I want to switch a pump on/off with a relay. However it is powered through some kind of breaker (residual current?)
Would it work with a relay after the breaker?
You could test a fingerbot/switchbot bot that presses that button when power is restored and optionally get a battery eliminator cable for it so that you don’t have to worry about replacing batteries in it.
Else the other option is to wire in an ESP32 to trigger the button remotely that way.
Yeah, installed a shelly mini between this thing and pump. Has worked for now. Let’s see if this is viable as a long term solution. Would not rather mix fingerbot in it - it is outside (albeit sheltered) and the button is rather heavy.
That’s how residual breakers are wired in your electrical panel, before any devices.
So relay between breaker and pump would be logical choice.
I connected a relay after this breaker. Unfortunatley it disconnects about one in five times after the pump is switched off by relay.
That indicates some problem in the relay circuit. What relay you use? Does it have flyback diode?
Relay is Shelly Mini PM gen3
Is the “flyback diode” the same thing as Shelly RC Snubber? Sorry, I am a software person, only very basic electricity knowledge.
Shelly has diode on it’s relay. That snubber could help though.
When you manually turn off that pump it never triggers the breaker?
I have no way of turning the pump off otherwise. The breaker on pic was directly wired to the pump, I installed the Shelly relay in between.
To understand your setup… So the pump doesn’t have switch? You just unplug your power cord?
Yes. The chord from the plug/residual current breaker goes straight to the pump. No switches. To switch the pump off, I can either unplug it or press the TEST button on the circuit. That is how my hot tub was delivered to me 
I installed the Shelly Mini inside the pump’s enclosure between this breaker and pump.
It’s all correct. There is always some spike when pump turns off and that breaker is too sensitive for that, something that doesn’t obviously matter originally when you unplug it.
You can try with that snubber or with line filter. Or replacing/removing that breaker.
Snubber is also protecting Shelly, so I would put it anyway.
