Sizing and protection of conductors

Conductor sizing and protection

Methodology and definition

Overcurrent protection principles

Practical values for a protective scheme

Location of protective devices

Conductors in parallel

Practical method for determining the smallest allowable cross-sectional area of circuit conductors

General method for cable sizing

Recommended simplified approach for cable sizing

Busbar trunking systems

Determination of voltage drop

Maximum voltage drop limit

Calculation of voltage drop in steady load conditions

Short-circuit current

Short-circuit current at the secondary terminals of a MV/LV distribution transformer

3-phase short-circuit current (Isc) at any point within a LV installation

Isc at the receiving end of a feeder as a function of the Isc at its sending end

Short-circuit current supplied by an alternator or an inverter: refer to Characteristics of particular sources and loads

Particular cases of short-circuit current

Calculation of minimum levels of short-circuit current

Verification of the withstand capabilities of cables under short-circuit conditions

Protective earthing conductor

Connection and choice for protective earthing conductor

Sizing of protective earthing conductor

Protective conductor between MV/LV transformer and the main general distribution board (MGDB)

Equipotential conductor

The neutral conductor

Sizing the neutral conductor

Protection of the neutral conductor

Breaking of the neutral conductor

Isolation of the neutral conductor

External links

• Electrical Conceptual information given in "Cahiers Techniques"
• Electrical installation software