Presentations and Papers
Summary - Earthing and Bonding - Who Needs It?
Presenter: Andrew Blakeley-Smith
Earthing & Bonding is perhaps the most interdisciplinary and iterative activity in the design process of a new 25kV a.c. railway system and seems to be the least understood - yet the underlying principles do not require much more than a basic appreciation of Ohms Law. Personnel hazards resulting from induction and earth potential rise (EPR) are, in practice, very rare events however care must be taken when focussing on the strict numeric requirements of standards we do not lose sight of the big picture, both in terms of immediate and consequential hazards. These can only be avoided by a top down approach to earthing and bonding, and therefore compromises in design are inevitable.
The design of earthing and bonding systems is well documented but frequently applied inappropriately as the origin of some of the practices and criteria often seems to have been forgotten, frequently subject to subjective philosophical decisions and much faith is often placed in highly accurate modelling derived from input data and assumptions of dubious accuracy.
This paper aims to demystify some aspects of this cross-disciplinary subject, reviewing past historical practices adopted by different rail authorities and suggests that a “one size fits all” approach is neither appropriate nor cost-effective even within a single project.
To this end the authors are suggesting that a Working Group be formed to harmonize the E&B Codes of Practice within Australia and New Zealand.
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