fault today at work 400v live to neutral

[jonney88]

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

 

[jonney88]

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

 

[Marvo]

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.

 

[Marvo]

My advice still stands, do a report and pass the decision to the client.

 

[guest119]

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?

 

[Darkwood]

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.

 

[jonney88]

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

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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

 

[Darkwood]

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.

 

[jonney88]

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

 

[Darkwood]

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.

 

[Marvo]

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.

 

[jonney88]

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

 

[efficiencyman]

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.

 

[Knobhead]

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?

 

[davesparks]

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?