OLP & Relay Wiring Diagram with Compressor

Hey, in this article, we are going to see OLP and Relay Wiring Diagram with Compressor and Connection between them. An overload protector or OLP is a safety device generally used in various electrical devices including compressors. The primary function of the OLP is to protect the motor from damage due to overheating. If the compressor motor draws excessive current due to overload conditions or any other faults, the overload protector trips and disconnects the power to the motor. This helps to prevent the motor from burning out due to the overload current as well as the power circuit.

On the other hand, a relay is an electrical switch that is used to control different types of electrical and electronic devices. So here also, the relay is used to control the compressor motor. It may be used as a bridge between the low-voltage control circuit (controlled by a thermostat or electronic control board) and the high-voltage power circuit that drives the compressor motor or it may be used to switch between the compressor starting and running coil operations.

So, in short, the OLP is primarily a safety feature to prevent motor damage, while the relay is part of the control system that manages the operation of the compressor. Now let's see the connection between these.

Wiring Diagram

Here, you can see the connection between OLP, Relay, and Compressor. This wiring diagram is basically for a refrigerator's internal circuitry where all these three devices are used.

OLP and Relay Connection with Compressor

Connection Description

As you can see in the above diagram the OLP is connected in series with the compressor common terminal. So in normal conditions when the compressor draws a normal current the OLP remains closed so the compressor will run. But when the compressor draws an overload current the OLP will be tripped which means its contacts will be open so no current will flow through the compressor and the compressor will be turned off.

On the other hand, you can see, the relay is connected to the starting and running terminals of the compressor which means it is used to switch the starting and running mode of the compressor. At the starting time, the relay will connect to the starting terminal of the compressor to the power supply and once the compressor is started the relay will connect the running terminal to the power supply and disconnect the starting terminal.


Now, let's learn how the OLP protects the compressor from overload faults. Generally, the OLP continuously monitors the current flowing through the motor winding of the compressor. This is done with the help of a heat-sensitive or current-sensitive element within the OLP. The OLP is preset with a specific threshold or trip point. This is the maximum allowable current or temperature beyond which the OLP will act. During normal operation, the current flowing through the motor remains within the acceptable range, and the OLP remains in a closed position, allowing electrical continuity. If there is an increase in current beyond the set threshold, indicating an overload condition, or if the temperature of the motor winding rises excessively, the OLP will be tripped.

The OLP is designed to respond quickly to overload conditions. Once the threshold is exceeded, the OLP trips or opens the electrical circuit and disconnects the power to the motor. By opening the circuit, the OLP prevents further flow of excessive current to the motor. This interruption of power will help to prevent the motor from overheating and sustaining damage. After the overload condition is resolved, and the motor has cooled down or the current is within the acceptable range, the OLP has a manual or automatic reset feature. In manual reset systems, we need to reset the OLP once the cause of the overload is solved.

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OLP & Relay Wiring Diagram with Compressor OLP & Relay Wiring Diagram with Compressor Reviewed by Author on December 27, 2023 Rating: 5
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