Neutral Current from 3-phase, 4-wire line connection

lightningrod; i would say for the maximum un balanced current & insulation for maximum voltage rating. perry

The neutral should be capable of handling all single phase connections on a 3 phase system.

garth; if the load is equal in all single phase loads there is very little or no neutral current

andy is right, double the neutral size, less heat from 3rd harmonics perry

I have (at the recommendation of my electrician) in the past doubled up on the neutral cable to prevent volt drops etc. up to the maximum allowed current for the circuit in use. This has worked well for me and I am not seeing any surges/drops when switching on and off any loads on those lines.....

Of course the fusing/circuit breakers will set the maximum allowed load current, and should not be higher than is correct for the circuit in question.

You are right the good practice is calculate short circuit currents and fault currents and size the neutral conductor in a three phase circuit i have seen 10 out 10 times it works out double the main conductors size still some countries the disgeners assume neutral conductor size as half the main conductors size and land every body in trouble

i am just sharing my experience

Very prudent Andy, with all the switch mode power supplies , inverters and fluorescent lighting excessive current can flow in the neutral due to harmonics which add to the normal single phase current in the neutral .

Some three-phase loads have a half-wave rectifier on each of the three phases. The net DC current is then routed through the neutral line. In other words even with a balanced line load there will be a very large DC current.

I know that some locations have restrictions on drawing currents from the neutral line.

lightningrod; generally there are 6 devices, i guess i could see a use for half wave, the peak voltage would be 120 degrees apart. we built a 5 phase generator with 10 diodes that worked out good. perry