Question about old BX cable (copper/aluminum)

14 years ago

Hi. I am embarking on my first electrical project in our new house (replacing a light fixture). When I removed the old light fixture, I discovered that the wiring in the ceiling is old metal BX cable with two rubber-insulated conductors that are sheathed in cloth. The wire itself is dull gray on the outside but appears to be solid copper on the inside. Our house was built in 1906 but I am guessing that the wiring is from the 1940's because that's when the last time major renovations were done on the house.

Yesterday I went to Radio Shack with a bit of the wire to ask them for comparable wire to make some pigtails. (There are several cables passing through the fixture box that were not well-connected -- I was planning to re-splice them with new wire when I connect the new fixture.) The salesperson there told me that the wire was actually aluminum and that I should really call an electrician because connecting aluminum to new copper wire can be very hazardous, and at the very least, I should use special wire caps and a reactive paste.

I'm not sure if he knew what he was talking about, but now I'm confused because to me the wire looks like solid copper, with only a thin dull gray covering, and I also thought the hazardous kind of aluminum wiring dates to the seventies rather than to the forties, which is when I think that my wiring is from. Does anyone have experience with the type of wiring in my house? Is it true that there's aluminum in the wire or is that just the way copper wire from that period looks? Do you anticipate any problems connecting this wire to modern 14 gauge solid copper wire, or can I just treat it like regular copper wire? Is it really necessary to call in an electrician, or can I handle this on my own?

Thanks in advance for any help you can offer!

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Comments (7)

saltcedar
14 years ago
You have 'tinned copper' which is acceptable for all copper conectors.
bus_driver
14 years ago
The conductors are tinned copper. Some people believe that the tinning was to aid in soldering, the predominate splicing method of that day. That was only an incidental benefit. The insulation on the individual conductors often was rubber. Copper hastens the deterioration of rubber. The tinning separated the copper and the rubber.
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joed
14 years ago
Radio Shack it last place to go for the wire. You should be able to get what you need for any harware store like lowes or home depot.
What you have there is tinned copper wire. It was tinned because the rubber insulation would react with the copper.
brickeyee
14 years ago
While it is called 'tinned' wire, the metal applied is mostly lead.
Tin is expensive stuff.

As noted, it was to prevent a reaction between the copper and the rubber insulation.

If it is very old you may need to lightly sand it to get a good connection in a wire nut.
westminster
Original Author
14 years ago
Thanks, that's great news, since I assume that's what's running through the whole house! I had a feeling I couldn't trust the guy at Radio Shack -- and of course, when I told the guy at Home Depot what the guy at Radio Shack said, he said, oh yeah, that's definitely aluminum wire without even barely looking at it.

Can I ask you -- does it sound based on my description like the cable is likely to be from the 1940's? Also, is that considered to be relatively safe? From what I can see, both the rubber and the cloth that are exposed are holding up pretty well. I realize that best practice would be to update the wire, but that's not in the budget right now!
brickeyee
14 years ago
It is most likely old AC cable.
The original BX was from the 30s.
One way to tell is if you see a thin bare metal bonding strip inside the armor.
The original BX had some issues acting as a reliable ground.
It was withdrawn and AC cable introduced with a bonding strip to ensure low ground impedance.

The biggest problem is the rubber drying out and getting brittle.
When you move the wires in a ox to disconnect them or reconnect them to a receptacle or switch the insulation can just crumble.

Heat from light fixtures accelerates the drying out.

Heat shrink tubing can be slid of any bare wire until it overlaps the insulation, then shrunk down with a heat gun to cover the bare wire.
joelbuckley
14 years ago
My house, which was built in 1936, has similar stuff. It's BX and has no bonding strip. When we had the house inspected by an engineer prior to purchase, he noted what appeared to be aluminum wiring in the panel, but it turned out to be just the tinned copper conductors. You'd think he would've known better.

Brickeyee speaks the truth about cracked and crumbling insulation, especially in ceiling light boxes. His heat shrink tubing suggestion is a good one if upgrading the wire and boxes is not an option.

Question about old BX cable (copper/aluminum)

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saltcedar

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Question about old BX cable (copper/aluminum)

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