It happens every time BC Hydro takes its northwestern customers off of its provincial grid so it can do maintenance or make repairs.

The provincial crown corporation then shifts to power produced by Rio Tinto鈥檚 Kemano generators which provide the juice to run the company鈥檚 Kitimat aluminum smelter.

But because Rio Tinto鈥檚 power has a faster hertz, or cycle rate, than does BC Hydro鈥檚 power, clocks using electricity also run faster.

BC Hydro calculations place its own power at 60 hertz and Rio Tinto鈥檚 at 60.3 hertz, fast enough to add 12 seconds an hour to a clock being run on electricity, a factor called 鈥渢ime error鈥�, said David Mosure from BC Hydro.

鈥淚n other words if the system is running fast for 10 hours, clock time will be 120 seconds faster than real time,鈥� he said.

In this most recent power switch of two weeks ago, electric clock users found them running approximately 15 minutes faster.

The switch affected BC Hydro鈥檚 northwestern customers as far east as Burns Lake with the crown corporation using Rio Tinto power as well as power from other independent power producers.

When BC Hydro isolates a region for maintenance or repairs, it鈥檚 then called an electrical island.

Power was back to normal over the weekend of Aug. 20-Aug. 21.

Clock applications in computers, smartphones or other devices tied into the internet are not affected as they take their times from the internet through satellite-based calculations.