what size of cable will i need for pizza oven, 3 Phase MCB?

[kevin1234]

How could you use T&E for three phase?

You're two wires short for a start....

ah ye,sorry i meant to say PVC singles!

 

[kevin1234]

18500 / √3 = 10680W per phase..

10680 / 230 = 46A per phase..

TLC recomends 10mm for a 20M run of 4C PVC SWA.. clipped direct

I think thats wrong?? isnt the other way right that was done up there?

 

[oharaf]

Just keeping it simple Rob!!! Of course there are all the factors, especially temp.

 

[plugwash]

Also remember if it's not fed from the main board you have to take into account any volt drop in the submain.

 

[ColJack]

nope.. 3 phase power to "per phase" power is divide by root 3..

you can't just divide it by 3 because the phases are not on the same angle..

while one is at peak, the other 2 are not..

unless the quoted is just the total of the element watage as if for a single phase supply..

which would be 6.166KW per element ( probably closer to 5.9KW with a bit for the conveyor and controls )

 

[oharaf]

Based on Col's basic reminder that each phase is out by 120 degree

I agree

18500/root3 = 10681

10681/230 = 46.4A

SO MCB 50A cable of 10mm

Well done Col, thanks for the refresher!!!!!

Apologies to Kev

 

[ColJack]

Kevin.. you quite clearly are planning to do it yourself.. so stop fibbing..

I am from scotland and i have just qualified as an electrician

from your very first post..

and you've asked on here about commercial stuff before..

 

[Spark123]

46A seems a bit on the big side for a 3 phase 18.5kw load

For a ballanced 3 phase load:

I line = P / (root 3 x V line)

= 18500 / (root 3 x 400)

I line = 26.7A

 

[ColJack]

rethinking..

 

[Spark123]

V phase is 230v. V line is 400v

 

[ColJack]

you were right the first time oharaf.. for 230V it's
P/(3x230)


so 26.8A..

 

[Spark123]

Still get the same answer even for ballanced star:

The power is spread over all 3 phases hence each phase carries a third.

W=Vphase x Iphase x 3

Vphase = VLine / sqrt3

Therefore

W = 3 x (VLine/sqrt3) x Iphase

W = VLine x sqrt3 x Iphase

therefore rearranged:

18500 / (400 x sqrt3) = Iphase = 26.7A

in star Iphase is the same as ILine therefore ILine is also 26.7A

 

[ColJack]

that's the problem with using 230 and 400 though..
230 x sqrt3 = 398.37V..

so depending on the method you use you get a different answer..

power / (3 x Vphase ) = 18500 / (3x230) = 26.81A..
power / (sqrt3 x Vline ) = 18500/ (sqrt3 x 400 ) = 26.70A..

 

[Lectrician]

Not going to make a huge difference though is it!

Atleast it is not tens of amps out which it would be if you had originally designed the circuit

 

[RF Lighting]

im wondering what it would be for PVC twin and earth?

ah ye,sorry i meant to say PVC singles!

its in trunking and parts behind a wall

Please employ the services of a commercial electrician.

You are so far out of your depth with this job it really does scare me.