Thanks for all the comments. I didn't know so many problems were out there that were time-of-day dependant.
This reminds me of a 'How do They Do It' type of TV show I saw once that described how the UK has a small hydroelectric power plant that is usually held in reserve. One of the main purposes of the plant is to pick up quickly on short term surge loads on the UK grid. The controllers watch soccer (football in the UK) as a part of their work! WHy? Because after a big match involving a British team, after the clock runs out, nearly every household in the country turns on their electric tea-kettles; causing a huge surge. They watch the game in the control room and start spooling up the turbines in the last seconds of the games to meet the sudden demand.
One of my favorites for same-time-each-day problems was the factory in India that experienced an energy surge every day around noon. Turns out factory workers were ifring up a factory heater each day to warm their lunches.
I recall a similar problem years ago at a small shop with outdated, badly-isolated wiring. In this particular case, the various automation processors (which, back then, were much more finicky about line power than today) would start glitching right around lunch time. It turned out that the root cause was the sudden loads and power factor fluctuations caused by all the microwaves in the break room being put into use at roughly the same time. Some circuit isolation and superior power conditioning fixed the problem.
When I was young and wore a uniform, (never mind which uniform, thats classified) we had a similar problem where distribution panel breakers often tripped a few minutes after 8:00 am. The reason was obvious - everyone returned to the labs/offices after morning parade and powered up the kettles for coffee.
We recently saw a similar issue on an assembly station that was primarily pneumatic. We had changed the schedule on the station to have break coverage instead of running over break. We saw an increase in productivity during the breaktime that we had not expected. On normal production times the other assembly areas on the same air compressor line were robbing air from the station causing it to run slowly. We corrected this issue by adding additional compressor capacity and increasing size and saw increased productivity on the entire line.
Long ago I worked on industrial control systems. The processor was a pdp-11/05, that like all of its era, had the bunch of LED's and the usual row of "teeth" - switches that let you directly examine memory, etc.
We had a site that was experincing daily failures, every morning about 2 hours into the shift. A discrete video monitor showed the problems. It seems that the crew had developed a game - they would hit the halt switch, count the number of lit bulbs, and then hit run. The number determined who was paying for coffee that day.
The computer lived in a controlled space, several hundred feet from the actual machine. It communicated with the factory floor with a serial line (current loop no less) that polled the various sensors, and ran the display and control relay box. If it happend to be doing a display update when halted, no big deal. If instead, it was recieving gauge data, the UART would overrun, which would be noiced after restart, and the "SERVICE" warning light would result in a service call.
The solution was fitting a lock to the door on the computer rack.
This is a classic Sherlock story in that it deals with the strange things that routinely happen at the same time every day. I recall another one about an electric billboard that was the cause of mysterious voltage drops at a nearby office. I'm always amazed that our readers can find the source of these peoplems. As I've said before many times, we've got smart readers.
I have seen a number of Sherlock Ohms stories that cover problems that happen around lunch time. That's the time of day when human behavior changes for an hour, then changes back. That's a huge clue in determining what's gone wrong.
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