18th Edition Updates- Electrodes to Supplement a Distributor’s Earth Facility

by Editor on October 28, 2017

What’s coming in the 18th Edition? Electrodes to Supplement a Distributor’s Earth Facility.

The second update in a series covering some of the proposed changes and additions that are likely to be included in the 18th Edition Regs.


Keep abreast of these proposals so they won’t be such a surprise when the new 18th Edition comes along!

Some significant changes will likely include:

  • The increased use of RCDs
  • Supplementary earthing
  • Special location changes
  • New Part 8 for Energy Efficiency
  • Protection against fire- AFDDs
  • Protection against overvoltage
  • Embedded Heating Cables
  • Restructuring of Inspection and Testing Part 6

Electrodes to Supplement a Distributor’s Earth Facility

542 – Earth Electrodes to supplement the earthing facility provided by the distributor.

  • To protect against dangerous touch voltages caused by the loss of a main earth.
  • This would not be easy on most existing installations but could mean that all distributor’s earth facilities would require the addition of an earth electrode.
  • This is not a surprising addition due to the age and poor condition of many thousands of old lead sheathed supply cables and their earth connections.
  • For new installations, a foundation earth would be recommended ie. a purpose made metal framework buried in the ground.
  • Also look out for new requirements of additional earth electrodes for Electric Vehicle Charging Stations.

RCDs For TT Calcs

Table 531.1 – Selection of RCDs for TT systems using measurement of RA. i.e. Resistance between body of earth and the exposed and extraneous conductive parts. In reality a 30mA RCD would be used but Table 531.1 would give the maximum values of resistance for each mA RCD.

Double Insulation for Metal Enclosures

531. – For metal enclosure in TT systems i.e. Metal Consumer unit housing an RCD fed from a non-RCD supply.

  • Double insulated non-metallic cables or glands are deemed to meet the requirement.
  • An insulated cable gland which routes both the live and neutral meter tails through a single hole is a good option for this. Unenclosed meter tails should always be double insulated.

More 18th Edition updates to follow soon!


{ 1 comment… read it below or add one }

John Advent November 16, 2017 at 08:35

Does this mean we can longer rely on the earth of a pme system when we go outside of the equipetential zone. i.e hot tubs, car chargers etc.

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