Voltage sensor

Hardware
1

hello.
i have a power shower (essentially an electric water heater that is used only for showering) with an external switch (mounted on the ceiling with a string to toggle it on and off, but that’s not important here). what i’d like to do is detect when the switch is on (so the power shower can be used). i don’t need to measure voltage or current, i just want to know if the switch is on or off so i can use that info to control the bathroom heater (also electric). can anyone recommend a piece of hardware that can do that for me? thanks.

PS i live in europe so it needs to work with 240V 50Hz. communication with home assistant should be via zigbee, but wifi is also acceptable (if there is a way to get my wifi password into the device. i will not run unprotected wifi for any reason).

2

Just install a relay like an Aqara T2 behind the socket or use a smart plug to monitor the power state.

3

Any smart relay can do it, Shelly, Sonoff etc. Just use it to trigger SW, without using the relay to switch anything.

4

unfortunately a smart plug is not an option because it is hard-wired, no plug involved.

5

“Just use it to trigger SW”

you mean make a connection from the switched line (from the switch to the power shower) to the SW input on the relay? yeah, that might work.

the only question is, what do british regulations say about that? can i just do it or do i have to get an electrician to do it for me?

6

You are best to have a certified electrician install relays and make sure its done properly regardless of regulations in your area.

As for what they mean is that when you install a relay you have only the live, switched live connected (and if the connection or relay requires it the neutral) as per the diagrams on the manuals for either dry or wet contact modes based on the load type, you don’t connect the physical switch unless you need to have it connected to control the relay manually if there is a physical switch to connect.

7

You said you have a switch to power it on/off. Is there any chance to get a neutral there? If so, you can install a small power monitor in there (like shelly PM Mini).

8

light detector
light detector871×397 127 KB

If your external switch has an LED you could use a photo resistor up against it. Replace the reed switch with the photoresistor in a door sensor. 433 door sensor needs to be one that detects open as well as closed. Then detect the 433mhz sensor with something like a sonoff RF bridge or OpenMQTTGateway on an esp32. Make it a binary sensor. Attach whole device to switch plate by velcro.No risk of electrical shock and easy to remove to replace the cell inside.

9

Yes. But you “need” electrician and neutral wire as well.
By the way, many boilers have small light on the thermostat that you could use to trigger a sensor or phototransistor.