The magnetic circuit breaker has ______ trip action.

The magnetic circuit breaker has ______ trip action.

Right Answer is:



Electromagnetic circuit breaker

This device relies upon the magnetic effect of a current-carrying conductor for its operation. If the current flowing through a thick coil of wire, in series connection with the circuit, rises to an excessive value, the magnetic effect associated with the current causes a moveable metal-core to be drawn into the coil. The metal then strikes a bar, which operates a trip mechanism, causing the circuit to be opened and the current flow to be stooped.

Because magnetic-type circuit breakers do not depend on heating a bimetallic strip, there is a very little time delay in the opening of the contacts when an overload occurs. For this reason, they are often referred to as instantaneous circuit breakers. As current flows through the circuit, a magnetic field is established around the coil. The magnetic field attracts the metal arm of a solenoid. If the magnetic field becomes intense enough, the metal arm mechanically opens the contacts of the circuit breaker. Circuit breakers that operate on this principle are referred to as magnetic circuit breakers.

Magnetic circuit breakers are designed to open quickly (“instantaneously”) under short-circuit conditions. The instantaneous trip current usually is on the order of 6 to 10 times (6x, or 600%, to 1ox, or 1000%) the current rating of the circuit breaker. A typical thermal circuit breaker will open a 10,000-A fault in about 40 or 50 ms, but a magnetic circuit breaker will open the same fault in about 10 ms. Under higher short-circuit current conditions, the operating speed of magnetic circuit breakers may be as fast as 3 to 4 ms.

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