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The American (Edison) System is different then single phase in Europe. The American System uses a centre tapped transformer. The end to end volatge is 240 V and the end to centre is 120 V. In the fusebox, the neutral centre is wired to the incoming water pipe as a ground (earth). The two end leads connect first to a master circuit breaker or fuse holder (on older systems) and then proceed to two columns of fuses or circuit breakers.

Thus, for 120 V service, the connection is line to neutral. For 240 V service, such as for electric heaters, air conditioners, clothes drying machines, electric stoves, etc. a protected outlet is connected line to line.

Single phase 120 V outlets are rated 15 A and 240 V outlets are rated 30 A. Some 120 V - 20 A are available also, but are not as common or are for industrial use.

Single phase appliances are limited to 1200 W @ 120 V. The frequesncy is 60 Hz and the 120 V sockets use flat pins and a rounded ground pin. There wire colours are black for "hot", white for neutral and either green or bare copper for ground (earth).

Hi John, and welcome to ECN. I see you're in Cleveland -- I have memories of waking up on the NYC-Chicago sleeper train to a very crisp, frosty morning in Cleveland and the conductor pointing out the sights on the city skyline as we passed through.

I rather like the 3-wire single-phase system used in North America. It gives the benefits of having 240V available (and thus lower currents) for heavy appliances, but still with only 120V to ground at any point in the system.

Don't you mean 1800 watts (on a 15A circuit) ?



[This message has been edited by pauluk (edited 07-31-2003).]

Kinda. For a fuseboxe the left hand column is on one leg, the right on the other. If 240V is required for a load, fuse holders on either side of the box are used, mostly beside each other. Since the 1960s, in some brands of fuseboxes, there is a speciall pull out assembly for the fuse sockets, and the ones to be used for 240V loads a so you have to remove the unit from the fusebox to replace the fuses, or to disconnect the circuit. For breaker panels, there are two usses, each to a supply leg, but the bus has a tab bent over, so that the odd tabs are on one leg, the even on the other. A fitting on the breaker grabs the tab. With that configuration, you can supply 240V loads with
a two pole breaker installed in any two adjacent positions.

Actually some appliances have neutrals supplied to them as well, to power 120V components inside them, such as ranges and clothes dryers. They used to get that neutral
from the ground, which is bonded to neutral at the service panel (in the USA).

Another outcome of 120/240V single phase system, is the shared neutral circuit, where there are two hots, each from opposite supply legs (never from the same) which
sher the same neutral an earth.

More and more 120V 20A circuits are being installed for GP outlets, and kitchens are also usually wired with 120V 20A.
Not all 240V outlets are 30A. In the home, they can be 15 or 20A (for window A/C),
to 50A, for a range (AKA Cooker). 30A is typically used for dryers.

The recepticals have a U shaped hole, Moulded plugs have a round prong, whilst
add-on plugs usually have a U shaped ground
prong. Also, the neutral slot is wider, for polarization of plugs without ground prongs.
In that case, usually the neutral prong is wider only at the end.

Classicsat,

What is the ruling on 240V 15 or 20A sockets in the domestic environment in Canada? In the US, NEC 210-6(a)(2) prevents receptacles (in dwelling units) with >120V between conductors supplying loads less than 1440VA or 1/4hp. How this is applied in practice I cannot imagine.


[This message has been edited by Hutch (edited 07-31-2003).]

It is 1200 W max for a single appliance. Even though the circuit is designed to carry 15 A x 120 V = 1.8 kW, it is not desirable that a single appliance take up the entire 1.8 kW.

Consider that multiple outlets or whole rooms in a house may share the same fused connection. If someone was using a 1.8 kW hair dryer and had a light going and maybe a music system, the circuit would be overloaded and hopefully the protective device would open the circuit. However, this would be an inconvenience to the user if he/she had to use his/her appliance in the dark.

Is there such limits in Europe? I know that on a 240 V European system, a product designed for the same power as an American product but for 240 V will draw only 50 % of the current. Thus, a 15 A system should be able to handle twice as much current load as the equivalent American system. Also, the I^2R loss in European systems is 25 % of American, thus less chance of wires overheating. Comment?

Ok..... how do i reply to a specific post where I can quote what someone said? The way Classicsat responded to my post.

BTW, he is correct, just a bit more specific then I was.

[This message has been edited by JohnS (edited 08-01-2003).]

John,

You can enclose various codes within square brackets for quoting, italics, bold, etc. There are also ways to insert a link and an image.

Go here for an explanation of UBB codes

You might find the other hints in the General FAQ useful too.

Most of Continental Europe uses receptacles rated at 16A maximum, wired on branch circuits protected at 16 or 20A. (A few places use 10A circuits as well.) Thus each circuit can supply about 3.5kW, which is adequate for most purposes, as they also use dedicated circuits for heavy appliances.

In some places (e.g. France) the code restricts the number of outlets on each branch circuit to help avoid nuisance tripping due to overloads.

Britain does things a rather different way and uses a 30A ring circuits which can provide up to 7.2kW. Each and every plug then carries its own fuse rated up to 13A maximum.

If you do a search on "ring" you'll find a lot of discussion about the pros and cons of this method.

John,

No and yes. [The following applies to Sweden] You can't put more than 100% load on the plugs*, but the circuits can have overcurrent protection which is less than the rating of the socket. Thus, you can plug a 16A appliance into a 10A circuit. Inconvenience is the user's problem, not the codemaker's. I.e. a design issue, not a safety issue.

* Cooker (range) manufacturers cheat a little on this: You will find that the 14kW cookers have 16A plugs on them. (16A at 400V 3-ph equals 10.8kW) The cooker in my home draws about 5kW and is on a 16A single ph. 2.5mm2 circuit. It has never caused any problems.


[This message has been edited by C-H (edited 08-01-2003).]

[This message has been edited by C-H (edited 08-01-2003).]

yes i would like to get rid of twin and earth cable,, why cant we use round cable like flex,, flat stiff cable is now old hat as you say..

cliping it neat and straight is a pain in the arse,,

your thoughts??