Not Cheating, honest

[cyko]

Ok, here it is.

Im currently working on my collage project and Im a little bit stuck with cable sizing selection of protective device on a 3 phase system.

Im not looking for answers here, so im not gonna post any numbers, just a push back on track.

Does anyone know, off hand, the equations for this?

Any help would be greatly appreciated.

Paul

 

[cagedanimal2010]

you got an osg?

danny

 

[Sparky Ninja]

To start with don't forget that design current (Ib) is different for 400V.

(Ib) = P/(√3xUL)​

Then select (In), In>Ib (or equal to)
Then calculate (It). You will first need to know the reference method, and any other correction factors you may need to apply (insulation, ambient temperature, grouping etc).

It = (Ib or In) / CaCgCiCcCf​

It>In>Ib (or equal to)


With (It), determine (Iz).

When obtaining (Iz), obtain (mV/A/m).

Then assess and verify volt drop.

vd=((mV/A/m)xIbxlength) / 1000​

If within tolerance, then the (Iz) cable size is your result.


Then, depending on the level of your study, you can go on to determine thermal withstand and shock protection.

 

[cyko]

Thanks guys, think it was the root of 3 that i missed.

Assuming the rest is the same as the single phase method i should have it sussed now.

Thanks again

 

[Paul.M]

Widdler I'll give you a thanks for your time and effort that went into your excellent reply. Hint hint