somme

Hi Guys, OH taking his peers course exam next week and the following question has him doughting himself and losing sleep if you could help please.

A three phase circuit is to supply a load of 75amps. It is intended to use V-75 3 half plus earth (round) insulated and sheathed cables, bunched together with other two equivalent circuits in air.

The circuit is to operate in an enviroment with ambient tempreture of 55 degrees. Route length from supply to load is 35 meters, conductor temp 60 deg.c

Calculate and determine the minimum conductor size required.
What is the voltage drop from the supply to the load? Does this comply with the permissible voltage drop as per As/NZS 3000:2000?

He is getting 70mm but does not think this is right and does not know where he is going wrong

Any help would be really appreciated

somme

Thanks for your help guys

geordie2008

35 sq mm,
table 22, derating factor 0.75 for bunched together with other two circuit, 75/0.75=100A,
table 12, 35sq mm.

voltage drop , table 42, 1.06mV/A.m,1.06*75*35=2782.5 mv.