Went to a house today to consult on a service upgrade. Problem is, I can't determine what I am upgrading from. There was no main disconnect either at the house distribution panel or outside at the meter. There was just a meter there! I think it's safe to assume, then, that if a house was wired back when this was considered legitimate practice, that it's probably a 60amp servive. However, I'd like to be able also to determine for sure what is the size of the existing wire, to see if it has to be changed to accomodate a 100a upgrade. But the wire from the meter to the distribution panel is unlabeled cloth-covered red and black, with uninsulated stranded neutral (no grounding wire). And of couse I can't tell what is coming into the meter from the mast since the poco is none too fond of us snipping off their little locks.
Determining wire size, insulation and ampacity used to be one of the test problems in the practical section of the NYC Electrician's exam. You have to measure the diameter of one strand with a micrometer, calculate the cross-sectional area and multiply it by the total number of strands in order to get the overall cross-sectional area of the conductor. You then have to determine the type of insulation. The old NYC code book is a bit different from our current NEC code book but you'll find the information in Chapter 9, Table 4 for wire size, then go to the ampacity tables.;)
BTW, this information is just for your reference, I'd rip the old stuff out too. The guy at the scrap yard only cares how much it weighs.
I wouldn't concern myself with what is existing. As long as you are upgrading the service, replace the SE cable with a four wire cable,(Two hots, a neutral and a ground) bond the water, the water meter, put in a new electrode, replace the meter can, add a main disconnect and charge the customer for all of it. Sounds like the existing dates back to mid 1950's or earlier and I'm sure it's not up to today's code anyway. In michigan, they still allow a 3 wire SE cable but, I know some states no longer do.
LK - I was concerned with wire sizes because we have not yet determined what would be torn out. Also, I will want to determine if the service entrance wires (from mast head to meter) are sized for 100a. Sometimes, even where the service was 60a, the wire installed was capable of carrying 100a.
Andy - thanks. I was wondering if there was some sort of caliper for measuring wire, and since you mention a micrometer I guess that answers my question. But i never heard of a micrometer. Where would I find one? Do people still even use these?