High speed on pump motor just hums then trips breaker. low speed works fine.

Check your voltage to that pump. If the pump is set to accept high-voltage of 240 V, and you are only providing low-voltage of the 110-120 V then you will be getting that symptom.

I'm going on somewhat limited information here not knowing if the tub is newly installed or if this is a spa that has been working in the past and just started doing this. It would be helpful to know if this is a recently installed pump as well. That said here are a few things to check.
If it's a new install: Your electrician has more than likely wired the spa incorrectly. Be sure that the spa pack has 220V going into the pack and that the GFCI is wired correctly.
If it's an old spa with a new problem: A lot of times a bad heater element can cause a spa to trip the breaker. If you have a bad element the spa will operate normally for about a minute when you turn the power on, then trip the breaker as soon as the heater kicks in.
If it only trips the breaker when the pump is turned on to high speed, more than likely there is a problem with the wiring of the pump or the relay on the pump itself.

running the pump on high speed will not have caused the problem, they are meant to run 3,450 rpm's continually. It's more than likely a supply power problem like you mentioned. Check GFI's, and breakers to see if anything has tripped.

if this motor has a cent sw it is bad / replace the sw and if is shaded pole the winiding are bad .. the motor needs repari .. mm

Check or substitute motor capacitor

Pump speed Selector Switch Contact Probably Missing, Checkout

The motor may have a thermal cutoff if the motor draws too much current. Do you have a sufficient large gauge circuit supplying the motore? If not the actual voltage at the motor may drop, causing it to draw more current to make up for the loss of voltage, thereby tripping the motor's protective breaker. I assume the motor will start again after serveral minutes of cooling down.

Curtis

Motor controller or motor itself has a short.
OR something stuck in the pump impeller.

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