Voltage Drop

[Jed057]

Hi any guru,

We need to supply load that Nominal load only 32 A.
Tthere is Main Juntion Box(3 phase)that will distribute to 3 Sub Juntion Box(each phase.

Base on Cable Datasheet;
4C-6 sq.mm. can carrying 61A.
2C-10 sq.mm. can carrying 81A.

If I used cable incomer for main junction box(3 Phase)- 4C-6 Sqmm lenght 30 m.(the reason we don't use 4C-10 sq.mm because material shortage)
,and sub Junction box (1 Phase)outgoing - 2C-10 Sq.mm lenght 90 m.
From calculation,
VD main JB - 0.5%
VD Sub JB - 1.5% (If we used 2C-6 Sq.mm VD will more than 1.5%)
So,Total VD -2 % will meet our specification.

My concern is that looks funny because cable sizing sub JB (2C-10) bigger than MainJB(4C-6 sq.mm).

Above solution is possible way or able to use or not ???

Thanks for any answer

 

[DRWeig]

Hi Jed057,

You can use larger conductors dowstream of smaller ones, sometimes we have to in order to limit voltage drop (as is your case) when adding to existing installations.

Only real requirement is that the smallest conductor be adequately protected by the fuse or circuit breaker at the supply end.

I couldn't double-check your math without distances, but the principle is OK I think.

Good on ya,

Goober Dave