TACO SR502-4 (02) PDF Document

When any thermostat calls for heat, the appropriate circulator is energized and the isolated end switch (X and X) will start the boiler.

When zone 2 is switched to the priority setting and is actuated, all other zones will stop operation until zone 2 is satisfied. When zone 2 is not switched to priority, all zones will operate independently.

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.

The jumper should be placed between terminals ZC and ZR. Connect the isolated end switch to the aquastat control on the boiler.

Connect 120 volt ac power input to terminals N and H. The Neutral wire connects to terminal N, and the Hot wire connects to terminal H.

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.

REMOVE the jumper between terminals ZC and ZR. Connect terminal ZC to ZC on the aquastat control. Connect terminal ZR to ZR on the aquastat control. Confirm polarity is consistent between the boiler aquastat and the switching relay.

When using the 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.

Externally visible lights show the 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 the red indicating light are energized.

Additional Specifications:

• 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.

• 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

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.

Recommended wire gauges:

• 12-18 gauge wire for 120 VAC connections

• 14-22 gauge wire for thermostat connections

• 14-22 gauge wire for 24 VAC source connections

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.