please let me know the formula to calculate the cable size.For example ,Total amps 400A and supply voltage 380

Answer 1

In the US, the National Electrical Code has tables in the Annex. The minimum size will depend on whether the cables are in conduit or not, and the type of insulation. Depending on the distance to be run, the cable size might need to be increased above the minimum

Answer 2

In general cable size is determined by the heat rating
of the cable insulation, the amperage the cable will
carry, resistance of the cable, and the installation,
(free air, conduit, etc.).
It's a thermal gain calculation, and in practice, tables
of common loadings are used.
If you want the formula, refer to NFPA 70.
(U.S. National Electrical Code.)

Answer 3

you will desire to understand the burden impedance (or basically resistance for DC) At certainly one of those intense modern-day point you will opt to account for the cable and connections impedance. The voltage required is discovered from Ohms regulation V = I * Z working at such intense modern-day stages is risky even at low voltages because of the opportunity of fire, arcing, and so on, the secure practices preparations require carefull layout. you will desire to seek for some expert suggestion.