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M-AP-001-EN Rev. Q
20.6.2 Circuit Grounding
Improper grounding or voltage in circuits connected to the compressor I/O board can lead to
component failures. In particular, the interlock and analog output circuits are sensitive to improperly
connected external circuits (refer to "Figure 20-7 Interlock and Motor Speed Connections").
Prior to connecting the control wiring to the compressor I/O board, check for improper grounding.
Improper grounding can be identified by measuring the voltage between the customer’s negative
terminals and the ground (J1 COM or Modbus shield) terminal on the compressor I/O board (refer
to "Figure 20-7 Interlock and Motor Speed Connections"). If the measured voltage is not zero (0),
determine the source of the voltage. The most likely cause of voltage is insufficient insulation of the
external circuit. In case of uncertainty of the grounding, connect the negative terminals of the external
circuit to a ground and then connect the external ground to the ground on the compressor I/O board.
Figure 20-7 Interlock and Motor Speed Connections
Power ON
Serial #
DEMAND
I/LOCK
STATUS
SPEED LIQDT
Float
Float
RUN
ANALOG
ENTRY LEAVE
SPARE T
SPARE P
OUT
OUT
OUT
OUT
Universal Analog Output +
Universal Analog Output -
Motor Speed Monitor +
Motor Speed Monitor -
Interlock Contact - Safety N/C
Interlock Contact - Safety N/C
IN
IN
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