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Guide to measurements on electrical installations (theory and practice)
Guide to measurements on electrical installations (theory and practice) – photo credit: cptam.com

Measurement of Insulation resistance

Appropriate Insulation Resistance between live parts and active accessible conductive parts is a basic safety parameter that protects against direct or indirect contact of the human body with mains voltage.

Insulation resistance between live parts, which prevents short circuits or leakage currents, is also important.

An example of bad insulation in connection box for permanent connection of a load and resulting fault voltage Uf
Figure 1 – An example of bad insulation in connection box for permanent connection of a load and resulting fault voltage Uf

Where:

  • If – Fault current
  • Uc – Contact voltage
  • Us – Voltage drop on floor and shoes resistance
  • ZB – Impedance of human body
  • RS – Floor and shoes resistance.
  • RE – Earth resistance of active accessible conductive parts
  • UF – Fault voltage.

Uf = Uc + Us = If ⋅ RE

The upper figure represents a connection box with bad insulation material between phase conductor and the metal housing. Due to this situation, there is a fault current If flowing to the protection conductor via earth resistance to ground. Voltage drop on the earth resistance RE is called Fault voltage.

Different insulation materials are used in different cases such as cables, connection elements, insulation elements in distribution cabinets, switches, outlets, housings etc. Regardless of the material used, the Insulation Resistance should be at least as high as that required by the regulations, this is why it must be measured.

Title:Measurements on electric installations in theory and practice – METREL
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Pages:124
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Measurements on electric installations in theory and practice - METREL
Measurements on electric installations in theory and practice – METREL

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Page edited by E.C. (Google).

2 Comments


  1. Dayo
    Jul 16, 2015

    Hi,
    I am unable to download the measurement of electrical installations, theory and practice.
    It reads that the docs isn’t a valid pdf docs.

    Can you please assist on how to download?


  2. mumtaz
    Jul 12, 2015

    Very useful to others

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