Electrical Installation Calculations: For Compliance with BS 7671:2008, 4th Edition
DescriptionManual calculations are still extensively used and in particular are necessary for checking and verifying various software calculation design packages. It is highly recommended that users of such software familiarise themselves with the rudiments of these calculations prior to using the software packages.
This essential book fills the gap between software and manual calculations. It provides the reader with all the necessary tools to enable accurate calculations of circuit designs. Rather than complex equations, this book uses extensive worked examples to make understanding the calculations simpler. The focus on worked examples furnishes the reader with the knowledge to carry out the necessary checks to electrical cable sizing software programmes.
Other key features include:
- Updated information on 230 volt references and voltage drop under normal load conditions
- New sections on buried cables that take into account soil thermal conductivity, trenches and grouping, allowing readers to carry out accurate cables sizing
- Information and examples of steel wired armour cables, new to this edition. This includes sufficiency during short circuits and, for cables with externally run CPCs, gives unique fault conditions.
- Covers calculations of cross-sectional areas of circuit live conductors
- Earth fault loop impedances
- Protective conductor cross-sectional areas and short circuit conditions
- Short circuit protection.
The last chapter combines all of the calculations of the previous chapters to enable the reader to complete an accurate design of an installation circuit under all conditions.
A unique tool for detailed electrical installation trade, Electrical Installation Calculations, Fourth Edition is invaluable to electricians, electrical designers, installers, technicians, contractors, and plant engineers. Senior electrical engineering students and technical colleges, junior engineers, and contracts managers will also find this text useful.
1 Calculation of the cross-sectional areas of circuit live conductors.
Circuits in thermally insulating walls.
Circuits totally surrounded by thermally insulating material.
Circuits in varying external influences and installation conditions.
Circuits in ventilated trenches.
Circuits using mineral-insulated cables.
Circuits on perforated metal cable trays.
Circuits in enclosed trenches.
Circuits buried in the ground.
Grouped circuits not liable to simultaneous overload.
Circuits in low ambient temperatures.
Grouped ring circuits.
Motor circuits subject to frequent stopping and starting.
Circuits for star-delta starting of motors.
Change of parameters of already installed circuits.
Admixtures of cable sizes in enclosures.
Grouping of cables having different insulation.
2 Calculation of voltage drop under normal load conditions.
The simple approach.
The more accurate approach taking account of conductor operating temperature.
The more accurate approach taking account of load power factor.
The more accurate approach taking account of both conductor operating temperature and load power factor.
Voltage drop in ring circuits.
Voltage drop in ELV circuits.
3 Calculation of earth fault loop impedance.
The simple approach.
The more accurate approach taking account of conductor temperature.
Calculations taking account of transformer impedance.
Calculations concerning circuits fed from sub-distribution boards.
Calculations where conduit or trunking is used as the protective conductor.
Calculations where cable armouring is used as the protective conductor.
4 Calculations concerning protective conductor cross-sectional areas.
Calculations when the protective device is a fuse.
Calculations when an external cpc is in parallel with the armour.
Calculations when the protective device is an mcb.
Calculations when the protective device is an RCD or RCBO.
5 Calculations related to short circuit conditions.
a. c. single-phase circuits.
The more rigorous method for A.C. single-phase circuits.
a.c. three-phase circuits.
6 Combined examples.
Appendix The touch voltage concept.