November 2018 – Earthing Standards update (Rail)

Earthing Standards Update. 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. And, 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 Earthing Designs standard update often referenced is: 

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

Therefore, this is a piece that not only applies to Rail electrification programmes. But also, 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 the need for computer software tools like CDEGS. For an accurate calculation of touch voltages. On anything but the simplest of grids.

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

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Moreover, in my experience, ALL grids are ‘unusually-shaped’ to some degree or other. Also the only exceptions I can think of, the simple generator earth or towers.

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

So, in my view, the train on hand-calculations 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, the technically secure design is well within reasonable reach of all projects?

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