Taco SR504-EXP-4 User Manual
Instruction Sheet
102-389
SR504-EXP-4 Switching Relay
SUPERSEDES: December 20, 2013 EFFECTIVE: January 18, 2017
Plant ID# 9300-2874
Cold Start Boiler
Application:
Tankless Coil Boiler
Application: (Alternative Wiring)
For Cold Start Boiler Application
Operation: When any thermostat calls for heat, the appropriate circu-
lating pump is energized and the isolated end switch (X and X) will
start the boiler.
For more wiring diagrams, visit www.taco-hvac.com.
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.
For Both Cold Start Boiler Application and Tankless Coil Boiler Application (Alternative Wiring)
Priority Operation: When the priority dip switch is set to ON and the
priority zone is actuated, all other zones will stop operation until priority zone is satisfied. When not switched to priority, all zones will
operate independently.
Mode Operation: When the dip switch is set to NORMAL, the end
switch relay will be energized if any zone is in operation. When the switch
is set to RESET, the end switch relay will only be energized if the priority
zone is in operation, or through the operation of a plug-in reset control.
Primary Pump Operation: When the dip switch is set to OFF, the primary circulating pump output will energize when any zone calls for heat,
except the priority zone. When the dip switch is set to ON, the primary
circulating pump output will energize when any zone calls for heat.
Post Purge Operation: When the dip switch is set to ON, the priority
zone output will stay energized for 2 minutes after its thermostat or
aquastat is satisfied, but not operate the boiler.
Priority Protection Operation: When the dip 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.
Pump Exercise Operation: When the dip switch is set to ON, the
solid state timer cycles all the circulating pumps that are attached to
the Expandable Switching Relay at the selected time interval. The time
interval can be set for the pumps to run for either 30 seconds every 2
weeks or for 4 minutes every 24 hours.
Low Limit (ZC) Operation: When the dip switch is set to ON and the
boiler drops below the set low limit (terminal ZC connected to boiler),
Specifications:
PRODUCT NUMBER INPUT MAXIMUM TYPE 1 ENCLOSURE
NUMBER OF ZONES VOLTAGE COMBINED LOAD WIDTH HEIGHT DEPTH
SR504-EXP-4 4 with Priority 120/60/1 VAC 20 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 Tankless Coil Boiler Application (Alternative Wiring)
Operation: When any thermostat calls for heat, the boiler will be enabled
and appropriate circulating pump is energized when the boiler temperature is above the set low limit and low limit (ZC) dip switch is set to on.
ZC and ZR Terminals: Connect terminal ZC to ZC terminal on the aquastat control. Connect ZR to ZR terminal on the aquastat control. Confirm
polarity is consistent between boiler aquastat and switching relay.
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.
all zone circulating pumps will stop. When the boiler rises above the
set low limit, the zone circulating pumps are allowed to operate.
End Switches (Dry Contacts): The main end switch closes when any
zone thermostat calls for heat and the mode switch is set to NORMAL.
The main end switch also closes when the mode switch is set to RESET
and a PC Series boiler reset power control is calling for heat. The priority
end switch closes only when the priority zone thermostat or aquastat is
calling for heat.
Expansion Connections: Set the expansion switch to MASTER on the
switching relay that has the designated priority zone or is utilizing the
PC Series plug-in option. Set all other daisy chained controls to SLAVE.
Using thermostat wire (18-22 gauge) connect between terminals A, B,
C on the master control to the corresponding A, B, C on the SLAVE
control(s). Controls may be daisy chained up to 20 zoning panels using
any combination of -EXP controls (120 zones if all are 6 zone panels).
Thermostat Input (24 vac):
R Hot side of transformer. Connect to R on thermostat.
W Switched R signal from thermostat. Connect to W on thermostat.
C Common side of transformer. Connect to COM on
thermostat (optional).
NET Network terminals 1 & 2 are tied together for wiring convenience
when using communicating style thermostats (optional).
120 VAC Connections (N is Neutral, H is Hot):
Power Input Connect 120 Volt AC power
Primary Primary Pump (optional)
Zone 1-3 Circulator Zones
Priority Zone 4 Priority Zone (if enabled) or Zone 4
N/C Zone 4 Normally closed terminals for the Priority Zone.
Will deactivate on a Priority Zone call.
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.
SLAVE
ZONE PRIORITY ON
RESET
PRIMARY PUMP FUNCTION ON
P
OST PURGE ON
PRIORITY PROTECTION ON
P
UMP EXERCISE ON
3
0 SEC/2 WK
MASTER
OFF
NORMAL
OFF
O
FF
OFF
O
FF
4
MIN/24 HOUR
L
OW LIMIT (ZC) ON
O
FF
Dip Switch Settings:
A Taco Family Company
2017
his device complies with part 15 of the FCC Rules. Operation is subject to the
T
ollowing two conditions: (1) This device may not cause harmful interference,
f
and (2) this device must accept any interference received, including interfer-
nce that may cause undesired operation.
e
NOTE: Resistor (1KΩ, 1⁄2W) may be needed
between W and C terminals.
2 Expandable Switching Relays Connected Together
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.
8the 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.
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
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
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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