SR502-4 Switching Relay
Instruction Sheet
102-377
SR502-4 Switching Relay
SUPERSEDES: March 1, 2013
Plant ID# 9300-2866
Cold Start Boiler
TO:
Application:
EFFECTIVE: December 20, 2013
"TT" ON
BOILER
(24 VAC)
See NOTE
X X
24 VAC
R
Tankless Coil Boiler Application:
(Alternative Wiring)
THERMOSTATS
W R
ZONE 2
PRIORITY
W
LED
INDICATORS
COM
TWO ZONE SWITCHING RELAY
(24 VAC)
X X
24 VAC
ON
OFF
ISOLATED ZONE 1 ZONE 2
PRIORITY
END
SWITCH THERMOSTATS
THERMOSTATS
See NOTE
R
W R
W
ISOLATED ZONE 1 ZONE 2
PRIORITY
END
SWITCH THERMOSTATS
COM
TWO ZONE SWITCHING RELAY
POWER
ZONE 2
PRIORITY
ON
OFF
LED
INDICATORS
POWER
ZONE 1
ZONE 1
FUSE
6 AMP
120 VAC
ZC
ZR
H
H
FUSE
6 AMP
FUSE
6 AMP
CIRCULATORS
ZONE2
PRIORITY
N H
N H
ZONE1
FUSE
6 AMP
ZONE 2
120 VAC
INPUT
120 VAC
N
H
ZC
ZR
H
H
FUSE
6 AMP
CIRCULATORS
ZONE2
PRIORITY
N H
N H
ZONE1
TO: "ZC"
ON BOILER
120 VAC INPUT
JUMPER
Power Input: Connect 120 volt ac power input to terminals N and H.
Neutral wire to terminal N. Hot wire to terminal H.
NOTE: Resistor (1KΩ, 1⁄2 W) may be needed
between W and C terminals.
This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device
may not cause harmful interference, and (2) this device must accept any interference received, including interference
that may cause undesired operation.
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 damage. 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.
Specifications:
PRODUCT
NUMBER
NUMBER
OF ZONES
INPUT
VOLTAGE
MAXIMUM
COMBINED LOAD
SR502-4
2 with Priority
120/60/1 VAC
15 amps
TYPE 1 ENCLOSURE
WIDTH
HEIGHT
DEPTH
103/4"
7"
23/4"
All circulator relay connections, including ZC/ZR, are rated 1/3 hp (6 FLA, 36 LRA) at 120 VAC.
End switch connections are rated 24 VAC, 1 amp.
All thermostat connections supply a 24 VAC class 2 output.
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 left or go to
our website: http://www.taco-hvac.com.
INPUT
120 VAC
N
H
120
VAC
TO: "ZR"
ON BOILER
Operation: When any thermostat calls for heat, the appropriate circulator is energized and the isolated end switch (X and X) will start the
boiler.
Priority Operation: When zone 2 is switched to the priority setting
and is actuated, all other zones will stop operation until zone 2 is satisfied. When zone 2 is not switched to priority, all zones will operate
independently.
Priority Protection Operation: When the priority switch is set to ON,
and if the priority zone calls continuously for more than one hour,
power is returned to all the other zones, allowing each zone to function
independently. Once the priority zone is satisfied, the control’s autoreset is activated and the priority zone is again allowed to have priority
for up to one hour starting from when it calls next.
Jumper Placement: The jumper should be placed between terminals
ZC and ZR. Connect the isolated end switch to the aquastat control on
the boiler.
ZONE 2
SR 502-4
SR 502-4
120
VAC
FUSE
6 AMP
120 VAC INPUT
Operation: When any thermostat calls for heat, the boiler is given a
signal to start. The appropriate circulator is energized only when the
boiler temperature is above the set low limit.
Priority Operation: When zone 2 is switched to the priority setting
and is actuated, all other zones will stop operation until zone 2 is satisfied. When zone 2 is not switched to priority, all zones will operate
independently.
Priority Protection Operation: When the priority switch is set to ON,
and if the priority zone calls continuously for more than one hour,
power is returned to all the other zones, allowing each zone to function
independently. Once the priority zone is satisfied, the control’s autoreset is activated and the priority zone is again allowed to have priority
for up to one hour starting from when it calls next.
Jumper Placement: REMOVE the jumper between terminals ZC and
ZR. Connect terminal ZC to ZC on the aquastat control. Connect terminal ZR to ZR on the aquastat control. Confirm polarity is consistent
between boiler aquastat and switching relay.
Power Input: Connect 120 volt ac power input to terminals N and H.
Neutral wire to terminal N. Hot wire to terminal H.
WARNING: When using Alternative Wiring diagram, wiring instructions 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.
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 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.
Two Standard Switching Relays Connected Together (SR502 – SR506)
AQUASTAT ON
DHW HEATER
A
T
TO: "TT" ON BOILER
X X
24 VAC
R
T
W R
T
W R
W
R
W
ZONE 4
PRIORITY
ON
OFF
ISOLATED ZONE 1 ZONE 2 ZONE 3 ZONE 4
END
SWITCH THERMOSTATS (24 VAC) PRIORITY
COM
LED
INDICATORS
FOUR ZONE SWITCHING RELAY
POWER
ZONE 1
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
ZONE 2
FUSE
6 AMP
ZONE 3
ZONE 4
120 VAC 120 VAC CIRCULATORS PRIORITY INPUT
ZC
H
ZR
H
ZONE1 ZONE2 ZONE3 ZONE4
N H N H N H N H
120 VAC
N
H
SR 504-4
120 VAC INPUT
JUMPER
T
T
T
DHW
HEATER
CIRCULATOR
X X
24 VAC
R
W R
W R
W
R
W
ISOLATED ZONE 1 ZONE 2 ZONE 3 ZONE 4
END
SWITCH THERMOSTATS (24 VAC) PRIORITY
COM
ON
OFF
FOUR ZONE SWITCHING RELAY
TO: "TT" ON BOILER
BOILER
ZONE 4
PRIORITY
LED
INDICATORS
POWER
ZONE 1
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
ZONE 2
ZONE 3
ZONE 4
120 VAC 120 VAC CIRCULATORS PRIORITY INPUT
ZC
H
ZR
H
ZONE1 ZONE2 ZONE3 ZONE4
N H N H N H N H
120 VAC
N
H
SR 504-4
H
120 VAC INPUT
JUMPER
Replacement Switching Relay fuses part number: SR6A-001RP
(Manufacture: Littlefuse, Part Number: 229006)
Optional power stealing thermostat resistor part number: SRTR-001RP
(Value: 1000 Ohms, 1/2 watt or higher)
N
OUTPUT
NOT
USED
LIMITED WARRANTY STATEMENT
Taco, Inc. will repair or replace without charge
(at the company’s option) any product or part
which is proven defective under normal use
within three (3) years from the date of start-up or
three (3) years and six (6) months from date of
shipment (whichever occurs first).
In order to obtain service under this warranty, it
is the responsibility of the purchaser to promptly
notify the local Taco stocking distributor or Taco
in writing and promptly deliver the subject product or part, delivery prepaid, to the stocking distributor. For assistance on warranty returns, the
purchaser may either contact the local Taco
stocking distributor or Taco. If the subject product or part contains no defect as covered in this
warranty, the purchaser will be billed for parts
and labor charges in effect at time of factory
examination and repair.
Any Taco product or part not installed or operated in conformity with Taco instructions or which
has been subject to misuse, misapplication, the
addition of petroleum-based fluids or certain
chemical additives to the systems, or other
abuse, will not be covered by this warranty.
If in doubt as to whether a particular substance
is suitable for use with a Taco product or part, or
for any application restrictions, consult the
applicable Taco instruction sheets or contact
Taco at [401-942-8000].
Taco reserves the right to provide replacement
products and parts which are substantially similar in design and functionally equivalent to the
defective product or part. Taco reserves the right
to make changes in details of design, construction, or arrangement of materials of its products
without notification.
TACO OFFERS THIS WARRANTY IN LIEU OF
ALL OTHER EXPRESS WARRANTIES. ANY
WARRANTY IMPLIED BY LAW INCLUDING
WARRANTIES OF MERCHANTABILITY OR FIT-
NESS IS IN EFFECT ONLY FOR THE DURATION
OF THE EXPRESS WARRANTY SET FORTH IN
THE FIRST PARAGRAPH ABOVE.
THE ABOVE WARRANTIES ARE IN LIEU OF ALL
OTHER WARRANTIES, EXPRESS OR STATUTORY, OR ANY OTHER WARRANTY OBLIGATION ON THE PART OF TACO.
TACO WILL NOT BE LIABLE FOR ANY SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES RESULTING FROM THE
USE OF ITS PRODUCTS OR ANY INCIDENTAL
COSTS OF REMOVING OR REPLACING
DEFECTIVE PRODUCTS.
This warranty gives the purchaser specific
rights, and the purchaser may have other rights
which vary from state to state. Some states do
not allow limitations on how long an implied warranty lasts or on the exclusion of incidental or
consequential damages, so these limitations or
exclusions may not apply to you.
Do it Once. Do it Right.®
TACO, INC., 1160 Cranston Street, Cranston, RI 02920 Telephone: (401) 942-8000 FAX: (401) 942-2360.
TACO (Canada), Ltd., 8450 Lawson Road, Unit #3, Milton, Ontario L9T 0J8. Telephone: 905/564-9422. FAX: 905/564-9436.
Visit our web site at: http://www.taco-hvac.com
Printed in USA
Copyright 2013
TACO, Inc.
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