If a clamp-on ammeter probe is clamped around both the power wires and the ground wires, shouldn't it read zero amps because the magnetic fields should cancel?
I recently measured the amps that my computer motherboard drew by clamping the AC/DC probe around the two yellow +12V wires of the auxillary 4-pin power connector. The meter read 4.7A, but when I tried also clamping the two black ground wires on the same cable, the reading dropped to 2.6A. I taped the wires together and even tried arranging them to alternate yellow-black-yellow-black, but the reading stayed at
2.6A.