Determine Old Wire Gauge

[rdagger]

How do you determine the gauge of very old wire (see pic)? The outer diameter of the insulation is .375" and the diameter of the wire itself is about .19". I need to extend it and want to make sure I use the correct gauge. btw, what is this type of wire called?

 

[Charles (in GA)]

From the finish on the strands, it looks like some sort of aluminumized copper. That is probably old BX wire.

THIS might help you identify the wire. Strip back some and carefully measure the diameter of an undisturbed area using a dial caliper or micrometer.

Truthfully, I'd look at pulling it all out and replacing it. You will have to make the splice in a box with a cover.

Charles

 

[nehog]

This is tinned wire (not aluminumized or aluminum). The only accurate way to measure what gauge it is is to measure the diameter of a single strand, count the number of strands in a wire and use a chart.

 

[Norcal]

What is the circuit used for? If it is a range circuit, you cannot extend it, it will have to be completely rerun to comply w/ current code.

 

[kert]

Looks like old BX. I replaced as much of that as I could in my house ( still have 2 lights that I couldn't get to easily). I don't see a ground wire and unless there is a bonding strip, the steel jacket is not an adequate ground. Add to it what looks like cloth insulation, and I'd replace it or put a GFCI breaker on it.

 

[rdagger]

This is tinned wire (not aluminumized or aluminum). The only accurate way to measure what gauge it is is to measure the diameter of a single strand, count the number of strands in a wire and use a chart.

There are 7 strands at 1.56mm diameter which has an area of 13.379mm² -- (1.56 / 2 )² x π x 7. According to a chart 6 gauge is 13.302mm².
Thanks.