Power in suite keeps tripping!

[titch]

Hope someone can help with this as its driving me mad.

 

Most mornings when I come in the power in our ict suite has tripped, which means I have to manually turn pcs on (instead of wol) which isnt to bad..but on mornings when Im not there I dont like the idea of other people having too turn the power back on via the switch box as if all the switches are turned on too quickly the power in the main switch cupboard will also trip.

 

 

Now a little background, Spiradically some of the psu have been dyeing in the suite, Im not sure if this is the cause or the effect of the constant tripping either way I know some of the psu's are on there way out although I have replaced 3/4 of them now.

 

Is there going to be a simple way to diagnose where the fault is coming from, and what time maybe the power has tripped to see if that has any relation. The strange thing is the power trips more in the night (when no pcs are switched on) than in the day when they are all on. The rccb says 80a 30ma on. And we have 34 pcs and monitors running from it. Our sparky (who I trust) has told us the fualt isnt with the switch but some of the units we are using, but is proving a mistery to me which ones are causing the fault.

 

If anyone has any ideas they would be greatly appreciated as it is very frustrating!

 

Heres a picture of the switch box if it helps anyone, each of the switches represents a row of pcs then the one that says pr1 is the projector.

 

http://www.orchard-jun.hants.sch.uk/IMG_0948.jpg

[plexer]

How many pc's in each row being feed by each of those rings?

 

Ben

[titch]

5/6 depending on row.

 

Cheers for quick reply

[plexer]

It could be the psu's in those units we have 6 - 8 I'd guess on a ring in the main suite and don't have an issue but I have seen it before.

 

Is there anything your sparky can do to test the pc's at all?

 

Ben

[FN-GM]

If you use WOL its probably not helping that all computers are going on at the same time. You could try staggering them like 8 at a time or something.

[plexer]

Marc's Technical Pages: Power Quality Symptoms and Solutions - Leakage Current in Technology bit of nice reading.

 

Are the monitors switched off at night?

 

Ben

[Jamman960]

Is it individual rows that trip? and is it the same rows that trip each time?

 

It may be worth ensuring the monitors aren't on standby overnight, I've known monitors to cause trips every now and then.

[Little-Miss]

Last time i had a classroom that kept tripping, it turned out to be a dodgy monitor! I only worked it out when the monitor finally cooked itself, was replaced and it never happened again.....

[p858snake]

Has every electrical device (monitors/towers/printers/network switches/vga split boxes ect) been tested and tagged?

[Cools]

i would up the trips to a higher amp trip and the RCD to, it will stop it. but its not the best fix.

 

its the CRTz that do it,thats if you have any?

 

Both my ICT rooms have 3 trips 30mA and both rooms have 32 PCs all WOL.

never triped once.

[titch]

If you use WOL its probably not helping that all computers are going on at the same time. You could try staggering them like 8 at a time or something.

 

Funny thing is has never tripped when waking all the computers at once.

 

 

Marc's Technical Pages: Power Quality Symptoms and Solutions - Leakage Current in Technology bit of nice reading.

 

Are the monitors switched off at night?

 

A light bit of reading...think I got the jist of it. I have tried turning monitors off (at button not power switch) but doesnt seem to make much difference. I take it its better to have them off then?

 

 

Is it individual rows that trip? and is it the same rows that trip each time?

 

Well the there is only 1 rcd so whatever trips take the lot with it. So what I do is turn all rings off, then rcd on, then one at a time switch the individual rings back on. I guess in an ideal world each ring would have its own rcd?

 

 

Last time i had a classroom that kept tripping, it turned out to be a dodgy monitor! I only worked it out when the monitor finally cooked itself, was replaced and it never happened again.....

 

 

Any way of diagnosing this before it frys you think?

 

 

Cheers for all the help.....off topic and sure its asy but how do you qoute more than one person at a time?

 

Thanks Rich

[Arcath]

Cheers for all the help.....off topic and sure its asy but how do you qoute more than one person at a time?

 

<< Multi quote, click on all the posts you want to quote than click "Post Reply"

 

I dont think theres any way of diagnosing a dodgey monitor (other than funny colours/lines) if its causing power issues your sparky might be able to test it, but even then it might only cause an electrical fault under certain circumstances

[robk]

Looking at that board, all of the leakage current for all of the machines is being measured by that one RCD. This lead to nothing but problems with us.

 

Leaking CRT monitors, power supplies and simple filtered sockets all add up to a large background level of earth leakage. Anything slightly off will push it over the edge.

 

We ended up fitting RCDs per bank of sockets, but its not a cheap fix.

 

Problem is, turning off banks of machines will drop the "background" level, and hide the issue!

 

Try unplugging a system (at the wall) one at a time, see if it stays on over night?

 

RobK

[Gerry]

Turn everything off at the plug except 1/2 the monitors. If it trips you know which 1/2 is causing the problem. Repeat until you're left with the faulty monitor(s).

[ICT_GUY]

We had similar probs in our new suite, we had the trip switches changed to be less sensitive.

[srochford]

I think 30mA RCD is too low for that many machines.

 

The page linked to by @plexer shows that you can have up to 3.5mA leakage per device and it's considered OK; with 34 machines you've got 68 devices so even if they each only have leakage of 0.5mA you're going to trip.

 

Murphy's law says that you get more leakage as the machines are switched on; it then drops to a lower value - this is why you can switch them on one at a time without problem.

 

You either need to increase the trip value for the RCD or split the circuits so that you have multiple 30mA RCDs (eg 1 per 10 machines)

[laserblazer]

We get it in one suite after holidays. I put it down to the lack of heating and the computers getting cold and damp. If I stagger the switch on it's ok.

[Andrew_C]

Not quite clear here; is it the RCD (far left) or the MCBs that are tripping?

 

I would concur with those above that a single RCD is wrong for that many PCs, but find it hard to explain why it trips overnight. Unless the cleaners' vacuum is the final straw?

 

Some bios have a facility to wake on power restoration, which whilst not curing the problem, could make your life a bit easier.

[ICT_GUY]

I think 30mA RCD is too low for that many machines.

 

The page linked to by @plexer shows that you can have up to 3.5mA leakage per device and it's considered OK; with 34 machines you've got 68 devices so even if they each only have leakage of 0.5mA you're going to trip.

 

Murphy's law says that you get more leakage as the machines are switched on; it then drops to a lower value - this is why you can switch them on one at a time without problem.

 

You either need to increase the trip value for the RCD or split the circuits so that you have multiple 30mA RCDs (eg 1 per 10 machines)

 

Ours have been changed to 100ma DCC not happy, but everything is earthed or double insulated and nothing is plugged or unplugged on a regular basis (read never).

[steveg]

If you've got a spare ups it may be worth setting that up on 1 pc and leaving that pc on 24 / 7. - It will then tell you the exact time the power cuts off, and will also tell you if you get any major fluctuations in voltage. (asuming its a reasonable ups!)

 

Steve

[BaccyNet]

Have had this kind of thing a few times now.

First time was with a re-wired server room. Every night it would trip, in the end the then NM stayed here all night and waited for it to trip, seemed the draw that came from the backups starting and then copying to USB disks caused it. Got trip changed for slightly less sensitive one and things were fine (server room has been re-wired again since then and this was taken into account this time!)

 

Second time was a dodgy PSU in a computer, it only tripped once though as the PSU gave up and it was during the day.

 

I agree with the suggestions that each ring should have an RCD on it. That way you wont lose all your computers every time and it will then narrow down whats causing it (only one RCD should then go)

 

Just my 2 cents:)

[elsiegee40]

Just to muddy the waters further...

when this became an issue in our suite, it turned out that the circuits weren't as 'dedicated' as I thought.

 

One ring had been expanded to put a socket in a room next door... and the problem was in there *harrumph*

[titch]

Cheers everyone for the helpful comments so good points to take home. Couple of bits I want to clarify.

 

Looking at that board, all of the leakage current for all of the machines is being measured by that one RCD. This lead to nothing but problems with us.

 

Leaking CRT monitors, power supplies and simple filtered sockets all add up to a large background level of earth leakage. Anything slightly off will push it over the edge.

 

We ended up fitting RCDs per bank of sockets, but its not a cheap fix.

 

Problem is, turning off banks of machines will drop the "background" level, and hide the issue!

 

Try unplugging a system (at the wall) one at a time, see if it stays on over night?

 

RobK

 

So when trying to find the fault I can only really do 1 at a time as turning off a whole bank makes the test a bit biased. I thought this in my head but wasnt sure if I was just making it up as when trying the method below never had a trip!

 

Turn everything off at the plug except 1/2 the monitors. If it trips you know which 1/2 is causing the problem. Repeat until you're left with the faulty monitor(s).

 

Im not sure if this method will properly work as stated above. If anyone could give a definate answer it would be helpful just to clear things up in my head.

 

I think 30mA RCD is too low for that many machines.

 

The page linked to by @plexer shows that you can have up to 3.5mA leakage per device and it's considered OK; with 34 machines you've got 68 devices so even if they each only have leakage of 0.5mA you're going to trip.

 

Murphy's law says that you get more leakage as the machines are switched on; it then drops to a lower value - this is why you can switch them on one at a time without problem.

 

You either need to increase the trip value for the RCD or split the circuits so that you have multiple 30mA RCDs (eg 1 per 10 machines)

 

I think this is the route we will take when I get some more money to play with. Add an RCB for each row rather than the lot. Just out of interest is this a quick job for a spark it would it take some time, I know the rcbs themseleves are a few quid each.

 

Not quite clear here; is it the RCD (far left) or the MCBs that are tripping?

 

I would concur with those above that a single RCD is wrong for that many PCs, but find it hard to explain why it trips overnight. Unless the cleaners' vacuum is the final straw?

 

Some bios have a facility to wake on power restoration, which whilst not curing the problem, could make your life a bit easier.

 

Yep sorry its the rcb not any of the mcbs they stay where they are. I have now turned the function on all the bios's to save me some time.....theres something about flicking a switch which turns on multiple appliances which I just dont like though.....

 

If you've got a spare ups it may be worth setting that up on 1 pc and leaving that pc on 24 / 7. - It will then tell you the exact time the power cuts off, and will also tell you if you get any major fluctuations in voltage. (asuming its a reasonable ups!)

 

 

Steve

 

 

Thats a spot on idea will fish out the one old ups we have and give it a bash to see what happens.

 

Just to muddy the waters further...

when this became an issue in our suite, it turned out that the circuits weren't as 'dedicated' as I thought.

 

One ring had been expanded to put a socket in a room next door... and the problem was in there *harrumph*

 

This is definately not the case...although of topic but upstairs in 1 of our classroms the people that installed 1 of the projectors/audio managed to install the switch for it in the classroom next door

[Andrew_C]

I think this is the route we will take when I get some more money to play with. Add an RCB for each row rather than the lot. Just out of interest is this a quick job for a spark it would it take some time, I know the rcbs themselves are a few quid each.

What you would need are RCBOs, which are combined RCDs and MCBs. Not cheap, but they are simple to fit and you won't need a new board.

something about flicking a switch which turns on multiple appliances which I just don't like though.....

Nothing wrong with that, unless you have a problem with the inrush current. This could cause fast acting (Type B or C) MCBs to trip. We suffered this, and had to put time delay contactors on 2 of the 3 circuits we have centrally switched.

[titch]

Would pat testing all my equipment help or would this be a waste of time, as Im not exactly sure what the a PAT tester tests for?