10 OM Centrif Micro ΙΙ-5
Field Wiring Diagram
NOTES for Following Wiring Diagram
1. Compressor motor starters are either factory mounted and wired, or shipped separate for
field mounting and wiring. If provided by others, starters must comply with McQuay
specification 7359999 Rev 29 available on mcquay.com. All line and load side power
conductors must be copper.
2. If starters are freestanding, then field wiring between the starter and the control panel is
required. Minimum wire size for 115 Vac is 12 GA for a maximum length of 50 feet. If
greater than 50 feet, refer to McQuay for recommended wire size minimum. Wire size for 24
Vac is 18 GA. All wiring to be installed as NEC Class 1 wiring system. All 24 Vac wiring must
be run in separate conduit from 115 Vac wiring. Main power wiring between starter and
motor terminal is factory-installed when units are supplied with unit-mounted starters. Wiring
of free-standing starter must be wired in accordance with NEC and connection to compressor
motor terminals must be made with copper wire and copper lugs only.
3. For optional sensor wiring, see unit control diagram. It is recommended that dc wires be run
separately from 115 Vac wiring.
4. Customer furnished 24 or 120 Vac power for alarm relay coil can be connected between
UTB1 terminals 84 power and 51 neutral of the control panel. For normally open contacts,
wire between 82 & 81. For normally closed contacts, wire between 83 & 81. The alarm is
operator programmable. The maximum rating of the alarm relay coil is 25 VA.
5. Remote on/off control of unit can be accomplished by installing a set of dry contacts between
terminals 70 and 54.
6. Evaporator and condenser paddle type flow switches or water pressure differential switches
are required and must be wired as shown. WDC dual compressor units require DPDT
switches. If field supplied pressure differential switches are used then these must be
installed across the vessel and not the pump.
7. Customer supplied 115 Vac, 20 amp power for optional evaporator and condenser water
pump control power and tower fans is supplied to unit control terminals (UTBI) 85 power / 86
neutral, PE equipment ground.
8. Optional customer supplied 115 Vac, 25 VA maximum coil rated chilled water pump relay (EP
1 & 2) can be wired as shown. This option will cycle the chilled water pump in response to
building load.
9. The condenser water pump must cycle with the unit. A customer supplied 115 Vac 25 VA
maximum coil rated condenser water pump relay (CP1 & 2) is to be wired as shown.
10. Optional customer supplied 115 Vac, 25 VA maximum coil rated cooling tower fan relays (CL -
C4) can be wired as shown. This option will cycle the cooling tower fans in order to maintain
unit head pressure.
11. Auxiliary 24 Vac rated contacts in both the chilled water and condenser water pump starters
must be wired as shown.
12. For VFD, Wye-Delta, and solid state starters connected to six (6) terminal motors. The
conductors between the starter and motor carry phase current and selection shall be based
on 58 percent of the motor rated load amperes (RLA). Wiring of free-standing starter must be
in accordance with the NEC and connection to the compressor motor terminals shall be
made with copper wire and copper lugs only. Main power wiring between the starter and
motor terminals is factory-installed when chillers are supplied with unit-mounted starters.
13. Optional Protocol Selectability BAS interfaces. The locations and interconnection
requirements for the various standard protocols are found in their respective installation
manuals, obtainable from the local McQuay sales office and also shipped with each unit:
Modbus IM 743 LONWORKS IM 735 BACnet IM 906
14. The “Full Metering” or “Amps Only Metering” option will require some field wiring when free-
standing starters are used. Wiring will depend on chiller and starter type. Consult the local
McQuay sales office for information on specific selections.
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