The electrical network is supplied with three-phase current produced by alternators. Most often, this three-phase current is transformed into single-phase current before it is distributed to individuals. Nevertheless, many industrial or commercial premises and the homes of individuals who request it can be supplied with three-phase current. This electric current offers a higher power particularly suitable for energy-intensive homes, i.e. equipped with a meter of 18 kVa or more, abnormally far from their electric meter or having equipment requiring three-phase (large oven power or machine tool, for example). The three-phase current is in fact made up of three sinusoidal currents with identical frequency and amplitude.
Three-phase, four wires and a balance to respect
The distribution of the three-phase current is carried out via four wires (one for each phase and one for the neutral) where the single-phase current only requires two (one for the phase and the other for the neutral
Any installation of a three-phase electrical panel must be studied to size it in order to allow phase balancing. In a circuit supplied with three-phase current, all the phases must be equal to each other. In concrete terms, in a 60 A three-phase circuit, each of the three phases must be 20 A. This balance, by avoiding exceeding the maximum admissible load, allows normal operation without tripping. Within the three-phase electrical panel, the power supplies must be distributed over the different phases so as to prevent the most energy-consuming equipment from being supplied by the same circuit. This distribution will allow the voltage balance necessary for the operation of the installation.
How to balance the phases?
The balancing operation begins with a careful study of the plan of the electrical installation. It is a question of listing all the circuits of the power supply (single-phase as well as three-phase) and estimating their need in terms of power and their period of use (day, night or both). The overview table obtained must allow a distribution in three columns (one column per phase) at the equivalent required power level.
Remember: the total current required for the operation of the three-phase electrical installation must be distributed equally over each of the phases. Failing this, exceeding the nominal value of a phase will lead to a voltage imbalance and a general outage by tripping of the subscriber circuit breaker.
What dimensions for the three-phase electrical panel?
The capacity of an electrical panel is defined by the notion of module. The latter is a standardized space with a width of 17.5 mm wide. The module is designed to accommodate the protection devices. We observe that:
a single-phase circuit breaker requires a module;
a 30 mA differential switch requires two modules;
a three-phase circuit breaker requires three modules.
In most domestic installations, the electrical panel is made up of several rows of 13 modules, but in the case of an installation supplied with three-phase current, only the study and the balance of the phases mentioned above can determine the capacity of the panel. electric to be installed, i.e. the one capable of accommodating all the essential accessories. The main manufacturers offer switchboards from one to four rows (or even more) of 13, 18 or 24 modules. Two capacity examples:
1. Table with 13 modules:
1 row = 13 modules
2 rows = 26 modules
3 rows = 39 modules
4 rows = 52 modules
2. Table with 18 modules:
1 row = 18 modules
2 rows = 36 modules
3 rows = 54 modules
4 rows = 72 modules
It should be noted that an electrical installation supplied with three-phase current requires a larger electrical panel due to the presence of the three phases and the neutral. On each row, each three-phase line occupies four modules. It is therefore advisable to move towards an electrical panel with 18 modules.