3 sp circuits off a tp isolator

[44ALLAN]

Fantastic thread guys.............well done to all.

Great stuff

 

[D Skelton]

You're definitely over thinking things now!

We were talking about three 20A circuits, not a local distribution network lol!

 

[netblindpaul]

What local distribution network, all of these things can be found on a small domestic install these days, I'm not going to back down and no one has yet given proof that the N cannot be overloaded in the scenario given by the OP.
So until this is done I stand by my arguments, I DESIGN, I DO NOT GUESS values, so the N can be overloaded, & if I was being paid for my consultancy then I would be bothered to calculate things, as I am not, it;s down to you lot to prove otherwise, which, as yet, you have failed to do.

 

[tom79bmth]

Well how come the supply distributors don't have a bigger neutral than the phases,

 

[netblindpaul]

Because it is not needed in that scenario, because it is not what is being discussed here, this is a very different situation.

 

[Guest55]

is it over ?
are we done yet ?
any more calcs to throw in ?

phew!
;-D

 

[lewlec]

Ok I may have missed some thing here, say you have a tp&n supply connected to a switch fuse with say a 4 core swa feeding a tp&n db and all loads on that db are single phase, would that be incorrect? Would you oversize your neutral?

 

[netblindpaul]

No it's not a tp+n supply & it's not to a db, it 3 off final circuits fed from the same 3p mcb, with a common N to all circuits, and the cct's are socket outlet circuits.

 

[Guest55]

*facepalm*

 

[D Skelton]

What local distribution network, all of these things can be found on a small domestic install these days, I'm not going to back down and no one has yet given proof that the N cannot be overloaded in the scenario given by the OP.
So until this is done I stand by my arguments, I DESIGN, I DO NOT GUESS values, so the N can be overloaded, & if I was being paid for my consultancy then I would be bothered to calculate things, as I am not, it;s down to you lot to prove otherwise, which, as yet, you have failed to do.

I never said never, I just said given the OP, it was highly unlikely.

On another note, PF is not cumulative in the sense that if a system is made up of loads at a PF of .9, the overall PF is still .9. The average domestic install is expected to average out at roughly .9 - .95, three of those domestic installs across three phases and the slightly negative effects caused by the non-linear loads within each dwelling become meaningless. The exact reason for this can be found within our discussion regarding our three 20A socket circuits.

We all suffer from a lack of understanding at times (myself included! ) you have since seen sense but still seem to be fixated on being theoretically correct. It seems to me that you're just not looking at the bigger picture.

 

[netblindpaul]

I am not talking about PF, I am mainly talking about distortion of the supply, I have never said anything about PF.
Supply distortion these days has a much bigger affect on installs than PF as this is normally taken care of, but, distortion IS cumulative.

 

[Silly Sausage]

Fantastic thread guys.............well done to all.

Great stuff

Hahaha...must have a proper read tomorrow!
The original Q just appears to be an unbalanced Star with a Neutral, what's the problem?!?! :sifone::smilielol5:

 

[D Skelton]

Is it? On a large scale you would not be wrong to expect that distortion would equal itself out across the phases.

 

[44ALLAN]

Hahaha...must have a proper read tomorrow!
The original Q just appears to be an unbalanced Star with a Neutral, what's the problem?!?! :sifone::smilielol5:

If you sort it out let me know mate.................I've agreed with at least 10 differing versions up till now lol

 

[netblindpaul]

TO be honest, whist there seems to be a lack of belief from posters here with regard to what I am saying, there seems to be a significant lack of understanding of what I am trying to put across as well, I don;t know how else to describe things.

Thing is see, I'm not a spark, I operate mostly as an Engineer, & consultant thus I am paid for my opinions, & I don't start throwing arguments about unless I can back them up, because that is how I make my living, and I'm doing OK, thank you and have been for a few years now, based solely on my own personal opinion, which is hen backed up by fact once the money starts flowing, why should I do otherwise when it is my living.
I'm not proposing anything as stupid as payment here, I'm here for the fun of it. but, I will never post anything that I cannot back up, and no one has managed to prove with science that my arguments are incorrect yet, once they do I will give an apology, until then I stand by them.

In the OP, the N conductor CAN be overloaded.
The circuit is not acceptable.
If anyone can PROVE otherwise in all scenarios then I will bow down, until then I await proof.