# How to Wire This Latching Relay

I am looking to switch a water solenoid valve using two water level switches, one will be placed at the top of a tank and will be NO (when water level is between full and empty) so that it will send a signal to the relay when the water reaches the top to stop the solenoid. The other switch will be at the bottom of the tank and will be NC so that it will send a signal to the relay when the water reaches the bottom of the tank to open the solenoid.

The switching will be done with a latching relay. The diagram of its pins is here:

I simply do not understand this enough to figure out how to wire this. The switches are SPST. The switches, solenoid valve, and relay are good for 120V.

What I am asking for is this: on that diagram, where do the switches connect? Where does the solenoid valve connect? Where does mains power connect? Lastly, do I need any resistors on the control side of the circuit?

I don't believe your application can be solved with the components you mention. Either you need switches that give a single pulse or a non-latching relay. My proposed solution is with a regular non-latching relay (and thus pin numbers may be wrong).

If the relay is rated for 120V, then my first attempt would look like this. The below is with a non-latching relay though.

simulate this circuit – Schematic created using CircuitLab

• I don't think this will do what the guy wants Commented Mar 19, 2013 at 8:25
• Thanks for the answer, however, I have confirmed that the signals need not be only a pulse. The latching relay will stay latched even if the signal remains on, goes off, and even comes back on. Commented Mar 19, 2013 at 13:19

simulate this circuit – Schematic created using CircuitLab

I think this will work. The stop switch (high water level) is trying to apply power to turn the relay on because it is a NC switch. If the start switch (low water level) is operated then power is fully applied to the relay and the start switch is bypassed by one of the relay contacts and this keeps the relay on. This operates the solenoid and it starts "pumping" water. When the top water level is reached the stop switch disables the relay and the system is reset until water level is low enough to close the start switch again. BTW the schematic editor is really coooool

• Thanks for the answer. I'll wrap my head around this and see if I can get it to work. Commented Mar 19, 2013 at 13:18
• @Andy aka You said once the start switch is operated and power is applied through the coil and one of the relay contacts, that the switch is bypassed. Does this mean that if the start switch is opened the relay will still remain activated (possibly from the power that was supplied through the relay contact?) ? Commented Aug 16, 2014 at 21:30
• @user2755399 yes it does Commented Aug 17, 2014 at 10:59

Power neutral connects to A and to one side of your solenoid. One switch connects to B. The other switch connects to 8. Power hot connects to either 11 or 21, your choice, and to the other terminal on each of the switches. The second solenoid wire connects to either 14 (if hot is on 11) or 24 (if hot is on 21), your choice.

There should be no requirement for any resistors, provided that the relay can tolerate 120V, 100% duty cycle, on its two actuating terminals.