Is it possible that the clutch/brake assembly in the lathe is sticking after a long period of inactivity, which is causing the overload on startup?

Had that issue with my lathe when it first came to me and some manual jiggling of the clutch plates combined with an oil change actually cured it.

Not before I spent 6 hours painstakingly checking the wiring for a fault I was convinced had to be with the control gear mind you…

I have a 1969 Colchester Student which has been run for the last 30 years from a 5HP Transwave static converter. I don't know if the wiring for a later Master will be different, I suspect it will be, but I am mentioning this because the power for the suds pump on my lathe was taken directly from the power input lines, not from the 'broken' side of the NVR. I had assumed that when the main motor was stopped, and the suds stopped flowing, that the suds pump had also been switched off. This was not the case and the output of the Transwave was still appearing at the pump motor which was obviously not powerful enough to trip out the starting capacitance of the converter and keep running. I think the pump motor just oscillated, all-but inaudibly, whilst getting hotter and hotter until over a period of time it burnt out at least one of the windings. This would not have happened had the lathe been running from a proper 3-phase supply but in the circumstances it cost me a suds pump motor rewind, so just check your wiring diagram in case the configuration presents the same issue I had.

My solution was to fit a small auxiliary NVR for the re-wound suds pump so that when the power was removed from the main motor the suds pump was similarly isolated although I suppose I could have just moved the factory wiring to the 'broken' side of the main NVR.