Old BX with aluminum conductors?

[tls]

I encountered a type of cable today I haven't seen before -- armored cable with what appear to be Al conductors (not the bonding wire, the actual insulated conductors). The conductors are silver in color and do seem to bend like Al, not like old Cu. The wiring in question probably dates from the mid 1960s so Al doesn't seem too unlikely.

I'm sure others here have seen this before. How uncommon is it? I can't seem to even find a picture of it or reference to it anywhere.

 

[mxslick]

It's most likely simply tinned copper wire..it fooled me too first time I ran into it.

Inspect a freshly cut end to be sure...

 

[infinity]

I agree with Slick. Old AC cable contained tinned copper conductors to keep the copper from reacting with the rubber insulation. I don't think that you'll find any aluminum BX cable from 45 years ago.

 

[al hildenbrand]

I encountered a type of cable today I haven't seen before -- armored cable with what appear to be Al conductors (not the bonding wire, the actual insulated conductors). The conductors are silver in color and do seem to bend like Al, not like old Cu.

Was the conductor insulation rubber? If so, then, as mxslick and infinity have surmised, the copper is tinned to prevent direct contact between the rubber and the copper.

However, the late Sixties into the Seventies is exactly the window that a lot of small gage branch circuits were wired with aluminum. I've never run across aluminum conductored BX, but that doesn't mean that someone back then didn't buy and install some. The aluminum almost certainly would have had thermoset plastic insulation, thick like old TW.

Taking a razor knife or other sharp blade to scallop off some of the side of the metal conductor is another way to see if its solid Al or tinned.

 

[LarryFine]

If I remember correctly, the old BX conductors had a nickel coating, technically not 'tinning'. We were instructed to scrape it with a knife blade, typically the smaller blade on the old Klein 2-blade pocket knife.