I'am trying to make an automatic irrigation system using an Arduino, a moisture meter and a water pump.

The issue is that I can't figure out whether there is some relay/contactor type component that can control a 400 V device such as water pump using max 5V from Arduino in the controlling circuit. As far as I have researched it's quite common to use Arduino controlled relays to control contractors, but it seems this approach comes with challenges of its own, so any advice is welcome.

  • \$\begingroup\$ There are not many challenges if your 400V pump can be switched direct online with one 3 pole contactor. What is the exact technical hurdle you're up against? \$\endgroup\$
    – Jeroen3
    Aug 21, 2019 at 9:54
  • \$\begingroup\$ Issue is that I am so very oblivious in electronics that I don't even know what keywords to use to research this so I am completely clueless wheter a contactor that can switch up to 400 V controlled by 5 V exists and whether there are some potential pitfalls to consider. \$\endgroup\$ Aug 21, 2019 at 10:03
  • \$\begingroup\$ If you can't find a large contactor that will operate from 5V, you could use a small 5V relay to control the large contactor. \$\endgroup\$
    – HandyHowie
    Aug 21, 2019 at 10:28
  • \$\begingroup\$ That's reasonable, thank you very much. \$\endgroup\$ Aug 21, 2019 at 10:37
  • \$\begingroup\$ What about this guy, or three of them? digikey.com/product-detail/en/omron-automation-and-safety/… \$\endgroup\$
    – winny
    Aug 21, 2019 at 13:46

1 Answer 1


You won't find a contactor capable of switching a 400V motor with a 5V coil.
12V is already rare.

What you can do is cascade relays.
A small 5V pcb relay that operates a larger 24V contactor (with flyback diode).

Or use high side output driver from infineon for example.

Or use a digital method and control a frequency drive by modbus or signal relays.


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