wire gauge by inspection

The 7 strand conductor you describe is close to #1 AWG Class A stranding (although it consists of 7 strands of 0.1093" wire whereas #10 AWG is 0.1019" diameter). The overall diameter of #1 Class A is 0.328" whereas yours would be 0.306".

If all that is correct, you could safely derate the ampacity of jacketed #1 AWG Class A (under the same operating conditions) by 7%.

Thanks! My stranding consist of 0.099" X 7 and the bundle measures 0.305" - 0.302" depending on which set of strands I measure across. If I treat the bundled six solids like a "hex" nut; the measure across flats is 0.283" and across the point is 0.305 largest set. Slight variance due to cutter squeezing the bundle.

Looks like I had better derate it by 7% from a #1 AWG Class A to be on the safe side. The strands are coated with a nylon film and the cable is constructed like a direct burial TEK cable, even though it is installed above ground.

You need to find the circular mil sum of all the strands in the conductor and then determine the equivalent AWG wire size from a AWG table.

Use a micrometer or your wire gage to measure a single strand.

Calculate or look up (in the AWG table) the equivelent circular mill cross sectional area for this single strand.

Multiply this value by the number of strands. This gives you the total cross sectional are of all the strands.

Go back to your AWG table and convert the cross sectional area back to equivalent AWG wire size.

Snakers

Yes I realize that I need to find the equivalent AWG by summing the circular mills of the individual strands. I am using a micrometer as well as a Brown and Sharpe wire gauge.

The question arose because I arrived at an answer that appeared to be in between a #2 and a #1 wire. Maybe the wires were over drawn so they are slightly thinner than what they wer supposed to be. One thousands of an inch in 100 ( 0.100") is 1% error. Is that an allowed tolerance when drawing copper wire?

To be on the safe side I will use fusing based on the cable being a #2 rather than assuming it is #1.

Thanks to all for the replies.