I have been told that the frequency was chosen to reduce vibration white finger. No one is old enough to remember when it was installed but it has a rotary frequency convertor connected to it which burned out, that is what caused us to notice it.
The box with the contactor contains the motor starter. The grinders plug in using some bizarre metal socket with a metal sprung lid.
No one knows what happens to that SY cable. I shudder to think
In the last pic, the earth has been disconnected. When it was re-connected, the breaker wouldnt stay on. That has all been re-wired since, we didnt even bother to find a fault.