# Estimating Amperage

I was taught to use the lowest capacity device to estimate amperage. For instance, if the panel is rated for 100amps and the meter is rated for 200 amps, then the amperage is 100. Of course, the SE cables have to be considered too. My question is how to determine the amperage of the SE cables and the main disconnect. Typically the main will be labeled but what happens when the main disconnect is not labeled? How do we estimate that?

Mains are generally always labeled or the fuses for the main will have the ratings. WIies will also have marking to show gauge size. Every situation is different.

If you are ever not sure then you should take pics, do homework or disclaim you could not determine the amperage.

As you gain more experience you should be able to visually gauge the wires compared to conductors and cables of a known size.

You need to assess the conductor size and the Main OCPD size. It is possible to have over sized condcutors which would make the service ampacity the smaller of the two or the OCPD size. For most dwellings you could look at NEC {2008} Table 310.15(B)(6) and use that to find the service conductor ampacity.

Based on type of wire and size …

http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_36_sec003.htm

Basically … #4Cu = 100a, #1 Cu = 150A, and 2/0 Cu = 200A. Try some plastic gauges if you dont have a good feel for wire size or cant read any cable markings.

You dont estimate it … it’s just an unknown ya have to deal with sometimes … :shock:

See this link for a good discussion … http://www.inspectapedia.com/electric/ElecAmps.htm