Neutral out in consumer unit

[Jim2287]

Had a problem where the neutral had came out in the consumer unit - which destroyed alot of things on certain circuits

I was wondering why this happens, since if the neutral is out then it breaks the circuit - so current doesnt flow

is it voltage build up in the cable and appliances ? or other reason ?

 

[Gary0]

Did it touch something it shouldn't have, when it came out ?

 

[Jim2287]

Dunno ^o)

 

[andy]

it shouldnt have done anything.... unless it hit another phase and made the circuit 400V, but this would never happen in a house anyway

 

[Adam_151]

maybe it had a bad connection and burnt his cu, maybe thats what he is getting at, and the lots of things destroyed were breakers and not appliances?

 

[Lectrician]

What was destroyed?

 

[Jim2287]

the house has 3 phase supply because its quite big

things like electric gates, garage doors etc were broken - and breakers need replacing too


it did have a little black burn from arcing

perhaps just the bad connections caused things to break because fluctuating current, not the actual "disconnection" ?

 

[Lectrician]

Was it the main neutral?? Some DB's have a ****e neutral terminal

 

[plugwash]

ahh 3 phase now it all makes sense

on a single phase system losing neutral just means you lose power but your kit is still live. not a brilliant situation to be in but not liable to destroy anything either.

on a blanced 3 phase system with resistive inductive or capacitive load losing the neutral will leave the system running perfectly but such a system is FAR FAR from a real life mains installation.

firstly unbalanced loads (which are basically unavoidable on any small-moderate install especially during light load periods) will lead to unbalanced voltages once there is no netural to make up the difference. in the worst case this could mean say 400V on two of the phases and close to 0 on the third (this could happen if a big single phase heater came on on one phase whist there were only trivial loads on the others) 400V WILL destroy mains equipment

secondly nonlinear loads: without the neutral to cancel them all those switching transiants/high frequency components have to be balanced somehow and that is very likely to mean large high frequency voltages everywhere. This really isn't good for equipment either.

 

[JohnD]

I once (under supervision) had to do a lot of repairs on an old theatre, where somehow a jointer making a repair had connected one of the phases to the neutral, and lots of 230v items had been damaged. Still, we did get a couple of free inspections from the REC out of it.


edited to say - that's what I was told at the time but perhaps it was like plugwash says (it was a 3-phase installation, but lots of single-phase lighting and heating in that one).

 

[kendor]

the house has 3 phase supply because its quite big

things like electric gates, garage doors etc were broken - and breakers need replacing too


it did have a little black burn from arcing

perhaps just the bad connections caused things to break because fluctuating current, not the actual "disconnection" ?

That'll be it then, dropped main neutral = appliances across two phases as the neutral connections of each of those items will have been commoned( not a problem when the main neutral is connected) causing two appliances to be in series across two phases.

Was on a job where i saw the results of just such a thing, neutral got dropped due to faulty generator interlock switch causing two floors of Flourescent lighting chokes to literally go up in smoke!
Quite amazing to watch as the lights glowed brightly then failed one after the other in a fast chase across the floor i was on. still got lots of overtime out of it