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Keeping Time On Time

Just as watches sometimes run fast or slow and must be adjusted, older electric clocks use electrical current’s frequency to stay accurate. To make this work, the electric grid’s frequency must be regularly corrected at power plants for “time errors.”

However, in mid-July, the North American Electric Reliability Corporation, the nation’s power grid watchdog, planned to begin a yearlong field test to discover if time error corrections hurt electric system reliability.

The grid runs in cycles, or hertz (Hz)—60 cycles per second—matching the 60 seconds per minute that keep time. Older electric clocks depend on that standard to remain accurate. Newer clocks contain electronics that stay accurate independent of the standard.

To adjust for fast time errors, the frequency is lowered slightly from 60 Hz to 59.98 Hz. The concern is that during a time adjustment, which can take several hours, the frequency is already below normal. If a problem drives frequency levels even lower, it could trigger emergency load-shedding measures.

The field trial will suspend time corrections in favor of stabilizing the grid’s frequency. As a result, older alarm and some appliance clocks could lose track of time a few seconds a day.


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