Xylem Goulds VS Manuel D'utilisation page 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.
1750
#0
1500
1250
1000
750
500
250
0
0
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
Percent Current Unbalance =
Sample Calculation
• Measure current in T1 L1
each leg. T2 L2
T3 L3
• Add leg currents to
determine total
current.
• Calculate average
leg current.
• Determine maximum 51 – 50 = 1
difference of any one 50 – 46 = 4
leg from the average. 53 – 50 = 3
• Calculate percent
unbalance using
50
formula above.
#2 #4
#6
0.5 1 1.5
Maximum Current difference in
any leg from average current
Average Current
1ST HOOK UP
L1
T1
T1 L1 ____________
51 amps
T2 L2 ____________
46 amps
T3 L3 ____________
53 amps
150 amps
÷ 3
50 amps
_____ – _____ = _____ _____ – _____ = ____ _____ – _____ = _____
max _____ – _____ = _____ _____ – _____ = ____ _____ – _____ = _____
➛
_____ – _____ = _____ _____ – _____ = ____ _____ – _____ = _____
4 x 100 = 8%
#8 Cable
2 2.5
Power Cable Ohms
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.
x 100
2ND HOOK UP
L2 L3 L1 L2
T2
T3 T3
T3 L1 _____________
T1 L2 _____________
T2 L3 _____________
÷ 3
x 100 = %
#10 Cable
#12 Cable
#14 Cable
3 3.5 4
3RD HOOK UP
L3 L1 L2
T1 T3
T2 T2
T2 L1 _____________
T3 L2 _____________
T1 L3 _____________
÷ 3
x 100 = % x 100 =
4.5
L3
SUPPLY
STARTER
T1
MOTOR
÷ 3
%
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