Understanding three phase.

[Rampage]

I've heard many a time on here that people don't understand three phase enough to work on it.
Im just wondering what exactly people don't understand?

 

[Rampage]

You mentioned something about the neutral being the same size on a 3ph circuit? Someone may have something to say about that soonish lol.

Yeah, there is something about increasing the size of the neutral in BGB, can't remember what though!

EDIT: 523.6

 

[Knobhead]

I don't have a day job to worry about. I've done my 40 year sentence.

If you seriously want information, just ask. But limit it to one subject at a time. The sticky section of the industrial and comercial forum is a good place to start.

 

[Guest55]

You mentioned something about the neutral being the same size on a 3ph circuit? Someone may have something to say about that soonish lol.

Why ? do you fit neutrals bigger than the phase conductors on your 400v circuits ?

 

[Rampage]

Smaller neutral: 524.2.3
Bigger neutral: 524.2.2

Don't read it before you go to bed though as it will give you nightmares!

 

[Rampage]

I don't have a day job to worry about. I've done my 40 year sentence.

If you seriously want information, just ask. But limit it to one subject at a time. The sticky section of the industrial and comercial forum is a good place to start.

Thanks for that, you are a genuinely helpfull person on here.
I didn't realise there was a Industrial & Commercial section on here, I will have to have a look. I'd like to work in this sort of area eventually, no offence but domestic would bore me to death!

 

[Knobhead]

Yeah, there is something about increasing the size of the neutral in BGB, can't remember what though!

EDIT: 523.6

Neutral has become a bit of a problem with the introduction of all the latest wiz-bang electronic drives and power supplies. Where as at one time 3½ cores would be used now it’s 4 core. Some places like data centres are now having to use neutral cores up to double the size of the phases. This is caused by the harmonics created by Switch Mode Power Supplies and the like. the 3[SUP]rd[/SUP] harmonic isn’t a problem (it’s the natural harmonic of 3 phase), 5[SUP]th[/SUP], 7[SUP]th[/SUP] and so on are the problem. This doesn’t just apply to cables, transformers are suffering as well. a 1000KVA transformer will give 1333A per phase, it’s now the neutral that’s going bang!!

 

[Bobster]

Well, if thats all there is to know my job would be a lot easier

 

[Rampage]

So, my OP was a genuine question.
What is it that people struggle with? Or is it something that I don't know about?

 

[sedgy34]

Possibly they dont understand that if you mess with it the shock hurts a damm site more than single phase

Deffinately it's more vialant

 

[johnboy6083]

So, my OP was a genuine question.
What is it that people struggle with? Or is it something that I don't know about?

It sounds like there's lots you don't know about. Eddy currents, inductance between phases in larger single core cables increasing volt drop, the correct way to cleat large single core cables because of the above, basic transformer theory and the list goes on.
Im not saying I know it all, because I don't.

The day you think you know it all it's time to give up.

A lot of people don't understand what 3 phase is. They see 3 supplies of 230v, and don't understand the basic theory.

If you want to get involved in commercial/industrial jobs, I suggest going to college and doing 2330 or equivelant. Theres a lot more to our trade than 3 weeks can teach you. Even the more experienced blokes on here haven't seen everything, and wouldn't say they know everything.

 

[Darkwood]

Think thats it. Pretty much everything on three phase that there is

And this one little sentence after your copied explanation is why your still learning the trade ... dont take it as a dig but just understand you have so much more to learn before putting a sentence like that.

To put it in concept you just told Einstein you think the world revolves around the sun if you get my drift.

 

[ackbarthestar]

I believe in the distant past 'they' experimented with 6, 9 and 12 phase systems but the benefits verses cost and complication reduced significantly. So we're stuck with 3-phase systems.

 

[Rampage]

It sounds like there's lots you don't know about. Eddy currents, inductance between phases in larger single core cables increasing volt drop, the correct way to cleat large single core cables because of the above, basic transformer theory and the list goes on.
Im not saying I know it all, because I don't.

The day you think you know it all it's time to give up.

A lot of people don't understand what 3 phase is. They see 3 supplies of 230v, and don't understand the basic theory.

If you want to get involved in commercial/industrial jobs, I suggest going to college and doing 2330 or equivelant. Theres a lot more to our trade than 3 weeks can teach you. Even the more experienced blokes on here haven't seen everything, and wouldn't say they know everything.

I'd love to do level 3 of 2330 unfortunately I don't think anywhere will let you do it with out doing level 2 first. I actually read the level 3 book before I did the 2382 course, I struggled a bit with induction so had to buy the level 2 book then understood it! The rest of level 2 is pretty basic stuff.

I do need to read up on eddy currents between conductors and things but I'm happy with how a transformer works. That was a memorable day when I finally got my head around induction!

And this one little sentence after your copied explanation is why your still learning the trade ... dont take it as a dig but just understand you have so much more to learn before putting a sentence like that.

To put it in concept you just told Einstein you think the world revolves around the sun if you get my drift.

That was a joke, I though the would make it obvious!
I need something that I can learn from everyday otherwise it's boring.

 

[Rampage]

I believe in the distant past 'they' experimented with 6, 9 and 12 phase systems but the benefits verses cost and complication reduced significantly. So we're stuck with 3-phase systems.

Not being one for maths, would the phase - phase voltage of a 12 phase system be:
SQUARE ROOT 12 x Uo ?
So if the Uo is 230v, the phase - phase voltage would be 796v ?

 

[simpson93]

just about your earlier comment about level 3 2330 as far as im aware there are no entry requirements im sure if you knew your stuff and explained it to the college they would put you onto a course after all your paying.

i myself dont get to do alot of 3 phase work normally do domestic, however i was on holiday last week and my grandfathers old house in france. and found out the immersion had broken and needed a like for like swap, took out the old immersion to find 3 phases and earth for my new 230 immersion, i was under the impression that you could connect between 2 phases and get 230v. not having my tester on me at the time i decided to get a light and connect it between the 2 phases to see if it would blow, and it did then i added a 2nd light in series and they both lit up brightly.