Complete guide:General method for cable sizing

 After a preliminary analysis of the power requirements of the installation, a study of the piping of each of the circuits and of its electrical protection must be undertaken, starting at the origin of installation to lead to terminal circuits.

Each pipe-protection combination must simultaneously meet several conditions that ensure the safety of the installation:

to carry the permanent operating current and its normal transient peaks;

do not generate voltage drops liable to adversely affect the operation of certain loads, such as motors during the start-up period, for example. In addition, the protection, circuit breaker or fuse, must:

 protect the pipe or the busbar for all overcurrents up to the short-circuit current; ensure the protection of people against indirect contact, in particular in TN and IT systems, where the length of the circuits can limit the level of short-circuit currents, thus making possible the risk of a non-instantaneous automatic shutdown.

Note: in the TT scheme, this condition is naturally satisfied by the compulsory installation of non-timed RCDs on the terminal circuits.

The section of the conductors is defined by the general method described in the Practical determination of the minimum section of a pipe section. Specific receivers may require oversizing the power cable and its protection.

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