3phase out of balance?

[i=p/u]

my sister could smell burning down back of the shop yesterday and phoned NIE power, when they came out they said they were lucky there wasn't a fire as phase 1 is overloaded with 67A and phase2 only 15A and phase 3 doing nothing............ she was told to use standby generator till loads was balanced

havent been up to have a look yet as she lives 40 miles away.. but surely im right in thinking it must of been neutral melting? nshouldnt the cable be able too take 67A@ 25mm tails

 

[i=p/u]

i really thought this would of been a good post

 

[Resu]

You need to give it more than half an hour mate.

 

[i=p/u]

half an hour thats like agesssssss pal..

 

[telectrix]

Well , just go out there and shuffle some breakers round.

 

[i=p/u]

nah they rang the guy who has worked on it for years.... lol

but this is where you come in and teach me on the science part.. is this the normaly for unbalanced loads.. even tho the cable can take take 100A minimum......

havent been to have look yet but im nearly sure it must of been the neutral burning/bubbiling

 

[telectrix]

even if all the load is on 1 phase, the N has only to carry the phase current. can't see it burning at 67A. suspect either a bad connection or your sister's burnt the cakes.

 

[snowhead]

The term overloaded is relative to what the supply, tails and board can take.

If it's a 100amp supply thro' 25mm tails thro' a 100amp switch, it's not over loaded, it's just out of balance.

The neutral could be taking the same max current of any single phase if there is no load on any other, so the max on the neutral at that time would have been 67a, but it's actually less because of the load on the other phase.

 

[i=p/u]

so i say loose connection . i knew it , i knew it....

 

[Knobhead]

With the figures you’ve given the neutral current would be 61A. To be honest that shouldn’t over stress the conductor unless it a very old 3½ core.
That said a bit of juggling is needed to balance things out a bit.

 

[Darkwood]

Your sister isnt a Electrician and the DNO would have talked to here as such, dont take what they or she has said as gospel if you was there when they were you most likely would have got a different story..... plus you state overloaded with 67 amps.... this may not be the current demand but as i read it could be the excess so if cut out fuses were 60amps its possible a 127amp load but you say a shop so is this possible does she have alot of lighting or heating loads, the fuses may not have opened if the load duration wasn't long enough but repeated peaking as such can generate alot of heat without operating the fuse oh! and loose connection would make it alot worse alot faster.

 

[Knobhead]

You’re making some wild assumptions there DW.

 

[oldtimer]

Sounds like your sister is a hairdresser ie lots of high loads instant hot water showers hairdryers tongs lightings so when she called the DNO out they will only check their side and will bot pass comment on the comsumer side that will pin them down for a quote in a court of law.
Also you are assuming that there is a burnt or damaged neutral and are quite eager to get confirmation on this forum well Mystic Meg we aint so best jump in the motor and and after 45 minutes driving you will be there

 

[Darkwood]

You’re making some wild assumptions there DW.

It was my shot in the dark Tony but from experience when a electrically educated person talks to a none electrically educated person it usually gets lost in translation... as alot of you have posted it wouldn't make sense what she's been told and likely senerio was a loose connection but gotta agree with oldtimer here and just jump in the car and pay a visit.

 

[ipf]

nah they rang the guy who has worked on it for years.... lol

but this is where you come in and teach me on the science part.. is this the normaly for unbalanced loads.. even tho the cable can take take 100A minimum......

havent been to have look yet but im nearly sure it must of been the neutral burning/bubbiling

They obviously sent for the right guy then, if he's worked on it for years. More idea of balancing than a tightrope walker eh?