As the previous posts have been focussed on Fault Finding, it may be of some use to people new to it to see how an electrical circuit works. Please note that I will focus on the circuit itself for this post and not on the standard symbols. We will cover the standard symbols at a later stage
For this post we will focus on a very simple Direct On Line circuit as the one below
We will now follow the path of the circuit one step at a time:
- Control Circuit Breaker is turned on
- Current flows through to Thermal Overload
- If the Thermal Overload is not tripped, the contact will be closed and current will flow through to the stop button
- The stop button contact is normally closed and current will flow through to the start button
- The start button is a normally open contact and in parallel with it is connected a normally open contact of the contactor C1. Current will not flow past this point of the circuit
- Once the Start Button is pushed, the contact closes and current flows through to the coil
- The other side of the coil is connected to the Neutral and that means we will now have voltage across the coil which causes the coil to energise. Once energised, the moving part of the core is pulled onto the fixed part and this causes the contacts of the contactor to change state. In other words, all normally open contacts will close and all normally closed contacts will open
- This change of state means the normally open contact that is connected in parallel with the start button closes and when the start button is released, the contactor will remain energised. This configuration is called the retaining contact
- In order to de-energise the contactor, the stop button needs to be pushed. By pushing it, the circuit is broken to the coils and it will de-energise returning all contacts to their original state. This is also referred to as “position of rest”
In the next post we will discuss how the contactor operates and also the difference between a contactor and a relay.
Hope this makes sense and apologies to those who know this already, just want to make it worthwhile for the new entrants into the wonderful world of Electrical Circuits as well.
Till next time, Stay Safe and always strive to be the best at what you do but don’t believe that you are. In other words, there is always more stuff to learn!