Do I have single-phase or three-phase?

Most flats in Belgrade are single-phase. Houses, shops and workshops usually are not, and knowing which you have decides what you can install.

The difference

A single-phase supply brings one live conductor and one neutral. Between them there is 230 V, and that runs lighting, sockets, a water heater and an air conditioner without trouble.

A three-phase supply brings three live conductors, each at 230 V to neutral, but 400 V between any two of them. That higher voltage is what larger equipment is built for.

How to tell

Open the consumer unit and look at the main switch. One or two modules with a single cable in means single-phase. A wider main switch with three cables coming in means three phases.

The meter says the same thing, and so does the contract with the distributor.

What genuinely needs it

An electric cooker with all its rings and an oven, which is the classic reason. Motors above roughly 2 kW, which is most workshop machinery. Compressors, larger pumps, lifts. Anything with a nameplate marked 400 V.

An ordinary flat with an induction hob is a borderline case: it works on a single phase, but the load has to be planned rather than assumed.

The problem nobody sees

When three phases are present, the load should be spread evenly across them. In practice it rarely is: over the years circuits get added to whichever phase was convenient, and one ends up carrying far more than the other two.

That shows up as a breaker tripping on one phase while the other two idle, and as voltage dropping on that phase under load. It is the most common hidden fault in shops and workshops, and the easiest to fix once it has been measured. That is part of the work covered under industrial installations.

Converting a flat

This is not a question of the board but of the connection and the contract with the distributor. Reworking the board comes second, after approval, and is then a consumer unit upgrade with a new main switch and a redistribution of circuits.