Earlier in March we heard about a quirk of the interconnected continental European electricity grid which caused clocks to lose about six minutes so far this year. This was due to a slight dip in the mains frequency. That dip didn’t put anything out of commission, but clocks that are designed to accumulate the total zero-crossings of the power grid frequency of 50 Hz don’t keep accurate time when that frequency is, say 49.985 Hz for an extended period of time.
An interesting set of conversations popped up from that topic. There were several claims that modern alarm clocks, and most devices connected to mains, no longer get their clock timing from mains frequency. I’ve looked into this a bit which I’ll go into below. But what we really want to know is: are your alarm clocks and other devices keeping time with the grid or with something else?