Figure 29: Vfd Terminal Strip; Table 3: Modulating Thermostat Cable Requirements - Roberts Gorden CoRayVac CRV-B-2 Installation, Operation & Service Manual

12.3.4 Cable Requirement
Table 3, on Page 51, lists wiring types, sizes and
distances for modulating thermostat communication.
Power Requirement
Programmable thermostats requires 24 volt, AC
power.

Table 3: Modulating Thermostat Cable Requirements

Wire Function
Digital Outputs
Modulating Outputs
Outdoor Air Temperature Sensor 18 AWG (0.75 sq mm)
Remote Sensor
Power Wiring
LonWorks ® (P/N 90424104 only) 18 AWG
MS/TP (P/N 90425109)
12.3.5 Sequence of Operation
Depending on the space temperature, the thermostat
will control the heat output based on demand signal
communicated from the thermostat program. The
thermostat will close contact on the transformer relay
(P/N 90417600K). The VFD run command is
energized by the transformer relay. When the VFD
energizes the pump and the vacuum has been
established, the pressure switch will close and
energize the burners. At high heat, a demand signal
will turn the pump speed to a maximum frequency
and burner(s) ON at maximum firing rate. As the
space temperature gets closer to the set point, the
thermostat program will slow the pump speed and
burner(s) firing rate down until the room temperature
reaches the thermostat set point.
NOTE:
To obtain Analog 0-10VDC signal, connect as shown
on Page 61, Figure 39 and set standard speed
source (parameter 05 inside VFD menu) to 03.
12.3.6 Analog Signal
An Analog Signal 2-10 Vdc (with 500 ohm resistor) or
4-20 mA output from a modulating thermostat
controls the ROBERTS GORDON
supplies a variable frequency output signal to the
pump that will vary based on the signal from the
modulating thermostat.
The ROBERTS GORDON
modulating thermostat wiring diagram is shown on
Page 59, Figure 37. When the temperature falls
below the setpoint, the modulating thermostat will
Recommended Wire Size
(Minimum)
18 AWG (0.75 sq mm)
18 AWG (0.75 sq mm)
18 to 22 AWG
(0.75 to 0.34 sq mm)
18 to 14 AWG
( 0.75to 2.0 sq mm)
(0.75 sq mm) nonshielded
18 AWG (0.75 sq mm) Shield
® VFD. The VFD
® ®
CORAYVAC with
Specification or
Requirement
Standard thermostat wire
1 pair
1 pair
Twisted pair wire
NEC Class II 140ºF (60°C )
1 pair
Belden cable #82760 or equivalent Refer to Thermostat Installation Guide
generate a demand signal to the VFD. The VFD will
output a signal to the pump to run at the desired
heater(s) firing rate. There are two means to set up
the analog signal from the modulating thermostat to
the VFD (See Page 51, Figure 29):
1. To obtain 4-20 mA signal, connect as shown on
Page 60, Figure 38 and set standard speed
source (parameter 05 inside VFD menu) to 04.
2. To obtain 2-10 Vdc (with 500 ohm resistor)
signal, connect as shown on Page 59, Figure 37
and set standard speed source (parameter 05
inside VFD menu) to 03.

FIGURE 29: VFD Terminal Strip

As the pump receives the analog signal from the
VFD, the heater(s) modulate to the corresponding
firing rate. As sensed air temperature rises closer to
SECTION 12: C M
ONTROL
Distance (Maximum)
1000 ft (304 m)
500 ft (152 m)
500 ft (152 m)
1000 ft (304 m)
Limited by line-loss effects on power
consumption.
Refer to E-bus Wiring Guide 74-2865
for maximum length and generic cable
specifications.
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