This article by AP has the makings of one of those email memes that spring up to scare everyone.
“A yearlong experiment with the nation’s electric grid could mess up traffic lights, security systems and some computers — and make plug-in clocks and appliances like programmable coffeemakers run up to 20 minutes fast.
“A lot of people are going to have things break and they’re not going to know why,” said Demetrios Matsakis, head of the time service department at the U.S. Naval Observatory, one of two official timekeeping agencies in the federal government.
“Since 1930, electric clocks have kept time based on the rate of the electrical current that powers them. If the current slips off its usual rate, clocks run a little fast or slow. Power companies now take steps to correct it and keep the frequency of the current — and the time — as precise as possible.”
So, I looked for a rational source of information and turned to, whom else, General Electric. Bill Pezalla, Industry Manager – Power & Energy, at GE Intelligent Platforms in Charlottesville, Va. told me:
NERC is conducting tests on the elimination of the amount of time the utility can be at above/below 60Hz over a certain period of time. Part of the test is to determine the impacts of grid variations on time keeping.
The North American power grid works on Alternating Current (AC) of approximately 60 cycles per second (Hz). Initially clocks were designed to use this as their time keeping method. However, as customer uses (loads) increase and decrease, generators come on-line and go off-line, the frequency can change from 60.00003 Hz on the high end to 59.95 Hz on the low end. In the early 20th century, this variation was even greater as it was controlled through mechanical rather than electronic means.
Clocks in the early 20th century therefore had some variation because they did rely on the power grid for their time keeping. Clock manufacturers realized that relying on the electric grid frequency was not a good way to base their time keeping. So many developed other methods. Many solid state devices have internal clocks, that are built into the circuit board and operate independent of the grid’s frequency. These use quartz resonators.
Utilities measure the frequency constantly as all generation sources that are connected to the electric utility grid need to be operating on the same frequency, but some small variations still exist. The utilities talk about changes in frequency in terms of speeding up or down in “number of clock- minutes” over a period of time. The NERC test may cause variation on the number of clock-minutes per day. This would cause slight daily errors on clocks that rely on the grid frequency.
Some manufacturers of devices that use a clock for a secondary purpose, such as turning on a coffee pot, may have gone back to relying on the grid frequency. It is unknown at this time how many different devices with built in clocks or actual clocks are using the grid frequency. It is highly likely that devices used for time keeping as their main purpose are utilizing quartz resonators and those with clocks built in for secondary purposes may be using the electric grid. This may cause a difference between some clocks around a customer’s house.