Electrical Distribution Circuit: Definition, Meaning, Examples

Distribution circuit: an electric circuit supplying one or more distribution boards [this term is defined in the IEC 60050-826-2022]. In some regulatory documents, instead of the correct term “distribution circuit,” the terms “distribution network” or “electrical distribution network” are still used unreasonably.

The British Standard BS 7671 defined the term “distribution circuit” as follows: a circuit supplying a distribution board or switchgear.

Note: A distribution circuit may also connect the origin of an installation to an outlying building or separate installation, when it is sometimes called a sub-main.

This definition has a significant disadvantage. Since switchgear is usually used to switch final electrical circuits, it generally cannot be part of distribution circuits.

The term “electric distribution network” should be used in international regulatory and legal documentation to identify the set of low-voltage electrical power installations to which the electrical installations of buildings are connected, and the term “electric distribution circuit” should be used to identify those parts of the electrical installations of buildings that are used to provide electrical power to its low-voltage switchgear.

In other words, the term “electrical distribution circuit” refers to those electrical circuits by means of which the individual parts of the electrical installation of a building are supplied with electricity. Low-voltage switchgear is usually connected to the electrical distribution circuits and is intended to distribute electrical energy between the final electrical circuits that are installed in these parts of the building.

Distribution Circuit Examples

In the electrical installation of an apartment building, the distribution circuits are the electrical risers that connect the floor distribution boards to the main distribution board (MDB). If consumer units are used in the electrical installation of apartments, the circuits by which they are connected to the floor distribution board are regarded as electrical distribution circuits. Since other low-voltage switchgear are used in the electrical installation of an apartment building, the electrical circuits connecting them to the main distribution board are also distribution circuits.

Figure 1 shows, as an example, part of the circuit diagram of a three-phase consumer unit. At the top left there is the inscription “input from the floor distribution board (FDB)”. This input is made by the electrical circuits by which the FDB and this consumer unit are connected. These circuits are referred to as electrical distribution circuits.

Part of the circuit diagram of a three-phase consumer unit
Figure 1. Part of the circuit diagram of a three-phase consumer unit

Figure 2 shows another example of using distribution circuits:

Electric energy distribution scheme
Figure 2. Electric energy distribution scheme

KEY:

  • 1 – supply transformer/incomer
  • 2 – main LV switchboard
  • 3 – intermediate distribution boards
  • 4 – final distribution boards
  • 5 – overhead line or underground cable
  • 6 – distribution circuits
  • 7 – final circuits

In an electrical installation of an individual dwelling house, as well as in an electrical installation of a multi-family residential building which is connected to overhead power lines, the distribution circuits are the electrical input circuits which connect the branch conductors from the electric power line to the input to the input terminals of the main distribution board and which are usually the input cables (wires).

If, in addition to the MDB, the electrical installation of an individual house contains other low-voltage switchgear, such as floor distribution boards, the circuits by which these are connected to the MDB are also electrical distribution circuits.

Does a Distribution Circuit Need RCD Protection?

No. A residual current device (RCD) is for all final circuits, not distribution circuits.

References

  • IEC 60050-826-2022
  • BS 7671
  • IEC 60364-8-1-2019

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