The clocks in my school make a loud motor noise every 59th minute in every hour. Why do they do that?

You have a synchronized clock system. A small solenoid is energized every hour to correct the minute hand (=to make sure it is accurate). The electrical pulse is usually about 2-3 seconds long. This happens at the 58 or 59 minute mark (depending on system configuration). Then, usually at 5:58, a longer pulse of about 6-7 seconds occurs, and that corrects the hour hand. What happens with the long pulse, it "binds" temporarily the minute hand with the second hand until all hands read 5:58. Notches on wheels align at 5:58 (one wheel for each hand) and released the minute and seconds hands and the clock continues to operate normally.

Now, if a power outage occurs, you might have to wait until 5:58 for a correction because the window of opportunity for the hourly correction is in the order of a few minutes on some systems, and the correction of the hour hand is only twice daily. If you get a power outage at 6:00 and the clock is stopped for 11 hours and 55 minutes, for example, the next correction will need to make the minute hand rotate twelve times, which takes twelve minutes. You will then miss the hourly correction, and if the minute hand is too far from the "window", you have to wait until the next 5:58 for a better correction.

This system is all mechanical and electric. There are no complicated computers originally. Nowadays, they are typically used with a master clock that is electronic as the mechanical versions are too difficult to maintain, parts are difficult to source and all that jazz.

You most likely have a 3-wire system, where you have a hot and neutral (120V) for the clock motors, and a second hot (also 120V) for the solenoid. The second hot is only energized during the correction pulse.

Hope this helps.

Moderns systems have PoE clocks and a CAT 5 or better ethernet cable is run to all locations needing a clock. The clocks are all wired into a PoE switch in some wiring closet(s) somewhere in the building. They are all configured to get the proper time from an NTP clock. This NTP clock is typically the one in the main firewall to the building or some other important machine, which itself gets it from the internet. With a system like this, you can mix and match digital and analogue clocks. I have never really seen such systems, only read up on them a bit online so I don't really know how it behaves after a power outage. Digital clocks would come online fairly fast, however I'm not sure how fast analogue clocks would reset. I'm guessing within the hour, but ...

These clocks are quite expensive, running usually in the 300 dollar range.

Here very common is an alternating polarity minute pulse stepper system. There the master clock (originally pendulum "grandfather" clock, recently electronic quartz digital system) generates 24V DC pulses, each minute with alternating polarity. This is then distributed by a telephone-like wire pair where needed.
The receivers then contain a stepper motor, advancing the slave clock mechanism (both hand "analog" or even "flip digit" digital were in use) for "one minute" per pulse.
Some advanced models used mains supply rotating a "seconds" hand once a minute, stopping it at 59second mark and advancing to "0" with each pulse. With that the "seconds" hand/digits (in case of a flip digit model) remain synchronized with the clock.
The system relies on the slave units never dropping synchronization with the master.
The master clock contained an auxiliary slave mechanism and a comparator switches, which send the pulses at high rate (~1second; when the slave mechanism lags behind the master clock) or stop any pulses (when the slave is too advanced; e.g. after time readjustment on the master clock) to the line till the slave mechanism becomes again in sync with the master clock. As the auxiliary mechanism sees the same pulses as all the slave display units, they remain i sync regardless what the power outages are doing.
More modern systems with electronic quartz master (in the 80's, they were using 8048 microcontroller for that) were using backup battery and so generate the pulses regardless of the mains power. The adjustment transitions were then handled by the firmware in a similar way what the comparator contact was doing in the mechanical original...

Thank you guys this really helps!

Member streetlight98 says the hourly correction (corrects the minute hand only) happens at 57 minutes and 54 seconds and has an 8 second pulse and the twice daily correction happens at 5:57 and 54 seconds and has a 14 second pulse. Is this true?

Thinking of that takes me back to grade school, where we had such a master clock system, with the approx. 8 second buzz around the top of the hour, and the second hand that continuously swept around the face instead of pulsing every second.  System was installed in 1979.

I remember when I used to be a sound engineer at the local hospital radio station in the early 80's. We had a big pendulum master clock in the engineering workshop that controlled all the clocks in the studios. In the days before everyone could get radio-controlled clocks, they were very useful at news time etc.

I will never forget the time that the BBC overran on a live outside broadcast event. We were due to close down at 10pm and switch output to BBC Radio 2. I had R2 all cued up on a spare fader and was just getting ready to do the changeover when they announced that they would be running late.

This was all very well, but I had my programme all timed to finish precisely at 6 seconds to 10 so we could switch out just as the time pips were sounding for 10pm..! So I had to fade up on whatever they were broadcasting, which was in the middle of someone speaking if I remember correctly, which did nothing for my professional pride.

THEN, after all that, they played the **** pips  

Those pips are electronically generated by a system linked to an atomic clock, and are only fed to broadcast stations every 15 minutes (why, I will never know, as they're only ever used on the hour). Those pips HAD to be recorded..! I have never heard of this either before or since, but I swear it is the truth  

My elementary school had these clocks. It also had record players, cassette TV combos, mercury gym lights F40 and incandescent hallway lights, a vintage PA system, asbestos tiles, radiator heating and a generally old vibe to it. We only had a few laptops from like the 90's. The teachers were also all old timers. Glad to have experienced the olden days in the modern Era.

I remember melting crayons like a jackass on the radiators lol. Also remember hearing the "scary pipe clanking" up in the dark hatch way going above the theatre. It was the boiler pipes I realize now! I'd love to hear that again. If I ever build a house it will have radiator heating.

The school is Coburn Elementary School in battle Creek michigan. I went there from the years 2005 to 2008 or 10 (I forget) I went there my entire elementary school cycle. The school closed in 2013 and I'm sure it has been remodeled by now unfortunately.

My elementary school had these clocks. It also had record players, cassette TV combos, mercury gym lights F40 and incandescent hallway lights, a vintage PA system, asbestos tiles, radiator heating and a generally old vibe to it. We only had a few laptops from like the 90's. The teachers were also all old timers. Glad to have experienced the olden days in the modern Era.

2005-2008 is awfully late for that equipment. Here, it was all gone for the most part by 1995. The last of that list to go were the F40 lamps and the VHS tapes. When I was in elementary school starting in about 1985, we had all that and in addition, we had an 8mm film projector, slide projectors and filmstrip projectors. The music room had a turntable/AM-FM radio/8-track combo unit. The 8-track was never used ; the teacher had a separate cassette player instead.

Oh, and all schools in my part of the district still have radiators, although they are modern with a finned pipe and a steel cover (as opposed to cast iron).

My elementary school had these clocks. It also had record players, cassette TV combos, mercury gym lights F40 and incandescent hallway lights, a vintage PA system, asbestos tiles, radiator heating and a generally old vibe to it. We only had a few laptops from like the 90's. The teachers were also all old timers. Glad to have experienced the olden days in the modern Era.

I remember melting crayons like a jackass on the radiators lol. Also remember hearing the "scary pipe clanking" up in the dark hatch way going above the theatre. It was the boiler pipes I realize now! I'd love to hear that again. If I ever build a house it will have radiator heating.

The school is Coburn Elementary School in battle Creek michigan. I went there from the years 2005 to 2008 or 10 (I forget) I went there my entire elementary school cycle. The school closed in 2013 and I'm sure it has been remodeled by now unfortunately.

I’m amazed that they were still using incandescent lamps in the hallways. I though that most of that was replaced by the 1960s for fluorescents. It must have been a pain for the janitors to have to replace all those bulbs every few months. It also must have cost a lot of money, considering how much money high wattage bulbs cost.

I have one of those clocks but I need to make a circuit that simulates the correction pulse.

Yeah, the last time I remember seeing a classroom record player in a school was around the late 90s. Cassettes I think were still in use until the mid 2000s. VHS I think stayed until the late 2000s. I think the schools I attended just tended to keep older equipment around, I gotten a few worksheets that looked like it was printed with a spirit duplicator instead of a photocopier. The overhead projectors pretty much stayed for the entire time I was in elementary/high school. I remember having to format powerpoint presentations to fit onto overhead slides since the classrooms weren't equipped with video projectors. I don't remember seeing a 8mm film projector but I do remember the film strips and the cassette/CD that accompanied them.

As for lighting I think the F40s started to get phased out in the mid late 2000s here with the last going by 2010. I remember seeing incandescent accent lighting but the school buildings I attended were newer so most of the lighting was fluorescent.

Pretty much all schools and university buildings here still use more modern radiators for heat, with the newer buildings also having ducts for air conditioning. Older schools still don't have air conditioning though. My elementary school was old enough to not have air conditioning but new enough to have the narrow opening awning windows that schools that had air conditioning typically had. Needless to say I baked in the classrooms every June. The teachers used to leave most of the classroom lights off in June to reduce the heat load in the classroom.

Dealt with a radio station that used a master clock in the engineers office to sync the studio clocks.This system was used at the VOA transmitter sites.The VOA studio used the clock system that used to be in schools.All have been replaced with digital systems.Ref to WWV and NBS time standards.

I have one of those clocks but I need to make a circuit that simulates the correction pulse.

You could probably build one with an Arduino.

My elementary school was built in 1991, and it had square clocks with a black frame, which were mounted on a rectangular metal grille, which was white. On one side it had the speaker and the other was the clock. I don't remember what name they said on them, but they had the sweeping second hand and were synched together.

In middle school, which was a little older, I think they had a similar setup but I can't remember.

At high school, there was one square speaker with a square clock next to it. The clocks said DuKane on them, but I think they were all battery powered and not synchronized. That school was originally built in 1970-71 but the newer parts were from the late 90s and early 2000s and they just had square Bogen speakers and cheap Ingraham battery clocks mounted on the bulletin boards.