Real-Life Math
Those wishing to become electricians should have a good understanding
of high school algebra and trigonometry.
Then, once you're in
an apprenticeship, you'll learn the other math you need to know for the
job.
One calculation that electricians must deal with
on a daily basis is figuring out the voltage drop that occurs with varying
lengths of wire.
This is critical because if you do not have the correct
length of wire or the correct capacity, you could ruin any equipment that
is plugged into the wiring. In some cases the problem is severe enough to
start a fire in the walls.
Use the following information to calculate
the voltage drop for the 14 AWG.
Will the drop be acceptable?
If
no, try using the 10 AWG numbers and decide if that is the correct size wire
to use.
Conditions:
You have a load of 7 amps at 120
volts.
It is located 200 feet from the power source.
The voltage drop
for a branch circuit is not to exceed 3 percent of the nominal voltage.
3
percent of 120 volts = 3.6 volts.
The circular mil area for 14 AWG is
4,110.
The circular mil area for 10 AWG wire (two sizes larger than 14)
is 10,380.
Vd = voltage drop
I
= current in conductor (amperes)
L = one-way length of circuit (ft)
Cm
= cross section area of conductor (circular mils)
K = resistance in ohms
of one circular mil foot of conductor
K
= 12.9 in this instance.
Equation for two-wire single
phase circuits:
Vd = 2KLI/Cm
or
Cm = 2KLI/Vd