Single-phase and three-phase installations


Electrical cable types and installations

Difference between single phase and three phase installation

Single phase installation

Most domestic installations are single-phase. They have a single phase with a single alternating current and a contracted power of up to 10 kW. Single-phase connects the home with two wires: active and neutral. The neutral wire is connected to earth at the switchboard.

Three phase installation

Three-phase installations are those formed by three different alternating currents that divide the installation into several parts which are reached by a constant power. Their standardised powers are currently adapted to 400 volts. Three-phase has four wires: three actives (called phases) and one neutral. The neutral wire is earthed at the switchboard.

Cables for a single phase installation

Difference between single phase and three phase power cables

Both single-phase power systems and three-phase cables are units that use (AC) electrical power with alternating current . The main difference between single-phase cables and three-phase cables is the constancy of delivery.

Cables for a single phase installation

The following cables can be used to supply a single-phase installation correctly:

  • Two conductors: blue (neutral) and brown (one phase).
  • Three conductors: blue (neutral), brown (one phase) and green-yellow (earthing). An example of tripolar would be the armored cable TOXFREE ZH RC4Z1-K (AS)

Cables for a three-phase installation

However, to supply a three-phase installation, we would use the following cables:

Three-phase cables

  • Three conductors

    Grey, brown and black (all three phases)

  • Four conductors

    Grey, brown and black (the three phases) and blue (neutral).

  • Four conductors

    Grey, brown and black (all three phases) and green-yellow (earthing). An example of a 4 conductor cable would be the low voltage cables TOXFREE ZH RZ1-K (AS).

  • Five conductors

    Grey, brown and black (the three phases), green-yellow (earthing) and blue (neutral).

The same installation can be done starting from single-core cables (using two, three, four or five) or starting from multi-core cables with outer sheath (2x, 3x, 4x or 5x).

The earthing conductor is commonly called the earthing lead. it joins the installation earthing terminal to the earth electrode or to the earth terminal provided by the electricity supply company. to request, for example, a three-core cable with a 1.5 mm² cross-section with earthing, we would indicate 3 g 1.5mm2 instead of 3 x 1.5 mm2. thus, the G indicates that one of the conductors is green-yellow.

¿What size should the earthing conductor be?

The size of an earthing conductor shall comply with your local standard regulation. The final selected size shall be based on the cross-sectional area of the line conductor.
Need any help with cable cross-section? Contact our technical support here, or download our cross-section Topmatic app.

Four conductors cable

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