Size of conductors is there some sort of a standard?

Old 06-07-15, 08:32 AM
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Size of conductors is there some sort of a standard?

Are electrical conductor sizes different in terms of the outside diameter?

I have a piece of regular stranded THHN #8 conductor.

I also have a piece of a conductor I removed from a #10 NM-B 12-3 wire. It is also stranded.

I lay them down side by side and it looks to me the #10 conductor from the NM-B wire is larger in diameter very slightly then the regular #8 conductor.

Is that typical?

Sometimes when trouble shooting or tracing a circuit that was installed by a previous owner...I have a hard time telling the size of a NM-B wire from inside the box because the marking is on the jacket and you only see an inch or two of the jacket inside the box or panel. The actual size is not marked on the conductors so how can you reliably tell the size? I tried to compare it with a regular individual marked conductor but these sizes don't match up. Is the only way to crawl into the dusty low attic and find the line and read it with a flash light?
Old 06-07-15, 08:55 AM
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You can't judge a cable size by the insulation. You need to look at the actual wire itself.
I work with wires everyday and sometimes have trouble judging between #10 and #12.... and #12 and #14.

It's a visual thing and also how easy the conductor bends. Some people use a marked stripper to gauge wire sizes.

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Old 06-07-15, 11:50 AM
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A piece of #10 will not be larger than a #8. Smaller numbers are larger conductors. The AWG, American wire gauge, is a standard.
Old 06-08-15, 06:55 AM
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Just to expand on the previous comments, the diameter of the copper has been standard for a long time (100+ years?). However the thickness of insulation has changed a lot as plastic technology has improved. You can compare the copper directly for solid conductors. Stranded is a little more challenging since they do have more compact versions now. You can't compare at all using the insulation.

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