When it comes to making sure the correct conductor for size over-protection devices (understanding exceptions for mechanical equipment) I have no idea how you can tell what size conductor I am looking at.
I have charts that say the diameter of different conductors, but that doesn’t help me say tell the difference between 14 AWG and 12 AWG and I’m not reaching into a panel with calipers or anything.
I understand this is something you just get a feel for over time, but if I can’t read it anywhere on the jacket, and don’t have that ability now, how does that familiarity eventually happen?
if they sold a labeled set on a key-ring I’d be a buyer, but I can’t find anything like that.
As Kevin stated, go to your local big box or hardware store and get a few inches cut and label them while your there. Keep them in your tool bag until your get comfortable in being able to eye them without having to pull out the backups.
As Kevin stated it does take time and there is no easy way to determine the conductor size just by looking at it unless you’re skilled in eyeballing it. One issue is that most of the time you’re looking at the insulation not the bare conductor and different insulation types will have different diameters. Newer insulation should be relatively easy and you can do as Kevin suggested with a few scraps of various size conductors.
For older conductors it’s more difficult due to the various insulation types that have been used over the years. You might see rubber insulated tinned copper in R or RW, or thermoplastic in TW or THW. All four of those examples will have a different insulation diameter for the same size conductor.
A couple of years ago some member created a group of plastic (printed) gauges with different wire sizes. I think he had a different group for aluminum conductors and copper. The gauges fit over the insulation of each conductor and was marked with the size. Had some around here somewhere, never really found a need for them. Maybe someone can remember his name.
Please don’t stick anything in a panel. Get a piece of 14 AWG and 12. Put them in your hand and just feel them. It will help. Other than that it just takes time and we all get confused at times.
The only real way to know a wire size is by its identification being labeled on it. if you are new get use to saying only what you can prove to be true. Don’t try to impress anyone. Look and simply state facts.
They have books so that we can look things up. I do code but I never cite it without opening the book and reading verbatim. That way I can say, remember when I read that to you?
If you can see the cable sheath/jacket (which btw should extend 1/2 inch into the panel, which seems to be the exception, not the norm), it is easy. #14 gauge has a white jacket, #12 is yellow, and #10 is orange jacket.
Good point about the NM cable jacket colors although there is no written standard associated with those colors manufacturer’s have just sort of adopted them.
Actually the requirement is 1/4" and it is a newer code requirement so for older panels you might not see any NM cable jacket extending past the connector.
None of which will help you if the wire comes through a trough, is armored cable, in a conduit or simply older cloth/rubber jacket. Pretty much all older homes.
Agreed. I was just pointing out the fact that sometimes you can see the jackets on NM cables inside the panel and, in those rare instances, it is easy.
