Berkeley 6S Series, Owner'S Manual, Page: 5 / 12

Current unbalance test (3 Phase only)
Determine current unbalance by measuring current in
each power lead. Measure current for all three possible
hookups. Use example and worksheet (Page 5) to
calculate current unbalance on a three phase supply
system and retain for future reference.
NOTICE: Current unbalance should not exceed 5%. If
unbalance cannot be corrected by rolling leads, locate
and correct source of unbalance.
If, on all three possible hookups, the reading furthest from
average stays on the same power lead, most of the
unbalance is coming from the power source.
However, if the reading furthest from average changes
leads as the hookup changes (that is, stays with a
particular motor lead), most of the unbalance is on the
"motor side" of the starter. In this case, consider a
damaged cable, leaking splice, poor connection, or faulty
motor winding.
3-Phase Current Unbalance - Example
Here is an example of current readings at maximum
pump loads on each leg of a three wire hookup. Make
calculations for all three possible hookups.
A. For each hookup, add the readings for the three legs:
Ex.: Hookup #1 Hookup #2: Hookup #3
L1 = 51Amps L1 = 50 Amps L1 = 50 Amps
L2 = 46 Amps L2 = 48 Amps L2 = 49 Amps
L3 = 53 Amps L3 = 52 Amps L3 = 51 Amps
Total 150 Amps Total 150 Amps Total 150 Amps
B. Divide each total by three to get average amps:
Example: 150/3 = 50
Example: 150/3 = 50
Example: 150/3 = 50
C. For each hookup, find current value farthest from
average (Calculate the greatest current difference
from the average).
Ex. #1 Ex. #2 Ex. #3
50 Amps 50 Amps 50 Amps
–46 Amps –48 Amps –49 Amps
= 4 Amps = 2 Amps = 1 Amps
D. Divide this difference by the average and multiply by
100 to obtain the percentage of unbalance. Example:
Ex. 1: 4/50 = .08 x 100 = 8%
Ex. 2: 2/50 = .04 x 100 = 4%
Ex. 3: 1/50 = .02 x 100 = 2%
Use smallest percentage unbalance, in this case Ex. 3.
3-Phase Current Unbalance - Worksheet
Use this worksheet to calculate curent unbalance for your
installation.
A. Add the readings for the three legs:
Ex.: Hookup #1 Hookup #2: Hookup #3
L1 = Amps L1 = Amps L1 = Amps
L2 = Amps L2 = Amps L2 = Amps
L3 = Amps L3 = Amps L3 = Amps
Total Amps Total Amps Total Amps
B. Divide each total by three to get average amps:
Hookup #1: /3 =
Hookup #2: /3 =
Hookup #3: /3 =
C. For each hookup, find current value farthest from
average (Calculate the greatest current difference
from the average).
Hookup #1 Hookup #2 Hookup #3
Amps Amps Amps
Amps Amps Amps
Amps Amps Amps
D. Divide this difference by the average to obtain the
percentage of unbalance:
Hookup #1: / = x100 = %
Hookup #2: / = x100 = %
Hookup #3: / = x100 = %
Use hookup with smallest percentage unbalance.
5
Current Unbalance Example and Worksheet