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Hazard scenarios

Consideration of appropriate safety criteria (usually an allowable shock voltage) is required for all electrical assets that form part of the network. Consideration should be made for substations (both inside and outside) and for the accessible portions of the powerlines and cables.

Touch and step voltages around a substation
Touch and step voltages around a substation

As fault current can be coupled to non-power system plant, so it is required to also consider the safety requirements at those locations outside the substations and easements.

The specific locations will represent a different risk profile by virtue of the fact that there will be different coincident probabilities of system events and human contacts and different series impedance (for example, footwear and surface coverings).

Consideration should be given to factors such as:

  1. Probability of multiple simultaneous human contacts (particularly in public places), (i.e. touch, step, hand-to-hand or transfer voltage impacts)
  2. Susceptible locations (wet areas)
  3. Controlled access areas (fenced easements or remote areas)
  4. Series impedance (surface coverings and footwear)
  5. Future possible encroachments upon the electrical network and the effect of system events on those encroachments
  6. Conductive and inductive coupling into non-power system plant such as communications infrastructure, telecoms, pipelines and conveyors.

Not all risk is imposed by the earthing system. There are external factors that may also impact upon the earthing system resulting in a change in the risk profile of the installation.

Figure below summarises the main risk elements in each category.

Some external factors that need to be addressed (during design and installation) are theft and/or vandalism of earth system components. Consideration should be given to protecting exposed components and/or monitoring key components to ensure an acceptable risk profile.

Earthing system risk profile
Earthing system risk profile

The interaction between the substation or powerline earthing systems and secondary systems (for example, SCADA) needs also to be considered as those systems can adversely affect each other.

Risk management

All life activities involve some form of inherent risk. The tolerability of injury or death to a member of the public is therefore dependent upon several factors including the types of hazards, the control measures implemented, frequency of occurrence, the likelihood of actions of the individual(s) exposed and the associated consequences.

Risk in this context is defined as ‘the chance of something happening that will have an impact on objectives‘ (i.e. a combination of the consequences of an event and their likelihood, frequency or probability).

The risk associated with a hazard is determined using a risk assessment process in which hazards are identified, analysed using quantitative methods and qualitatively assessed against specific criteria.

Once the risks are evaluated, the appropriate risk treatment process shall be implemented where appropriate to effectively and efficiently manage the risks.

Title:Power System Earthing Guide – Energy Networks Association Limited
Size:7.2 MB
Download:Right here | Video Courses | Membership | Download Updates
Power System Earthing Guide
Power System Earthing Guide

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  1. Bakhshi
    Mar 04, 2023

    Thanks for this kind usefull article.

  2. Kanchori
    Apr 25, 2020

    Great and happy for this updates….. How can I get started…..I want to learn more of this earthing and electrical concept

  3. Juan Antonio Díaz Jiménez
    Apr 25, 2020


    Thanks, Edvard

    Dec 30, 2018

    Please Keep Me Informed on All Electrical engineering News

  5. Hocine Meng Fodil
    Sep 06, 2018

    maximum allowable earth resistance is 8 ohms.

    Sep 02, 2018

    Thanks for your best technical knowledge. My need is HTV/LTV Powe Distribution System From Generating Station To Consumers End Supply.Over Hand And Under Ground Net Work .

  7. Mohammad Fayaz Ahmed
    Oct 04, 2016

    Iam not able to download power system earthing guide it is showing invalid format. please change format.

    • Omer Mirza
      Jan 22, 2018

      Same here. When I try to click download it opens a home instead of pdf :(

    Apr 28, 2015

    plz keep me on list.

  9. luis gonzalez
    Apr 27, 2015

    tremendo material, muchas gracias

  10. Bahiru Tenkir
    Dec 07, 2014

    can a flat steel be used for substation earthing grid instead of stranded copper conductor

  11. shuaib salam
    Feb 24, 2014


  12. Mostafa Dezfulian
    Feb 23, 2014

    Thank you for very very useful information in your site
    I want information about Basics of stackless earth resistance meters.

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