went to work today, on a hospital we’ve been working atand we got there and a phase of works that we’ve have already done I tested itan powered it up last week, the lights were all flickering and one light sw onone circuit was switching another light on another circuit very strange, I tookthe db lid of then checked voltages I got L1-N 400 L2-N 230, L3-N 69v,
even neutral earth 230v, so I immediately turned the full db off faults didn'tdisappear, went down to section board it was an old proteus fitted in the1970's,,we used a spare way on it to feed the new db checked the voltages antthat they were fine,, so I took some loop reading l-n l-e l-e was fine l-n werehigh and unstable to I’m thinking loose neutral I turned off and on thesw a few times put contact grease n the fault cleared all is good,,,but whydid I get 400v down l-n is it due to an unbalanced load trying to balance itsself, and finding an alternative root back to the source via another phase anwhy did the rcbo not trip,,,rcbo only has neutral tail no earth,,,id reallyappreciate people opinions on this took me 3 hours of scratching my head onthis


 
Classic symptoms of lost neutral, should only have cost about one second of head-scratching! Yes, the different P-N voltages occur due to the imbalance of load currents, the difference of which would be the neutral current under normal circumstances. Make sure you really did find the fault as lost neutrals can wreak havoc, set things on fire, destroy valuable pieces of kit, cause major insurance claims!

Why would you expect the RCBO to trip? There's nothing specifically to cause overload (although it could happen when things are overrun/damaged) and nothing leaks to earth.
 
Classic symptoms of lost neutral, should only have cost about one second of head-scratching! Yes, the different P-N voltages occur due to the imbalance of load currents, the difference of which would be the neutral current under normal circumstances. Make sure you really did find the fault as lost neutrals can wreak havoc, set things on fire, destroy valuable pieces of kit, cause major insurance claims!

Why would you expect the RCBO to trip? There's nothing specifically to cause overload (although it could happen when things are overrun/damaged) and nothing leaks to earth.

I think the cause was a sw fuse on the old section panel,, the sw fuse has never been used and is from the 1970's so I think it was just poor contacts,,, once it was turned on and off a few times the fault cleard,, how else can I ensure that was the cause ive never come across the fault before ive been doing the job for 9 years now always learning
 
Bull in a china shop fault finding that is. If you are fortunate enough to have it under fault condition in front of you, be methodical and treat with kid gloves. Otherwise you will be guessing.
 
I think the cause was a sw fuse on the old section panel,, the sw fuse has never been used and is from the 1970's so I think it was just poor contacts,,,
Given the cost implications to the customer with this type of fault I'd suggest removing, stripping and overhauling the switch fuse or replacing it entirely with a new item. A floating neutral could cost tens of thousands in damage to equipment quite easily in a hospital....if not more.... so I wouldn't take the chance that switching it on and off a few times has ensured it won't reoccur.
 
Given the cost implications to the customer with this type of fault I'd suggest removing, stripping and overhauling the switch fuse or replacing it entirely with a new item. A floating neutral could cost tens of thousands in damage to equipment quite easily in a hospital....if not more.... so I wouldn't take the chance that switching it on and off a few times has ensured it won't reoccur.

why did this have to happen on my job, ive go five other conections to make on to this sction panel,,to remove the sw fuse would be no easy task
 
Lol, I'm not sure what to say really, **** happens. Maybe make a report for the client with a quotation and highlight the risks involved with the high likelyhood of equipment damage and leave the ball in their court plus you cover yourself that way.
 
if my l-n loop reading are coming back at 0.05 on all phases would u say that's a safe bet the fault has cleared
A better test would be to monitor the voltdrop across the contacts when it under a decent load or preferrably full load but like I say I'm not usually a gambling man when it comes to hospital equipment ;)
 
I am trying to help you mate. Let them know and then sleep easy that they are aware. You did not create the problem, but you found it, so advise and then go from there.
 
A better test would be to monitor the voltdrop across the contacts when it under a decent load or preferrably full load but like I say I'm not usually a gambling man when it comes to hospital equipment ;)

in its current state thers not much load on the db yet,, next year other phases start in the hospital and we will be loading the board up more then,, but the voltage seems stable,,, so wat would be a volt drop indicating a poor connection under full load verses a decent conection under full load
 
who would usually overhaul the sw-fuse an outside company or would u normally do it by one self
and the other sw fuses that iv not used yet how would u best test them for the same fault
 
The fact you're asking the question would mean you should get someone in who can do the overhauling. Sometimes it's easier and cheaper to replace plus if this unit was from the 70's there might no be parts available and then there's always a risk it's got asbestos flash dampers etc.
 
Soon as possible or even sooner, open the switch fuse and put a henley on the neutrals and stop p155ing about. Do you realise the dangers here?
 
What make is the switch gear?...

Plus as above - no knock at your competence but in asking and not knowing why, you are a tad out of depth here and under normal circumstance this can be a highly dangerous issue, what makes it even more pressing is its a hospital so get in a firm more experienced in the systems your working on, you need to find where the N was lost and not just second guess things!!!! Most of the old switchgear is extremely durable and will outlast most of the crap sold today so unless its obviously falling to bits then don't assume its the culprit because its old.
 
What make is the switch gear?...

Plus as above - no knock at your competence but in asking and not knowing why, you are a tad out of depth here and under normal circumstance this can be a highly dangerous issue, what makes it even more pressing is its a hospital so get in a firm more experienced in the systems your working on, you need to find where the N was lost and not just second guess things!!!! Most of the old switchgear is extremely durable and will outlast most of the crap sold today so unless its obviously falling to bits then don't assume its the culprit because its old.

Its not quite as simple as that its not like your usualswitch fuse,,, this sw fuse is on the essensial side of a proteus dual supplysection panel (miniform),,the switch fuse is 4 pole and when engaged pulls backon to the bus bars,,i work for a decent sized company but its something we don’toften come across, other items supplied of the section panel are absolutely fineits this one sw fuse that i have an issue with,,1 db only and its the submainfrom this panel thats affected,,all tests done to eliminate cable all lugs areterminated correctly with calibrated hydraulic crimper, what more can i doapart from think its the sw fuse,,, to get the sw fuse out to look at repairingit would require a full shut down of the hospital, which is next to imposible
The oldpanel, im suspecting has some sw fuses with phase issues already noted on someof the ways so as not to use them,and because of the age of the change over forthe gen set weve done a full upgrade to a deapsea panel for the new gen set
 
Everything points to lost neutral here and if its definately not a cable fault which may only be present under load then it has to be the connection at either end as your have a local issue at one board and not a global issue.... have you stripped the DB to access the N bar and internal links (dependent on board)....is the sw/f switching N or a solid link... check any removable testing links .. these are often overlooked when looking for poor connections...if the N is switched then it should be early make late break but Proteus are not on my tick list as high quality systems so you could be right.
 
Everything points to lost neutral here and if its definately not a cable fault which may only be present under load then it has to be the connection at either end as your have a local issue at one board and not a global issue.... have you stripped the DB to access the N bar and internal links (dependent on board)....is the sw/f switching N or a solid link... check any removable testing links .. these are often overlooked when looking for poor connections...if the N is switched then it should be early make late break but Proteus are not on my tick list as high quality systems so you could be right.

I got to the bottom of this today,, i got to site today andswitched on all the lights and as soon as i put, the zip boiler on the lightswent back to flashing, so with my new found knowledge, shut of went through thetest voltages, L1-N 400,L2-N 400,L3-N 400,,,,N-E 230,,L1,2,3 –E 230,, turnedoff all possible loads including meters,, L1-N 38, L2-N 39,, L3-N 38,,,N-E 0,L1,2,3 – E 230,,
THEREFORE CAN ONLY BE NEUTRAL, WENT BACK TO SW FUSE AGAIN, stripped it down and managed totake it out of the section panel,,and the bit that gripped the neutral bus bar,was black carboned up,,,,,so obvious culprit,,cleaned it all up closed the gapwith my grips to make a tighter conection and put some electrical grease on andput it back it so feeling alot happier now,, everything works as it should,,and now have learnt how a floating neutral effects the installation via using aphase as a return path, and sendind 400v down items of equiptment that arnt ment to carry these sort of voltages,,allthis has made me realise i don’t know as much as i would like to and in jan imgoing to do my electrical design and in sept going to start my hnc which ivebeen meaning to do for years,, i do understand it when told and i read up onthings but i have no one to turn to these days
 
Good to hear jonney now without the input of the knowledged amongst us on here, can you explain the lights flickering and how some equipment would still function correctly even though you had no neutral?...

When you understand the effects you know next time what your seeing and can quickly isolate before damage is done.
 
I'm glad it sounds like you've treated the actual problem rather than just encouraging the symptoms to disappear. I'm not sure greasing is a good idea but if it was a knife/blade type isolator some contact cleaner and either a diamond contact file or fine emery will usually clean them up. Re-tensioning can be done but if the contact has been overheated because of a poor connection they often become soft and lose their springiness and won't maintain tension, this means the problem has a high likelihood of reoccurring. Usually I'd replace the contact assembly that was problematic but obviously this depends on availability of spares.
 
The lights flickering,,not 100% but presume is it down tothe frequency of 50hz and the sin wave of using the three phase system as a path back to thetransformer,,but i know why they wer still working because of the path down theneutral back to the neutral bar up the neutral of a circuit on a nother phasedown th line conductor and back to the transformer to the center point, therfor neutral having 400v,, i think thisis right

 
Cleaning up, flattening the contact surfaces, tensioning, etc. is only a temporary stopgap.
As this was on the Neutral make it solid with a Henley block.
Lack of replacement spares to me could possibly lead to future problems, make sure you have reported this problem, keep yourself in the clear.
 
Something is puzzling me here. MiniForm switches are 3P with a bolted neutral link. To change one would take me about two minutes without shutting the board down. The connections to the bars are as you say but where has the 4[SUP]th[/SUP] pole come from?
 
Something is puzzling me here. MiniForm switches are 3P with a bolted neutral link. To change one would take me about two minutes without shutting the board down. The connections to the bars are as you say but where has the 4[SUP]th[/SUP] pole come from?

What's puzzled me slightly is that miniform are a GE product, yet the OP refers to them being proteus?
 
I’ve been using GE System4 and MiniForm for near 40 years, damn good reliable switchgear.

I only had one switch over heat and that turned out to be the fuses had been incorrectly installed.
 
Tin hat on - I have no practical knowledge of 3P systems only theory, but I am a bit surprised that the switchgear appears to interrupt the neutral as well as the 3 phases, given the implications and dangers highlighted in this thread, is this usual?
 
my appologies the section panel is proteus I was using the term mini-form,, it's not your usual section panel filled with 60947-2 mccb's there bs 88 so thought that's were called miniforms,, thinking bout it miniforms have the sliding fuse tray,, but this section panel Engadget on to the neutral bar behind the switchgear its a rubbish set up no room to work m6 terminals for connections which are incredibly difficult to get to, I hope they don't make these things any more ther s nightmare to work on
 
Tin hat on - I have no practical knowledge of 3P systems only theory, but I am a bit surprised that the switchgear appears to interrupt the neutral as well as the 3 phases, given the implications and dangers highlighted in this thread, is this usual?
Switchgear with 'early make' - 'late break' Neutrals should be used to avoid a floating N on switching which can do alot of damage even if just for a short period....... the need for switching N is another debate altogether and on a domestic level it is required that all Lives are isolated at the main switch (L/N in domestic case been 1ph commonly) as it is a switch that a general member of the public may be expected to operate - - commercial and industrial especially 3ph becomes a whole different kettle of fish
 
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Hmm,
There are three things that spring to mind.
1. I do think you need to inform the powers that be that you found a fault that would have caused a catastrophic failure of all equipment connected to that switch fuse with the risk of fire.
2. Do you have an inspection program for main switch gear including thermal monitoring / inspection?
3. What lock out procedures do you have and do you know what the term arc flash means?
 
Hmm,
There are three things that spring to mind.
1. I do think you need to inform the powers that be that you found a fault that would have caused a catastrophic failure of all equipment connected to that switch fuse with the risk of fire.
2. Do you have an inspection program for main switch gear including thermal monitoring / inspection?
3. What lock out procedures do you have and do you know what the term arc flash means?

What the hell are you talking about?
 

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fault today at work 400v live to neutral
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