Originally Posted by VanK
I suggest you hire an electrician to check to current (AMPs) and power (Volts) to the breaker under different conditions. HClarkX is mistaken in his claim that lower voltage equals lower current. It's actually an inverse relationship. The electrician will have a multimeter with a hold function to measure the highest AMPs drawn during start-up. The breaker trips on heat or over-current. Breakers are also only rated to trip seven times in their life. I hope this helps. If you are in or near Charleston SC I'll be glad to help at no charge since I am a fellow traveler and retired electrician.
Not mistaken. Been designing systems to start motors on weak systems, maybe before you were born. Or, read more carefully. Once the motor is near or at speed, as I stated, current does increase when voltage drops as slip increases (offset somewhat by a drop in exciting current). But, during start up the motor is just a short-circuited transformer. The stator is the primary winding and the rotor bars are the secondary winding. The end rings that short the longitudinal bars (windings) in the rotor are the short circuit. Under this condition, just as in a transformer, the leakage impedance between the primary and secondary windings is all that limits current. The motor is thus simply an impedance (mostly reactive, very little resistance). Under this conditon, by ohms law, higher voltage results in higher current. Typically, the high current causes voltage to drop in the wires feeding the motor and the motor current drops as a resuult, but is still in the range 5 to 10 times full load running current.
I left out details about capacitor-start and starting winding and such. But, those are just impedances so again, it's an ohms law thing.
It's often the high initial starting current that trips a weak or undersized circuit breaker, especially if voltage is low and the starting time is increased due to lower accelerating torque. In this case the initial high current may heat the breaker and make it more likely to trip moments later, but isn't the problem per se.