cable calculations single phase / 2 phase

[pjlelec]

Hello all

Just doing some cable calcs for a shepards hut site, the site has an incoming supply of 2 x 250a single phase supplys, was hoping to run a 4 core down from incomer to a board then split off to each hut.

Do i have to work it out on single phase 230v or can i work it out on 400v

 

[James]

single phase calcs.
even if you are sharing the N you could be in a situation where all the load is on one hut and none on the other.

 

[pjlelec]

single phase calcs.
even if you are sharing the N you could be in a situation where all the load is on one hut and none on the other.

Cheers
There is only 1 neutral entering the site and comes in on a phase cable and isolator but only 2 phases are used

 

[brianmoooore]

Single phase/2 phase, commonly known as split phase is 230 - 0 - 230 volts, with the two phases 180 degree apart. Not the same as using 2 phases of a three phase supply, where the phases are 120 degrees apart.
If there are no loads which run off of the 400V (or 460V) supply, then as above, calculations are for the worst case scenario, where all the load is on one phase.

 

[pjlelec]

Single phase/2 phase, commonly known as split phase is 230 - 0 - 230 volts, with the two phases 180 degree apart. Not the same as using 2 phases of a three phase supply, where the phases are 120 degrees apart.
If there are no loads which run off of the 400V (or 460V) supply, then as above, calculations are for the worst case scenario, where all the load is on one phase.

Cheers

theres no 3 phase on site just the split phase

il work it out on single phase am i ok working it out on saying if its a 200a total supply i can do 100a on each phase and use same cable

 

[brianmoooore]

So it is 460V across phases?
The size of the neutral will need to be calculated for the maximum load on the phase which has the highest calculated max load. This is the worst case scenario.
When a load is applied to the other phase, the current in the neutral will decrease, as will the total voltage drop.
If both phases are drawing the same load, the current in the neutral will be zero, and the voltage drop will be half of that when just one phase is loaded.