Premium Membership ♕

Save 50% on all EEP Academy courses with Enterprise Membership Plan and study specialized LV/MV/HV technical articles & guides.

Home / Technical Articles / 6 Voltages a Person Can Be Exposed To In a Substation

Dangerous voltages in substation

Figures 1 and 2 show the voltages a person can be exposed to in a substation. There are many definitions related to these voltages, but the following six are the most important.

5 Voltages a Person Can Be Exposed To In a Substation
5 Voltages a Person Can Be Exposed To In a Substation (photo credit: Terry F Luehmann via Flickr)

These definitions are:

  1. Ground potential rise (GPR)
  2. Mesh voltage
  3. Metal-to-metal touch voltage
  4. Step voltage
  5. Touch voltage
  6. Transfer red voltage

1. Ground potential rise (GPR)

The maximum electrical potential that a substation grounding grid may attain relative to a distant grounding point assumed to be at the potential of remote earth. Ground potential rise is the product of the magnitude of the grid current, the portion of the fault current conducted to earth by the grounding system, and the ground grid resistance.

Basic shock situations
Figure 1 – Basic shock situations

Go back to Dangerous Voltages ↑

2. Mesh voltage

The maximum touch voltage within a mesh of a ground grid.

Mesh voltage

The actual mesh voltage, Em (maximum touch voltage), is the product of the soil resistivity, ρ; the geometrical factor based on the configuration of the grid, Km; a correction factor, Ki, which accounts for some of the errors introduced by the assumptions made in deriving Km; and the average current per unit of effective buried length of the conductor that makes up the grounding system (IG/LM):

3. Metal-to-metal touch voltage

The difference in potential between metallic objects or structures within the substation site that can be bridged by direct hand-to-hand or hand-to-feet contact.

Typical situation of external transferred potential
Figure 2 – Typical situation of external transferred potential

Important Note //

The metal-to-metal touch voltage between metallic objects or structures bonded to the ground grid is assumed to be negligible in conventional substations.

However, the metal-to-metal touch voltage between metallic objects or structures bonded to the ground grid and metallic objects inside the substation site but not bonded to the ground grid, such as an isolated fence, may be substantial.

In the case of gas-insulated substations, the metal-to-metal touch voltage between metallic objects or structures bonded to the ground grid may be substantial because of internal faults or induced currents in the enclosures.

Go back to Dangerous Voltages ↑

4. Step voltage

Step voltage is actually the difference in surface potential experienced by a person bridging a distance of 1 m with the feet without contacting any other grounded object.

Go back to Dangerous Voltages ↑

5. Touch voltage

Touch voltage is the potential difference between the ground potential rise and the surface potential at the point where a person is standing while at the same time having a hand in contact with a grounded structure.

Go back to Dangerous Voltages ↑

6. Transfer red voltage

A special case of the touch voltage where a voltage is transferred into or out of the substation, from or to a remote point external to the substation site. The maximum voltage of any accidental circuit must not exceed the limit that would produce a current flow through the body that could cause fibrillation.

Assuming the more conservative body weight of 50 kg to determine the permissible body current and a body resistance of 1000 V, the tolerable touch voltage is:

Tolerable touch voltage

and the tolerable step voltage is:

Tolerable step voltage

where //

  • Estep – Step voltage, V
  • Etouch – Touch voltage, V
  • rs – Resistivity of the surface material, V-m
  • ts – Duration of shock current, in seconds

Since the only resistance for the metal-to-metal touch voltage is the body resistance, the voltage limit is:

Voltage limit

The shock duration is usually assumed to be equal to the fault duration. If re-closing of a circuit is planned, the fault duration time should be the sum of the individual faults and used as the shock duration time ts.

Go back to Dangerous Voltages ↑

Reference: The electric power engineering handbook – L.L. Grigsby (Purchase hardcover book from Amazon)

Premium Membership

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you to shape up your technical skills in your everyday life as an electrical engineer.
More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Sagar
    Aug 27, 2019

    Dear Edvard,

    This is very important and helpful information that you shared.

    Thank you.

  2. Mushtaq
    Aug 27, 2019

    I m a commissioning engineer and i highly value ur article for me as well as for all substation related personnels.

  3. Siddiqui, Idris
    Jul 13, 2017

    Dear Edvard Casany,
    it is a very important hint to people who go in the operation group. So I can just appeal all those who delegate an engineer for an Operational work he must take your article in his laptop! A good job indeed, dear colleague!

    Apr 09, 2017

    Dear Edward!

    Good Morning!

    Your articles are very nice. It is very useful to gain more knowledge for all electrical engineering persons.

    Thank You

  5. Tyrone Armstrong Jr
    Oct 23, 2015

    Great article

Leave a Comment

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

sixty five  +    =  seventy

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Courses - A hand crafted cutting-edge electrical engineering knowledge