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

[capa666]

Hi guy's
I am trying to seek some help on surges..... we have currently been carrying out testing across different sites for a big client.
We have switched an isolator on whilst on load at the mains and it has cooked the equipment

the particular building to give you an idea is a storage area with offices ect, the only equipment that was switched on and/or plugged in was CCTV, the phone hub, small server with UPS back up, electric fence, small area of fluorescent lighting a couple of PCs, fire alarm and a printer.

the site is large but nothing switched on, we had had everything disconnected and unplugged but when we put stuff back we had forgot to record the characteristics off the main switch.

Any how we put the switch back on, the lights come on and within a short amount of time there was a smell of burning and it was a surge adapter in the office, then security told us there cameras went off 1 by 1.

after investigation, fuses had blown on the electric fence, fuses had blown on plug tops to PCs, circuit boards on the cctv power packs were cooked, monitors are broke, fire alarm had blown fuse......

We have found borrowed neutrals around the final circuits, no earth bonding ect to structural's, pipes ect, LV mixed with ELV on long runs, a mess really.....

We have to provide the client with a report to why this has happened ?? was it because we switched with load on the switch ? could it of been because of anything else? is it complete coincidence and could of been a surge ?

I really don't know the correct answer and would greatly appreciate and welcome any advice or opinion's

I know its not great to switch on load, but the most i've ever been aware of is an inrush of current and it would normally trip MCBs
Neutrals at the mains were tight BTW, i checked as i understand that loose neutrals can increase rms voltages, this is why i mentioned borrowed neutrals further a field in the installation.. but enough to fry equipment ?

thanks guys i hope to her some opinions.

 

[Marvo]

Was the isolator in the CU or distribution board? Was it a 3 phase or single phase isolator? Did you test the voltage on the circuit after you blew all their IT equipment to smithereens, if so what was it?

 

[capa666]

The isolator is 3 phase and feeds a section board, the incoming mains fuses are 200amp, and the voltage after the problem is what we would expect, 238-240v per phase and 428v ish accross the phases.

 

[Strima]

And here's me worrying about accidentally knocking an mcb off and taking out the local t-mobile 3g...

:lol:

 

[Marvo]

Was all the damaged equipment on the same circuit or supplied by the same phase? Given that the damage didn't happen immediately power was restored I'm thinking it wasn't a surge or high voltage transient, more likely over-voltage on one phase due to missing/floating neutral on a 3-phase supply perhaps. Was the neutral switched by the isolator as well as the 3 phases?

 

[capa666]

no, cctv and ringmain with the PCs on are on different phases, the isolator has a fixed neutral terminal and that was tight and a good connection. there has been loose neutrals picked up all over the job and i dare say a lot still around loose. we have brought it to the clients attention as we need further investigation. some screws in the neutral bar were finger tight if that in some DBs. do you think this could have been part of why this happened.

 

[Marvo]

It's all guesswork really but a neutral problem would be high on my suspect list although if the neutral is floating or partly floating it would more likely result in damage to equipment on one phase due to overvoltage, not across all of them.

Just out of interest are you insured for the damage? It sounds like it's going to cost quite a bit to fix that little lot

 

[micknew]

no, cctv and ringmain with the PCs on are on different phases, the isolator has a fixed neutral terminal and that was tight and a good connection. there has been loose neutrals picked up all over the job and i dare say a lot still around loose. we have brought it to the clients attention as we need further investigation. some screws in the neutral bar were finger tight if that in some DBs. do you think this could have been part of why this happened.

Yes, definately.

 

[capa666]

Marvo, i have just checked the schedules and they are on the same phase, i was convinced i checked this !!!
would a final circuit neutral disconnected cause this, it does have a back feed on it but we don't know what it is feeding and cant go knocking off the MCBs 1 by 1 to find it as we passed the arranged shut down time for the day. circuits are not all marked.

 

[Marvo]

I'm having problems picturing the supply installation from the info you've given, can you attach a drawing and the schedules as a jpg or pdf? Maybe you could black-out any info like the company name etc.

 

[capa666]

Thanks Micknew, if this is the problem i need to try and explain this to the client some way so he understands, i am considering shutting the site down until we can carry out further investigation, convincing the client wont be easy but i feel this install is so unsafe and it's our responsibility now. ive carried out a lot of inspection and testing and consider myself to be competent but never had this amount of problems, and to energise the system and this to happen worries me even more. Loop test's ect seem spot on but i feel theres something we have not found yet underlying.

 

[capa666]

I'm having problems picturing the supply installation from the info you've given, can you attach a drawing and the schedules as a jpg or pdf? Maybe you could black-out any info like the company name etc.

how do i attach to posts ?

 

[Marvo]

Under the reply box you should see a button labeled 'Go Advanced'. Toward the bottom of the advanced reply editor you should see an attachment system.

If you attach something and your post doesn't show immediately when yOu've posted it please send me a PM and I'll dig it out of the moderation queue.

 

[capa666]

I cant blank out the names Marvo, can you PM me your Email and ill send you the layout and schedules we have off the consultants.

 

[Marvo]

....i am considering shutting the site down until we can carry out further investigation, convincing the client wont be easy but i feel this install is so unsafe and it's our responsibility now.

This is kinda closing the stable door after the horse has long gone. If you shut the site down now citing safety issues they're going to ask why you powered up after your testing and damaged the equipment when by your own admission it was unsafe to do so.

It's a rock hard a hard place though because if you don't shut it down and further damage or even injury occurs you'll also be in a very bad place. My best advice would be to get your paperwork in good order for the testing you've done and issues you've found so far and if you suspect an underlying problem then methodically go through the entire installation from start to finish even if it costs you some unpaid time.

 

[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!