Shopsmith Forums

The motor has a start switch, not a start relay.

Now regarding 'assumptions'; I think we all would agree that there is conflicting descriptions. In an effort to sort through them, several different 'questions' have raised. Those 'questions' have inherent assumptions, but are asked to determine if those 'assumptions' are correct.

Initially the 'problem' was, it starts ok with no spt, but trips the breaker when one is attached. From there we discussed motor getting hot and that got us into start circuit discussions. All the while more information was provided that was missing at first.

I have to agree with Fredsheldon. We now know it is a A.O.Smith 3/4 hp motor with an internal start switch and lastly a non functioning speed control.

If the speed is set to a speed considerably above slow, it would act as initially described(motor no load ok, spt attached - trips breaker).

I'm still waiting for the rest of the story as Paul Harvey would say.

I have worked in the electrical industry for about 20 years. I do not do installation but I have sold electrical products for 20 years. The bottom line is if the motor is running fine and all the other mechanical parts in the Shopsmith are moving freely it probably is NOT the Shopsmith. There are several things to consider on the tripping breaker.

1. Bad breaker
2. Bad connection to the breaker on the supply side
3. Bad connection to the breaker where it connects into the panel.
4. Bad connection to the receptacle.

The clue might be in the amount of time it takes to trip the breaker. While 30 seconds is not long it is not tripping immediately. If there were mechanical problems with the Shopsmith it would trip almost immediately It takes some time. Time for something to heat up. A 20amp breaker is only rated for 16 amps continuous use (80% of the name plate) The breaker is a thermal/magnetic device. Thermal on the long-term and mechanical where there is a dead short. 30 seconds to trip means that the breaker is tripping on thermal. Something is causing it to heat up. Any of the above could be the cause. Just my opinion!