Instructions / Assembly
120 VAC INPUT
FOUR ZONE SWITCHING RELAY
120 VAC CIRCULATORS
ZC
INPUT
120 VAC
ZONE 1 ZONE 2 ZONE 3 ZONE 4
ZONE1
ZONE2
ZONE3
THERMOSTATS
SR 504-4
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
XX
RW
RW
RW
RW
ISOLATED
END
SWITCH
THERMOSTATS (24 VAC)
PRIORITY
120 VAC
ZR
HHNHNHNHNH NH
ZONE4
ZONE 2
POWER
ZONE 1
ZONE 3
ZONE 4
LED
INDICATORS
ZONE 4
PRIORITY
OFF
ON
PRIORITY
TO: "TT" ON
BOILER
JUMPER
24 VAC
COM
120 VAC INPUT
FOUR ZONE SWITCHING RELAY
120 VAC CIRCULATORS
ZC
INPUT
120 VAC
ZONE 1 ZONE 2 ZONE 3 ZONE 4
ZONE1
ZONE2
ZONE3
THERMOSTATS
SR 504-4
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
FUSE
6 AMP
XX
RW
RW
RW
RW
ISOLATED
END
SWITCH
THERMOSTATS (24 VAC)
PRIORITY
120 VAC
ZR
H H NH NH NH N H NH
ZONE4
ZONE 2
POWER
ZONE 1
ZONE 3
ZONE 4
LED
INDICATORS
ZONE 4
PRIORITY
OFF
ON
PRIORITY
TO: "ZC"
ON BOILER
TO: "ZR"
ON BOILER
24 VAC
COM
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 4 is switched to the priority setting
and is actuated, all other zones will stop operation until zone 4 is sat-
isfied. When zone 4 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 auto-
reset 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.
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 4 is switched to the priority setting
and is actuated, all other zones will stop operation until zone 4 is sat-
isfied. When zone 4 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 auto-
reset 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 ter-
minal 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.
The Taco Connection:
Combine the reliability of the Taco Zone Valves, Priority Zoning
Circulators, Thermostats, and the “00” family of circulators with the
advanced features of the Taco Zone Controls to achieve total system
integration. No matter the application, Taco now provides the products
to maximize system performance while simplifying both installation
and service.
External Diagnostics:
Externally visible lights show full functionality of the switching relay.
The green light should always be on, indicating that power is connected.
When the thermostat calls for heat, both the appropriate circulator and
red indicating light is energized.
Cold Start Boiler
Application
Tankless Coil Boiler
Application
(Alternative Wiring)
Instruction Sheet
SR504-4 Switching Relay
102-381
SUPERSEDES: New EFFECTIVE: May 1, 2010
Plant ID# 9300-2868
Features:
External Indicator Lights
Switchable Priority
Priority Protection
Simplified Wiring
Sealed Relays
Fuse Protected Outputs
Compact Design
100% Factory Tested
Isolated End Switch
Contractor Friendly PC Board
Layout
Universal Thermostat
Compatibility
UL Approved
24 volt Power Input or Output
Terminal
Extended 3 Year Warranty
Made in the USA
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
SR504-4 4 with Priority 120/60/1 VAC 20 amps 10
3
/4"7" 2
3
/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.
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 thermo-
stat connections, and 14-22 gauge wire for 24 VAC source connections.