Factory Mounted & Wired - McQuay MicroTech Unit Controller Installation And Maintenance Data

FACTORY MOUNTED & WIRED
MicroTech panels are completely factory assembled tested and
mounted on centrifugal chillers. Sensors are located as shown
in Figure 6 and are pre-wired with shielded cable to their ap-
propriate termination. Field wiring connections need only be
made to the terminal strip located on the left side of the con-
trol panel.
The following provides general wiring information of interest
for service, and for those installations where the control panel
will be retrofit to an existing installation.
INTERCONNECTING WIRING
Interconnecting wiring to the MicroTech control panel consists
of:
Sensor wiring to the analog input terminals.
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24 volt wiring to the compressor motor starter (field installed
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if a remote starter is used), and to chilled water and con-
denser water flow switches and interlocks, alarm relay and
external cycling or reset control.
POWER R INTO
Further, care must be exercised in routing these interlock
lines. They must not be sufficiently long to produce a
voltage drop, and they must not be run in conduit with high
voltage lines.
115 volt wiring to the compressor motor starter MCR coil
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circuits, to the control power source, and to condenser
water pump and chilled water pump relay coils. 115 volt
wiring is also required if relays are used to stage cooling
tower fan operation. Two stages of tower control are possi-
ble. (See subsection "Cooling Tower Fan Control").
Communications wiring.
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A typical field wiring diagram is shown (Dwg. No. 706107C-01).
Wire and components used must comply with the following:
1. Sensor wires must be shielded cable and must be ground-
ed only at the MicroTech terminal strip end.
2. 24 volt wiring must be AWG No. 18 or larger depending
upon length of run, and must be installed as NEC Class
I wiring system, but must be run in a separate conduit from
115 volt or higher voltage wiring.
115
3. volt wiring shall be AWG No. 12 or larger size depen-
ding upon length of run. Maximum voltage drop shall be
3%. This maximum voltage drop shall be considered in
conjunction with the length of run in the determination of
wire size. (See McQuay SVT-WS).
Figure 6. Analog Sensor Locations. (See Table 3 for Component Descriptions).
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Page 6 IM 403
interlocks, flow swit-
contacts
be dry
VAC control cir-
AC CONTROL
If the customer will furnish a 0 to 20 milliamp signal to field
connection terminals numbered 1 and 2 in lieu of a 0 to 5
volt AC signal, then a 249 ohm resistor, &lo/o, 1/4 watt must
be connected across terminals 9 and 10 on the TS4 terminal
strip. In addition, the transmitter must be capable of span ad-
justment to permit a final resolution of the peak control signal
for 100% amps display on the MicroTech panel.
a 0 to 7 volt AC signal. If the starter's current transformer and
resistor circuit supplying this voltage is grounded, the ground
must be connected to the side of the control circuit connected
to the terminal 2 in the MicroTech panel Field Connection ter-
minal strip.
to the daughter board, will be disconnected at the daughter
board prior to shipment. A qualified start-up technician, us-
ing an accurate voltmeter, and with interlock contacts closed,
should read the voltage at each socket of the terminal strip
TS1 before reconnecting the terminal strip to the daughter
board. Voltage between each socket and terminal G should
read approximately 24 volts AC. Following this verification,
and with the power disconnected to the panel the TS1 ter-
minal may be connected as shown in Fi'gure 15.
Transmitter wires providing a reset signal based upon
chiller water temperature or motor current should be run
in a separate conduit.
Communications wiring shall be standard insulated
telephone wire, for telephone modem communication. In
all other cases, use shielded twisted pair similar to Belden
#8760. For complex communication and control systems
see the wiring recommendations in other appropriate
publications.
A Hayes or compatible modem with its own 115 volt power
supply is required if phone communication will be used.
Baud rate required is 1200. Communications interface shall
be RS232. If direct, hardwired communication will be us-
ed, a dedicated, shielded twisted wire pair may be extend-
ed to not more than 50 feet. Where hardwired communica-
tions of over 100 feet will be required, an extended range
kit is recommended (McQuay part number 654870B-01).
Miscellaneous chilled water pump, condenser water pump,
cooling tower fan motor control relays and an alarm relay
are normally field supplied. These relays require either 115
volt or 24 volt coil, and are limited to a 25 VA maximum
power consumption, per coil. (See Table 8 and the
schematic wiring diagram).
A 0 to 7 volt AC, to 0 to 4 volt DC signal converter, or 4
to 20 mA, DC load signal is required at the customer fur-
nished starter; or a separate factory mounted signal con-
verter will be supplied if required.
The optional factory supplied signal converter will accept
Terminal strip TS1 used to connect field interlock wiring