Cable calc

[i=p/u]

I want to install a 3ph dis circuit, giving roughly 90a supply to 3ph board, keeping vd under 1%

so say my ze is 0.35 ,using 3 ph 32a type c breaker and length of circuit is 40m, im comming up with 16mm conductors ???

Does this seem right...

When it says kw/vx1.732xpf im getting this part wrong , any help..?

 

[i=p/u]

Dis circuit , I want 90A roughly on 3ph board
tnc-s =0.35
length of circuit = 40m
Ib = 22000/400x1.732 = 96A= 32A per phase
protective device= 32A type c 3ph bbreaker
no correction factors
It =16mm ref method c
vd= 40x32x2.4/1000= 3v keeping around 1%
shock protection= ocpd32A. Max zs 0.58corrected
caculated zs= 0.35 .+0.11x1.2= 0.55
Pfc= 230/0.35= 657 x 2 = 1314 A , 1.3kA

 

[ezzzekiel]

Is this a question or a statement?

 

[i=p/u]

its whatever you want sweet cheeks. but id like some feedback if you get out of your scratcher and think thiink think.. for me, i dont mind if im wrong

 

[i=p/u]

it aint easy i know untill doing this 10 years..

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another 6 to go

 

[Spoon]

Looks right to me. It looks like you have to go that big if you want the vd under 1%.
I put your info into a excel sheet I have been messing about with ( pinched from a pdf that someone posted ) and this is what I get.
View attachment i=p_u.pdf

 

[Badged01]

By my calcs if you want around a 1% VD then 16mm[SUP]2[/SUP] is the way to go!

P = √3 x V x I so 22000 = 1.73 x 400 x I Giving I = 31.75A per phase. 32A C/B is OK

16mm[SUP]2[/SUP] singles to method C gives current capacity of 79A and VD of 2.4 mV/A/m
Over 40m VD = 2.4/1000 x 31.75 x 40 = 3.04V (Equates to ~ 1.3% so OK or go for 25mm[SUP]2[/SUP] if you want under!)

32A Type ‘C’ C/B Z[SUB]s[/SUB] = 0.58Ω ( At an ambient temp of 10 deg)

Assuming you use a 10mm[SUP]2[/SUP] CPC then R[SUB]1[/SUB]+R[SUB]2 [/SUB] = 2.98 mΩ/m ( At an ambient temp of 20 deg)
Correction factor for 10 deg = 0.96 so R[SUB]1[/SUB]+R[SUB]2 [/SUB] at 10 deg = 2.98 x 0.96 = 2.86 mΩ/m

R[SUB]1[/SUB]+R[SUB]2 [/SUB] = 2.86/1000 x 40 = 0.1144Ω

Taking Z[SUB]e[/SUB] = 0.35Ω then Z[SUB]s[/SUB] = 0.35 + 0.1144 ~ 0.46Ω
This is less than 0.58Ω so OK

So yep I reckon you are right. If you want around a 1% VD then its 16mm[SUP]2[/SUP]!

 

[i=p/u]

il just use 16mm cpc as well as armouring or if can find 5 core happydays..

 

[i=p/u]

this my first 3 phase dis circuit attempt and got it.. nice one thx

 

[telectrix]

the 32A MCB is just on the limit of In>Ib. as In must be <Iz, i'd be inlined to use a 40A MCB as long as your Zs is equal to or below 0.46ohms.

 

[i=p/u]

slightly under if use 32A Ib and with 40A protective device... if i up the cable size it doesnt drop much.. getting .43 calculated and 0.46 max

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Iz is irrelevent as using 16mm to control vd.??

 

[telectrix]

what i meant was that In<Iz so you have plenty of latitude to up the breaker rating provided that Zs complies.

 

[Badged01]

Think what Telectrix is driving at is the 16mm cable can handle ~80A so using a 40A C/B instead of 32A is not a problem and it potentially avoids the C/B tripping if the load demand goes higher than 32A. ( But from memory I think a 32A can take about 45A before tripping?)

However, 40A C/B has a Z[SUB]s[/SUB] which is virtually identical to the calculated Z[SUB]s[/SUB]

For me I’d use the 32A C/B but you pays your money and takes your choice as to whether you want to be on the cusp of the C/B value or the Z[SUB]s [/SUB]value!

 

[i=p/u]

also have ze of 0.07 = 3.9ka x 2 =8kA under 6kA when/400

i think basket is going to be best suited on this job just tapping out of it in pipe..... was thinkiing 100mm pvc trunking but looks like it would look bad and bend ???

any expieriences to help ty

 

[Guest55]

if the cable runs are above a suspended / false ceiling & out of sight i'd choose basket hung from joists / roof purlins.
if cable runs can be seen throughout , then trunking on side walls.