be a cable clamp.

[quote} Putting aside the scenarios you laid out about how they were wired (which were also very helpful, thank you), I'm guess that the two dark wires were attached to the lighting fixture. Where it is swtiched I don't know - there actually IS no switch anyway. But I have a feeling that a timer in the attic which controls another nearby newly light might also control this.

In any case, I'm guessing the two dark wires "fed" one fixture (sound right?) and the newer white wire fed the aforementioned new light.{Quote}

Every outlet and fixture using 110 volt power requires connection via TWO wires, a 'hot' and a "neutral". By convention, installers who know what they are doing always route hot in colored wire (usually black or red, may be
other except NEVER green) and neutral in white. Modern wiring also links every outlet and fixture with a ground wire, which may be bare copper or sheathed in green insulation. Older wiring in conduit usually uses the metallic conduit as ground. Older wiring done using cable [two-wire, no ground] does not have a separate ground wire.

[Yet another edit] The above color coding is USA, and (I think) North America standard. Europe is definitely different. I know you are in L A, but don't want someone else fooled. [End edit]

[Edit} When I moved a couple of outlets in my house, using cable, I found it impossible to distinguish the hot and neutral wires inside the original conduit-both were a faded light brown. Had to energize with the junction box open and use a circuit tester. {End Edit}

HOWEVER..... it gets complicated. When a [light] fixture is controlled
by a switch, and cable is used, both the white and colored wire connecting them may be "hot'. When connected this way, the white wire should be marked in some way to redesignate it as hot, but there's no guarantee every installer does this.

And don't get me started on three-way circuits (one or more lights controlled by two different switches in different locations),

You say there's no obvious switch. It could well be that when the light was taken down, the switch that controlled it was changed to control something else.

You say you suspect that a timer controlling something else may have controlled this too? PLEASE BE CAREFUL around the wiring in this box. I envision a scenario where you turn off the circuits that you think are present here, test them and find them apparently dead, and then start working. The timer trips, and HomeWrecker bites the dust.

[quote] Could that be right? It seesm so. But if so, what confuses me is - these two wires fed into a fixture, right? Then how can the fixture be removed...and the two wires just attached to each other? Isn't that a short-circuit?[quote]

It would indeed, if one is hot and the other neutral. This is unlikely, with three wired together. They are (or perhaps were) either all hot or all neutral.

I wish we could be more help to you in sorting this out, but there are just so many different possibliities that it's next to impossible to be sure what was done here without being there to look at it.

And I'm by no means sure that I could figure it out even then.
 

Last edited by aq_guy; 02-22-07 at 08:21 PM.
 

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