trying to determine the
size of the electrical service,
the primary factor is the
size of the cable coming into
the house. The size can be
determined by measuring the
width of the cable as follows:
60 amp cable is approximately
• 100 amp cable is approximately 15/16"
• 150 amp cable is
• 200 amp cable is
cable will dictate the size of the fuses or breaker
needed to protect it.
Sizing the Fuses or Breakers
The size of the fuse or
breaker is dictated by the
size of the wire as follows: 1. ) 14 gauge wire = 15 amp 2.)
12 gauge wire = 20 amp 3.) 10 gauge wire = 30 amp.
14 gauge wire is normally the smallest wire that
you will find in the service panel. 12 gauge
is a little thicker than 14 gauge, and 10
gauge is thicker than the 12 gauge, and is normally
used for 220 volt circuits.
You may be able to read the wire size on the outer
insulation of the wire or you can buy a wire
gauge from an electric supply store.
How to Determine the Condition
The condition of the old wire depends on the
amount of usage, the age, and the manufacturer.
The concern with the wire is the
insulation around the wire more than the
wire itself. This is because the insulation is
the more vulnerable component.
easiest way to know the condition of the wire
is to bend it where it has not been bent. If
you can bend it 180° and
you do not expose
the conductor, t e wire is very good.
If you expose the conductor, the wire may
still be okay. This will depend on how
much it is exposed and how resilient the
If you cannot bend the wire 90° without
exposing the conductor,
the wire is probably marginal
If the insulation around the wire falls apart when
you bend it, the wire probably needs replacement.
220 Volt Circuits
Almost all residential electrical services are single
phase, which is what you need to make
220 volt circuits. This means there are two
110 volt poles and a ground.
The easiest way to determine if you have a single
phase service would be to look at the weather
head or most head that is bolted to most
houses up at or near the roofline. If you
can see three wires connected, you have a
single phase 220 volt service. If you have underground
service, you will have to remove
the cover panel to determine if you have
single phase or not.