Discuss Help with three phase power in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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If you were using just one out of the three you’re almost right. Try 400/1.732 instead.

But if you have unbalanced load on each phase interacts with the others giving the 1/3[SUP]rd[/SUP] harmonic current.

For a balanced load (P/3)/(V/√3) = In. but the currents cancel themselves out making the neutral unnecessary. Run a neutral to a star connected motor and it won’t be a happy bunny.
 
Get some decent cable calculation software (cd). It requires the inputs you need most. As with alot of things you don't know. Do your research. Add it up. If all what your powering is 3 phase then n is ok.. So long as your circuit is rated to your breaker then you should be ok..
As I said do your research, and if its safe it is safe!!!
 
pure inductive load , and what about these super conductors in sern


my questioning comes from a lack of understanding on my part not questioning yours but as i was taught

Ib = P/(400x1.732xpf) example 10kW so 10,000/(400x1.732x0.8)= 18.04

selection of protective device

In= 20A

then It = In/rating factors ca cg etc

then on to VD

mVxIxLoR/1000
 
Multiply 400 by 1.732 and you get 693.

Despite that the answer is right? Somehow?

:bucktooth:
 
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i dont understand 3 phase at all.... il have to start off like for like swaps and build on it...

the sums you have done below is that for 3phase circuit breaker and 18.04A will flow on each phase????

or isit a sum of a sum multiplying by a sum, yeh one of them ones;)
whats is loR in vd sum??

my questioning comes from a lack of understanding on my part not questioning yours but as i was taught

Ib = P/(400x1.732xpf) example 10kW so 10,000/(400x1.732x0.8)= 18.04

selection of protective device

In= 20A

then It = In/rating factors ca cg etc

then on to VD

mVxIxLoR/1000
 
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i dont understand 3 phase at all.... il have to start off like for like swaps and build on it...
Oh come on. something that you freely admit you don't understand but you're still prepared to work on it and use that to further your knowledge?
If you don't understand it you should leave well alone. For example, guys like Tony work with massive voltages on huge transformers without any real worry on a day to day basis. Now I've done the theory of this stuff when I served my apprenticeship but the practicalities of doing it? No bloody way man. And that's because I have zero experience of it
 
well ive worked on jobs which had 3phase boards but never have 3phase equipment... i dont design install 3 phase equipment, just nosey

so ok,

i lied above have worked in a cafe which has 3 phase ovens.. but never designed and installed one from scratch...

so say i haqve circuit to design and install for one of these ovens where do you start from,, can you give me insight, we are only moving into 3phase theory next week in classes, so now i tell you this you can tell i stay well clear..
 
So you have taken on a job for which you have no idea how to do, you have no idea of the theory or the practicalities of it and you want to get guidance from the forum as to how to carry this work out?
 
i dont understand 3 phase at all....

It's not that difficult at all, not some 'Black Art' that some might like to make it out to be.
I'll recommend some reading if you want.

It's just the extra danger of a potential (!) 400 volt shock that you need to be wary of.
 
interested archy on 3 phase calculations, since ive started ive spend hundreds on books along with my courses and i can grasp single phase installations..

i know want to move on with 3phase and learn about it.... none of books i have mention 3phase in great detail...

so yeh ill fill me boots on your offer...
 

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