When we look at a star/delta starter, there are some basic rules to follow. I know we have had a look at this type of starter before, but thought it might be worth doing it again to assist with fault finding tips. The first schematic shows how NOT to wire the circuit. You will notice it relies on just the timer to switch between the star and delta contactors. This means it relies on the normally closed contact to be fully open before closing the normally open contact. This is commonly referred to as split second timing and is not good practice. There may be an instance when the two contacts are both in the closed position for a split second. That will lead to both the star and delta contactors being energised which leads to a not so good result. Take a look at the circuit and see if you agree.
Now let’s take the same circuit and make a few changes to it. These changes will add electrical interlocking between star and delta which eliminates the issue discussed above. You will notice I also added a normally open of the main contactor here which is something I prefer to have in the circuit.
Hope you find this useful and please always remember that the tips and posts on this blog are only intended as guidelines. Please ensure any installation you do meets all your local Legislative Standards at all times.
And for those who have not done so, remember to collect your copy of the Manual for Electricians Volume one which you can find at: www.lulu.com/spotlight/SparkyHelp
Till next time, always put safety first. Think before you do and always ask yourself “what if” when you prepare your job safety analysis. Hope you all have a great week