Filter
Top Products
Application – Single-Phase Motors
3 hp, 230 V
Single-Phase Motor
310 ft #6 AWG
(41.3% of allowable cable)
160 ft #10 AWG
(53.3% of allowable cable)
Depending on the installation, any number of
combinations of cable may be used.
For example, in a replacement/upgrade installation, the
well already has 160 feet of buried #10 cable between
the service entrance and the wellhead. A new 3 hp,
230-volt, single-phase motor is being installed to replace
a smaller motor. The question is: Since there is already
160 feet of #10 AWG installed, what size cable is
required in the well with a 3 hp, 230-volt, single-phase
motor setting at 310 feet?
From tables 11 & 11A, a 3 hp motor can use up to 300
feet of #10 AWG cable.
The application has 160 feet of #10 AWG copper
wire installed.
Using the formula below, 160 feet (actual) ÷ 300 feet
(max allowable) is equal to 0.533. This means 53.3%
(0.533 x 100) of the allowable voltage drop or loss, which
is allowed between the service entrance and the motor,
occurs in this wire. This leaves us 46.7% (1.00 - 0.533
= 0.467) of some other wire size to use in the remaining
310 feet “down hole” wire run.
The table shows #8 AWG copper wire is good for 470
feet. Using the formula again, 310 feet (used) ÷ 470 feet
(allowed) = 0.660; adding this to the 0.533 determined
earlier; 0.533 + 0.660 = 1.193. This combination is
greater than 1.00, so the voltage drop will not meet US
National Electrical Code recommendations.
Tables 11 & 11A show #6 AWG copper wire is good
for 750 feet. Using the formula, 310 ÷ 750 = 0.413, and
using these numbers, 0.533 + 0.413 = 0.946, we fi nd this
is less than one and will meet the NEC recommended
voltage drop.
This works for two, three or more combinations of wire
and it does not matter which size wire comes fi rst in
the installation.
EXAMPLE: 3 hp, 230-Volt, Single-Phase Motor
Two or More Different Cable Sizes Can Be Used
FIG. 3
Formula:
+
=
1.00
Actual Length
Max Allowed
Actual Length
Max Allowed
12