Direction of Rotation

There is a 100% chance that it will rotate in the direction determined by the direction of rotation of the phases. To change direction on a three-wire connection, simply swap any two of the three phase conductors in the motor terminal box.

If you connect RYB to ABC you should get clockwise rotation when looking at the shaft.

Note: Should get clockwise rotation it doesn't always work like that. Many years ago I was supervising the installation of a new plant, over 100 motors. The contractor's forman confidently told me they would all go the right way. I didn't have the heart to tell him that from the early days the works generated it's own power and the phases were reversed!

Phase sequence detectors are there to deterine phase sequence. Then according to the sequence you can determine the direction of rotation.

So you change a burnt out motor replacing it with one that has been rewound at some time in the past. You connect the terminals the same as the motor you've taken off. Check for rotation and it goes the wrong way. You can never be 100% sure of the internal connections. In the real world many things come in to play, you can't be sure what the person before you has done. A favourite way of reversing a motor is to swap the phases in the starter panel for the simple reason there's more room to work.

Going back to my last post I made the contractors change the rotation at the motors so that the cable phasing was correct.

That is a good point...............

Every electric motor has a end shaft. Sometimes if there is a motor with two shafts, one is main and the other is secondary.

If you stand on the side of the main end shaft, and look at the motor, the rotation can be clockwise (right) and counterclockwise (left).

The real leg up here is to maintain the phase relationship throughout your facility. Each time a motor must be replaced, especially if the load can't inadvertantly be run in reverse, test run the unloaded motor at a bench where you know the relationship will be the same as the actual working location. Mark the T-leads appropriately and off you go. No guesswork.

Just leave the coupling bolts out or don't put the drive belts on until you know the direction. A lot quicker than rigging to a test bed.

Keeping phasing uniform is a good one. Unfortunately the works where I served my time had 12 different plants all running with reversed phase rotation, in the 60's 2 new plants were built. The then senior engineer took the decision to correct the rotation on these 2 plants. It caused chaos for year afterwards. The 2 plants used this weird new voltage 440V, every one was used to 550V! Motor spares were in chaos, we used to keep 1 spare motor for every 5 in use, add the new voltage, stand back and watch the fun!