Why does a circuit breaker need a dc for tripping

A circuit breaker doesn't actually need a DC (direct current) to trip. In fact, most circuit breakers are designed to operate on AC (alternating current) power.

So, why do I say "a DC for tripping"? Well, it's because some circuit breakers use a small DC power source, often referred to as a "trip coil" or "trip current", to trigger the tripping mechanism. This DC power source is typically used to energize a solenoid or a relay that opens the circuit breaker contacts.

Here's how it works:

  1. When a fault occurs in the circuit, the current flowing through the circuit breaker exceeds a certain threshold (called the trip current).
  2. The trip current flows through a small DC coil, which is connected to the trip coil or trip current source.
  3. The DC coil energizes a solenoid or relay, which in turn opens the circuit breaker contacts, disconnecting the power supply to the circuit.

The DC power source is used for several reasons:

  1. Reliability: DC power is more reliable than AC power for triggering the tripping mechanism. AC power can be affected by voltage fluctuations, harmonics, and other issues that might prevent the circuit breaker from tripping correctly.
  2. Speed: DC power can respond faster than AC power to changes in current, allowing the circuit breaker to trip more quickly in response to a fault.
  3. Sensitivity: DC power can be used to detect smaller changes in current, making the circuit breaker more sensitive to faults.

In summary, while a circuit breaker doesn't need a DC power source to trip, some circuit breakers use a small DC power source to trigger the tripping mechanism, providing improved reliability, speed, and sensitivity.