I am a bit of a home automation enthusiast too, so love these kinds of challenges. Let my try and explain my suggestion a little better.
Below is a circuit diagram of a Direct Online Starter - DOL, which is controlling your dusty now. When the correct voltage is applied to A1 & A2 by pushing the start button, the contactor coil energizes and the contacts change state, powering the motor.

DOL Power circuit.JPG


The existing contactor coil would be either 240V or 415V, but they are available with all kinds of voltages - including less lethal 12V & 24V DC. I was suggesting a low voltage DC coil in case you wanted to tinker with that side of the wiring yourself. Have the sparky install all the bitey stuff in an enclosure and leave you a pair of wires to A1 & A2 to connect to whatever control system you choose.

If you prefer to let the sparky do the whole thing, you could get them to replace the existing DOL push button controls with something like a Sonoff Dual (assuming it's a 240V coil) - SONOFF DUAL: WiFi Smart Switch to control 2 devices | SONOFF Official
It's wifi based, not zigbee, but will work with Alexa and the Sonoff phone app.

I suggest the dual as it has been approved for use in Australia by ESV (although the link above is for Revision 2 so you may need to confirm) - ERAC National Certification Database - ESV180440

As the sparky would be replacing the existing controls, I would suggest an emergency stop & or isolator to ensure it doesn't start unintentionally.

If you have a zigbee hub in your shed, you could get any compatible zigbee remote Tuya ZigBee 3.0 Wireless 4 Button Portable Remote Works with Smartthings Conbee Deconz Stick Domoticz Hub Required|Home Automation Modules| - AliExpress and configure it to control the relay as back up in case Alexa doesn't want to do as she is told.

Quote Originally Posted by emgeecay View Post
PS - Im still working on "Alexa, take out the bins" and "Alexa, clean the gutters out". My wife has given up on "Darling, take out the bins" etc. She says that ecosytem is very unreliable.
Have the same issue in my place. All the whizz bang gizmos I have installed over the years still won't put dinner on the table automagically.