May 2010 Palo Alto California
A group of doctoral students at Stanford could not figure out why their electrical bill was high even when they used very little power.
The reason was that the building wiring was messed up and their meter was actually the neighbours meter and visa versa.
I expect that this mix happens a lot when electricians do not pay strict attention to what they are doing because the the pressures of time. PG&E admitted in 2010 that 23 thousand Smart Meters had been installed incorrectly.