Friday, August 28, 2015

What is Overload Protector and What is role of Overload Protector in Refrigeration

Welcome back to the refrigerator topic, and in this post we discus the overload protector which we use to protect refrigeration compressor. In this post you will learn the function of overload protector and it's working principles.

What is overload protector and it's function in refrigerator and air conditioners.

A overload protector is an electrical device which we use for compressors protection, whenever the compressor temperature high form his range the compressor overload cut off the electric supply form compressor motor that's why we called him thermal overload.
The connection of overload with compressor in series and inside the overload we connect a heating resistance and with heating resistance we connect a bimetallic strip metals. The heating resistance and bimetallic strip metals both make a overload relay.
The working of overload relay is simple whenever the compressor motor getting heat up, due to the overload connected with the compressor body, the internal overload heating resistance heat up and due to heat up the bimetallic strip metals cut up the connection between one another and its make  comprssor circuit to a open electric circuit. When the compressor come back to his normal state/temperature, the thermal overload protector make a close electric circuit inside, and connect the electric supply to the motor.

Note that compressor is getting heat by flowing a high amount of current, however if compressor getting normal current (Ampere) and it is  heating, then also Overload protector will be trip or make open circuit if it's connected with compressor body.

The cut off the supply overload make safe compressor motor form internal winding damages/ burned. However you will not understand the working principles of overload with out a diagram. That's why i designd a diagram about the internal structure of a thermal overload protector.

overload protector diagram

In the above figure, i shown overloads 2 types and i lights it's terminals with the name of IN and Out. The (IN) means that we gave electric supply to this terminal and (Out) means that we get electric supply for compressor or we can say that this point is goes to connect the compressor common terminal.

Also read
How to find out Start,Run,Common terminals in a Compressor

I also shown a internal structure of overload in above example diagram. In diagram i shown the bimetallic strip metals with heating resistance with incoming and outgoing supply. When ever the compressor start getting high current the heating resistance heat up and create an open electric circuit.
This one of main reason that we use thermal overload protector in refrigerator compressor, i hope you will get a good information from this post, however we will soon discus the main reason of compressor getting high current or heat up.

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Sikandar Haidar khan is a electrical technology student who love to learn about new things in electrical technology and share with world. He writes about electrical related articles on his blog.


  1. hi
    my friend
    i am Kurosh from Iran
    i have one question about overload relay in refrigerator 's hermetic compressor
    where is this equip location in circuit
    and whether both overload relay and current relay have been ever combined together?

    1. This comment has been removed by the author.