Help with three phase power

[i=p/u]

there is a we bit to observe and i am only learning it so sorry i cant help you as i dont fully understand it cause im a we fish in a big pond but i bark

 

[UNG]

which is why i suggested he got some expert help with the job. it may be to power motors or other industrial equipment. get it wrong and you're in it up to the neck. apart from that, public liability insurance may not cover him for 3 phase.

How many electricians check their insurance before every job to see if they are covered, would seem to be a stupid exclusion for an electrician

 

[The Ranger]

1.7 x cos o<i x pf

surely for design current

In = P/(400x1.732) = ?A

note: no power factor given

 

[telectrix]

How many electricians check their insurance before every job to see if they are covered, would seem to be a stupid exclusion for an electrician

it's common. just a way for the insurance companies to screw more out of you.

 

[Knobhead]

surely for design current

In = P/(400x1.732) = ?A

note: no power factor given

In if your referring to 3Ph neutral current it is

In = √((Ia²+Ib²+Ic²)-((Ia*Ib)+(Ia*Ic)+(Ib*Ic)))

 

[i=p/u]

yous boys are good

 

[i=p/u]

pure inductive load , and what about these super conductors in sern

surely for design current

In = P/(400x1.732) = ?A

note: no power factor given

 

[Knobhead]

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.

 

[Edward Amsden]

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!!!

 

[The Ranger]

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

 

[Knobhead]

Multiply 400 by 1.732 and you get 693.

Despite that the answer is right? Somehow?

:bucktooth:

 

[The Ranger]

Multiply 400 by 1.732 and you get 693.

Despite that the answer is right? Somehow?

:bucktooth:

it's under a / and in brackets!

 

[i=p/u]

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

 

[trev]

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

 

[i=p/u]

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..