How can I compare two types of relay control circuits?

I've been asked to write an essay where I will have to compare the construction and operation of two different types of stop/start/retain rela circuit for an AC or DC machine. I don't know how to go about it, how to start and I have no good circuits to compare. Can you help me please? Maybe some good... show more I've been asked to write an essay where I will have to compare the construction and operation of two different types of stop/start/retain rela circuit for an AC or DC machine.

I don't know how to go about it, how to start and I have no good circuits to compare. Can you help me please? Maybe some good websites that can explain me a bit more

Thanks in advance
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