Why MCB Trips Frequently
Generally, there are 10 main reasons for MCB tripping.
1. Overload: All MCBs are designed for carrying particular current in Amperes. If the load takes more current that the set value for more than the rated time, MCB trips. For example from a 16A MCB if Load draws more than 16A like 20A current the condition is said to be overload. And if the MCB is B Curve, after 13 second it will trip.
Reasons For Overload: Sometime people connect more load or use extension board with load, which is the main cause of tripping.
2. Short-Circuit: When there is a short-circuit between phases or phase to ground, the current gets an easy path and takes very high current, known as short-circuit. The short-circuit rating also, depends on Curve of MCB.
Reasons For Short-circuit: The main reason for short-circuit is accidently touch or cut of wires/cables.
3. Ground Fault: This is similar to short-circuit. If any phase touches the ground, the current gets an easy path and takes very high current, known as Ground fault. The short-circuit rating also, depends on Curve of MCB.
Reasons For Short-circuit: The main reason for aging of wires or accidently touch or cut of wires/cables.
4. Surge Current: There are few equipment which draws high current at starting and then takes normal current. But if at starting it draws more current for a longer period that the rating of MCB, it trips. The surge current rating also, depends on Curve of MCB.
Reasons For Surge Current: The main reason for surge current is motor load or electronic equipment. The battery charger or inverter takes surge current after power restore.
5. Under Voltage: You know power in a circuit is P=V I cos θ. Means I=P/(Vcos θ)
For constant load(Motor), If the voltage decreases, current will increase. Hence, due to under voltage, the MCB will overloaded and trips due to over current.
Reasons For Under Voltage: High load on transformer, High load on circuit, Manual tap at transformer, Unbalance load, Short-circuit, long distance from the transformer are the main reasons for under voltage.
6. Over Voltage: You know power in a circuit is P=V I cos θ. Means I=P/(Vcos θ)
For Resistive load, If the voltage increase, the current will also increases as per Ohm’s law. Hence, due to over voltage, the MCB will overloaded and trips due to over current.
Reasons For Under Voltage: Low load on transformer, low load on circuit, Manual tap at transformer, Unbalance load, Short-circuit are the main reasons for under voltage
7. Loose Connect: Loose connection causes heating of MCB terminals and then to bi-metalic strips, which trips the MCB
Reasons For Loose Connection: Wires may used without lugs. Or the load is varying very much from 0% to 100% which expands the terminals at full load and contract at low load and making the terminals loose.
8. High Room Temperature: As room temperature is high, MCB terminals and bi-metals are not getting cool timely and tripping the MCB.
Reasons For High Room Temperature: Small size room, no exhaust fan or AC, Summer season, AC ODUs are main reasons for high panel room temperature.
9. Wrong Method of Connection: Some MCBs are marked with polarity of connections. If care is not taken during connection, the MCB may trips.
10. Defective MCB: If the MCB is defective, it may trip..