HELLO , in optional method NEC specified single phase voltage 120/230 V, but the electrical system in iraq is 240/380 V 3 phase , first can i use optional method to calculate electrical loading here in Iraq . second can i used 240 V to calculate general lighting load amperage instead of 120 V used in USA.

general lighting load= 2400 watt

ampacity is 2400/120= 20 amp in USA

Can I use the following instead:

2400/240=10 amp (for 240 v single phase here in Iraq)

thank you I'm waiting your answer

The result of a load calculation is typically in units of volt-amperes (VA). After demand factors are applied you calculate the load amperes dividing your result by the nominal system voltage* for 1Ø, the higher value in its designation (note over here we put the higher number first for 3Ø, the lower number first for 1Ø). For 3Ø, you divide by the system voltage times √3... assuming the load is well balanced; otherwise, you have to track your load by phase (line) through the load calculation and divide each by the lower number.

* You do not have to use conventional US voltages.