Features:
External Indicator Lights
Simplified Wiring
Sealed Relays
100% Factory Tested
Contractor Friendly PC Board
Layout
Universal Thermostat Compatibility
UL Approved
Extended 3 Year Warranty
120 VAC Application:
1 zone switching relay with boiler
enable or 2 zone without boiler
enable.
240 VAC Application:
1 zone switching relay when switch-
ing both of the circulator
hot leads (L1 & L2).
Operation:
Connect a thermostat to the R & W1
and/or W2 terminals on the switching
relay. When the thermostat(s) call for
heat, the relays are energized and
power is given to the circulator(s).
Zone Control Power Input:
Connect 120 volt AC power input to terminals N and H.
Neutral wire to terminal N. Hot wire to terminal H.
External Diagnostics:
The external lights show full functionality of the switching
relay. The green light should always be on, indicating that
power is connected. When either thermostat calls for heat, both
the appropriate relay and red indicating light are energized.
Terminal Description:
R
Hot side of transformer. Connect to R on thermostat.
W1
Switched R signal from thermostat #1. Connect to
W on thermostat.
W2
Switched R signal from thermostat #2. Connect to
W on thermostat.
C
Common side of transformer. Connect to COM
on thermostat (optional).
N
Neutral wire of power input.
H
Hot wire of power input.
X1
Dry contacts for relay 1 (W1).
X1
Dry contacts for relay 1 (W1).
X2
Dry contacts for relay 2 (W2).
X2
Dry contacts for relay 2 (W2).
ONE ZONE HC
SWITCHING RELAY
SR 501-HC-4
LED
INDICATORS
R
W1
24 VAC
THERMOSTAT
W2
COM
24
VAC
T T T
N H
X1
RELAY 2
RELAY 1
120 VAC
INPUT
120 VAC
CIRCULATOR
X1 X2 X2
N
ZR
ZC
H
POWER INPUT
(120 VAC)
POWER
RELAY 1
RELAY 2
See
NOTE 1
NOTE 1:
Resistor
(1K
Ω
,
1
⁄
2
W)
may be needed
between
W
and
C
terminals.
ONE ZONE HC
SWITCHING RELAY
SR 501-HC-4
LED
INDICATORS
R
W1
24 VAC
THERMOSTAT
W2
COM
24
VAC
T T T
N H
X1
RELAY 2
RELAY 1
120 VAC
INPUT
POWER
INPUT
(120 VAC)
120 VAC
CIRCULATOR
X1 X2 X2
N
H
BOILER
CONTROL
POWER
RELAY 1
RELAY 2
See
NOTE 1
Instruction Sheet
SR501-HC-4 Switching Relay, High Current Capacity
102-418
SUPERSEDES: March 1, 2013
EFFECTIVE: December 20, 2013
Plant ID# 9300-2795
NOTE 2:
When using Alternative Wiring diagram, the boiler operating
control’s ZC terminal will see the load of the circulator(s).
WARNING:
When using Alternative Wiring diagram, wiring instruc-
tions must be followed so power originates from the boiler aquastat.
Failure to follow these wiring instructions may result in a secondary
source of power being connected to the boiler that may activate it
under certain circumstances, causing injury or death.
Specifications:
PRODUCT
NUMBER
INPUT
TYPE 1 ENCLOSURE
NUMBER
OF ZONES
VOLTAGE
WIDTH
HEIGHT
DEPTH
SR501-HC-4
1 or 2
120/60/1 VAC, 90 mA
4
7
/
8
"
6
5
/
8
"
2
3
/
8
"
RELAY RATING:
3
/
4
HP (13.8 FLA, 82.8 LRA at 120 VAC) (6.9 FLA, 41.4 LRA at 240 VAC)
The thermostat connection supplies a 24 VAC class 2 output.
WARNING:
Wiring connections must be made in accordance with all
applicable electrical codes. Use copper wire only. Failure to follow this
instruction can result in personal injury or death and/or property
damage. 12-18 gauge wire recommended for 120/240 VAC connec-
tions, 14-22 gauge wire for thermostat connections, and 14-22 gauge
wire for 24 VAC source connections.
Typical
Wiring:
Alternative
Wiring:
This device complies with part 15 of the FCC Rules. Operation is subject to the following two con-
ditions: (1) This device may not cause harmful interference, and (2) this device must accept any
interference received, including interference that may cause undesired operation.
Troubleshooting:
• Problem:
Digital thermostats do not work correctly when
connected to a switching relay.
• Solution:
Some thermostats are a “Power Stealing” type which
means they are powered by the switching relay with just 2
wires (
R
&
W
). A resistor may be needed in order to have the
thermostat work properly. This resistor should be placed
between the
W
&
C
(
common
) terminals of the switching
relay. If the thermostat manufacturer does not supply a resis-
tor, a 1000 ohm ½ watt resistor has proven to work with most
models and is readily available at electronic supply outlets (e.g.
Radio Shack). If the thermostat is battery powered, then check
that the batteries are fresh and installed correctly.
• Problem:
No heat in a zone or room of building.
• Solution:
LED diagnostic lights will help find a component
that is not working properly. The green LED should always be
on, indicating that power is connected and the solid-state fuse
is good. When there is a call for heat, the red LED will come
on indicating power to the zone circulator. This indicates the
thermostat is working correctly. If the red LED does not come
on, then check the thermostat and thermostat wiring for
errors.
For information on Taco’s Switching Relays (SR)
including catalog sheet, instruction sheets, Visio
stencils and our highly praised Zone Controls
Wiring Guide, scan the QR code to the right or
go to our website: http://www.taco-hvac.com.
