Wiring Guide
WIRING DIAGRAMS – ACCESSORIES
14 6-461.1
Wiring Multiple Single Stage Units to a Single Thermostat
DPDT CONTROL
RELAY
(BY OTHERS)
Y
G
R
C
W
W
1-STAGE LOW VOLTAGE
ROOM STAT (NO SWITCHING)
(BY OTHERS)
R
TERMINAL STRIP
ON UNIT HEATER #1
MODELS HD/HDB, HDS/HDC, AND PTS/BTS MODEL PTC
243
687
0
243
687
1
Y
G
R
C
W
TERMINAL STRIP
ON UNIT HEATER #2
243
687
0
243
687
1
W
1-STAGE LOW VOLTAGE
ROOM STAT (NO SWITCHING)
(BY OTHERS)
R
243
687
0
243
687
1
243
687
0
243
687
1
T2
FG
CVT1
T2
FG
CVT1
DPDT CONTROL
RELAY
(BY OTHERS)
DPDT CONTROL
RELAY
(BY OTHERS)
DPDT CONTROL
RELAY
(BY OTHERS)
TERMINAL BOARD
ON UNIT HEATER #1
TERMINAL BOARD
ON UNIT HEATER #2
TO ADDITIONAL
UNIT/RELAY PAIRINGS
(IF APPLICABLE)
TO ADDITIONAL
UNIT/RELAY PAIRINGS
(IF APPLICABLE)
Notes on Wiring Multiple Single Stage Units to a Single Thermostat
When two or more unit heaters are controlled by one thermostat, it is necessary to electrically isolate each unit by using relays. If
relays are not used, feedback in the low voltage circuits can occur. This feedback may cause operational problems, damage the
electrical components in the low voltage circuit, or cause burnout of the low voltage transformers.
The figure above shows that the thermostat, powered from the terminal strip of unit heater #1 (UH-1), energizes the relay coil of the
first relay (RE-1). When the RE-1 coil is energized, the first set of normally open (NO) contacts of that DPDT relay close and
activate the gas controls of UH-1. The second set of normally open (NO) contacts on RE-1 are used to energize the relay coil of
the second relay RE-2, powered through the terminal strip of UH-2. The first set of NO contacts on RE-2 close and activate the
gas controls of UH-2. If a third unit is to be controlled from the same thermostat, a third relay RE-3 coil is wired to the second set
of contacts on RE-2. This procedure is repeated for each additional unit which is to be controlled by the thermostat. Generally,
there should be a quantity of DPDT relays that is one less than the quantity of heaters to be controlled.
Accessory Wiring for Model PTC Units
NOTE:
FOR FIELD WIRED CONDENSATE PUMP AUX SWITCH AND/OR CONDENSATE DRAIN
LINE SAFETY OVERFLOW SWITCH, REMOVE TERMINAL BOARD JUMPERS AS FOLLOWS:
-FOR ONE ACCESSORY, REMOVE "T1" TO "C" JUMPER
-FOR TWO ACCESSORIES, REMOVE "T1" TO "C" & "C" TO "V" JUMPERS
FOR FURTHER INSTRUCTIONS, REFER TO THE LATEST REVISION OF INSTALLATION
INSTRUCTIONS 6-585 FOR THE CONDENSATE PUMP AND/OR 6-586 FOR THE
CONDENSATE DRAIN LINE SAFETY OVERFLOW SWITCH.
TERMINAL BOARD
ON UNIT HEATER
T2
FG
C
V
T1
ACCESSORYACCESSORY
SEE NOTE BELOW
FOR REMOVAL OF
JUMPER BARS