Why 220 volts?

GopherT

Joined Nov 23, 2012
8,009
Aha! I see what the deal is.

It's strange how different electrical systems can be in two parts of the world. Parts which otherwise try to keep up with each other.
As they race to keep up with each other, they never look over their own shoulders to see that each part started running down different paths years ago.

Voltage, medical care, unemployment, role of public education, college education costs, retirement & pensions, taxes, currency, liability & civil courts, public transportation, gun laws and urban sprawl - lots of difference while trying to maintain or advance a civil society.
 

tinkerman

Joined Jul 22, 2012
151
Our house hold current in western world is NOT "two phases". It's one phase (single phase). The "hot" legs are 180 degrees apart. One hot leg to neutral is 120 volts. The opposite hot leg to neutral also 120 volts. Hot leg to hot leg is 240 volts. Opposite ends of the same winding.

Three phase power has three legs each 120 degrees apart. Three separate windings, connected either delta or star.
 

studiot

Joined Nov 9, 2007
4,998
I have said this before and here it is again

The strangest difference is that

In the UK it is illegal for the consumer to earth the supply neutral.

In the USA it is illegal not to.
 

studiot

Joined Nov 9, 2007
4,998
So...do the supplys "float" in the UK, or is this a requirement to pay retail for an electrician to pound a metal rod into the planet?
You obviously haven't tried my search-the-forum advice.

In the USA domestic consumers provide their own earth spike, as you suggest, and connect this to the centre point of their transformer, which also forms their neutral (or at least their electrician does).

In the UK there is no transformer.
The supplier provides three connections, phase (line), neutral and earth which have a fixed electrical relationship and the consumer uses these and doesn't mess with them.
 

vk6zgo

Joined Jul 21, 2012
677
I cannot speak for the UK,but in Australia,which has a similar system,the Neutral line is earthed at the point where the service enters the house (fusebox),as well as at the power station,or in many cases,major distribution transformer.
 

studiot

Joined Nov 9, 2007
4,998
I cannot speak for the UK,but in Australia,which has a similar system,the Neutral line is earthed at the point where the service enters the house (fusebox),as well as at the power station,or in many cases,major distribution transformer.
But not by/at the consumer??
 

richard.cs

Joined Mar 3, 2012
162
I don't know why it was set up this way. It would be interesting to know.
I remember reading it's mostly to do with the manufacture of carbon filament lamps, the optimum voltage for those was around 100V and initially the primary use of electricity was for lighting.

In the UK there is no transformer.
In the US system there are many small (a few hundred kVA at most) single phase transformers, usually powering 1 - 3 houses. Each of those has a centre-tapped secondary giving the split phase. In the UK and most of Europe there are much larger 3-phase transformers, typically 500 - 2000 kVA, and these supply whole streets of houses with 240V to neutral and 415V between phases (in reality it has not been changed to 230V). The smaller transformers exist but are only used in rural areas for isolated farms and similar.

The neutral is grounded at the transformer and one of three systems is used depending on location/age. TT where the grounds in the house are connected to a local earth spike, TNS where there is a seperate earth conductor (often a lead cable sheath) back to the transformer, and TNCS which is most similar to the US system where a single conductor is used for both earth and neutral and split before the meter.

In the UK it is illegal for the consumer to earth the supply neutral.

In the USA it is illegal not to.
Sort-of. The neutral is always earthed, all that changes is who is responsible for doing so and where the earth wires in the house join to the neutral. Adding additional eath connections to the provided earth in a TNCS or TNS system effectively earths the neutral and is legal, but they must be after the netral and earth split - there should only be one connection betwen them. If you draw out the UK and US system you'll see it's not that different at all.

In reality the US electrical system is simply the curse of the early adoptor. You're stuck with it because it already exists and is hard to change, even though it has several major downsides, such as:

1) It's difficult to get all of the commonly used voltages on one supply and have three phases. Where domestic and industrial appliences must both be used you end up with separate transformers, 240V appliances under-run onm 208V or crazy things like high-leg delta.
2) Many domestic appliences are woefully underpowered compared to their European counterparts.
3) Linked with the above, there's a much greater use of specialist supplies for large appliances. In the UK I can buy a clothes drier, or a small welder, a space heater or a compressor and put it anywhere I like in the house or an outbuilding. Most of the time in the US these would have to go where the 1 drier outlet is.

Longer term if there was a will to change then it could be done. Imagine adopting a small 4-pin plug suitable for domestic use that could provide both 120V and 240V split phase, there could be a transition period of 30 years or more where all appliences use this plug, all houses get the outlet and gradually it most appliances become 240V transparently to their users.
 
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