Three-phase electric power: Household distribution

[greypilgrim]

Hi.

How is three-phase electric power distributed in a household with mainly single-phase power plugs? Do they just connect a phase at random to every plug?

As far as I understood, it's best if all three phases deliver the same current, since then neutral cancels. Do electricians take into account which power plugs normally are in use simultaneously?

 

[berkeman]

Hi.

How is three-phase electric power distributed in a household with mainly single-phase power plugs? Do they just connect a phase at random to every plug?

As far as I understood, it's best if all three phases deliver the same current, since then neutral cancels. Do electricians take into account which power plugs normally are in use simultaneously?

Where have you seen households with 3-phase power connections to the Grid?

It's common to have 2-phase connections in US households, with 220V across the outer Lines and two 110V phases between each Line and the single Neutral. And yes, you try to balance the two 110V phase loadings...

 

[russ_watters]

Do they just connect a phase at random to every plug?

As far as I understood, it's best if all three phases deliver the same current, since then neutral cancels. Do electricians take into account which power plugs normally are in use simultaneously?

Yes, but not exactly random, because...yes.

It also isn't very critical for the phases in a single house to be balanced. But on a street or apartment building, yes.

 

[greypilgrim]

Where have you seen households with 3-phase power connections to the Grid?

In Switzerland, it's quite common that some washing machines, dishwashers or electric stoves use three-phase power. So there's usually a three-phase plug in the kitchen and in the laundry room.

 

[CWatters]

In the UK houses normally only have one phase. A few houses have a three phase supply to a workshop for power tools (eg wood working). A few have a three phase supply if they have a large solar PV array (>4kw).

In other European countries i think they sometimes have three phase supplies to specific appliances such as cookers and electric heaters, with all other sockets on one phase.

Its usually considered dangerous to have a situation where there are single phase sockets on different phases in close proximity. For example i think different phases can be used on different floors of a building but not on the same floor.

 

[Babadag]

At first, in Europe, the standard for new building-usually- is 3 phases household supply-3*400/sqrt(3) 25[40] A and neutral and earthing [grounding].
The 3 phases are mainly for HVAC [about 4 kW] and all other equipment as stove, washing machine, dryers, receptacles and other are single phase.
The panel is provided with MCB and/or MCCB as required.
The utility panel is provided with single phase 40 A [or more as required] fuses and neutral. The neutral-unprotected-is grounded only in one point.
The neutral may convey up to one phase rated current and it is, usually, unbalanced system. See IEC 60364-1-for instance.