15
TABLE C.2 — POWER CABLE RESISTANCE
The values below are for copper conductors. If aluminum conductor drop cable is used, the resistance will be higher
for each foot of cable of the same size. To determine the actual resistance of aluminum drop cable, divide the ohm
readings from this chart by 0.61. This chart shows total resistance of cable from control box to motor and back.
#0
#2
#4
#6
#8 Cable
#10 Cable
#12 Cable
#14 Cable
Pump Setting (feet)
0
0
0.5
1
250
500
750
1000
1250
1500
1750
1.5
2
2.5
3
3.5
4
4.5
Power Cable Ohms
3. CURRENT UNBALANCE TEST:
A. For three phase units, after correct rotation has
been established, check the current in each of the
three motor leads and calculate the current unbal-
ance as explained below. If the current unbalance is
2% or less, leave the leads as connected. If the cur-
rent unbalance is over 2%, current readings should
be checked on each leg using one of three possible
hook-ups indicated in the table below. Roll the
motor leads across the starter in the same direction
to prevent motor rotation reversal. This procedure
is commonly known as "rolling the leads". THE
HOOKUP THAT RESULTS IN THE LOWEST
PERCENT CURRENT UNBALANCE SHOULD
BE USED FOR THE FINAL CONNECTION OF
THE POWER LEADS.
B. Current unbalance is determined by measuring
the amperage of each of the three legs and then
calculating the percent current unbalance using the
formula below. This calculation must be performed
using each of the three hookups shown.
Maximum Current difference in
Percent Current Unbalance =
any leg from average current x 100
Average Current
Sample Calculation
• Measure current in
T1 L1 51 amps T1 L1 ____________
T3 L1 _____________ T2 L1 _____________
each leg.
T2 L2 46 amps T2 L2 ____________
T1 L2 _____________ T3 L2 _____________
T3 L3 53 amps T3 L3 ____________
T2 L3 _____________ T1 L3 _____________
• Add leg currents to
150 amps
determine total
current.
• Calculate average
÷ 3
÷ 3
÷ 3
÷ 3
leg current.
50 amps
• Determine maximum 51 – 50 = 1
_____– _____= _____ _____ – _____ = ____ _____ – _____= _____
difference of any one 50 – 46 = 4
max _____– _____= _____ _____ – _____ = ____ _____ – _____= _____
leg from the average. 53 – 50 = 3
_____– _____= _____ _____ – _____ = ____ _____ – _____= _____
• Calculate percent
4 x 100 = 8%
unbalance using
50
x 100 = %
x 100 = %
x 100 = %
formula above.
1ST HOOK UP
L1
L2
L3
T1
T3
T2
2ND HOOK UP
L1
L2
L3
T3
T2
T1
3RD HOOK UP
L1
L2
L3
T2
T1
T3
SUPPLY
STARTER
MOTOR
➛
