Help required on selecting Underground cable

40kVA at 220V gives about 182A. If you have the specific resisteance of Al you can do your own voltdrop calc.

I would suggest you use a 400/380V 3-phase supply and take some trouble to balace the load at the Distribution Board. This means you have 105A per phase. You may need a single core neutral in addition to the existing cable to cover for unbalanced load.

If you want to continue with 220V, 1-PH supply atleast another 2x35 sq.mm Al. cable is required for 40KVA load. The voltage drop in this case will be about 14V at 182A (40 KVA). Alternatively. if a 2x50 Sq.mm Al. cable is laid the voltage drop will be about 12V.

For all good reasons, it is better to go for a 400V, 3-PH supply with the existing load almost equally balanced (in each phase). In such case, the existing 3 1/2 core cable is enough and the voltage drop will be only about 4V at full load.

In your case you will have no drop unless the transformer is very old and connected to two other residences in you immediate area as a transformer willl usually deliver 100 to 200 AMP loading to up to three homes at a time.

-You will definitely need 2x50 Sq mm aluminum cables with that kind of load. As near as I can tell 50 Sq mm AL cable is only rated for 115A. Running 2ea 50Sq mm cables in parallel will allow you to "pull" up to 230A.

As noted previously you will also reduce the voltage drop by 50%.

Are you sure it is 40KVA? If really so, (hard to believe) you will need additional cable. Instead of investing in more Aluminum cable, throw it away go for Copper, and three phase system. You would be much better off.

Wangito.

Hi;

I had checked the BICC data table for 4 Cores Aluminium (Sorry I do not have it on any web site, it is an old copy) and the voltage drop for the 50 sqmm is 1.4 mV, so this is OK.

Mustafa

Thank you very much for all your postings and Help. For safety sake I am installing an additional 50Sq mm Cable. Now the 2 cables will run side by side and in future if any one of the cable has a problem I can still survive with the other cable.

Mine is a 3 Phase supply. I mention 40 KVA - that is because I have ordered a 40 KVA Diesel generator and they calculated the full load of my house to be about that. Even though all the load will not be "On" at the same time.

If I have a problem in future, will dump the Aluminium for Copper.

Cheers

Jay

Conclusions,

I wish I had the same house...

Wangito.