hi all,

Im off to Adelaide next week and still not quiet sure about the ccc calcs.

Q 6 pg 71 Question asks

A three phase 415v circuit is to supply a load of 75A.It is intended to use V-75 4 core plus earth (round) insulated and sheathed cables,bunched together with other equivalent circuits in air.
The circuit is to operate in an environment with ambient temp of 55 degrees,route lenght from supply to load is 35 metres,conductor temp 75c

Calculate and determine the minmum conductor size required?

and

what is the volt drop from the supply to the load,does this comply with the permissable voltdrop as per az/nzs3000?

I made it from table 12 35mm
and vd of 3.88v

max permissable= 5v

am i correct with these or do i need to add a derating factor for ambient temp

any help would be appreciated

many thanks Richard

Table 12, Table 22, 27 for the derating factors.
table 42 for the second part

so from table 22(3x circuits bunched in air)

derating factor is 0.75

table 27 (ambient temp 55c)

derating factor is 0.72

So the calc is 75(A) x 1/0.75x1/0.72= 75x1.33x1.38=137(A)

Table 12= 137A = 70mm cable

on the vd do I use the original 75A or the 137A ?

Is this the correct calc im using?

Cheers Richard

Thats what i got

I used the 75A load current for my calc of volt drop.

so using table 12 137A =70mm cable

table 42= 70mm at 75c =a factor of 0.583

vd = mV/Am x length x Current=0.583 x 35(m) x 75(A) /1000

= 1.53volts

is this correct?

many thanks Richard

yes you have the right answer

Hi Richard,
Thanks for your helpful postings...
In your info:

Table 12= 137A = 70mm cable

(How you have found this 70mm from 137am? Can you please tell me?