Saturday, July 23, 2016

What is is Auxiliary Contacts and it's working in Contactor?

In Electrical Power wiring we use different types of relays and contactor / motor starters and these have some contacts which we know with names of main contacts and coil contacts but this is not end we have also other contacts which we known with name of auxiliary contact. These contacts are available in every contactor but these auxiliary contacts in different types just lick Normally close and normally open which can set or fit on the contact or / motor stater and person can use it for different types of works. But the reason of this post to learn that what is auxiliary contacts and what is the work of auxiliary contacts on a motor starter.
So lets start it step by step.

What is Auxiliary Contact and A Contacts on Contactor?

Auxiliary means helper or we can said these are helper contacts in magnetic contact or relay which help us to done our work easily. And one thing more with out these contacts we can not control any thing by using magnetic cont actor.
So these are also important contacts lick main contacts. On thing more these contacts are available in in ever motor starter but in Small and low ampere (load) contactor we have these contacts only on one side but in big and high loaded motor starter we have these contacts on both sides. In these contacts one is normally close (NC) and other one is normally open contacts (NO). Which we use for different purpose.

What is the work or Auxiliary contacts on a motor starter ?

These points are very important in motor starter and without these contacts a contactor is incomplete. As i written in my above words that in these contacts in one is normally close and 2nd is normally open circuit.
These contacts is directly proposal to the setting coil and when magnetic contactor coil energize and set, the normally close contacts become a normally open contacts and normally open contacts change to the normally close contacts.  Form these change we can control many things which can see it in my last published post about controlling three phase motor using cont actor. So get look on these post.

Also reed below:
How to wire a three phase induction motor with contact?
How to wire a phase failure relay for 3 phase appliances?
What is MC?
MC / motor stater instillation for single phase motor

You can also get an idea about the working principle of auxiliary contact s from the above post links however lets get an review the working of these contacts.

For example

  • With out these contacts we can't do proper connection of a 3 phase motor or a three phase appliances.
  • By using these A-C (A cont...) we can do the star delta starter connection for three phase 6 wire motor.
  • By using these A-C we can control a two contactor with one another, i.e if we have 2 contactor which we instill in our main board and both are instill for different machines. But if we want that if a machine is start then other one does not start then we can easily use these contacts for that type of work.

The above example is not too close to understand completely, however you can get an idea and if you try and think about that, i hope you will do it. However every thing when we start learning is not complete learned in a short time and it's required some time.
Further in our post we will use these contacts in circuit and IN SHA ALLAH you will learn if you gave it short time.

Now lets get a view about these Auxiliary contact s, in the below image i shown these contacts in animation - type look + images from which you can learn it easily.
Now one thing more in ever A contacts we have tow types of contacts in which NC and NO. But in contactor we have move able contacts when circuit or A-C in normal state the NC will NC and NO will be NO but when conactor energize  or these contacts are set by using any force the NC contacts will change to NO (normally open) and NO will be change to NC (normally close). You can get an idea from the below image plus diagram.

auxiliary contacts diagram

I hope after the above image + diagram of auxiliary contact 's , know you understood completely, however as i told in my above words that further we will publish the diagram in which we use these contacts and you will completely understood how to use these A-C.


  1. Hello,I have a 5hp , 380 volt ,3 phase motor that bends reinforcing had 3 contactor's wired to it ,one energised when power was put on and the other two were for toward and reverse with the overload connected in the bottom.its set at 9 amp overload.I purchased this motor in auction and all the wires are missing and the contactor's are not working.I want to replace all the contactor's and over load,the machine has 3 buttons ,one for stop the other two are toward and reverse pilot lights or indicators are connected.can u kindly assist me with a proper wiring diagram for this motor please.the motor is working as I connected directly to the supply and it turns.

    1. Dear i designed a diagram about this and it is save in my system and IN SHA ALLAH soon i will published it.

  2. Bro, please write whatever you've written in proper grammar. There are some spelling mistakes like you have written 'lick' instead of 'like'. It's really difficult to understand what you want to say. But it seems you have made a sincere effort.