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Soil resistivity data

Hi all

A couple of times recently (example) there’s been mention of the BGS soil electrical resistivity model. I looked it up (here) and indeed it does look like a helpful resource as a first-pass check prior to - and a sense check for - a proper survey. But the pricing model direct from BGS isn’t sensible for a single site due to handling fees and they’re not replying to emails anyway... has anyone got experience of actually using the data or an alternative and where was it obtained from?

Sparkingchip‍ mentioned that he’d seen a wall poster available which would be ideal. But I can’t see where he’d get it from?

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0 Former Community Member over 5 years ago

Whilst you will eventually need to measure it, you can do a lot of design based on an assumption of resistivity and a design solution that is "flexible enough" to make minor modifications later on.

As an example, I did a 60MVA substation (x2) for a data centre client recently based on an assumption of 50ohm/metre resistivity. Using a number of modified equations for the foundation and interconnection to a typical hollow square and grid array we had a workable design based on 3.6m driven rods and tape - on measurement, the more global nature of the earthing arrangement allowed us to shorten to 2.4m rods - most of the design remained unchanged.

I appreciate a degree of conservatism does cost money - but you can often spend more money than you save if you look for fine granularity at the wrong time (ie too early).

I'd use the map to get a RoM value and go from there for the initial design - you can refine once you get closer to site

Regards

OMS

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0 Former Community Member over 5 years ago

Whilst you will eventually need to measure it, you can do a lot of design based on an assumption of resistivity and a design solution that is "flexible enough" to make minor modifications later on.

As an example, I did a 60MVA substation (x2) for a data centre client recently based on an assumption of 50ohm/metre resistivity. Using a number of modified equations for the foundation and interconnection to a typical hollow square and grid array we had a workable design based on 3.6m driven rods and tape - on measurement, the more global nature of the earthing arrangement allowed us to shorten to 2.4m rods - most of the design remained unchanged.

I appreciate a degree of conservatism does cost money - but you can often spend more money than you save if you look for fine granularity at the wrong time (ie too early).

I'd use the map to get a RoM value and go from there for the initial design - you can refine once you get closer to site

Regards

OMS

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Soil resistivity data

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