in my apartment I noticed recently that my bedside clock and oven clock, which are both powered from the wall, were about 15 minutes ahead. I changed them back to the correct time, but the next day they were already a few minutes ahead. I have also had a few WiFi routers suddenly stop working over the past few months.

Could this indicate that something is wrong with the electricity in my apartment? If so, what can I do to check it myself before calling an electrician?


Update: I contacted the power company and it turns out that the mains frequency was, in fact, higher than normal. There was a water main that burst (and caved in part of the street) in my neighborhood and the city feared that it would damage the underground powerlines, so they turned on the emergency power generators to ensure that nobody would lose power, even temporarily, while they fixed the water pipes. They said that they had to increase the mains frequency in order to prevent damaging the generators. They ran the generators for about a week, but service is back to normal now. My clocks are functioning normally again and it turns out that my router issue was unrelated. Thanks for everyone's input!

  • 1
    Don't be two fast to accept an answer. Are these digital clocks or analogue. There is NO way the supply frequency will be of more than 1 hz. Digital clocks in close proximity to a RFI electrical noise source can cause the problem.
    – Ed Beal
    Sep 13, 2017 at 13:32
  • These are both digital clocks. This is a relatively recent occurrence that seems to be worsening. The routers started going bad over the past few months. I only noticed the clocks a few days ago. After resetting them to the proper time the other day, I was surprised to see how quickly they lost time. I am suspicious about the electricity in the apartment because these are two different clocks in different rooms with the same problem that seems to have appeared at the same time.
    – Iceape
    Sep 13, 2017 at 13:35

3 Answers 3


These types of clocks usually keep time by counting mains cycles rather than using any sort of internal timer chip.

So, if your mains frequency is too high, they will run fast. The fact that two clocks are running similarly fast is another clue that this may be the case.

It is conceivable that too high a frequency is upsetting your routers. If you have a technical manual for them that might give a frequency tolerance figure.

To check the mains frequency yourself, you'll need an oscilloscope. Pretty much any oscilloscope will do.

There is a quality standard for the frequency of the mains supply. You can always challenge your electricity supplier and get them to measure it.

If your frequency is different from other nearby homes, then something is interfering.

You could try an online tester such as this one but I can't vouch for their accuracy. It might at least give you an initial guide but it seems black magic for a webapp to tell you your mains frequency.

  • Would an oscilloscope like this work? Or should I not worry about checking it myself and just go ahead and call the electric company? amazon.de/Digital-Oszilloskop-Handheld-Taschen-Elektronische/dp/…
    – Iceape
    Sep 13, 2017 at 9:30
  • Pretty much any oscilloscope will do the job.
    – Chenmunka
    Sep 13, 2017 at 9:36
  • Wow that online one is really cool. I'll start with that as I can at least get a point of comparison from a few different places then see what my apartment shows. Thanks
    – Iceape
    Sep 13, 2017 at 9:39
  • 1
    Wow for a clock to gain that much time the frequency would be way higher. Digital clocks do not use the supply frequency they have oscillators that are crystal based for the time much higher than 50/60 Hz. This was marked as an accepted answer but is out in la la land. -
    – Ed Beal
    Sep 13, 2017 at 13:22
  • 1
    Update: You were correct that the mains frequency was too high. It was intentionally done by the power company and affected the whole neighborhood.
    – Iceape
    Sep 24, 2017 at 7:34

Digital clocks convert the AC line voltage to DC and in most cases use a crystal oscillator but in some designs multi vibrator circuit or rc time constant circuit at many times the line voltage frequency for improved accuracy. I have seen RFI (radio frequency interference) that can screw up the internal oscillator. Power spikes & drooping can cause the Power supplies that power routers to hiccup requiring reboot. You may have voltage fluctuations and or RFI problems but I have never seen frequency variations of more than + - 1Hz when measuring in the U.S. , Japan or Singapore. An inexpensive way to reduce electrical noise is to add an RFI filter, these require a ground to work well and they are just some basic electronics that dump higher frequencies protecting the equipment. I would purchase an inexpensive inline one to test if it works a few more on the affected clocks & routers would solve the RFI problem.


Ask your power company

Because mains frequency is serious business, and if anybody will know that -- they will!

Yes, many mains-powered clocks either use synchronous motors or count power pulses to keep sync with time. In the industrialized West, mains power frequency is considered a "gold standard" and many devices are built with this expectation. Before really good crystal-based clocks, this was the only way to have really reliable time.

In the third world, not so much. Also anytime you have to fall back onto locally generated emergency power.

In the UK, the mains frequency often lags very slightly during the heavy-load working day. In evening at lower load, they intentionally hasten the generators slightly to make up the exact number of cycles that should exist in a day.

If you can't make it work, you may need to resort to Internet powered clocks or ones with onboard crystal timekeeping.

I suspect the router problems are unrelated. However extremely high line noise might create the illusion of false cycles, which might throw off a line-listening digital clock. Wouldn't affect a synchronous motor clock, as motors can't double their speed suddenly like that.

  • I'm going to contact my power company. My concern isn't about my clocks, as I rely on my phone for time, but that there is something wrong with my apartment. I am just suspicious that two clocks coincidentally having the same issue at the same time is a symptom of a larger electrical problem. At minimum, I am afraid of more electrical equipment being damaged such as my routers, but at most I am worried about an electrical problem with my apartment leading to a fire. Thank you for your explanations!
    – Iceape
    Sep 13, 2017 at 16:22
  • Update: you were correct that the router issues were unrelated.
    – Iceape
    Sep 24, 2017 at 7:27

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