How to connect a boiler through a contactor?

Vlad asks:
I plan to install a boiler of 100 liters. I want to power it only when the light is NOT turned on in the bathroom. That is, if someone enters the bathroom (including the light), then the boiler is de-energized (for safety reasons at the time of water withdrawal). After the light turns off, the boiler is connected to the network.

I don’t know what to apply: contactor? some kind of relay? (you need something with NZ (for a boiler) and with BUT (I plan to connect an outlet in the bathroom to them) with contacts) What do you recommend?


The answer to the question:
Well, the simplest option is to connect the contactor coil via a 220V relay with a normally closed pair of contacts (NC). Through the contacts of the relay, apply phase to the contactor coil or zero.

That is, this circuit will work like this: you turn on the light, from the switch or from the lamps we take the phase to the relay coil. When the light is turned on, the relay will turn on and its contacts will open - the contactor coil will be de-energized and its contacts will open and turn off the boiler.

Then you turn off the light and turn off the power of the relay coil, so its contacts are closed again (NC) and the contactor coil is energized, and its contacts are closed, including the boiler.

It can also be simpler, but I do not quite believe in this option. Just use a relay with NC contacts. Many indicate a current of the order of 10A, which is quite enough for a boiler up to 2 kW (by the way, what kind of power is it?). I do not believe in this option due to the fact that in my opinion the relay is not intended for switching such a powerful load.

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Posted: Updated: 28.01.2019 6 comments
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6 comments

  • Vlad
    01/29/2019 at 19:40

    Is it really impossible to feed the contactor coil (with NC contact) immediately from 220 volts in parallel with the lighting? Why through a relay?

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    • Admin
      01/29/2019 at 20:15

      Maybe we misunderstood each other, can you send the model of the contactor you are talking about? In my answer, I had in mind an ordinary power contactor in which all the contacts are BUT, so I suggested a relay to invert the signal (this is what it is called correctly)

      To answer
  • Vlad
    01/30/2019 at 00:12

    Specifically, there is no contactor yet. But I suppose to use the "Soviet" magnetic starter PME-071.

    To answer
    • Admin
      01/31/2019 at 19:33

      So in the same place the power contacts are open in the normal state, well, yes, if the block contacts, but this is not for power circuits.

      To answer
  • Vladimir
    01/31/2019 at 17:08

    A passage switch and a conventional Permanently open contactor can be used. After turning off the light, the second contact of the switch closes, from which voltage is applied to the contactor winding. 90 percent of boilers have protection against electric shock. If there is grounding, put the DIF machine in the bath and the issue will be resolved, angrily and reliably. Good luck.

    To answer
    • Admin
      01/31/2019 at 19:36

      Yes indeed! This is the easiest and best option! The only interesting thing is how long the contacts of the Chinese passage switch in the coil control circuit will live ...

      But if you use a straight-through switch of normal quality, then a quite practical solution

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