Expert: Tony Serwatuk - CID CIC CLIA - 4/23/2008

Question
Will a Rainbird ESP6 controller turn a pump off and on? It has an MV spot to hook to but how would I do this.

Answer
Hello Robert

The Rain Bird controller you mention will indeed turn a pump off and on as required via the MV terminal through a unit known as a Pump Start Relay.  In a nutshell, there are two different voltages that are part of this scenario.  First thing to understand is the RB controller only has the ability to send 24 volts through the MV (master valve) terminal. A residential pump typically requires 110 volts to operate (.5 HP - 1 HP), so the controller doesn't have the ability to operate the pump by itself.  

This is where the relay switch comes into play.  Like it's name implies, the switch turns the pump power on and off through the 24 v signal it receives from the MV terminal of your controller, much like you supply power to a light bulb when you flip a switch in your house.

The switch typically has 4 high voltage leads for the pump & power (two for the load and two for the pump)supply and 2 low voltage leads for the controller supply (1 for the 24v and 1 for the common).  You must supply the appropriate power for the pump to operate once the relay switch receives the 24 v signal from the controller.  Standard 18 gauge irrigation wire from the controller to the relay switch is all that's required.  Rain Bird has a unit called a Pump Start Relay which can receive the signal from the controller and activate the pump.  The required pump power is usually supplied from an appropriate source, either hard wired from the relay switch directly to a circuit panel with a breaker or through a pig-tail plugged into a standard 110 v outlet.(Product ID: RELAY-100 for pumps up to 1.5 HP/110- 240 v and the R-200 to operate pumps up to 5 HP).  Visit the following link to get more information on the relay switch:

http://www.rainbird.com/landscape/products/controllers/pumpstart_relays.htm

There is a potential set back when using a MV terminal to operate a pump, and that is if there are any zones in your irrigation system that don't require help from the pump, there's no way to regulate or control when the pump comes on - it simply comes on when a zone is scheduled to come on and there's a call for irrigation.  If you need more control over the pump operation then you have to upgrade your controller to something like the Hunter Pro C which allows you to designate which zones need the pump and which ones don't.

I hope this helps.

Regards
Tony