Table of Contents
Advertisement
5.12 Field testing of the
circuit breakers
A test can be performed using the procedure
outlined in the following discussion to verify that
a circuit breaker trip mechanism is functioning.
1. Wire the three circuit breaker poles in series.
2. Connect the series combination of breaker poles to
a variable low voltage high current power source.
3. Gradually increase the current from "0" until the
circuit breaker trips. If the circuit breaker fails to
trip when the test current reaches 150% of
the largest trip setting, the trip unit is not
functioning properly and the circuit breaker
requires replacement.
5.13 Overload relay
For proper overload relay coordination, the cables
on the load side of the overload relay should be sized
in accordance with the tables in Article 310 of the
National Electrical Code. The wire for motors with
full load currents of 100 amperes or less may be
selected from the 60 °C or 75 °C column. Select wire
from the 75 °C column when the motor current is
greater than 100 amperes. When conditions dictate
the use of cables larger than these, the relay tripping
time may be affected. Another condition which may
affect tripping is a long acceleration time such as
that caused by a motor driving a high inertia load.
If either of these conditions exists, consult Siemens
for overload relay application instructions.
tiastar™ Motor Control Centers Instruction Manual Maintenance
41
Advertisement
Table of Contents
