Our electric power provider delivers 240 V, 60 Hz split-phase power to residential buildings. I've been checking our three-prong receptacles and I normally get the following measurements:
line-to-line: 240 V
line-to-ground: 120 V
However, there are two receptacles which have a different line-to-ground reading: 60 V instead of the expected 120 V. For both, line-to-line is also 240 V; only the line-to-ground voltage is different.
What possible connection/grounding error could have caused this?