What factor can affect readings of a clamp-on ammeter?

• A. The color of the meter case.
• B. Temperature changes only.
• C. Nearby conductors causing magnetic field interference.
• D. The phase of the current.

Answer: (C)

Clamp-on ammeters measure current by capturing the magnetic field produced by the conductor inside the jaws, essentially working as a current transformer. When nearby conductors carry current, their magnetic fields also thread the clamp, adding to or opposing the field from the conductor you’re measuring. That stray flux changes the amount of flux the core sees, so the meter’s internal signal reflects not just the target current but also these nearby fields, giving an inaccurate reading. To get a clean measurement, clamp around a single conductor and try to keep other energized conductors away from the jaws. Other factors like the color of the case don’t affect the measurement, and while temperature or waveform quirks can influence accuracy in some meters, the primary factor described here is magnetic interference from nearby conductors.