ES = Errored Second
1 ES means there was a second-long period of time where errors were counted on the line. It is more of a statistical construct than anything else, and helpful for constructing a "mean time between errors" (MTBE) value.
The errors themselves are identified by failures in the CRC checksum process, and are counted in the CRC counter, and there can be many more CRC than ESs. A big burst of CRCs within one single second period is still only considered as 1 ES.
CRC errors are almost invariably caused by some noise/interference on the line. Which can indeed be caused by faulty appliances, or even just the act of turning things on or off.