Service Size?

New Inspector trying to determine the service amperage.
I have recently received my license and have been doing a few mock inspections and the electrical has been my Achilles’ heel.
When looking for the service amperage I understand that you can base your determination on a few factors, one being the diameter of the cable when the markings on the sheathing are not visible. Knowing that it is beyond the SOP to stick anything in the panel, my quest for the answers led me to buying a plastic digital caliper to take measurements off the cables. My question is this, what are the approximate diminsions of the various cables sizes, i.e. AWG 6, 4, 2, 1, 1/0, 2/0?

I have found 2 CONTRASTING sources.

The first being this ASHI pdf (see final page):
Of the panels I’ve looked at none of the service cables come close to the sizes they are suggesting.

The other source is this chart from InspectAPedia:
Which seem to be a little more inline with my findings.

Thanks in advance for any advice and help clearing my cloudy head.

Read the SOP’s. It is not your job. You can always refer to a professional, if you are not sure. Here in KC, most all homes are either 100 amp or 200 amp. The size of the wires between the two are obvious, as are the size of the meter cans.

Are you measuring the bare wire or the wire with insulation? First link is with, second without.

Personally I think trying to measure hot wires with a caliper is a really bad idea.

Go to Home Depot or an electrical supplier and obtain 6" samples of everything from 14 ga up to 2/0, label them and keep em in your tool box. You should be able to match the sizes by eye, holding a sample in your hand about a foot (or more) away from the live wires.

I realize it’s not popular to measure the wire sizes nor does the SOP require it. I just know a lot of homeowners want to know their service capacity and I’ve just read that measuring the wires is a more accurate way to determine the amperage.

I am measuring the exterior of the insulation. I’m willing to take the risk to a certain level but I won’t touch exposed wire. Unfortunately, I’m still getting opposing data.

I did get wire samples for the common branch circuits. I will take your suggestion and get some for the service cables as well.
Thanks Ya’ll

The main disconnect “Breaker/Fuse” should be the size of the service .
Example 100 amp breaker then it is a 100 amp service .
Not your job to become too technical .

Write it up and then see what you find in the rest of the service .

Thanks, Roy.
I guess I just feel like the main breaker could be sized wrong. Plus, I’m trying to determine if the Breaker, Cables and Panel are all compatible.
Also, when there is not a main breaker, I obviously cannot base the service size from it.
But perhaps you’re right, I may be trying to get too technical.

The service cable or conductors should be labeled as to their size.

If there is no main breaker, it needs to be noted and referred. You need to explain if you are after the appropriate meter wire size, or amperage size of the meter. Often you will see wires smaller from the meter to the panel than that of the incoming power line. Determining the size of the power line is not, and should not be, your concern.

Do you have a copy of the NEC? There are tables that give the dimensions of various conductors.

I went and picked up some larger sized wire samples for comparisons. None of them are labeled btw. At least on the 6 inch section I bought.

Perhaps I’m confused about the main breaker? I thought a panel was ok if it took 6 throws or fewer to shut down the power if no main breaker was installed.
I’m referring to the conductor coming from the meter to the panel. I won’t be going anywhere near the power line.

No I do not have a copy of the NEC. It’s on my shopping list.

Labeling is required but it only has to repeat ever so often.