thanks for helping me out.
You're welcome Tom. By the way, the diagrams Ryan linked to were drawn up a couple of years ago to illustrate the various supply and earthing (grounding) methods used on British installations. I only sketched out the rough diagrams -- Credit goes to two other members of the forum for drawing them up neatly in AutoCAD.
All American residential supplies are equivalent to the British PME or TN-C-S arrangement. In fact the TT system which is common here in rural areas would not be allowed under the NEC anyway.
plugwash said:
i belive that 3 phase in the USA is uncommon in houses but common in commercial buildings and blocks of flats.
Yep. In fact the general philosophy of U.S. distribution differs somewhat. To feed a given number of homes. they use a larger quantity of smaller transformers compared to Britain, with single-phase transformers being the norm in residential areas. Contrast that with the British system which tends toward 3-phase distribution systems for all but the smallest groups of houses. Of course, given the way that homes in the U.S. tend to be much more widely spaced than here, that makes sense as it keeps the longer cable runs at higher voltages.
Commercial 3-phase supplies come in what might seem like a bewildering range of types compared to the British 240/415 system, The basic wye system is 208Y/120V as you describe, and for higher powers there is also a 480Y/277 service. Older 240 and 480V delta supplies can also be found in many areas, as can the uniquely North American "4-wire delta" system.
As commercial buildings supplied with higher voltages still need 120V for general small appliances, they may have either a transformer to step down to 208Y/120 or sometimes a second service from the utility (either 208Y/120 or maybe a 3-wire 120/240V one).
lectrician said:
Our distribution network uses the split phase very often, but only distributes one of the phases and the neutral to the property, so again, our neutral is carrying all the current until it hits the street.
There's quite a lot of 240/480V 3-wire distribution in my local area (rural Norfolk). You'll see it where there are maybe a dozen or two houses strung along a rural backroad fed by a quarter-mile 11kV spur line where the old Electricity Board didn't want to go to the expense of running a full 3-phase spur. Some of the farms do actually take a 3-wire service.
From the diagram above, It looked like there where two sides inside the board
I can certainly see how that diagram could lead to that impression.
Another American wiring method unknown in British homes (for obvious reasons) is the "multiwire" circuit, where a 3-wire branch circuit is used to feed only 120V loads. A typical application might be to feed a dishwasher and garbage disposal from a duplex receptacle (double socket) under a kitchen worktop.
A 3-conductor (plus ground) cable is run from panel to receptacles, with one half of the duplex on the black hot, the other half on the red. The neutral is shared, carrying the difference in current when both appliances are run simultaneously.
andrew2022 said:
, houses are fed from a 3 phase supply where all the neutral are together, so if there are 3 houses, all using the same current, then the neutral only carries the load to the neutral in the 3 phase cable, and not back to the transformer since its balanced, therefore it does only carry the unbalanced load
Ah, but out here in the boondocks we also have an odd one or two houses standing on their own fed from a simple 2-wire 240V secondary.
{Edited to correct typo}
