Overload Relay Trip Class | Types of Overload Relay

🎥 If you want to know how overload relays trip and how long it takes for overload relays to trip under an overload condition, watch this video until the end.
By watching this video, you’ll get the answer to these questions:
- What are two types of overload relays?
- How does a dashpot overload relay work?
- What is the trip class in the overload relay?
- How does a bimetallic overload relay work?
- How does a melting alloy overload relay work?
- What are two types of thermal overload relays?
- What are two types of magnetic overload relays?
- How does an electronic (solid-state) overload relay work?
- How long would it take for an overload relay to trip under an overload condition?
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💬 Video Summary:
Overload Relay Explained
- An overload relay is a sensory safety instrument that protects an electrical motor from a continual high current draw, preventing it from overheating. When the overload relay senses an overload condition that has persisted for a while, it will trip and notify a contactor of the problem, so the contactor interrupts the current flow and shuts off the motor.
Overload Relay Types
- There are two different kinds of overload relays: thermal overload relays and magnetic overload relays. Two types of thermal overload relays exist, bimetallic and melting alloy. And the two main types of magnetic overload relays are dashpot and electronic.
Bimetallic Thermal Overload Relay
- When an abnormally high current flows through the heating element, the bimetallic strip receives the heat produced by the heating element. As a result, the strip bends and causes the insulated rod and lever to be pushed to activate the tripping mechanism, which opens the normally closed contact, interrupts electricity to the contactor coil, and opens the power contacts to stop the motor.
Melting Alloy Thermal Overload Relay
- When an overload condition happens, excessive current flows through, causing the heater coil to heat up sufficiently to melt the inner eutectic alloy. So, it enables the inner ratchet shaft to spin and releases the pawl, causing the spring-loaded contact to open, thus de-energizing the contactor coil and opening the power contact to stop the motor.
Dashpot Magnetic Overload Relay
- Once the tripping current passes through the coils in the event of overloading, the magnetic field becomes more powerful, causing the plunger and piston to start moving upward against the displacement of viscose oil through the orifice. Due to the completion of upward movement of the plunger and piston, the normally open contact closes in the trip circuit and de-energizes the contactor coil, thus opening the power contact to turn off the motor.
Electronic Magnetic Overload Relay
- When continual overloading occurs, the created current flowing through the CT wire increases, which is then processed by the circuit board. After the internal circuitry finds out that the motor is pulling a high current, it will send a command to open the auxiliary normally closed contact, thus interrupting the power to the contactor coil and deactivating the power contacts to stop the motor.
Overload Relay Trip Class
- Each manufacturer should provide a graph displaying tripping time as a function of current. On a logarithmic scale, this graph shows tripping time on the y-axis and illustrates current as a multiple of the overload current on the x-axis.
- The trip class describes how long it takes for an overload relay to trip while carrying a current equivalent to six times its existing setting.
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⏰ TABLE OF CONTENTS ⏰
00:00 Overload Relay Explained
00:31 Types of Overload Relay
00:55 Bimetallic Overload Relay
02:32 Melting Alloy Overload Relay
03:35 Dashpot Overload Relay
04:30 Electronic Overload Relay
05:18 Overload Relay Trip Class
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