Basic Electrical Circuits Continued

I thought we could spend a bit of time looking at something you would come across quite regularly. Actually, you are bound to find this on almost every machine. I am talking about a remote stop/start station.

Now consider the circuit. On the control board you have a stop and start, and somewhere near the machine you have another. If you had to wire this unit into the circuit using only three wires, how do you do it?

Let us go back to the basic circuit rules first. The Stop buttons have a normally closed contact and the Start buttons have a normally open contact. Whenever you connect more than one Stop button into a circuit, they are always connected in series. The Start buttons however, are always connected in parallel.

Have a look at the following rough sketch to better understand why we do it this way.

If you look at this, you can see what would happen had the Stop buttons been incorrectly connected in Parallel. When it is pushed, the machine would not stop as it would still have a completed circuit via the other stop button. In the case of the start buttons, had they been in series, the machine would not start unless you could push both buttons at the same time.

Now look at how the remote station could be wired using three wires only. The sketch is almost a give-away of this already. At the remote station, you have a bridge between one side of the stop to one side of the start. Also from this “middle” section, you have a wire to the control board. The bridge described here would normally have been at the single stop and start in the control board which you would now remove!

Let’s do another rough sketch to explain.



What we have done is to remove the original bridge from stop to start and place the second stop in its place. So from stop 1 we have wire 1 down to one side of stop 2. The other side is connected to one side of the start as well as wire 2. The other side of start2 is connected to wire 3. If you follow it, you will notice we have the two stops in series and the two starts in parallel. Job done!

Again, I hope you find this useful and until next time, you guessed it, stay safe and be proud of your work

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