NIOB Taco SR501 Switching Relay The SR501 is a single-zone switching relay designed to control the operation of a circulator pump in a hydronic heating system. It simplifies wiring and provides a reliable interface between a thermostat and the circulator pump. Features: External Indicator Lights: These lights help diagnose the relay?s functionality. Universal Replaceability: The snap-in PC board allows easy replacement without rewiring. Simplified Wiring: The layout streamlines installation and service work. Sealed Relays: Ensures durability and reliability. Fuse Protected Outputs: Protects against overloads. Contractor Friendly: Designed for ease of use. Universal Thermostat Compatibility: Works with various thermostat models. UL Approved: Meets safety standards. Operation: Connect a thermostat to the ?T T? terminals on the switching relay. When the thermostat calls for heat, the relay is energized, and power is given to the circulator. Power Input: Connect 120V AC power to terminals N and H. Jumper Placement: The factory-installed jumper between terminals H and 3 switches power on terminals 4 (normally open) and 4 (normally closed). Wiring Example: Connect the thermostat as follows: T T: Thermostat connection. COM: Common terminal for 4 (normally open) and 4 (normally closed). W: Boiler operating control. 24VAC: Thermostat output. A resistor (1K?, 1?2 W) may be needed between W and C terminals for digital thermostats to work correctly. Ensure proper wiring to avoid secondary power sources activating the boiler unexpectedly. Specifications: Input Voltage: 120V AC, 60Hz, 1 phase. Maximum Combined Load: 12 amps. Enclosure Dimensions: 4 7/8" (width) x 6 5/8" (height) x 2 3/8" (depth). Circulator Relay Connections: Rated 1/3 hp (6 FLA, 36 LRA) at 120V AC. Thermostat Connection: Supplies a 24VAC class 2 output. Remember, the SR501 is a workhorse in heating systems, ensuring efficient circulation and comfort.