sizing the neutral conductor on 120/240V services

[k2panman]

What factors should be considered when sizing the neutral conductor on a single phase 120/240V service? A lot of utilities use a reduced neutral (ie Aluminum 4/0 for the two hot legs and a 2/0 neutral), but I understand harmonics from electronics can require a neutral at least as large as the hot legs. Anyone have any comments on this?

K2ofKeyLargo

 

[wareagle]

The NEC says to caculate the max unbalanced load and use that figure to size the neutral. Utilities buy triplex
#2AL, 1/0 AL, and 4/0 AL. The 120/240 volts does not have as much problem with harmonics because the hot legs are 180 degree out of phase and the triplen harmonics cancel.

 

[tinfoil]

For single-phase 120/240 services, the rule of thumb for utilities is to provide a neutral two sizes smaller than the two 'hots', as the hots are 180° out of phase and tend to cancel, so the neutral need only carry the imbalance.

WRT harmonics, as already pointed out, the triplens DO cancel.

So if the phase wires are 1/0, the neutral will be #2. If the phase wires are 3/0, the neutral will be 1/0.

After the utility/facility demarcation, the NEC or CEC (or OESC) applies.