The Arcing Neutral

[La Poste]

Why do the Neutral connections seem to burn out more than the line?

Is it because the Neutral collects more debris, harmonics and all sorts of junk like that?

It seems that the Neutral conductor connections are the ones to watch and I am not sure why.

Any opinions are welcome.

Thanks very much.

 

[Richard Burns]

Probably people are more diligent on tightening up the line (cos it is dangerous) and not the neutral because there is no voltage on that!

Not really a good answer but cannot really see a effective difference between the two same current in each case but as you say normally the neutral.

 

[Silly Sausage]

Probably people are more diligent on tightening up the line (cos it is dangerous) and not the neutral because there is no voltage on that!

Not really a good answer but cannot really see a effective difference between the two same current in each case but as you say normally the neutral.

That's what I was thinking but didn't dare post it!

Interesting question though.

 

[vernam616]

Yes that is interesting

I went to a job the other day where upstairs lights had gone out, all lights were on one circuit however downstairs still working, anyhow i had a look in the db and to my horror there was 5 cables into the one mcb, and not one was caught tight in the terminal they were purely sat in the back of the mcb

Had been like that for years and not one sign of burning/arcing etc

 

[Silly Sausage]

La P might be referring to high current Neutrals, Isolator/RCD to neutral bar???

 

[Knobhead]

With three phase systems and dirty neutrals much more emphasis must be placed on neutral continuity.

By dirty I mean.
Switch mode power supplies
VSD’s

It just gets worse the more I think of it.

Gone are the days of 3½ core cable. Now 4 core or even 3&1.5N core are specified.

Progress at what price?

 

[GLENNSPARK]

surely if there isn`t a voltage on the neutral then you can get inert currents just sitting there=heat buildup....and in time the difference in expansion and contraction rates of copper V brass/steel will have the effect of causing loose neutrals......but whenever i am terminating multi-stranded conductors....such as tails etc...when i have tightened the terminations....i always manipulate the cable a bit.....usually wants to nip up again after that.....

 

[Knobhead]

I’m drunk….

Please tell me your contemplating life.

 

[Marvo]

Triplens and unbalanced loads.

 

[Silly Sausage]

I’m drunk….

Please tell me your contemplating life.

Good work, sober to drunk in an hour!
I'll have what you're on thanks

 

[Knobhead]

I'm sober for the moment. Have a look at http://static.schneider-electric.us/docs/Electrical%20Distribution/Low%20Voltage%20Transformers/Harmonic%20Mitigating/0104ED9501R896.pdf

 

[ackbarthestar]

Another useful piece of info, it all builds up the big picture. Nice one.

 

[Knobhead]

Thanks to all these new fangled wiz bang machines the calculation for neutral current has gone out of the window. It used to be fairly easy
In = √(Ia²+Ib²+Ic²)-((Ia*Ib)+(Ia*Ic)+(Ib*Ic)).
But now with the higher end harmonics it’s all gone belly up. Even you're average clamp meter will struggle to give a sensible reading.
From what I’ve been reading distribution transformers are suffering particularly in town centers due to high neutral currents, they can reduce the rating by 75%

 

[Marvo]

Much of this is due to cheap nasty SMPS's on IT equipment.

 

[Knobhead]

Much of this is due to cheap nasty SMPS's on IT equipment.

You just hit the nail on the head :6:

 

[Engineer54]

It's not just the IT stuff these day's seems like anything that is electronic controlled these days will have these things fitted!!

Never installed 3 1/2 core cables to be honest, they had there uses, but were generally abused and basically installed for every application, even mains and sub-mains!!! I've condemned more than a good few of them in my time though!! ...lol!! Some have been in a right state too, having had to carry currents way in excess of what they were designed for!!

 

[spark 68]

I have built switchgear in the past where the Neutrals are rated at 200%, or the N busbars are doubled up WRT the Phase bars, these were usually for Datacentres (lot's of IT equipment).

 

[telectrix]

never had these problems when computers had valves in 'em.

 

[Darkwood]

Another area to look at is if said installation is a TNCS and also has a neutral earth fault somewhere in the circuits then its possible for eddie currents that can flow within the earthing systems between different premises to jump into the neutral which can effectively have devastating effects but usually taking out the weakest link in the system with overload burnout, also another area is incorrectly rated and doubled up busbar clamps usually 100a, 200a etc etc - the number of times ive seen 3 or 4 cables stacked up on one clamp with total disregard to it designed rating.

 

[barnzi]

Could also be down to EMC issues where you have lots of wandering currents finding their way back through the neutral conductor in the mains wiring... and that's before thinking about unbalanced phases!