What is an Overload Relay? Connection & Working Principle

🎥 If you are curious to know what an overload relay is, what an overload relay consists of, how an overload relay is coupled into a contactor to protect a motor, what differences it has with a circuit breaker, and how to test an overload relay to check if it is functioning, watch this video until the end.

By watching this video, you’ll get the answer to these questions:
- What is a motor starter?
- What is motor overload?
- What is an overload relay?
- How to test an overload relay?
- How to wire an overload relay?
- What causes overload current?
- How does an overload relay work?
- What are the components of an overload relay?
- How to connect an overload relay to a contactor?
- What is the difference between a circuit breaker and an overload relay?

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💬 Video Summary:

What is Motor Overload
- If a motor draws too much current and generates too much heat, it indicates running in overload. So, to protect products in industrial automation, an overload relay is used to attach to a contactor to prevent motors from operating in overload.

Overload Relay Operation
- Once the overload relay detects an ongoing overload condition for a considerable time, it will trip and send feedback to the contactor, so the contactor breaks up the current flow and stops the motor.

Motor Overload Causes
- When a rotor gets jammed, and there is a mechanical obstruction.
- When the process of aligning shafts with each other is not properly executed.
- When the ambient temperature is high, and there is inadequate ventilation.
- When a motor is undersized to handle a load which causes additional stress on a motor, and
- When bearings, responsible for supporting the shaft inside a motor, have been damaged.

Parts of an Overload Relay
- Adjustable current setting: By using this dial, you can specify the amount of current the motor must draw to be considered overloaded. In other words, the motor's rated FLA or Full Load Amps can be set here.

- Built-in auxiliary contacts: A pair numbered 95 to 96 is normally closed, whereas a pair numbered 97 to 98 is normally open.

- Reset button: This design allows you to toggle between manual and automatic reset modes and functions as the reset button.

- Test trip button: It may be utilized to simulate a trip off the overload relay to check if the overload relay is working correctly.

- Trip indicator: provides the status of the overload relay visually. Meaning, when an overload condition happens, this indicator turns on.

Difference between Overload Relay and Circuit Breaker
- Using a circuit breaker, you can protect a motor from sudden high-current events caused by a short circuit.

- On the other side, an overload relay protects a motor from the excessive current being drawn from the supply.

Overload Relay and Contactor Connection
An overload relay cannot be used to operate a motor on its own, so you need to pair it with a contactor. Typically, an overload relay is positioned beneath a contactor, often having three prongs extend outside its housing coupled into the contactor load side terminals.

Overload Relay Testing Procedure
Finally, we will show how to test the overload relay using a multimeter set to the Continuity Beeper.

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⏰ TABLE OF CONTENTS ⏰
00:00 Motor Overload Explained
00:52 Overload Relay Working Principle
01:22 Motor Overload Causes
02:02 Overload Relay Components
03:35 Overload Relay vs Circuit Breaker
04:34 Overload Relay Connection With Contactor
05:14 Overload Relay Wiring Diagram
06:46 Overload Relay Testing

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