Circuit Design Calculations

Summary

Nowadays, it is becoming increasingly popular to perform cable calculations using one of the widely available computer software packages, rather than to do it manually. The aim of this chapter is to provide basic information for use when determining the cross‐sectional area of a cable in an electrical installation design. Every circuit has to be designed to meet the relevant requirements of BS 7671, relating to electric shock protection, overcurrent protection and voltage drop. An installation design must start by determining the supply characteristics, including the particular earthing arrangements. Once the design current has been established, the circuit protective device can be selected. Electricity distributors will generally declare a maximum prospective short‐circuit current at their cut‐out of 16 kA; however, the fault level will only be that high if the installation is very close to the distribution transformer.

Controlled Vocabulary Terms

earthing; electric shocks; Integrated circuit synthesis; overcurrent protection; short‐circuit currents