I have a workshop vac with power take-off (ie. plug tool into socket
on vac, vac operates when tool trigger pulled). I plugged a 200W
sander into it, it fired up for a second and then the vac shut down -
although the sander continued to run.

I assumed the vac was knackered (it was cheap) but I plugged an 800W
tool in to check and it worked fine. A 250W sander worked fine too.

Then I plugged an extension lead into the vac with no tool connected
to the extension - and it fired up for a fraction of a sec and then
shut off.

I'm assuming there's a minimum load for the power take-off to work
properly and I've never noticed before because I've never connected
such a low-wattage tool. Is that right?

But what's the deal with the extension leads?

Thanks for any help.....