I have a question regarding a relay based water pump setup which is triggered by a float sensor in the water tank.

As you can see in the figure, I have two relays which are single phase AC. Both relays are RM22LG11MR Schneider.

Data sheet are hereSchneider electric

Numbers 11, 12, 14, A1 and A2 are based on European EN50005 relay terminology as indicated here. Though there is not much info

The actual setup is like this that as soon as water level in the water tank (not shown in the figure) falls down, the float sensor activates relay 1 via the "Min" connection. Note that relay 1 is in "Fill" mode

The "12" pin from Relay 1 charges the relay 2. But Relay 2 only activates the waterpump when the water level in the pump is above E2.

The connection 14 of Relay 2 is directly connected to the power cable of the waterpump.

Later if the water in the pump falls below E1, the pump stops pumping water in the tank.

As relays are AC, A1 and A2 can be swapped, and hence A1 is connected to main power supply.

But i am not sure what is the difference between 11, 12 and 14 in this case, and if the connections in the figure fit the purpose. Any help would be appreciated. Thanksenter image description here

  • \$\begingroup\$ From the EN50005 link you provided, terminal 11 is Common, 12 is Normally Closed (NC) and 14 is Normally Open (NO). \$\endgroup\$ Commented Dec 18, 2020 at 21:36
  • \$\begingroup\$ Edited to show that Relay 1 is in Fill mode, and updated the figure with the "water tank" \$\endgroup\$
    – Mark Jeep
    Commented Dec 21, 2020 at 7:46

1 Answer 1


The two key diagrams from the datasheet are the timing diagram

timing diagram

and the wiring diagram.

wiring diagram

Note the timing diagram shows two relays, but the device only contains one. The one that takes effect is selected by a dial on the front of the device.

It's not shown very clearly in the wiring diagram, but as you indicated, A1, A2, 11, 12 and 14 are standard relay terminology with the following meaning:

  • A1: coil contact
  • A2: other coil contact. Supply AC power across A1 and A2 to energise the coil.
  • 11: relay common
  • 12: relay normally closed (connected to 11 when coil is not energised)
  • 14: relay normally open (connected to 11 when coil is energised)

The C/min/max terminals override the normal relay behaviour as indicated in the timing diagram. Specifically, if max is asserted then the relay is opened even if A1/A2 are energised. The relay doesn't resume normal operation until either power is cycled, or min is asserted.

Armed with all that information, we can answer your questions.

Contacts 11 on both relays are the common contact, which is closed on to 12 or 14 depending on the relay state. Both relays have contact 11 connected to the supply, which means they will normally (that is, in their "off" state) connect the supply to contact 12. When the relay is energised (that is, in its "on" state) it will disconnect the supply from contact 12 and connect it to contact 14 instead.

So given that relay 1's coil contacts (A1/A2) are always energised, the relay is always in its "on" state, which connects contact 11 to contact 14. However this state is overridden by the min input according to the timing diagram. Although, without the max input connected, it's hard to see how this will behave desirably.

Relay 2 is turned on by relay 1's output. When relay 2 turns on, it connects contact 11 to contact 14 which energises the pump. The min/max overrides are in effect, as you describe.

  • \$\begingroup\$ So, the intention was to keep Relay2 by default "on" and control it by the electrodes of the water pump. Only input from Relay 1 comes when the tank is full, and the float sensor kicks in to de-energise relay 2. Plz note that Relay 1 is in "Fill" mode, and float sensor connected to "Min" should be enough. When the tank is full, then the float sensor is deactivated, so input to "Min" vanishes and hence the relay 1 should not send anything anymore on 12. That was the intention on not using "Max" on relay 1. Does it makes sense? \$\endgroup\$
    – Mark Jeep
    Commented Dec 21, 2020 at 7:44

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