I recently obtained one of those big 35L ToolPro vacuums from Supercheap Autos which I intend having semi permanently connected to a DeWalt job site saw.  The vacuum has a pass through power socket that senses when current is being drawn, and automatically turns on.  The problem is that the socket is rated at 1000W and the saw draws 2000W.  I rather stupidly thought I'd make a box with a power relay, but quickly realised that this wouldn't work as turning on the saw will not be seen by the relay's coil. 

I feel sure that it is doable, but I am not clever enough to work out how.  I thought about connecting the saw to the vacuum's pass through socket and have it power a relay which switched power in parallel to the vacuum socket, but it would need to split power between relay and vacuum socket or the vacuum would shut down. Would a power relay be fast enough or would the initial surge from the saw have time to damage the pass through circuit. 

I have a vague memory that thyristors are very fast and are available in that sort of current range, but I don't even know if they can handle main voltage, although it seems reasonably that they can.  If that worked it would need to unlatch to let the vacuum shut down.

I spent most of my working life designing and building test instrumentation at Ford Product Development in the UK, but I was mechanical although I did almost as much electronics because it was a small team.  That was a long time ago though, and I am out of my depth working out the above circuitry.  So any ideas would be welcome. It might be simpler to power the vacuum via the saw for instance, but I have only had the saw a few weeks and am reluctant to drill holes in the power box already.  Perhaps I could get an additional cable through the existing cable gland?

Incidentally, my standby solution is a power board with a remote ($29 on TradeMe).