On Mon, Mar 11, 2024 at 1:35 PM Lawrence Winiarski via EV <ev@lists.evdl.org> wrote: > That means our 240 has a slight advantage in that each leg is only 120v above > ground, while I think some countries have a 240 with a hot and neutralleg.
The USA 240V is a split-phase system, meaning two 120V phases in 180 deg offset, simply created by a single winding with center tap off a 11kV mid voltage line and distribution transformer AKA "Pole Pig" if it is one of the round barrel, pole mounted transformers. The split phase is helping to reduce the amount of copper needed to transport the 120V, because the Neutral return current from one phase cancels the return current from the other phase. THat is one of the reasons that you are requested to do a load analysis and phase balance calculation when requesting the permit for a service panel. So, the Neutral does not need to carry *twice* the current of the two phases, but it needs only to be as large as a single phase, so your copper use is 75% of a single 120V feed with double the copper in the phase and double the copper in the Neutral return, instead you have 3 wires, each 50% smaller conductors, so a saving of 25%. In Europe all power is 3-phase, every single home has 3 phase plus neutral coming into the utility closet, but often only a single phase meter gets installed, though you can get it swapped for 3 phase when you need more power. Typically a house is provided at least with 25A single phase 230V and in a block of houses every 3rd house is on the same phase as your house. (babyphones that send the signal over the power wires work best if you visit the neighbors 3 homes over) Since all power is 3-phase and the returns of the current in the Neutral again cancel each other out, the Neutral only needs to be as big as one of the 3 phases, so the saving in copper is 33% as you only need 4 wires instead of 6, or 2 wires of 3x the amount of copper, to transport the necessary power. That is also why upstream of the mid voltage distribution transformer, all USA grids are also 3-phase and commercial sites are supplied with 3-phase, either 480V (3x277V) or 208V (3x 120V). _______________________________________________ Address messages to ev@lists.evdl.org No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
