Electrical problems in school

[carlday]

Hi All


I work in a school and we have started having problems with our computers/computer rooms.

The problem is every morning when we come in the trips have gone supplying the computer rooms. It never happened till after half term we have not changed any computer or changed the way they are wired.

Trips that go a square d Kq 40A type c they are connected from a distribution unit to another single phase board.

Current usage during day on mcb is 11A, voltage at school seems to vary from 235 to 245 during the day.

I think we are have big brown out between 7am and 8am every morning which is causing trips to trip on voltage rise back to normal because of the computers high leakage. I am right

Could the brownout be caused by school heating coming on (massive pumps) or could it be grid voltage drops.

Should we consider changing mcbs to type d.

Does anyone know a way we can data log the mains voltage?

Any ideas would be great.

Thanks

Carl

 

[ricicle]

You could ask the local supply company if they are having any network problems or any other businesses etc in the local vicinity if they are experiencing the same.

 

[carlday]

I thought about asking eon but I thought they might not admit to having problems if they were. There are no business in the area only houses.

 

[TicklyT]

you could find out when the trip is occurring by plugging a cheap n cheerful mechanical time switch into one of the affected sockets, and reading the time off the dial before re-setting the breaker.

 

[dannyboi2003]

The trips that are tripping out, are they the main breakers that then feed a separate board in the IT room(s), if so are they just standard type c mcb's or are they rcbo's ?

Also what sort of computers do you have in the rooms in terms of brand and have they got flatscreen or crt monitors?

I work in a college so have experienced similar problems, usually to do with rcbo's though. We replaced all the machines in our IT block last year, we had a power cut some time later and when it came back the surge of the newer pc's coming back on threw the main breaker for the first floor (100amp 3-phase). Hasent happened since - so far!

Anyway i digress, when this happens are the pc's still switched on at night or powered off, maybe try turning all the plugs off in one of the rooms and see what happens. Its probably just a brief brownout in the night and the inrush current of all the power supplies is enough to trip the breakers.

All the best
Dan

 

[carlday]

The trips that trip are standard mcb powering the board that has the rcbo's, the board with the rcbo's in have 5 radial circuits covering the it suites. (32 computer)

The computers are desktop computers (HP) with flatscreens. We now know that the problem happens at around 7.15 most mornings.

The computers are powered off when it happens.

 

[dannyboi2003]

Its probably a brownout in the area around that time in the morning, are you able to ask any neighbours if they have noticed the power going off then back on again in the mornings? If its a network problem then your DNO will need to look into it. Only way i can see round it for now is to ask staff to make sure the systems are switched off at the wall at the end of every day.

There are devices you can get to monitor the incoming mains supply but i dont know much about them so someone else will probably reply to suggest something.

 

[mikeyd]

Do these computer have wake on lan enabled?
I wonder if they are all being remotely told to turn on at the same time and the high inrush is tripping your breaker.
If they are all connected to a network hub/switch serving just that room you could try unplugging it overnight.

 

[TicklyT]

Wake on LAN would require the machines to remain powered up overnight, but in a dormant state and drawing little from their power supplies. There would be no cold inrush current, as the power supplies are already running, just an increase from the dormant to the normal running current.

Are there any other devices supplied from the affected circuits?

One school installation I have seen had a router and LAN switches powered through a time switch set to switch off at about 5PM, and on again at about 8AM. I still don't know why they chose to switch the router off instead of using time dependant routing policies implemented in the software - At least it kept me in business swapping popped power supplies and installing software updates that were normally downloaded overnight by the network operator.

 

[RF Lighting]

I can't see why voltage fluctuations would trip an MCB

 

[mikeyd]

Wake on LAN would require the machines to remain powered up overnight, ....

Wake on LAN can actually power up a machine, assuming it's an ATX power supply, it's still plugged into the mains and the motherboard supports it.

 

[Aragorn84]

Yep, even when "off" an ATX PSU provides a low current 5v feed to the motherboard which it can use for WOL and suchlike.

 

[Steve]

Yep, even when "off" an ATX PSU provides a low current 5v feed to the motherboard which it can use for WOL and suchlike.

Indeed, because otherwise, the "on" button on the front of the case would have to be wired to the 230v mains supply!

 

[sdavies21216]

It's not very likely but some motherboards have a 'resume by alarm' where you can set the computer to automatically turn on at a certain time. This could be creating the inrush current that is tripping the breaker. Just a thought as I would think it would be very unlikely that anyone has turned it on.

 

[mikeyd]

Good idea sdavies21216, some bored kid set all the computers to wake up at the same time. Thinking back (a long time) it might have been something to do for a laugh. The PC's will have had their clocks synchronised automatically so they would all power up at the same time.

I suggested the Wake-on-LAN theory for the same reason, it must be something that is causing all the PC's to turn on at once.

Hopefully carlday will update us.

I can't see how an external power dip could cause a MCB to trip in this case. I do know that switching power supplies will try to draw more current if there is a voltage drop but that only works if more current is available, which there won't be if it's a power dip that's causing the voltage drop.