100A 3-Phase Cutler Hammer Pump - Breaker Model HMCP100R3C

Put a scope on a shunt and monitor current draw.

The first answer is a great one.If that doesn't show the problem I would get an IR heat sensing tool and shoot all of the lugs in your system. I would certainly not invite your electrician back. They sound like parts changers. From what you have stated the problem is "up stream" from your pumps and the breakers. If in the same leg on all breakers has been failing back track the system and find the loose connection or deteriorated connection. There must be a commonality.

This problem can be resolved with a good control or boiler technician and about 2 hours of research and real troubleshooting.

Typically losing a leg on a breaker usally indicates a loose connection. The termination heats up and destroys the breaker caused by improperly tighting of the breaker lugs.

Do you have an infrared temperature gun? They're cheap enough and will save you from a lot of down time.

One other thing, you may be losing one leg on the motor? This also would also cause the conductor to heat up. Use an amp probe. There could also be a slight ground fault which will not trip the breaker but burn up the wiring and equipment.

And! Your electrician isn't a trouble shooter. Get a new one.