Are all electrical sockets of my house in the same phase?

Here in North America, each house is fed from a single phase of the distribution system thru a step-down transformer. The secondary of that transformer is 240 V center tapped. All three lines go into your house.

The center tap is earth grounded near where it enters the house. Ordinary 120 V circuits are between one of the ends and the center, which is ground. High-power 240 V circuits, like for a range or dryer, are between both ends.

Therefore the hot side of one 120 V circuit will either be the same phase or 180° out of phase with others. It will also be the same phase as one side of the high power circuits, and 180° out of phase with the other side of these high power circuits.

The two responses given have been from a North American members. I'll give a European perspective.

In parts of Europe (I know for sure about Belgium, The Netherlands, Germany, France and the UK), they use a 230 V/400 V (230 V between line and neutral, 400 V between phases) three phase system. Most houses are provided only one of the three phases, and hence the outlets will be on the same phase. Often, it is possible (although, in general, not very common) to get 3-phase in your house, in order to run larger machines (heat pumps, big ovens, ...). In this case the electrical installer will wire different sockets to different phases if it is a new installation.

In either case, even if a house is provided with multiple phases, since most rooms have all their sockets wired up to a single breaker (specific to that room or group of rooms) it is quite likely that they are still all on the same phase.

It depends on your location. China, India, EU, UK, NA, Africa, NZ, AU are different.

Many of the 220Vac residences are only single phase.
many with √3 * Vac for 2 of 3 phases.
North America is generally split phase with center tap = Neutral like below with 120/240V 60Hz

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