Installation, Operation and Maintenance 3 - 7
Figure 18
Solid State Starter Connections
Note that even a Solid State Starter with its triacs “in
the line” represent a similar hazard. Should a person
contact any of the motor terminals, even with the
motor off, the triac “off-state” leakage and finite
snubber impedance would be enough to cause a
severe, even fatal, electrical shock. In the case of the
“in the phase” starter, the currents available could be
quite high, as little or no impedence would be in
series with the voltage source.
Figure 19
Caution label on starters panels equipped with solid-state
starters
WARNING
Contacting any of the motor termi-
nals, even with the motor off can
cause a severe, potentially fatal,
shock.
IMPORTANT! WHEN EVACUATING THE
CHILLER’S REFRIGERANT SYSTEM, ALWAYS
HAVE THE MAIN POWER DISCONNECT/CIRCUIT
BREAKER OPENED.
EVEN WHEN THE COMPRESSOR IS NOT
RUNNING, VOLTAGE IS PRESENT AT THE
COMPRESSOR MOTOR TERMINALS,
PROVIDING THE POTENTIAL FOR CURRENT TO
FLOW THROUGH A LOW IMPEDANCE PATH.
As the chiller is evacuated below atmospheric
pressure, the dielectric strength (resistance to arcing)
of the gaseous atmosphere is significantly reduced.
Because the SCRs are connected “inside the delta,”
three of the motor terminals are connected directly to
the line voltage. An “arc over” can occur between
motor terminals under conditions seen in the
evacuation process. If this occurs the circuit breaker
(or other external protective devices) will trip in
response to high fault currents, and motor damage
may also occur. This can be avoided through being
certain that the chiller is
fully disconnected from all
power sources before beginning pumpdown or
evacuation procedures
, as well as guaranteeing
that the disconnect cannot be accidentally closed
while the chiller is in a vacuum.
T6
T1
T4T2T5
T3
Bypass
Contactor
Shunt Trip Circuit
Breaker\Disconnect
Triac "In
the Phase"
L1
L2
L3
Line
Phase
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