What principle does a clamp-on ammeter use to measure AC current without breaking the circuit?

What principle does a clamp-on ammeter use to measure AC current without breaking the circuit?

• A. Direct connection in series with the circuit
• B. Magnetic coupling between the clamp and the conductor
• C. Measuring voltage drop across a shunt
• D. Inductive coupling with an external coil

Answer: (B)

Measuring current without breaking the circuit uses magnetic coupling. The conductor carrying the current acts as a single-turn primary winding inside the clamp. When AC flows, it creates a changing magnetic field in the clamp’s core. The clamp contains a secondary winding that picks up this changing flux, inducing a signal that the meter converts into a current reading. This transformer-like action lets you measure the current without opening or altering the circuit. That’s why it’s different from methods that require putting a resistor (shunt) in series to measure voltage drop, which would involve breaking the circuit, or any setup requiring a direct series connection. It’s also distinct from relying on an external coil that isn’t enclosing the conductor.

Measuring current without breaking the circuit uses magnetic coupling. The conductor carrying the current acts as a single-turn primary winding inside the clamp. When AC flows, it creates a changing magnetic field in the clamp’s core. The clamp contains a secondary winding that picks up this changing flux, inducing a signal that the meter converts into a current reading. This transformer-like action lets you measure the current without opening or altering the circuit.

That’s why it’s different from methods that require putting a resistor (shunt) in series to measure voltage drop, which would involve breaking the circuit, or any setup requiring a direct series connection. It’s also distinct from relying on an external coil that isn’t enclosing the conductor.