Contactor wiring

[Stevie h]

Hi 

It's a long time since I've been on here, the place looks like its gone from strength to strength, well done to you all. 

This is a contactor I came across yesterday, my knowledge on contactors could be written on the back of a stamp. 

Could anyone explain how the bottom half of this one works, the only ones I've ever come into contact with have a A1&A2 as a input to open or close. 

Thanks 

 

[roys]

That bottom one, presume you mean the right hand, is an overload unit.

The contactor above does the on off switching of the mains power to the motor and the overload gives it, as the name suggests overload protection. When it senses an overload it will switch over a set of internal contacts which will (usually) open the control circuit going to the contactor, so de energising the contactor, switching of the supply to the motor. Also in the control circuit to the contactor will be things like emergency stops.

The overload unit has normally open and normally closed contacts giving various control options, alarms as well as trips for example.

The overload can also usually be set to auto reset or manual reset once it has cooled down.  We use to set ours to manual reset so that the plant operator had to involve the electrician if a motor tripped on overload otherwise they would keep starting the motor although it make have a fault like seized bearings or the pump attached to it choked.

 

[Stevie h]

Excellent, thanks, brilliant explanation