Ian
You should not be having so many problems with tripping fuses with that machine.
I think thre is a short in the machine somewere causing the problem.
I once has a single vac 135 psi machine with a inline heater.The machine had one plug on t that conrolled all 3. It ws a grat little machine I just used for Upholstery with no poblems at all.The one day it started to trip fuses,sometimes as soon as I put the machine on and other times after it had ben running for an hour.
I thought at first it was the customers electirc or they had sensitive trip switches in the houses.But after getting totally hacked off with it doing it one day I decided it was the mahine and look for the fault.
After a process of elimination I found out it was the vac motor.I replaced the motor and it was fine,never had a prolem off it again.
I have also had a similar prob in the past with a larger porty and on that occasion it was he inlin heater that was tripping the electric,after it was replaced it stopped tripping.
Any short in your system will cause this, sometimes just a cracked cable wire on the plug run will cause a short.