Correct testing of thermal overload relays is very important to ensure the normal operation of electrical equipment. Here we outline a variety of test methods to help you comprehensively test and deeply understand the function and status of thermal overload relay.
What is a thermal overload relay?
Thermal overload relay is a common motor protection device, which is mainly used to prevent the motor from overheating due to overload. Its working principle is based on bimetallic sheet: when the current is too large, the bimetallic sheet will bend due to heating, which will trigger the relay to trip and cut off the power supply of the motor. The thermal overload relay usually has an adjustable current setting to ensure the normal operation of the motor within the rated current range.
Main functions of thermal overload relay:
- Prevent overcurrent damage: if the current of the motor exceeds the set safety value, the relay will disconnect the power supply in time.
- Protect the motor from overheating damage: by monitoring the current, the overload relay ensures that the motor will not overheat due to long-term operation under overload conditions.
- Manual reset function: after the relay trips, it usually needs to be reset manually to restore normal operation.
Why testing on the thermal overload relay becomes necessary?
The test of the thermal overload relay is necessary to guarantee the normal working of the motor protection. Due to long-term usage, internal components of a relay can be worn; thus, it will not work as it is designed. Periodic inspection of the thermal overload relay can be performed to:
- Ensure that the relay can cut off the power supply in time when overload occurs to prevent the damage of motors.
- Ensure that the relay settings are accurate to avoid frequent tripping or unnecessary motor shutdown.
- Find out possible faults of the relay in advance to avoid long shutdown time of equipment.
How to test thermal overload relay
You can test the thermal relay in three different ways - using the test button, using the test kit or machine, and using a multimeter. Each overload relay test method has its own procedures as described in the following guidelines.
Thermal overload relay test button
This is the easiest method for testing. The test button or switch for the thermal overload relay is usually situated on the front of the relay. It simply tricks the overload by opening up the NC contact and closing the no contact. Please note that this process involves the use of a multimeter. The steps are as stated below:
- Find the relay's test button or switch.
- Using your multimeter, set to read ohms resistance.
- Connect the multimeter lead to terminals 95 and 96 of the relay:continuity should be read
- When the multimeter probe is still connected to the 95 and 96 contacts, press or slide the test button to simulate tripping.
- This will open the NC relay contacts and close the no contacts. The multimeter should also read 0 to show connectivity.
- Press the reset button to reset the device.
Thermal Overload Relay Test Kit
The thermal overload relay test kit is a precision machine that tests parameters like operation and tripping accuracy of a relay. The principle of working is to inject very high (but controlled) current into the relay to simulate the situation that the relay should trip. Here is how to use it.
- Turn off all power to the relay; disconnect it from the circuit.
- Connect the test kit for the thermal relay by following the instructions given in the user manual.
- Ensure that all the terminals are correctly connected. After some seconds, switch on the power
- the current and voltage reading should be displayed on the tester screen.
- Ensure that the tested parameters are within the recommended range.
- Using the test results, determine whether the relay operates normally or needs to be replaced.
How to measure thermal overload relay with Multimeter
Another device that can be used to test thermal overload relays is a multimeter. The usage process is also very simple. The following is the method for checking the thermal overload relay using a multimeter:
- First, turn off the power supply and disconnect the thermal overload relay. Then:
- Choose the resistance mode on the multimeter to display in ohms.
- Connect the one end of multimeter probe to L1 to T1. Usually, this should have continuity and be reading 0 ohms in a multimeter; if it is showing infinite reading-OL, the problem exists within the thermal overload relay.
- Then connect the probes to these contacts: 97, 98. These contacts are no and should read open, so the multimeter should read ol. If continuity exists, the relay is no longer functioning properly.
Thermal Overload Relay Maintenance
Cleaning: Ensure all places are clean and free from dirt or dust accumulation, as this will affect the performance of the equipment. Thermal relays usually absorb dust and dirt from the environment; therefore, it is important to keep them clean and barrier-free.
Tightening: Make all screws and terminals tightened since loose connections will definitely alter the accuracy of the thermal overload relay. Please take note that any loose connection can cause false tripping leading to unnecessary shutdowns.
Inspection: The thermal overload relay unit should be periodically inspected for wear or damage. Check for damaged terminals, loose connections, and other components. These may indicate problems that need to be solved immediately.
Motor overload: ensure that the motor operates within the rated load range and avoid frequent tripping.
summary
Mastering the correct test methods and troubleshooting skills can effectively improve the safety and reliability of the equipment.
If any problem is found during the test, timely repair or replace the faulty relay will help to ensure the long-term stable operation of the motor and electrical system.
FAQ
How to adjust the setting of thermal overload relay?
Thermal overload relay usually has an adjustable current setting knob, which can be adjusted according to the rated current of the motor.
What if the thermal overload relay trips, but the motor is not overloaded?
The setting value of the relay may be too low, or the internal components of the relay may fail. Check relay settings and perform necessary maintenance.
Can I replace the thermal overload relay by myself?
Yes, you can replace the thermal overload relay by yourself as long as you ensure safety and have appropriate tools and replacement parts.
Can the thermal overload relay protect the motor from all types of faults?
Thermal overload relay mainly protects electric
