| Faults |
Reasons |
Solutions |
| Thermal overload relay malfunction. |
- The setting value is too small.
- The starting time of the motor is too long.
- The number of repeated short-term work operations is too high.
- Strong shock and vibration.
- For unsuitable working system (such as frequent switching).
- The connecting wire is too thin.
|
- Reasonably adjust the setting value, if the rated current of the thermal overload relay or the model of the thermal element does not meet the requirements, the product should be replaced.
- According to the requirements of the motor starting time, select a thermal overload relay with a suitable returnable time (tf) series, or take measures from the line (such as a short circuit of the thermal relay during the starting process).
- Reasonable selection with reference to the selection conditions of thermal overload relays.
- For occasions with strong shock and vibration, a special thermal overload relay with an anti-shock device should be selected.
- Reasonable selection according to the selection conditions of thermal overload relays.
- Select standard conductors according to technical conditions.
|
| Thermal overload relay does not operate. |
- The setting value is too large.
- Poor contact of contacts.
- The thermal element is blown or desoldered.
- The action mechanism is stuck.
- The guide plate comes out.
|
- Reasonably adjust the setting value.
- Remove the dirt from the contacts.
- Replace the product.
- Repair (but the user shall not adjust it at will. Otherwise, the action characteristics will change).
- Put it back in and push it a few times to see if the action is flexible.
|
| The control circuit of the thermal overload relay is not working. |
- The adjustment knob or adjustment bolt is turned to an inappropriate position, so that the contacts are pushed open.
- The contact is burned out or the movable contact rod is elastically lost.
|
- Readjust to the proper position.
- Repair or replace a new contact or moving contact rod.
|
| Thermal element burns out. |
- The load side is short-circuited and the current is too large.
- The number of repeated short-term work operations is too high.
- The mechanism is faulty, and the thermal overload relay cannot operate during the starting process.
|
- Check the circuit, troubleshoot or replace the product.
- Reasonable selection according to the selection conditions of thermal relays.
- Replace the product.
|
| The electrical equipment operates normally but the thermal overload relay operates frequently or the electrical equipment is burnt but the thermal overload relay does not operate. |
- The thermal overload relay setting current does not match the rated current value of the protected equipment.
- The fixing screw of the adjustable part of the thermal overload relay is not loose at the original setting point.
- After the thermal overload relay has passed a huge short-circuit current, the bimetal has been permanently deformed.
- The thermal overload relay has not been calibrated for a long time, dust is accumulated or rusted, or the action mechanism is stuck, worn, and bakelite parts are deformed, etc.
- The adjustable parts of the thermal overload relay are damaged or misaligned with the scale.
- The thermal overload relay cover is not covered or not covered properly.
- The external wiring screw of the thermal overload relay is not tightened or the connecting wire does not meet the requirements.
- The installation method of the thermal overload relay does not meet the regulations or the installation environment temperature is too different from the environment temperature of the protection electrical equipment.
|
- Replace the thermal overload relay according to the capacity of the protection equipment.
- Tighten the screws and re-adjust the test.
- Re-adjust the thermal overload relay.
- Remove dust and dirt, re-calibrate, normally once a year.
- Repair the damaged parts, align the scale, and readjust.
- Cover the cover of the thermal overload relay.
- Tighten the screws or replace with appropriate wiring.
- Install the thermal overload relay in the specified direction and configure the appropriate thermal overload relay according to the temperature difference between the two places.
|
| The thermal overload relay operates fast and slow. |
- Some parts of the internal mechanism are loose.
- Bending the bimetal during maintenance.
- External screws are not tightened.
|
- Reinforce and tighten the mechanism parts.
- Test several times with high current or remove the bimetal for heat treatment to remove thermal stress.
- Tighten the external screws.
|
| The main circuit fails after the thermal overload relay is connected. |
- The thermal element is burned out.
- The external wiring screws are not tightened.
|
- Replace the thermal element or thermal overload relay.
- Tighten the external screws.
|
| Thermal overload relay control circuit is not working. |
- The contact is burned or the elasticity of the moving piece disappears, and the moving and static contacts cannot touch.
- The contact head is pushed open because the dial or adjusting screw cannot be turned to the proper position.
|
- Repair contacts.
- Adjust the dial or adjust the screw.
|
Thermal overload relays are protective appliances used for overload protection of motors or other electrical equipment and electrical lines. In the actual operation of the motor, for example, in the process of dragging the production machinery to work, if the machinery is abnormal or the circuit is abnormal and the motor is overloaded, the motor speed will drop and the current in the winding will increase, which will make the winding temperature of the motor. If the overload current is not large and the overload time is short, and the motor winding does not exceed the allowable temperature rise, this overload is allowed. However, if the overload time is long and the overload current is large, the temperature rise of the motor winding will exceed the allowable value, which will cause the motor winding to age, shorten the service life of the motor, and even burn the motor winding in severe cases. Therefore, this overload is unacceptable for the motor. Thermal overload relay is a protective appliance that uses the principle of thermal effect of current to cut off the motor circuit when an overload that the motor cannot bear, and provide overload protection for various types of motors. But what if the thermal overload relay fails? Next we will troubleshoot the thermal overload relay.