[time-nuts] And, for my next trick, 50Hz

Chris Cheney chris.cheney at tesco.net
Fri Oct 3 08:31:29 UTC 2008

On 3 Oct 2008 at 13:41, Steve Rooke wrote:

> Call me crazy but I wonder if my accurate relative period of time
> could be derived from the 230VAC 50Hz mains supply over here. Now,
> before you yell at me, consider this, I have a couple of mains driven
> clocks in the house and only seem to need to change the time on them when
> we go from Standard Time to Daylight Saving Time. Agreed, the
> instantaneous frequency of the mains is not always spot on but the long
> term average seems to be kept pretty accurate or we would all have to keep
> changing our mains timed clocks. If I knew the standard deviation of the
> mains, I could probably calculate the period of time I'd have to gate my
> breadboard "frequency counter" to achieve a certain accuracy.

A bit of Googling finds:

Frequency: "a variation not exceeding 1 per cent above or below the 
declared frequency;"
parentActiveTextDocId=1590332&ActiveTextDocId=1590368&filesize=4590 - 
section 27(3)(a))

Electric clock time: "NGET will endeavour (in so far as it is able) to 
control electric clock time to within plus or minus 10 seconds"
57338C31C86A/9922/BC3_i3r18.pdf - section BC3.4.3)

BTW wrt earthing via the incoming water main - in the UK, plastic pipe is 
commonly used for incoming water mains these days.


More information about the time-nuts mailing list