throwing a switch on small load has fried equipment !! any advice please !!

[capa666]

We are only 50% of the way through the testing to date, there is multiple DBs across the site, ill send you info to help you understand. Its an awkward predicament to be making the decision to shut a site possibly costing the company thousands of pounds, you question yourself if you are doing right, but a line has to be drawn somewhere i suppose.

 

[Knobhead]

One problem with 3 phase isolators is the contacts not making or breaking together. That is why they are isolators, off load only!

 

[capa666]

One problem with 3 phase isolators is the contacts not making or breaking together. That is why they are isolators, off load only!

Tony i agree with you, it was a silly school boy error made and i should of never chanced doing it, it will be the last.... :6: I am just trying to get an understanding what has happened and why.

 

[Knobhead]

One problem with 3 phase isolators is the contacts not making or breaking together. That is why they are isolators, off load only!

You've most likely had a floating neutral for a split second.
Blame it on the custmers crappy switch, if they swallow that, they'll swallow anything!

 

[Darkwood]

This deffo sounds like you created a star point because of a loose neutral or you through embarrasment & your lack of admittance you forgot to tag it back in.... either way you will have fed upto 400v down the single phase circuits and fried anything that is suseptable hence everything you brought up...... long and short of it is your company insurance.... just like you ask us on here for answers they may get another company in to establish what occured and because you will have a hard time proving anything else was to blame you may be up the creek..... if your lucky you may blag your way out and they claim on theirs.

 

[Darkwood]

Most 3ph boards come with a main disconnector switch that is rated for switching under load AC22 and AC23 rated so this shouldn't be an issue, most manufacturers will provide clear warning lables regarding 'Do not switch under load' when needed and thats my experience over most of the market of recognised brands.

 

[capa666]

i have a good relationship with this company, or did i have never had to claim on liability before........ without naming the company they are a power distribution company so the clients are not stupid and understand principles of electricity. We did make the stupid decision of throwing the switch with little load on, but i am convinced it is there poor equipment and down to the condition of the neutrals connections and borrowed neutrals that has caused this... i think researching on this subject and listening to you guys there has been an over voltage , i think this has occured with poor neutrals (resistive) and with inrush currents of the load, the phase in question has potentially distributed overvoltage throughout the section board > sub boards > final circuits cooking up the equipment eeeek. if i can explain this to the client i am sure they will accept i shouldn't of switched on with even a small load but the severity of the damage and effects were unforeseen.
does anyone know of any documents that fully explain the effects of loose or resistive neutrals ?

 

[Knobhead]

Use the forum search. It's been covered before and I'm to tired to upload the drawings and explanation. Look for floating neutral.

 

[SimpleSimon]

Sorry to jump in, but if you where diing your final tests did you do your live tests before loading the phases?


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[Darkwood]

Look at the switching rating of the main switch as mentioned before it would be like a AC23 rating etc if as i suspect it is its adequete for switching on load including medium inductive loads then if all other avenues have been drained it sounds like the 'N make first' contact failed to do so and to be honest il be supprised if a split second difference was the cause with the amount of equipement damaged this sounds like N was off line for quite a few seconds if not longer.

Even if the switch is adequate for load switching its a practice you shouldn't get into doing as you rely on the the switches 'Make N-first' and 'break N-last' as any issue with this may damage sensitive equipment but i see you already realise your error..... even after throwing the main switch on i would always check N is present before bringing the loads on line.
Obviously we are discussing a 4pole device here as 3pole pose lesser risk as long as they are adequate for load switching.

 

[capa666]

Look at the switching rating of the main switch as mentioned before it would be like a AC23 rating etc if as i suspect it is its adequete for switching on load including medium inductive loads then if all other avenues have been drained it sounds like the 'N make first' contact failed to do so and to be honest il be supprised if a split second difference was the cause with the amount of equipement damaged this sounds like N was off line for quite a few seconds if not longer.

Even if the switch is adequate for load switching its a practice you shouldn't get into doing as you rely on the the switches 'Make N-first' and 'break N-last' as any issue with this may damage sensitive equipment but i see you already realise your error..... even after throwing the main switch on i would always check N is present before bringing the loads on line.
Obviously we are discussing a 4pole device here as 3pole pose lesser risk as long as they are adequate for load switching.

hi Darkwood, the neutral is in a fixed terminal so was never disconnected, the links are tight and connection !!!

does this help any more ??

 

[capa666]

Sorry to jump in, but if you where diing your final tests did you do your live tests before loading the phases?


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Hi Simon, this is an ECR we are carrying out, i don't understand what you are saying, the testing is progressive and a large commercial property.

 

[SimpleSimon]

Hi Simon, this is an ECR we are carrying out, i don't understand what you are saying, the testing is progressive and a large commercial property.

Oh sorry I thought this was an installation certificate you where carrying out. My bad.

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[Darkwood]

hi Darkwood, the neutral is in a fixed terminal so was never disconnected, the links are tight and connection !!!

does this help any more ??

Prior to switching on were you testing the Sub-main supply cable, if so did you have a collegue/apprentice at the other end of the cable..... maybe they forgot to reconnect neutral but covered there backs. The reason i ask is with the info given it all points towards a missing neutral when 3ph was re-established and for several seconds at least, had it been a DNO issue the effects would have been seen from every 3ph DB and as you say its a solid neutral 'unswitched' connection then it would seem we are not getting the full story here, the items mentioned all have Selv control or monitoring systems and its the fact that the control boards have burnt out which would take several seconds in some cases as the transformers get hot before melting and failing which rings true regarding some of your posts.

If all the effected items were on only one of the 3-phases its possible the phases didnt close properly but left a small enough gap to arc across this could damage sensitive equipment but only a diagnostics of the failed equipment could establish whether it burnt out with a large sustained voltage (missing neutral effect) or component/chip failure through spiking.

 

[polo1]

cappa666, really sorry to learn of the problems you have had. Unfortunately I have nothing to add to the ideas already floated by Darkwood and others. I do hope you'll let us know how this all pans out, in particular if you find the cause....it's certainly got me thinking. All the best!