MR-04427 SM SERIES PUMPS
TROUBLESHOOTING PAGE B - 3
Be certain to refer to the wiring diagram(s)
in the Installation Section of this manual be
fore reconnecting any electrical compo
nents which have been disconnected.
Test Equipment
A volt/amp/ohmmeter and megohmeter of ade
quate range and quality will be required to conduct
the following electrical tests. The suggested equip
ment indicated below is commercially available, or
an equivalent substitute may be used.
Equipment Use
Ammeter To check AC Voltage
and current (amperage)
Ohmeter To measure resistance
(ohms) to ground
Voltage Imbalance
Each phase of the incoming three‐phase power
must be balanced with the other two as accurately
as a commercial voltmeter will read. If the phases
are balanced, check out the motor as described
below. If the phases are out of balance, contact
your power company and request that they correct
the condition.
a. Use a voltmeter, amprobe, or equivalent me
ter to read the voltage across terminals 1 &
2, 2 & 3, and 1 & 3 in the control box. All three
measured voltages must be the same, as
accurately as the meter will read. If possible,
measure the voltage with the pump off, with
the pump running but out of the water, and
with the pump running in the water at full
load. All the measured voltages at each con
dition must be the same.
b. Use an amprobe or equivalent meter to
measure the current draw of each phase
while the pump is running at full load and at
no load. All three amperage readings must
be the same at each condition, as accurate
ly as the meter will read. Nominal amperage
values are listed in Table 1, but these apply
only when the actual voltage at the site is the
nominal voltage listed.
c. If the voltages are balanced with the pump
off, but are unbalanced when the pump is
running, a thorough check of the power
source, all interconnecting cables, and the
pump motor is required to isolate the defect.
Motor And Motor Power Cable Continuity
To check continuity, zero‐balance the ohmmeter
set at the RX1 scale, and test as follows:
a Disconnect the motor power cable leads
from the control box and connect the test
leads to any two of the three power cable
leads (not to the green ground lead or yellow
ground check lead). If there is a high resis
tance reading on the ohmmeter, there is an
open or broken circuit cause a break in the
power cable or motor windings, or by a bad
connection between the motor and the pow
er cable. Switch one test lead to the third
power lead, and test again.
b. If an open or broken circuit is indicated,
check the power cable for obvious damage,
and replace as necessary (see MAINTE
NANCE AND REPAIR). If there is no appar
ent damage to the motor cable, remove the
terminal housing (see MAINTENANCE
AND REPAIR) and check the continuity of
each power cable lead at the terminal posts.
c. If an open circuit still exists after each lead
(terminal) has been tested and tightened,
then the entire motor power cable must be
replaced. Splicing or other means of repair
are not recommended.
d. If no break is found in the power cable,
check the motor leads for continuity. If the
test reading indicates an open or broken cir
cuit, there is an open circuit in the motor.
NOTE
It is recommended that a pump with a defective mo
tor be returned to Gorman‐Rupp, or to one of the
Gorman‐Rupp authorized Submersible Repair
Centers.
