TOPIC: Determining Electrical Service

Not judging!  1979 is a later version so there is no aluminum branch circuitry, at least!  Those are typical FPE attachment screws too!

Carrying around cable samples is a good idea too!

Yeah first thing that caught my eye was the aluminum wiring, which clued me in to see if any branch wiring was aluminum tool.

Cable samples was my instructors idea, until we can gauge it with our eyes.  I went to Lowe's and got short samples for free!

It looks like the panel is in good shape with the exception of that one wire having some indications of heating.  But that looks like it might have been caused from when they stripped the insulation and cut into the wiring.

Whatever the cause, its no bueno.

By Jeff Pope:

In newer services, the service disconnect (main breaker) is the most accurate measurement of the service capacity - 100A, 125A, 150A, 200A and 400A are the most common on modern homes.

The size of the service entrance conductors (SEC) is your first indicator - note: the SEC's should not be confused with the drop or lateral conductors, which are the responsibility of the utility company. The conductor size of the drop or lateral has no correlation on the residential capacity.

When there is no single service disconnect, use a "conductor ampacity" chart to determine the max current for a given conductor size. The SMALLEST conductor between the bus bars and the utility connection point will be your maximum service capacity indicator. The next limiting factor is the panel rating.

Example; The utility is connected to the SEC. The SEC are 2/0 copper (visible entering the mast) with a capacity of 200A.

The SEC entering the panel are 1/0 copper from behind the meter (many times this is not visible), which have a max rating of 175A.

The panel is rated for 200A with a split-bus, requiring six throws for disconnecting all power.

Your maximum service capacity in this example is 175A based on the smallest conductor.

You cannot use the meter rating or the lateral/drop conductors when factoring service capacity.

Hey Billy,

Nice to see you participating on the forum