Circuit Breaker Tripping Units.
Draw-Out Circuit Breaker A trip unit is the part of a circuit breaker that automatically opens the contacts of the circuit breaker in the event of a short circuit, ground fault, or thermal overload. There are two types of trip units; the thermal-magnetic trip unit, and the electronic trip unit. A thermal-magnetic trip unit has moving parts. It consists of a bimetallic thermal device that opens the circuit breaker with a delay depending on the magnitude of overcurrent. It also consists of a system where magnetic forces proportional to the current flowing through the circuit breaker are used to actuate the breaker. Simply put, in the event of a short circuit, high current flows and a strong magnetic field is created. This magnetic field is used to actuate the trip mechanism. An electronic trip unit is a programmable device that measures and times the current flowing through a circuit breaker and initiates a trip signal when appropriate. There are 6 common current protection