LOW VOLTAGE ELECTRICAL CONNECTIONS - ROOM THERMOSTAT (Optional)
A low voltage (24VAC) room thermostat can be used for room temperature control with the ThermElect
Hydronic system. If so, Steffes recommends using a digital
thermostat. To initiate a heat call, the system needs a switch
closure from R to H. This energizes the primary loop pump
outputs.
12-Position Low Voltage Terminal Block Coding
R
= Low Voltage Hot
O
= Reversing Valve Input
C
= Low Voltage Common
O2 = Reversing Valve Output
Y
= Compressor/Stage 1 Heat Call H
= Hydronic Heat
W = Stage 2 Heat Call
OS = Outdoor Temperature Sensor
Y2 = Compressor Output
SC = Temperature Sensor Common
G = Fan Call
DS = Duct Temperature Sensor
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LOW VOLTAGE ELECTRICAL CONNECTIONS - OUTDOOR TEMPERATURE
SENSOR (Optional)
NOTE:
Theory of Operation:
The outdoor sensor monitors outdoor temperature and provides this in formation
to the system. The system responds by automatically storing heat in its brick core according to outdoor
temperature and the heating requirements.
Location of:
The outdoor sensor must be placed in a location where it can accurately sense outdoor
temperature and is not affected by direct sunlight or other abnormal temperature conditions.
Installation Methods:
The outdoor sensor can be hard-wired to the system’s “OS” and “SC” terminals
(default) or it can be connected to the Power Line Carrier (PLC) transceiver. When using BACnet control for
outdoor temperature, the outdoor sensor will not be used.
Wiring:
• Route low voltage wire from the outdoor sensor to the electrical compartment through one of the low
voltage wire knockouts.
• Connect to “OS” and “SC” as shown in Figure 10.
• If the sensor wiring is routed through an external wall, the opening through which the wire is routed
MUST be sealed. Failure to do so may affect the accuracy of the outdoor temperature sensor.
• The outdoor sensor is supplied with a lead length of 40 ft. If a greater wire length is needed, it can be
extended to a total of 250 ft.
•
No other loads can be controlled or supplied through this cable. It is for connection of the outdoor
sensor ONLY.
• This low voltage cable MUST not enter any line voltage enclosure.
• Unshielded Class II (thermostat) wire can be used as extension wire provided it is segregated from any
line voltage cabling.
• If using BACnet control, the outdoor temperature sensor may or may not be used. Follow the
instructions included with the BACnet Controller.
• Outdoor sensor wire MUST NEVER be combined with other control wiring in a multi-conductor
cable.
LOW VOLTAGE CONNECTIONS
HYDRONIC HEATING
SINGLE ZONE SYSTEM
FIGURE 10
Outdoor Sensor
Hydronic Heat Thermostat, Zone
Valve, End Switch, or Pump Control
SC
H OS
W
O2
O
G
Y Y2
C
R
12 Position Terminal Block
DS
