Franklin 2007 ユーザーズマニュアル

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

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