cable sizes

[bugsy]

**** went to the wrong college

 

[james king]

so 70mm is way to big then if each phase only needs to caryy 24amps????????

 

[pushrod]

back to page 123 of osg and read post 32 again to calc It

no point telling you the answer if you can't explain it

 

[james king]

hehe just tell me ok il go get it

 

[pushrod]

so 70mm is way to big then if each phase only needs to caryy 24amps????????

way too big, but not there quite yet

 

[Jimmyb]

I would say 16mm but because of 125amp breaker 25mm

 

[pushrod]

It = In (24A)/Cg (o.8)


you can hit the thanks button if i'm helping

 

[Jimmyb]

so 70mm is way to big then if each phase only needs to caryy 24amps????????

is it not 24.73amps

 

[james king]

yes sryy

 

[james king]

so how would the layout work then can u explain of where the come out from the DB ?

 

[pushrod]

is it not 24.73amps

approx 24A is Ib

Load is probs inductive so 32A type C or D MCB

 

[james king]

were is the thanks button?

 

[pushrod]

so how would the layout work then can u explain of where the come out from the DB ?

Haven't answered this bit yet ... you got an answer to It?

 

[james king]

32A mcb is that it? surly not you have been a great help thnk u

 

[pushrod]

cable size??

It =24/0.8 = 30

can you find the cable size from table 6D1 page 128 of OSG?

 

[bugsy]

whats the run?
Im off to the van to get me book

 

[james king]

huh 6mm that what i got from 30A 6mm??

 

[pushrod]

whats the run?
Im off to the van to get me book

50M he said originally- volt drop turns out ok at about 7 or 8 volts i think

 

[bugsy]

What a complete knob I am , sitting in bed watching Darren Brown doing calcs in me head, plonka plonka plonka
anybody else want throw in a few insults its open season for me

But only unit 6am tomorrow so get in quick

 

[pushrod]

huh 6mm that what i got from 30A 6mm??

Well done.

column 5 (ref method B) shows 6mm can be used for an It of up to 36


[thanks button is on bottom left of post]

 

[pushrod]

remember voltage is 400V so can expect to get considerably more power and 3x that because there are 3 phases

You would also see if Vd was ok using Vd = Ib x Length x mV/A/M (value found from table 6D2) it turn out ok - well less than 5%

These lecturers always keep the really tough questions til last means they won'tbe stuck withnothing to do at the end of the lesson

hope i've been some help and not made some stupid mistake somewhere.

 

[pinkonthebrain]

Think your all wrong here . 50kw is 217.39 amps split over 3 phases , 72.46amps per phase. its oven resistive load. nearest breaker 80amp triple pole . instaled in trunking ref meth 4 , 3or more cables . requires 35 mm cables. rating 89amps. from quick look . night all. Michelle.

 

[james king]

so how would the lay out work? i take it its just ran out the CU

you have been a great help thank you very much

 

[james king]

huh???????????????????????????????????????????????????????

 

[pushrod]

Think your all wrong here . 50kw is 217.39 amps split over 3 phases , 72.46amps per phase. its oven resistive load. nearest breaker 80amp triple pole . instaled in trunking ref meth 4 , 3or more cables . requires 35 mm cables. rating 89amps. from quick look . night all. Michelle.

I wouldn't bet my life on me but your 217A figure comes from using 230 volts! It is 3 phase so you should use 400V and root 3

 

[james king]

he has done 50Kw / 230 /3 hasnt he

 

[pushrod]

so how would the lay out work? i take it its just ran out the CU

you have been a great help thank you very much

probs to an isolator then to the motor - remember there is an mcb for each phase and if it is a motor they won't be type Bs

you still not seeing that button lol

 

[bugsy]

brain in gear (just)

50x1000 50000
1.73x400 692 = 72.25a ( no correction factors taken into account)

 

[pushrod]

he has done 50Kw / 230 /3 hasnt he

yep think so - you're getting it

 

[bugsy]

And Ill run it on cable calc in the morning !

 

[james king]

i cant se it i looked how do i get on to it?

what do u get bugsy?

 

[pushrod]

brain in gear (just)

50x1000 50000
1.73x400 692 = 72.25a ( no correction factors taken into account)

correct and then share between 3 phases.

Edit: on reflection think your 72A is Il (line current) as the formula is for total power! so factors and mcbs should be done on that figure oops!

 

[james king]

wat type mcbs for motors?

 

[pushrod]

wat type mcbs for motors?

C or D

 

[james king]

cheers mate

 

[pushrod]

cheers mate

Hey - you found that button

Edit ; when you have time have a read of the OSG chapter 6 and Scadden is a brill book for the theory - believe there is a new edition out now as well - well worth buying to get you thru your exams.

 

[bugsy]

just logged on to the office pc and computer says---

50kw - 90.32 amps length 50m voltage drop 11.29a type d mcb didnt allow for correction factors


Good Night

 

[i=p/u]

have you a programme does all calcs for you...

 

[james king]

soo what you are saying is the total power is 72A this then needs to be shared with 3 phases witch brings it to 24A per phase?

 

[ezzzekiel]

calculate the desing current w/1.732 x 400 and that will supply current per phase (is what i should of said) unless there is a pf involved