Physical installation of earth electrode

The answer is not in BS 7671, but in the standard that BS 7671 refers to for this ... BS 7430.

If you are looking at driven rods, there are a couple of things to consider, which would be usual good practice:

(a) The parts of the earth electrode that are not buried 600 mm below ground are ineffective in freezing conditions
(b) Terminations should ideally be 250 mm below ground, in a suitable inspection pit (the pit itself being approx 500 mm deep).
(c) All terminations should be suitably protected against corrosion - suitable compounds are readily available for this.

Reasons not to leave rods protruding above ground (even if there is a suitable length at a depth of 600 mm and below) are:
(a) Rods protruding from the ground where people move around are seen as a health & safety hazard, with risk of impaling, and this must also be considered under CDM.
(b) Terminations above ground outdoors are more susceptible to contamination and damage.


There are, however, other alternative earth electrode types, which are potentially easier to install, and help avoid risks of striking anything buried in the ground (including underground services), which may well offer an overall cheaper approach when all of the time, trouble and H&S risks are considered. For example, a suitable earth mat, say 600 mm x 600 mm, buried at a depth of 600 mm or more, with terminations in a suitable inspection pit.

Thanks gkenton,

Really great info.

I am aware of the other “earth rod alternatives” .l and the list exists in the regs.

it is clear that the information is not well known and I would have thought something would be in both the On-line guide and the Regs.

i know I wouldn’t want my granddaughters to be rear a rod not buried to sufficient depth!

Thanks gkenton,

Really great info.

I am aware of the other “earth rod alternatives” .l and the list exists in the regs.

it is clear that the information is not well known and I would have thought something would be in both the On-line guide and the Regs.

i know I wouldn’t want my granddaughters to be rear a rod not buried to sufficient depth!

Your worry about touch voltages for people is probably displaced. Remember that we expect a TT installation to disconnect in less than 200 ms (depending on the fault current) and even at 230 Volts this is considered safe(ish). There should not be a situation where an Earth electrode is "live" for a significant period, the only time being as part of a TNC-S system with an open circuit PEN conductor. Earth faults on a TT system should result in quick ADS, and so be cleared, but this does not apply to a few particular faults on TNC-S systems. Earthing systems should not be considered a particular risk, and this is probably why you find little advice.

Ziggie said:

it is clear that the information is not well known and I would have thought something would be in both the On-line guide and the Regs.

You may find this changes very very soon. More installations will require earth electrodes ... not simply TT ... for example, if you want island mode ('backup power') capability if you have a battery storage system fitted, then TN-S and TN-C-S earthing arrangements would require an additional consumer earth electrode connected to MET, as BS 7671 says you can't rely on the distributor's earthing terminal for switched alternative supplies (in case the DNO is working on your cable specifically).