Lost neutral

[Tim]

Hi guys,

Today i went to a hotel that had lost its neutral at the main incommer, and has been presumed out for around a year. The neutral link had been undone during a previous refurb and tightened up in the undone position. The problem has only been found after a small fuse board from the blue phase caught fire. Most down light transformers/florries/coffee machines etc have been fried, though it has only really affected things on the blue phase.

My questions are how does everything keep working, as it has been for a year, without a neutral, im thinking either the neutral has only recently dropped out (but then why was it done up so tightly in the undone position) or the earth has been a return path for a year or so.

My other question is why is it that almost all of the equipment affected is fed from blue phase? Could it just be that blue phase just happens to have almost all of the electronic equipment on it.

I do not have a lot of details for the job, i expect i will be back there in a week or so, we only went down today for a few hours to rig up some tempoary lights to get them back up and running.

I do not know the earthing arrangement, and by all means correct me if my assumptions are wrong.

Here are a couple of photos of stuff i found whist investigating.

If the breaker doesnt fit? cut up the board.

Breaker doesnt fit? Bend the board

Some lovely melted cables

Getting a bit hot?

Oooh pretty colours

Cable doesnt fit? Give it a haircut.

Cheers,
Tim

 

[MDJ]

Sounds like the earth did the JOB haha

 

[La Poste]

This is a very interesting subject and I am looking forward to reading peoples replies.

 

[Tim]

Follow up question:

There was an AC board that was really buzzin, we took the cover off and measured the current on each phase.

Red 100A
Yellow 2A
Blue 2A

I turned off all the breakers on the red phase and 1 by 1 the buzzin got quieter (each breaker was pulling approx 15A) then once they were all off the buzzin stopped. I reset them and all was fine, no buzzin.

We ran out of time to investigate further, but my only guess is that the pcbs in the ac units had shorted enough to allow more current to flow and turning them off and on stopped the arcing.

Correct me if im wrong.

Cheers
Tim

 

[telectrix]

crying out for a rip it out and start from scratch.

 

[Tim]

Sounds like the earth did the JOB haha

I am with you on that, but unless its a tncs system (i think unlikly on a building this size but not impossible) where is the n-e link? In the electronics maybe?

 

[Tim]

crying out for a rip it out and start from scratch.

Im working for someone else atm and thats what ive advised, but i know they wont pay for it as the bodged refurb was only a year ago.

Ive counted over £1000 of led lamps blown already lol

 

[Guest55]

what a mess lol !

the biggest surprise is that an installation as crappy as that actually has anything as "hi-tech" as rcbos.

as for still working without a neutral for a year , well its still tracking back to the origin somewhere , not difficult really if its tnc-s.

those incomer tails must be huge lol , as a 125a switch is good for 35mm and half the cores have been trimmed just to get it in.

not surprised youve lost a phase with all that heat damage , single phase voltage can rise to over 300v when the neutral drops out , which will will fry any electronics plugged in at the time.

its this exact reason why i never use a 4 pole main switch for the neutral on a commercial 3 phase db , it makes a complete mess if the neutral contacts fail - bolt direct to terminal bar , always ;-)

 

[Silly Sausage]

Ah, Lost Neutral, interesting stuff!

I predict the company who did last year's refurb will be receiving some interesting communications in the near future! :smilielol5:

 

[Tim]

what a mess lol !

the biggest surprise is that an installation as crappy as that actually has anything as "hi-tech" as rcbos.

as for still working without a neutral for a year , well its still tracking back to the origin somewhere , not difficult really if its tnc-s.

those incomer tails must be huge lol , as a 125a switch is good for 35mm and half the cores have been trimmed just to get it in.

not surprised youve lost a phase with all that heat damage , single phase voltage can rise to over 300v when the neutral drops out , which will will fry any electronics plugged in at the time.

its this exact reason why i never use a 4 pole main switch for the neutral on a commercial 3 phase db , it makes a complete mess if the neutral contacts fail - bolt direct to terminal bar , always ;-)

Hi biff,

The rcbos were installed with the new db (the one with the dodgy tails) in the refurb a year ago.

I guessed it would be returning through the earth, but what if it is not a tncs system? (just trying to cover all bases untill i know more about the job)

What would cause the voltage to rise differently on different phases? As most the damage is on the blue phase, why were not all phases damaged equally?

Have a look at the pic with the tails, the red phase has heated up so much that the mccb has started to burn.

Cheers,
Tim

 

[Bobster]

All to do with vectors and balanced loads on 3phase systems.

If the load was higher on the red and yellow phase with no neutral to tie them together the blue would float causing the voltage to rise. (In a nutshell)

 

[Tim]

All to do with vectors and balanced loads on 3phase systems.

If the load was higher on the red and yellow phase with no neutral to tie them together the blue would float causing the voltage to rise. (In a nutshell)

Cheers rob, I get the rough idea of what your saying but what do you mean by tie them together?


Does anyone have any idea about my question on post 4?


Cheers,
Tim
Cheers,
Tim

 

[Stroppy]

There is good information about lost neutrals on this thread: http://www.electriciansforums.net/e...309-suppliers-neutral-break-2.html#post674305 I had a lost neutral at a hotel a while ago and had the same problems of over-voltage frying lots of things.

Edit: Tony's post has the clearest explanation IMO: http://www.electriciansforums.net/electrical-wiring-theories-electrical-regulations/69309-suppliers-neutral-break.html#post670565

To answer your questions, if the loads on all phases were roughly the same then their voltages would stay reasonably close to your nominal 230v, and bearing in mind a lot of kit is designed to work within a range of, say, 200-250 volts or even 100-250v no-one would be any the wiser that the voltages on the phases were varying with load. Only when the voltages go outside the tolerances of the appliances (too high or low) would you notice they stop working, or catch fire.

 

[Tim]

Those diagrams are good, now i can visualise it.

Cheers stroppy

 

[Engineer54]

what a mess lol !

the biggest surprise is that an installation as crappy as that actually has anything as "hi-tech" as rcbos.

as for still working without a neutral for a year , well its still tracking back to the origin somewhere , not difficult really if its tnc-s.

those incomer tails must be huge lol , as a 125a switch is good for 35mm and half the cores have been trimmed just to get it in.

not surprised youve lost a phase with all that heat damage , single phase voltage can rise to over 300v when the neutral drops out , which will will fry any electronics plugged in at the time.

its this exact reason why i never use a 4 pole main switch for the neutral on a commercial 3 phase db , it makes a complete mess if the neutral contacts fail - bolt direct to terminal bar , always ;-)

All incoming breakers on a main switchboard, especially if the switchboard has 2 incoming breakers and a bus coupler, will Always be 4 pole!! Can't remember the last time we've used a 3 pole isolator/breaker on any sub-main Distribution boards either. The whole idea is to be able to isolate ALL live conductors from an installation, not just the phase conductors....

I agree with you on those cables feeding that 3 pole isolator (they look like shaped conductors too). If there was a need for that sized cable, for whatever reason, the isolator should have been provided with spreader extension bars of a suitable size to accommodate those cables. Or some other means being provided, to accommodate those cables before connection to the isolator....

 

[Tim]

To answer your questions, if the loads on all phases were roughly the same then their voltages would stay reasonably close to your nominal 230v, and bearing in mind a lot of kit is designed to work within a range of, say, 200-250 volts or even 100-250v no-one would be any the wiser that the voltages on the phases were varying with load. Only when the voltages go outside the tolerances of the appliances (too high or low) would you notice they stop working, or catch fire.

Cheers, its all making sence now, and that does explain how they have been up and running for the past year untill a recent big event at one end of the building, then stuff caught fire.

Thanks very much

 

[Norwich]

I will stand corrected. But on three phase there is no need to isolate the neutral at a dist board on the incommer. Of course bus coupler amf panels etc require 4 pole I agree. But I never use 4 pole on DBs as prefer a solid connection.

 

[Engineer54]

Without being able to check the installation myself i'm not even going to hazard a guess at what's happened and why!! The overall installation looks a mess, and should now be down to the company that is responsible, to be held to account.

I fully expect the company to be NICIC registered too, not that they will be too interested, they suddenly go deaf, dumb and blind in situations like these!! ...lol!!

 

[Tim]

Without being able to check the installation myself i'm not even going to hazard a guess at what's happened and why!! The overall installation looks a mess, and should now be down to the company that is responsible, to be held to account.

I fully expect the company to be NICIC registered too, not that they will be too interested, they suddenly go deaf, dumb and blind in situations like these!! ...lol!!

It was definatly a lost neutral, i saw the link had been removed and based on the explanations given on here and the problems the hotel has had it all make sence.

The company responsible for the problems is NIC registared i wish i could give you the name, when i read it on the cert i thought the guy had just made up a company name because he messed up the job.

 

[Engineer54]

I will stand corrected. But on three phase there is no need to isolate the neutral at a dist board on the incommer. Of course bus coupler amf panels etc require 4 pole I agree. But I never use 4 pole on DBs as prefer a solid connection.

Explain to me why you would use a DP main isolator/breaker on Single phase installations but wouldn't use a 4 pole main isolator/breaker on a 3 phase installation. What's the difference?? I'm not saying your wrong, it is allowed, in many instances, but probably has more to do with costs, than anything else!! lol!!

 

[Guest55]

All incoming breakers on a main switchboard, especially if the switchboard has 2 incoming breakers and a bus coupler, will Always be 4 pole!! Can't remember the last time we've used a 3 pole isolator/breaker on any sub-main Distribution boards either. The whole idea is to be able to isolate ALL live conductors from an installation, not just the phase conductors....

I agree with you on those cables feeding that 3 pole isolator (they look like shaped conductors too). If there was a need for that sized cable, for whatever reason, the isolator should have been provided with spreader extension bars of a suitable size to accommodate those cables. Or some other means being provided, to accommodate those cables before connection to the isolator....

there is no requirement from bs7671 to switch the neutral at a 3 ph db unless its TT as far as im aware.
as i stated earlier , bolting direct is just something less to go wrong , just my preference.
and ive seen a dropped db neutral connection burn out every emergency light in a warehouse and i'd rather not have that happen on any jobs in my name lol.

 

[Richard]

We attended a very similar case some years back - 3phase db lost it's neutral, however got neutral though a borrowed neutral at a light fitting (completly different board) and as far as we know melted the entire length of that lighting circuit. Scary stuff really! Very difficult to find via normal periodic testing.

 

[GLENNSPARK]

everyones chunterin on about whether..or not the neutral should be switched at the incomer on 3ph....so if theres a 4 pole switch..that doesn`t mean you cant still take the neutral around it...and into the neutral termination...does it...
just caus the spare pole is there...doesn`t necessarilly mean you have to use it....

 

[Engineer54]

there is no requirement from bs7671 to switch the neutral at a 3 ph db unless its TT as far as im aware.
as i stated earlier , bolting direct is just something less to go wrong , just my preference.
and ive seen a dropped db neutral connection burn out every emergency light in a warehouse and i'd rather not have that happen on any jobs in my name lol.

Haven't had, or seen a 4 pole breaker or isolator with it's neutral connection going down. I would put such cases of failing units, more down to the original installer not ensuring that solid connections were made.

 

[chilliwilly]

everyones chunterin on about whether..or not the neutral should be switched at the incomer on 3ph....so if theres a 4 pole switch..that doesn`t mean you cant still take the neutral around it...and into the neutral termination...does it...
just caus the spare pole is there...doesn`t necessarilly mean you have to use it....

Unless its a TT supply.

 

[Knobhead]

 

[Guest55]

nice tent you got there T
4 or 6 man ?
;-)

 

[Norwich]

Explain to me why you would use a DP main isolator/breaker on Single phase installations but wouldn't use a 4 pole main isolator/breaker on a 3 phase installation. What's the difference?? I'm not saying your wrong, it is allowed, in many instances, but probably has more to do with costs, than anything else!! lol!!

cost may be, off the shelf availability more likely the case, but as you know losing neutral on three phase incommer leads to over voltage, not so on single phase. I agree failure of 4 pole devices on the neutral is extremely unlikely.

 

[baldsparkies]

I have said it before and I will say it again. The size of the company and its registration with a recognised body NICEIC or otherwise mean Jack Sh#t.
Its the man on the tools that count. And that is one big bodge for sure. Lost N or not. Its a mess.
Lets be thankful the whole lot didnt go up and people didnt lose there lives as a result.

 

[Engineer54]

cost may be, off the shelf availability more likely the case, but as you know losing neutral on three phase incommer leads to over voltage, not so on single phase. I agree failure of 4 pole devices on the neutral is extremely unlikely.

Well i'll stick with the 4 pole isolator/breaker option, not that i have too much choice in the matter!! lol!! If it's in the spec's then it generally get's provided and installed...

 

[markc123]

Im working for someone else atm and thats what ive advised, but i know they wont pay for it as the bodged refurb was only a year ago.

Ive counted over £1000 of led lamps blown already lol

To be honest, if they don't take you up on your offer of a rewire, then id probably be walking away.

You need to push for a rewire as strong and as hard as possible - it'll then teach people to get the job done correctly in the first place, and not always going for the cheapest option all the time. You any idea who's caused this carcrash? Like Archy said, get the client to give them a phonecall.

 

[Tim]

To be honest, if they don't take you up on your offer of a rewire, then id probably be walking away.

You need to push for a rewire as strong and as hard as possible - it'll then teach people to get the job done correctly in the first place, and not always going for the cheapest option all the time. You any idea who's caused this carcrash? Like Archy said, get the client to give them a phonecall.

I have told my boss that i wouldnt settle for less than a full rewire as we have no way of telling how many melted cables there are in ceiling void.

I know what company did the work, but i will refrain from mentioning them as its possible (but unlikly) that they were not the last to work on the buildings electrics. They are NIC members though.

Tim

 

[Guest55]

if a spark insisted on a rewire of a commercial without at least providing a test & inspection report first they'd probably get laughed out of the building.

no ones gonna cough up the serious money needed for the work without proof - end of.

 

[MDJ]

Biffs right, to add, suggesting a rewire to the customer without a report is not only laughable but could be embarrassing, I would have you removed from the building haha

 

[markc123]

To be honest, you're right on the EICR for the mess and use it as evidence.

But with the pictures the OP has provided the client can't be very bright if he can't see the danger for himself lol.

Aye, Mr.OP EICR it then label unsatisfactory...if it comes back satisfactory i will enter a civil partnership with MDJ :38:

 

[Guest55]

Biffs right, to add, suggesting a rewire to the customer without a report is not only laughable but could be embarrassing, I would have you removed from the building haha

exactly.
even though it looks terrible , alot of the C2's could be fixed in a couple days so pulling a £5000 rewire quote out of your arse on the basis of some burn marks wont look too clever lol.

 

[Tim]

I understand where your coming from, my view was that given the amount of melted cables we found, i only took pictures of a couple of bits, testing may not show up the damage as the cables may not be touching anything else yet. There are cables with the insulation completly melted off for around a foot but the copper is not touching anything else.

I have only been to the job for half a day but there are guys from my firm still up there and they are backing what i have said as they have found more horrors in the ceiling, some is damage from the lost neutral and some is the botched refurb.

I will conceed that an eicr first would be the better route if nothing else but to provide proof of the faults that are possible to find through testing.

Thanks for the continued advice.

Tim