Electrical Circuit Diagnostics

We have had a look at a few control circuits during some of the posts and now it is time to make it a bit more interesting. What we will do is to build some diagnostic tools into the circuit that will assist you in fault finding.


Start with the very basic Direct on Line circuit. What can we possibly include on this circuit to show us what went wrong? Easy! The majority of faults on this particular circuit will be caused by the thermal overload tripping. If you now look at the overload, you will note that we have used the normally closed contact in our control circuit.


To go the next step, we will use the normally open contact and connect that to an indication lamp. Label this lamp “overload” (you would normally use an amber lamp for this purpose but that is not a fixed rule.)


What will happen now is that, should the motor exceed the setpoint of the thermal overload, the overload will trip and the motor will be turned off. That means the contacts have changed state on the overload and hence you have your indication lamp turned on.


That gives you a clear indication that you have an overcurrent fault as you walk up to the panel. What we will do next is to add a green lamp to the circuit. This lamp we will connect in parallel to the contactor coil and label it “running”.

There we go. Basic introduction of some circuit diagnostic tools. We will use this principle in the next post where we will use a relay to monitor emergency stop buttons, flow switch etc.

In the meantime, implement this on some of your circuits. You will find this method will greatly reduce your downtime on a machine. So until next time, stay safe and be the best at what you do!

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