Cable size

You could determine the current carrying capacity of the existing cable by measuring the diameter of the conductor, (excluding the outer insulation) and refer to the table: http://www.powerstream.com/Wire_Size.htm

If the cable is being used for transmission, then a "OOOO" (four-ought) cable would be needed whereas, if the cable is being used for chassis wiring (a short run) then a "OO" would be adequate.

As noted by tropical speed, there is a little more to "correct" cable size than just the current rating of the cable- specifically, the allowed voltage drop due to resistance over a distance. Also, the cable insulation has a significant impact on the rated current-carrying capacity of the cable...

It depends on the regulations in your country.

There are olso other factors to consider:

-Length of the cable

-type of the cable,

-heat in the environment

for a few meters I would think that 3*95q whould be enough in 25°C environment or if you like to use single cable 3*1*70q , then you may need one more for ground connection.

4cX120mm2 cu +1cx70mm2 yellow greeen is enough to carry 250A,400v load

Keerthi,

The question posted seems to be a homework/ assignment for the guy.

When you suggested the cable size what was the allowed maximum voltage drop you considered. Also what were the derating factors considered by you as the question does not give information on the site conditions. Have you recommended PVC insulated cable or XLPE insulated cable OR even for that matter EPR insulated cable.

The point being put forward is that all these factors need to be accounted for while cable sizing and the questionnaire Mr Mohamed needs to understand the same.