No such thing as simple electrician, quite a skilled job.
Most wireless systems will work beyond 20 metres.
WiFi is probably total overkill unless you need something like a smart phone to control the contactor.
These things are available commercially if you don't want to do it yourself.
If you search the web using "wireless controlled switch", you will come up with quite a few options. Add "DIN rail "to the above to get plenty of other commercial options.
If security of control is needed, some will be better than others, you may need to send a character sequence rather than a simple on/off command, the character sequence would need decoding to verify a legit signal.
The low power control signal would need to drive a small relay in all likelihood, particularly if the contactor is rated at 40A, and its coil is rated above safety voltage levels.
Cheers,
Richard
