Reversing single phase motors

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First and foremost never play with electrics unless you are sure you know what you are doing. Never ever make do, always make this the one thing that is properly done. I always recommend that you have earth leakage trips fitted to your supply, it safeguards you and your family from electrocution. If you dont have an electronic tester, it would be wise to borrow or buy one, you can then check your motor or anything else for earth leakage before you do anything.

Secondly, anything you have bought may be dangerous so check it out. I can categorically say that every item of engineering equipment I have bought second hand has been defective, some were lethal, some were just dodgy.

Reversing motors is usually simple enough, all you need to do is reverse the polarity to the field windings. To do this you need to see if your motor has 4 wires in the junction box, better yet four terminals, not counting the earth. Quite a few of todays motors do have the four wires in the JB(junction box) but only three terminals, ie live neutral and earth, but providing you have the four wires excluding earth you can always modify the teminal block or replace it. I am not going into great depth on the motor as you either have the wiring or you dont and if you dont then the subject becomes much more difficult than I can explain here. This is mainly how to get the switch wired correctly to achieve reversing and to this end I have two illustrations, one using the common Dewhurst switch found on many modern lathes, the other using a three phase switch, which is basically only capable of reversing two of the three phases, but can still be used for our purpose.

This is the Dewhurst example, and although this is brand related will apply to many other similar types of switch.

The next one is a typical three phase switch, as fitted to my Meddings bench drill, which I converted to single phase.

And that's it. If your motor has a three terminal block, one of which is the earth, but two wires go to one of the power terminals then that is the reverse and usually what the manufacturer does is provide you with the ability to reverse this by taking one of these leads to either the live or to the neutral, so for constant switching you need another terminal, that's all. BUT dont go using the earth, do it properly, it's your life you are playing with if you mess up.