The SR504-EXP-4 from Taco is a 4-Zone Expandable Switching Relay with Priority. It  Combines clearly labeled PC board layout with advanced features that allow for total system customization. Taco expandable switching relays allow to expand up to 20 zones, while built-in PowerPort slots allow to utilize the advanced features of the PowerPort Cards and Add-on Power Controls. External indicator lights provide instant diagnostic feedback, making a snap of service calls or new installation start-ups. Taco SR504-EXP expandable switching relay is UL and CSA listed, uses standard “ice cube” replaceable relay and is compatible with conventional and programmable thermostats.
 

Features:

• External Indicator Lights;
• Switchable Priority;
• Simplified Wiring;
• Fully Enclosed Snap-Out Relays;
• Compact Design;
• Fuse Protected;
• 100% Factory Tested;
• Isolated End Switch;
• Contractor Friendly PC Board Layout;
• Universal Thermostat Compatibility;
• UL and CSA Approved;
• 24 Volt Power Input or Output Terminal;
• Extended 3 Year Warranty;
• Made in the USA;

 
Additional Features:

• (3) Plug-in PowerPort Card Slots;
• Add-on Power Control Plug;
• Expandable to 20 Zones;
• Interface with Expandable (-EXP) Taco Zone Valve Controls;

Technical Specs:

• Zones: 4;
• Power: 120VAC;
• Max combined load: 20.0 AMPs;
• Dimensions: 10.25" wide x 6.75" high x 2.75" deep.