SR 501-4
N H 3 4 4
5
6 6
N/O
N/O
N/C
N/C
COM
COM
120 VAC
INPUT
T T
COM
R W
24
VAC
TO: 120 VAC POWER
CIRCULATOR
TO: ZC
THERMOSTAT
TO: ZR
ONE ZONE
SWITCHING RELAY
FUSE
6 AMP
POWER
ZONE 1
LED
INDICATORS
FUSE
6 AMP
NOTE 1:
Resistor
(1K
Ω
,
1
⁄
2
W)
may be needed
between
W
and
C
terminals.
See
NOTE 1
TACO SR501-4 REPLACEMENT CROSS-REFERENCE
MANUFACTURER
MODEL
CONNECTIONS
Taco
SR501-4
H
N
3
4 NO 4 NC 5
6 NO
6 NC
R/T
W/T C
Argo
AR821
1
2
3
4
5
6
T
AR822
L1 L2 3
4 NO 4 NC 5
6 NO
6 NC
R/T
G/T
C
Colombus
MR10
L1 L2 3
4 NO
4 NC 5
6 NO
6 NC
R/T
G/T
C
Erie
SR100
L1 N
3
4 NO
4 NC 5
6 NO
6 NC
R/T
G/T
C
Honeywell
RA89A
1
2
3
4
T
T
RA832A
1
2
3
4
X
X
T
T
R845A
1
2
3
4
5
6
T
T
White-Rogers
889-189
1
2
3
4
T
T
829-845
1
2
3
4
5
6
T
T
Features:
External Indicator Lights
Universal Replaceability
Snap-in PC Board
Simplified Wiring
Sealed Relays
Fuse Protected Outputs
100% Factory Tested
Contractor Friendly PC Board Layout
Universal Thermostat Compatibility
UL Approved
Extended 3 Year Warranty
Operation:
Connect a thermostat to the “T T” terminals
on the switching relay. When the thermostat
calls for heat, the relay is energized and power
is given to the circulator.
Power Input:
Connect 120 volt ac power to terminals N
and H.
Jumper Placement:
The jumper is factory installed between ter-
minals H and 3 to switch power on terminals
4 n/o and 4 n/c.
Terminal Description:
T & T
Thermostat Connection
COM
Common side of transformer, to power some
setback thermostats
N
Neutral wire of power input
H
Hot wire of power input
3
Common terminal for 4 n/o and 4 n/c
4 n/o
Normally open terminal
4 n/c
Normally closed terminal
6 n/c
Normally closed terminal
6 n/o
Normally open terminal
5
Common terminal for 6 n/o and 6 n/c
Alternative
Wiring:
ONE ZONE
SWITCHING RELAY
SR 501-4
FUSE
6 AMP
POWER
ZONE 1
LED
INDICATORS
FUSE
6 AMP
N H 3 4 4
5
6 6
N/O
N/O
N/C
N/C
COM
COM
120 VAC
INPUT
T T
COM
R W
24
VAC
TO: 120 VAC POWER
CIRCULATOR
JUMPER
TO: TT ON
BOILER
THERMOSTAT
See
NOTE 1
Instruction Sheet
SR501-4 Switching Relay
102-375
SUPERSEDES: March 1, 2013
EFFECTIVE: December 20, 2013
Plant ID# 9300-2865
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
MAXIMUM
TYPE 1 ENCLOSURE
NUMBER
OF ZONES
VOLTAGE
COMBINED LOAD
WIDTH
HEIGHT
DEPTH
SR501-4
1
120/60/1 VAC
12 amps
4
7
/
8
"
6
5
/
8
"
2
3
/
8
"
All circulator relay connections, including ZC/ZR, are rated
1
/
3
hp (6 FLA, 36 LRA) at 120 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. 120 VAC wiring must
have a minimum temperature rating of 75°C. Failure to follow this
instruction can result in personal injury or death and/or property dam-
age. 12-18 gauge wire recommended for 120 VAC connections, 14-22
gauge wire for thermostat connections, and 14-22 gauge wire for 24
VAC source connections.
Typical
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
) termi-
nals of the switching relay. If the thermostat manufacturer does not
supply a resistor, 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.
