Vermont Energy Control Systems

Practical monitoring and control for the real world

Control a Circulator

Control a Circulator | Vermont Energy Control Systems

Vermont Energy Control Systems

Practical monitoring and control for the real world

Control a Circulator


One of the most basic applications of relays is to allow a low voltage signal to control a high voltage load. In this example, a discrete output of the Vesta controller is used to control a 120VAC circulator. We use the RC-4DD (formerly RM-1207) Relay Module which is controlled by the Vesta controller and can switch loads up to 220VAC.

This example shows a circulator, but the same process applies to any high voltage load that needs to be turned on and off by the Vesta, such as fans, lights, valves, or other electrical devices.

Required Items

  • Configured and installed Vesta controller
  • RC-4DD Relay module
  • Code-compliant electrical cable (14-2 w/ground armored cable in this example)
  • Cat5 (Ethernet) cable to connect Vesta and RC-4DD (Blue color preferred)
  • Network-connected computer


In this example, power for the circulator comes from standard 120VAC line voltage. One motor connection from the circulator is connected directly to the 'neutral' wire. The other lead is connected to a normally open contact in the RC-4DD. Finally, the common contact from the same relay contact set is connected to the 'line' wire.

A schematic of the basic circuit for a circulator control

When the Vesta controller energizes the relay, the circuit is completed and power is applied to the circulator.

NOTE: This is only a concept drawing. All wiring must be performed in accordance with applicable codes. Final design is the responsibility of the system designer or installer.

Physical Wiring

Physical wiring follows the schematic above. In this case, we're using relay 1, which is at the bottom right. We're only using one of the two contact sets, and we're connecting to the common (C) and Normally Open (NO) contacts.

A picture of the wiring set up properly

120VAC line in is the cable at top center, and the cable at top right goes to the circulator. The blue Cat5 cable goes to a discrete output connector on the Vesta. In this example we're using the connector labeled ''5-8'.

At this point, physical setup is complete. The next section deals with setting up the Vesta to control the circulator.

Control a Circulator | Vermont Energy Control Systems

Vermont Energy Control Systems

Practical monitoring and control for the real world

Control a Circulator

Setting Up The Vesta Controller

In order to activate the relay with the Vesta, you must configure the Vesta to use the discrete output channel that the relay is connected to. In this example, we'll connect the RC-4DD to Vesta discrete outputs 5-8. That means that relay 1 in the RC-4DD is Vesta discrete output 5, relay 2 is output 6, and so on. We're using relay 1, controlled by discrete output channel 5. The overall process for configuring the Vesta is covered in the User's Guide, but we'll show the steps for this example here.

We'll go to the 'Physical I/O' tab on the Vesta and find the discrete output section. On the line for channel 5, we'll click 'Create Element':

Screenshot of the Physical I/O tab

Next we'll go to the 'Data Elements' tab and rename our discrete output to 'Demo Circulator':

A screenshot of a discrete output being renamed

Eventually we'll have rules to control the circulator, but for now we can test it by going to the control graphical user interface. Click the 'GUI' tab on the Vesta user interface twice:

Screenshot of the GUI tab

Clicking on the button next to 'Demo Circulator' will turn the circulator on and off. If power isn't applied to the circulator yet, you'll still hear the relay click on and off in the RC-4DD.


Finally, we need rules to control the circulator. In this example, we'll turn on the circulator when the boiler outlet temperature goes above 170, and turn it off when the boiler outlet drops below 165. This is accomplished with a differential rule. Details are documented in the rule programming manual, but the rule that we need looks like this:

Screenshot of the rules to control a circulator

The 'deadband' term in this rule will keep the circulator on until the temperature drops 5 degrees below the setpoint. This will prevent the circulator from cycling on and off too frequently when the temperature is fluctuating right around the setpoint of 170.


That's it - you now have a circulator that will turn on and off automatically based on boiler outlet temperature. It can be monitored from anywhere, and the datalogs will allow you to go back and see when and for how long the circulator was active.

You can of course use more complex logic, change setpoints, and add other devices.