Taco SR502-4 User Manual
Instruction Sheet
SR502-4 Switching Relay
102-377
SUPERSEDES: December 20, 2013
Plant ID# 9300-2866
Cold Start Boiler
Application:
Operation: When any thermostat calls for heat, the appropriate circu-
lator 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.
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, 1⁄2W) 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 INPUT MAXIMUM TYPE 1 ENCLOSURE
NUMBER OF ZONES VOLTAGE COMBINED LOAD WIDTH HEIGHT DEPTH
SR502-4 2 with Priority 120/60/1 VAC 15 amps 121/4" 8" 3"
All circulator relay connections, including ZC/ZR, are rated
End switch connections are rated 24 VAC, 1 amp.
All thermostat connections supply a 24 VAC class 2 output.
1
/3 hp (6 FLA, 36 LRA) at 120 VAC.
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.TacoComfort.com.
EFFECTIVE: January 18, 2017
Tankless Coil Boiler Application:
(Alternative Wiring)
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: REMO
VE 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) 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.
Two Standard Switching Relays Connected Together (SR502 – SR506)
A Taco Family Company
2017
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)
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
FITNESS 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.
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