After serious thinking Clanger wrote :
When it trips the CU, it trips the whole board and not just the circuit it is
plugged in to.

That sounds like an RCD, is there a test button on the item which
trips?

In which case there is some leakage from L or N to the earth, which
most probably is due to carbon (or moist sawdust) accumulating in the
motor from the motor brushes. Try removing the motor, leaving it for a
while on a warm radiator to dry out, then blowing it out via the vents
with an air line.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk