I have a 20HP vacuum pump for hold-downs on both of my 4x8 routers. Yesterday, I was milling a new vacuum sheet for one of the machines, and the pump worked fine.
This morning, it wouldn't stay running for more than 30 minutes -- it blew its 100A breaker after 25-30 min. This afternoon, the same (so, not an incoming voltage issue... about 243VAC, 60Hz).
Lacking a high-current ammeter loop for my meter (one ordered), I removed the breaker and ordered another. They can fatigue with age and near-capacity current. While it was apart, I did some exploring.
I tested the pump's rotor by hand. It turns freely. All the capacitors in the 2ph-to-3ph converter are 'oil' caps, and should not age; normally those last for decades. I couldn't find anything obvious.
But, while it was 'down', anyway, I did a routine cleaning on the vacuum pump's in-line filter. I was appalled! It was full of MDF dust! And it was clearly new dust, because it was loose and powdery, and still had it's color. Hmmm...
It took nearly an hour to air-clean that filter, it was that-badly plugged-up. It's not perfect, but worth testing. I've ordered a new one. But in the meanwhile, I re-installed it, and put the breaker back in the box, so I could test.
It ran fine for over an hour. DARN! 'Simple problem, but not expected.
Lloyd
