Contractor

Look in any motor control equipment manufacturer's literature on contactors, there is always a description of these IEC standard terms.

There are many Utilisation Categories for Contactors as per IEC 60947-4. It would not be practicable to discuss all of them here. You must study the standard. If you find that IEC is very expensive, you can buy the Indian Standard IS13947-4 which is identical, available easily from BIS, and far less expensive....if you are in India. For your ready reference... here is an extract from a catalogue.

You must do your homework though if you want to know more, since there are 4 more categories ... AC5, 6, 7 and 8 !

"Contactor" instead of Contractor.

There is a good amount of theory and graphs relating to different Duty of contactors you can find it in any reputed manufacturers catalouge, However practically speaking, AC-3 Duty is used for mainly Motor Applications ( slightly resistive & inductive loads), AC-1 is for pure resistive loads, AC-9 For capacitive loads I do remember only a few but you can go throught the catalogues of L&T or Siemens or BCH or ABB to get more details. I Think this has given you a more clear picture.

A couple of small corrections if you don't mind.

Capacitor switching is covered by AC6b. But that is not the whole story. Most often, capacitors are switched on sequentially, depending on how the power factor (which needs to be corrected) varies due to the load characteristic. In such a case, the peak inrush current has been seen to be >130 times the rated current. NEMA ICS 2 gives a good picture of this.

AC3 covers switching of squirrel cage motors : Make 6I @ 1.1 U and break I @ 0.17 U at 0.35-0.45 pf.