IOMM Starter 13
Control Wiring
Control wiring is required between the starter and the unit for three purposes:
1. Transmit start and stop commands from the unit to the starter.
2. Transmit electrical information concerning motor operation from the starter to the unit
control system.
3. Supply control power from the starter transformer to the unit control panels.
General Practice
Signal wiring refers to wires connected to the control terminals that are low voltage, below
15V.
• Shielded wire is required to prevent electrical noise interference from
causing improper operation or nuisance trips.
• Signal wire should be rated for at least 300V.
• Keep signal wire as far away as possible from control and power wiring.
Control wiring refers to wires connected to the control terminal strip that carry 24V to 220V.
• Use only UL or CSA recognized wire.
• Use copper wire rated for 60/75°C.
Control Power Wiring
Control power wiring for starters covered in this manual is shown on Figure 5 on page
16. Low voltage starters may have additional control wiring as shown on Figure 4 if the
optional full metering package is ordered with the unit.
The control circuit on the McQuay centrifugal packaged chiller is designed for 115-volts.
Control power can be supplied from three different sources:
• If the unit is supplied with a factory-mounted starter, the control circuit power supply
is factory-wired from a transformer located in the starter.
• A free-standing starter furnished by McQuay, or by the customer to McQuay
specifications, will have a control transformer in it and requires field wiring to
terminals in the compressor terminal box.
• Power can be supplied from a separate circuit and fused at 20 amps inductive load.
The control circuit disconnect switch must be tagged to prevent current interruption.
Other than for service work, the switch is to remain on at all times in order to
keep oil heaters operative and prevent refrigerant from diluting in oil.
DANGER
If a separate control power source is used, the following must be done to avoid
severe personal injury or death from electrical shock:
Place a notice on the unit that multiple power sources
are connected to the unit.
Place a notice on the main and control power disconnects that
another source of power to the unit exists.
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