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The US electrical system

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rstofer:

--- Quote from: NiHaoMike on June 25, 2020, 04:21:37 am ---The "2/3" 120/208V system is common in apartments and condos in densely populated cities. There, heating appliances running cooler keeps apartment owners happy by reducing maintenance costs.

--- End quote ---
120/208V 3 Phase 4 Wire is quite common for industrial and commercial applications.  Obviously, it is used for all small receptacle loads in both applications since the voltage between neutral and any of the 3 phases is 120V.
277/480V 3 Phase 4 Wire is the other common industrial supply and most large commercial and industrial lighting runs on 277V and the motors run on 480V.  Industrial applications will have both 120/208 3 Phase and 277/480V 3 Phase distributed internally.  The utility will provide just the 277/480V and the owners will use small transformers to create 120/208V 3 Phase where necessary.
120/240V 3 Phase 4 Wire is an oddball configuration (called 'wildcat' by some) where one transformer is the common 120/240V single phase and the second transformer provides the other 240V leg.  Between the neutral and the 2d transformer output is 208V and this leg is never used for a non-3 Phase application.  This is known as an open delta arrangement.  It requires only 2 transformers so the utility tends to like it but the 240V 3 Phase is a little low for larger motors.  The transformer delivering 120/240 single phase will be larger than the transformer providing just the 3rd phase for motor loads.

None of these 3 phase configurations are delivered to residential occupancies, as far as I know.  Those are strictly 120/240V Single Phase.

We have all kinds of transformer schemes.  For 3 phase transformers, the secondary can be either wye or delta connected.  Loads are usually delta connected and have no use for the neutral.  The neutral is always grounded, sometimes solidly, some times with a resistor.  These resistor grounded systems exist to limit fault current, most typically for large motor installations. 

In thinking about it, it's a real mess!

richard.cs:

--- Quote from: rstofer on June 26, 2020, 07:41:53 am ---120/208V 3 Phase 4 Wire
277/480V 3 Phase 4 Wire
120/240V 3 Phase 4 Wire
120/240V Single Phase.

In thinking about it, it's a real mess!

--- End quote ---

There are too many different voltages, and too many of them are too similar to really be useful, e.g. 208/240/277 are all too similar to have significant advantage, but are different enough to be incompatible for many types of equipment.

tom66:
The idea of 400A 240V service to me is just baffling.  In the UK it's rare to see any home over 100A 240V service, single phase, and many older homes have 63A or 80A service.  Some larger homes have 125A.

This creates a real hassle for EV adoption because there isn't enough local capacity to have two car chargers @ 32A each on someone's driveway.  Many DNOs (the local network operators) have designed the power distribution networks with the assumption that all customers will use an average of 4-5kW at peak.  That falls apart when people are charging their cars and heating/cooling their homes with heat pumps. Local upgrades are going to be necessary.

richard.cs:

--- Quote from: tom66 on June 26, 2020, 10:13:52 am ---Many DNOs (the local network operators) have designed the power distribution networks with the assumption that all customers will use an average of 4-5kW at peak.

--- End quote ---

And the expected average for a house without electrical heating is 2 kW, this is the assumption used for network design. The UK approach with fewer larger transformers compared to the North American one does allow designing more for the average because there are more customers per transformer, but you still have to get that average right.

GlennSprigg:
As a 'fun' diversion here...   :P
Many years ago in the bush, (I worked for that power authority), we would just string a 'clip' up
to the powerlines above with a pole, when out on the road. And connect it to a 're-wired' 30-Amp
kettle to make coffee. Took about 15 secs to boil !! Though it shook like hell,  haha...   8) ;D

Also, in regards to effective energy management, ref a few times in this post...
I also worked more recently with a major company, ('Honeywell' actually!), where I was responsible
(amongst countless other things/equipment) for Energy Management systems in multi-story buildings.
Now, 'some' buildings owned & occupied by one company, are 'interested' in such savings...
However, multi-story bldg owners with MANY other companies residing within, would SCOFF at my
offerings of savings!!!  Why?... Because they would individually meter the whole bldg, and on-sell the
power to all the bldg customers!  Often making from $100,000 to $500,000 profit, JUST from re-sale
of electricity per year!!  They actually WANTED all their customers to be as in-efficient & wasteful as
possible!!  Always made me laugh, when the Govt was pushing for 'efficient' buildings... hahaha...   :palm:

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