Magnetic Overload Relay Testing with the CB-845

  • Uncategorized

Magnetic overload relays are protective devices often used in motors. It trips the current if it senses the motor draws current above its rating. This protects the electrical system from overloading and the motor from overheating. These devices have a time-delay to prevent tripping every time a motor starts.


The initial in-rush current when a motor starts usually exceeds its rated current. However, since the surge is only brief, it doesn’t harm the motor. A magnetic overload relay should have a time-delay mechanism to prevent it from tripping during motor starts. You cannot set the trip point higher because if the motor draws current above its rating, the relay won’t be able to protect the motor because the setting is too high. It is essential to regularly test these protective devices to ensure continuous service and prevent accidents. A high current test set like the CB-845 from Megger test equipment is used to test magnetic overload relays. It simulates over current conditions and determines if the relay will trip according to its specifications. It can provide a continuous current of 1200 Amperes and an instantaneous current of 5000 Amperes. 

If you are interested in the CB-845, get it from Protec.