Having trouble with a 240v AC motor

Idigimyva · Apr 20, 2021

Im in the process of fabricating a motorized flatbar roller, and I have a 240V 5hp AC motor with 4 leads. Im controlling it using a dual foot pedal box, that controls 2 contactors, which these 2 contactors are there to reverse the motor by having one contactor T1+T5 & T4+T8, while the other switches T5 and T8. However when both contactors are wired in, the 30 amp breaker and the 200 amp main trip, but when only one contactor is connected, it works fine. Any help would be greatly appreciated.

Side note, the dual foot pedal consists of 4 micro switches, 2 per pedal. I have it wired so that pressing one pedal turns the other one off to avoid accidents.

LoriePetty · Apr 20, 2021

Hi....I have a 240v(two hots and ground,no neutral),single stage, bandsaw that would just murmur.

After all the ordinary cleaning and focuses documenting and practically tolerating that the engine was scrap,I exchanged the leads and by one way or another it worked and accomplished for quite a while.

I can just think that our provincial electrical framework was low on one stage for a brief timeframe and when I had done my switch, it was back up to speed.

westward10 · Apr 20, 2021

Are you sure both contactors are not energizing at the same time.

Lucien Nunes · Apr 20, 2021

If you have just two of those contactors it is not going to work. I guess you've inter-connected the windings both straight and crossed to the outputs of the contactors, so the whole thing is permanently short-circuited. You need either two 4-pole contactors or three 2-pole contactors.

In the first case, each contactor connects the correct leg of the AC to each of the four motor terminals when it operates but leaves all four legs isolated from one another when it releases. In the second case one contactor closes whichever direction is required, to connect the supply to the main winding, plus one of the other two to connect the supply to the auxiliary winding in the correct sense relative to the main winding.

Forward and reverse contactors should be interlocked electrically and preferably mechanically. I cannot honestly recommend tackling machine controls unless familiar with these fundamental requirements - there is a reason that control gear is made to specific standards for operational safety.