How does us standard 208-120 AC voltage differ from standard European 415-240 AC voltage?

Answer 1

Generally 220v anything works easier or with less effort so can be cheaper to run. Appliances that run off 240V draw less current than 120V appliances so lighter wiring and fixtures can be used. However, 240V is more prone to arcing than 120V. Also, 240V is more likely to blow you away than 120V, whereas 120V is more likely to "grab" (Cause your muscles to involuntarily contract, i.e. making your hand grab a conductor) you. Also the US uses 120V because Edison originally used 100V. It was upped over the years to cope with demand. The US also has 240V in residential service for large appliances like ovens and dryers.

Answer 2

North American and European countries use completely-different residential supply systems.

To start with, North American supplies are not 208/120 V, as suggested in your question. This implies that the secondary winding of a transformer is wye connected whereas, in fact, they are delta-connected. Homes in North America use a split-phase system which provides both 240 V and 120 V, which would not be possible using a wye-connected secondary.

The standard nominal voltages in Europe are now 400/230 V. The UK still uses 415/240 V but its allowable voltage variation is in compliance with the European 400/230 V nominal voltage requirement (for this reason, the UK nominal voltage is stated as being 400/230 V!).

So, in North America, the secondary of a three-phase distribution transformer is delta-connected. One of the three phases is centre-tapped, providing a neutral, and the opposite ends of the same phase provide two line conductors, each with a potential of 120 V relative to neutral, and 240 V relative to each other. This is called a 'split-phase' system (sometimes, erroneously, called a 'two-phase' system). Residences are thus supplied with two voltages, 240 V for heavy loads, and 120 V for lighter loads. It's unusual, in North America, for residences to be supplied with three phases.

In European countries, the secondary of a three-phase distribution transformer is star (wye) connected. This provides a line voltage (i.e. between lines) of 230 V, and a phase voltage (i.e. between any line and neutral), of 400 V -the relationship between these two voltages being the square-root of 3, or 1.732. Residential supplies are connected between line and neutral and, thus, are provided with a nominal voltage of 230 V for all loads. While residential supplies in most European countries are single phase, some countries (e.g. Cyprus, parts of France, etc.) use three-phase supplies.

While 230 V might seem a dangerous voltage to North Americans, in fact it is somewhat safer than the 120 V supply used in the US and Canada. In the UK, for example, all socket outlets (receptacles) are shuttered, preventing children from inserting foreign objects into them, and the pins of the corresponding plugs are partially-insulated so that, even when partially inserted into the socket, there are no live parts accessible. The cross-sectional area of the UK plug's pins are significantly larger than the North America equivalent, despite accommodating roughly the same current (13 A in the UK, and 15 A in North America) and, thus, the plug never becomes hot, or even warm, to the touch even when continuously supplying maximum load. Finally, the connection between UK plugs and socket outlets are significantly firmer than North American plugs and receptacles, and it is impossible for them to 'jiggle about' when in use, or to be accidentally pulled out of the wall in normal use.

Another advantage of the 230-V system is that it allows heavier loads to be supplied from ordinary socket outlets. For example, in North America, a 120-V receptacle can supply 15 A, limiting its load to around 1800 W whereas, in the UK, a 230-V socket outlet can supply 13 A, limiting its load to just short of 3000 W. This means, for example, that a standard UK kettle is typically rated at 3 kW, enabling it to boil much more quickly than a North-American kettle while using roughly the same overall amount of energy.