November 2018 - Earthing Standards update (Rail)

For the past few years. GreyMatters has been fortunate enough to support the rail electrification and upgrade programmes across the UK for Earthing Design. And maintaining a consistent approach across a building programme of this scale can be a massive engineering headache for all design teams concerned.

Especially, when Earthing Standards touches on so many disciplines along the way - from civils, OLE (Overhead line equipment), signals, EMC, 3rd parties, ecologies, geophysical as well as the more obvious general E&B (earthing and bonding).

The one thing that provides a form of "glue" to help keep the various disciplines and schemes on track (excuse the pun) are the codes of practice or earthing design standards and their correct interpretation. I say 'interpretation' because the codes cannot account for all the scenarios encountered.  Invariably, there are the not-so-common, or damn right awkward scenarios that no-one has foreseen which get everyone scratching their heads to resolve.

In addition, an electrification scheme has to consider the interface between two sectors, i.e. rail and the energy sectors.  Both are regulated environments in the UK / EU and both have subtly different requirements and focus.

Earthing standards Update

The latest updated standard that is often referred to in Earthing Designs is 

  • ENA's EREC S34 as of November 2018 - A guide for assessing the rise of earth potential at electrical installations

This is a piece that not only applies to the Rail electrification programmes and upcoming national infrastructure investments like CP6 in the UK, but it also applies to all high voltage earthing installations more generally.

Key Change to be aware of

There are a number of "upgrades" in S34 issue 2 that build on the hand calculations from its predecessor. However, the guide explicitly recognises and concedes that computer software tools like CDEGS are needed for an accurate calculation of touch voltages on anything but the most simplest of grids.

Quote: For unusually shaped or non-symmetrical grids, computer software tools are needed for an accurate calculation.

In my experience, ALL grids are 'unusually-shaped' to some degree or other - the only exceptions I can think of are the simple generator earths or towers.

So, I struggle to understand how the old calculations still retain their validity, relying on oversimplified plate electrode concepts, which are known/proven to be inaccurate.

In my view, the train on hand-calcs has left the station a long time ago! For those that don't or won't invest in modern methods for safety-critical calculations. 

I guess, using hand-calculations still provides a limited ability to approximate the rise of earth potential and safety voltages. But why take the risk in today's litigious, street-wise world knowing that reliable, accurate, technically secure design is well within reasonable reach of all projects?

Why not drop us a line or chat with our team?

Ian Griffiths SelfieIan Griffiths This post is written by Ian Griffiths, Principal Engineer at GreyMatters, an Earthing & Lightning Consultant of 27 years, one of the top 1% accredited CDEGS consultants and professional advisor to international utility companies, data centre and infrastructure developers.

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