Sixty Hertz Line Frequency Change

For decades, electric clocks have used the 60 Hz AC line frequency as a convenient source of accurate time. Many ESE clocks have used this as a reference (with the exception of clocks which use an internal crystal timebase, such as "Quartz Controlled" clocks, GPS, NTP, CDMA, WWV or Modem referenced clocks, or those economy clocks with "Option C" installed). Since the 1930's, the AC power grid has been regulated to maintain overall long-term accuracy for line-referenced clocks, adjusting the frequency fast or slow to compensate for drift. Recently, the North American Electric Reliability Corporation (NERC), which runs the nation's interlocking web of transmission lines and power plants, has proposed a yearlong experiment in which the AC frequency would be allowed to drift, without compensation. It is felt that adopting this new standard will lower costs and improve the reliability of the power grid, as the compensation process involves the rather precarious adjustment of many power plants on the grid. The experiment is proposed to begin in mid-July 2011.

The effects of this change will vary depending on the region - East and West coasts may gain or lose at different rates, with the East expected to be worse. Texas, which has its own power grid, is expected to be more accurate. Overall Estimates vary from 2-20 minutes per year, or possibly several seconds per day in parts of the East.

The solution to this, if it proves to be a problem, may be to add "Option C", or Crystal Timebase option. This allows the clock to run from the internal quartz crystal reference. The short-term accuracy is better with the quartz timebase - which has particular advantage in Timers - provided the crystal is adjusted accurately. The disadvantage is that the long-term accuracy may not be as good as the old line-frequency reference, as any inaccuracy in the crystal adjustment, or temperature drift effects, are not automatically compensated for and will add up over time. Of course, if this new power 'standard' is adopted this issue becomes academic - the crystal accuracy will likely be better than the power grid in any case.

In ESE clocks manufactured in the last 20 years or so, installing "Option C" involves adding a trimmer capacitor to accurately adjust the existing crystal (using a frequency counter) and disconnecting the AC reference component. See the Product Manual layout/schematic, or contact the factory for details. Of course, a GPS clock, such as the ES-185U, is the ultimate solution!