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PAGE 24 — ST4125G/ST6125G SUBMERSIBLE PUMP • OPERATION MANUAL — REV. #0 (11/18/10)
MAINTENANCE
Electrical Insulation Testing
Why perform electrical insulation testing?
Electrical insulation starts to age as soon as it is made.
Harsh environments, especially those with extreme
temperature changes and/or chemical contamination,
cause further deterioration of the insulation (power cord).
As a result, personnel safety (electrocution/shock) and
power reliability can suffer resulting in higher operating
cost and maintenance.
What is Insulation Resistance Testing
Insulation resistance testing applies a regulated stabilized
high voltage (Figure 20), typically 500 VDC or greater
across a dielectric (power cord). Measuring the amount of
leakage current fl owing through the dielectric will yield a
resistive measurement in megohms.
Insulating Material Testing
To verify the integrity of the pump's insulating material
(power cable) it will be necessary to perform an electrical
insulation test. Any electrical insulation must have the
opposite characteristic as the conductor: it should resist
the fl ow of current, keeping it within the conductor.
To measure the IR (current x resistance), the use of an IR
tester must be employed. This IR tester is a portable device
that is a resistance meter (ohmmeter) with a built in DC
generator that develops a high DC voltage.
The high DC voltage from the IR tester is usually 500 VDC
or more. This voltage, when applied causes a small current
to fl ow through and over the insulation's surfaces. The tester
provides a direct reading of IR in megohms.
A high resistance reading would indicate a "good"
insulation, meaning very little current is escaping through
the insulation. While a relatively low resistance reading
would indicate a poor insulation, meaning a signifi cant
amount of current may be leaking through and along the
insulation.
Figure 20. Insulation Tester Application
NOTICE
Insulation resistance is moisture and temperature
sensitive. When temperature increases, insulation
resistance decreases, and vice versa.
When performing this test measurement, perform the
test using the same test parameters as used in the
initial testing. Contact an authorized Multiquip service
center if the measured cable insulation is 10 megohms
or less.
V
OFF
20M
MEGGER™
SET
UP
MW
W
KW
W
W
GROUND WIRE
(GREEN)
POWER CABLE
INSULATION
500 VDC INSULATION
TEST METER
SUBMERSIBLE
PUMP
DANGER
Read and follow the manufacturer's user's
manual prior to operating insulation tester
(megaohm meter). This meter generates
a test voltage of 500 volts or greater. Only
qualifi ed and trained personnel should
use this equipment. The possibility exists of severe
electrical shock, electrocution even death, when
using insulation tester.