Specification
Effective: December 8, 2020
Supersedes: December 15, 2006
Submittal Data Information
Job: Engineer:
Contractor:
Rep:
ITEM NO. MODEL NO.
101-052
Switching Relay
2020
Switching Relays
Product Number Transformer Maximum Dimensions of Enclosure
Number of Zones Voltage Combined Load Width Height Depth
SR501 1 Zone 120 VAC Input 12 amps 4-7/8” 6-5/8” 2-3/8”
SR501-HC 1 or 2 Zone 120 VAC Input 20 amps 4-7/8” 6-5/8” 2-3/8”
SR502 2 with Priority 120 VAC Input 15 amps 10-1/4” 7” 2-3/4”
SR503 3 with Priority 120 VAC Input 15 amps 10-1/4” 7” 2-3/4”
SR504 4 with Priority 120 VAC Input 20 amps 10-1/4” 7” 2-3/4”
SR506 6 with Priority
120 VAC Input 20 amps 12-1/4” 8” 3”
Expandable Switching Relays
Product Number PowerPort Power Control Transformer Maximum Dimensions of Enclosure
Number of Zones Slots Plugs Voltage Combined Load Width Height Depth
SR501-EXP 1 Zone 0 1 120 VAC Input 12 amps 4-1/4” 6-5/8” 2-3/8”
SR503-EXP 3 with Priority 3 1 120 VAC Input 15 amps 10-1/4” 7” 2-3/4”
SR504-EXP 4 with Priority 3 1 120 VAC Input 20 amps 10-1/4” 7” 2-3/4”
SR506-EXP 6 with Priority 3 1 120 VAC Input 20 amps 12-1/4” 8” 3”
All circulator relay connections, including ZC/ZR, are rated 1/3 hp, 6 amps at 120 VAC. End switch connections are rated 24 VAC, 1 amp.
All thermostat connections supply a 24 VAC class 2 output. SR501-HC has a single phase motor rating per zone of 3/4 hp (13.8 A) @ 120 VAC
Switching Relays
Taco Switching Relays combine clearly labeled PC board layouts with advanced features that
allow for total system customization. Whether using basic priority switching or the advanced
features of the -EXP controls, the job is made easy. External indicator lights provide instant
diagnostic feedback, making a snap of service calls or new installation start-ups. All switching
relays are UL listed, are compatible with conventional and programmable thermostats.
Taco Expandable Switching Relays
Whether you want to expand up to 120 zones or utilize the advanced features of the Add-on
Power Controls, Taco -EXP controls allow for simple integration of advanced features. Built-in
Post Purge and Pump Exercise functions can optimize the operation of any system.
Features
Front Diagnostic Lights
Switchable Priority
Built-in Priority Protection
Simplified Wiring
Premium Sealed Relays
Compact Design
Fuse Protected
100% Factory Tested
Isolated End Switch
Contractor Friendly PC Board Layout
Universal Thermostat Compatibility
24 Volt Power Output for hard
wired thermostats
Field Replaceable Transformer
UL Approved
Extended 3 Year Warranty
Additional -EXP Features
Add-on Power Control Plug
Built-in; Post Purge and Pump
Exercise Functions
Switchable Primary Circulator Output
Two boiler contacts, utilizes full
functionality of Mod-Con boilers
Expandable to 20 Zoning Panels
(120 zones if all are 6 zone panels)
Interface with -EXP Zone Valve Controls
The Taco Connection
Combine the reliability of the
Taco Zone Valves, Priority Zoning Circulators,
Thermostats, and the 00® family of circula-
tors 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
It’s no longer necessary to open the box
to troubleshoot the system. 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.
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
X X R W R W R W R W
ISOLATED
END
SWITCH
THERMOSTATS (24 VAC)
PRIORITY
120 VAC
ZR
H H N H N H N H N H N H
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
X X R W R W R W R W
ISOLATED
END
SWITCH
THERMOSTATS (24 VAC)
PRIORITY
120 VAC
ZR
H H N H N H N H N H N H
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
Cold Start Boiler
Application
Tankless Coil Boiler
Application
(Alternative Wiring)
Wiring Diagram
Add-on Power Controls*
PC700 Boiler Reset Control
PC702 Two Stage Boiler Reset Control
PC705 Variable Speed Pump Injection Mixing Control
*For use with -EXP controls.