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

 

[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...