TP-6322 9/04 13Section 3 Scheduled Maintenance
3.2.3 Other Tests
Hazardous voltage.
Will cause severe injury or death.
Only authorized personnel should
open the enclosure.
DANGER
Testing live electrical circuits. Hazardous voltage or
current can cause severe injury or death. Have trained and
qualified personnel take diagnostic m easurements of live
circuits. Use adequately rated test equipment with electrically
insulated probes and follow the instructions of the test
equipment manufacturer when performing voltage tests.
Observe the following precautions when performing voltage
tests: (1) Remove all jewelry. (2) Stand on a dry, approved
electrically insulated mat. (3) Do not touch the enclosure or
components inside the enclosure. (4) Be prepared for the
system to operate automatically.
(600 volts and under)
Every Year
Use a millivolt drop test to help locate high-resistance
contacts in the ATS under a moderate and balanced
load. The objective is to locate a contact that is of
significantly higher-resistance than others. This manual
cannot give an exact value to look for because the value
is a function of the physical condition of the contactor
and the loading of the unit, which is impossible to
predict.
Millivolt Drop Test Procedure
1. Carefully measure the voltage on each phase from
the source lugs to the load lugs when a balanced
load of at least 10% of the switch rating i s
connected to each source. To obtain accurate
readings, keep the meter as far as possible from
current-carrying conductors and the meter leads
as short, direct, and at right angles to
current-carrying conductors as possible. This
minimizes the effect of induced voltages
(transformer effect) in the vicinity of the
current-carrying conductors. The reading may be
erratic because of the small voltage measured,
load fluctuations, and meter circuit contact
resistances, so take several readings to ensure
accuracy. Look for approximately 0.1 mV per
ampere of load current.
2. The highest voltage on a phase should be within
1.5 times the lowest voltage measured on other
phases of the same source. This factor is high
because all lines may not be exactly balanced, the
construction of each c ontactor circuit may be
slightly different, and there may be residual heating
from prior load conditions. If an unusually high
voltage is found, disconnect power, check the
connections and lug torques, and repeat the test. If
the problem cannot be found, replace the contactor
assembly.
Every Three Years
Perform a wire insulation breakdown test.
Wire Insulation Breakdown Test Procedure
1. Disconnect all power sources by opening
upstream circuit breakers or switches to the
transfer switch. Disconnect the load from the
transfer switch by opening circuit breakers or
switches leading from the transfer switch.
Disconnect the contactor wiring harness from the
controller at connector P1. See Figure 4-2.
2. Use a hi-pot tester or meggar to check the
insulation resistance phase-to-phase and
phase-to-neutral, and phase-to-ground if neutral
and ground are isolated. If using a hi-pot tester, the
maximum potential is 500 VAC and the maximum
test time is 1 second. The insulation resistance
must exceed 1.24 MΩ. If the hi-pot tester indicates
wire insulation breakdown or if the measured
resistance is less than the minimum, use an
instrument designed for this purpose to isolate the
leakage current and replace the faulty components
with voltage breakdown. It may require
disconnecting power conductors from the lugs to
isolate the problem. If the power conductors are
disconnected from the lugs, see Section 6.2.2 for
reconnection instructions.
Every Five Years
Check normal and emergency s ource setpoint
calibration according to the procedures in Section 4.9
and 4.10.
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