Electrical resistance is defined as the property of a conductor which opposes the flow of electrical current and is measured in ohms (Ω).

It is related to the voltage and current through Ohms law where:
Resistance = Voltage / Current

The resistance of a conductor, however, depends on the length, area of cross-section, and the nature of the material used in the conductors manufacturing. Resistivity is an inherent characteristic of the material and is defined as the resistance offered by the material per unit length for a unit cross-section and is measured in ohms-meter (Ωm):
Resistivity = (Resistance x Cross sectional area) / Length

Resistivity is therefore used to compare different materials. There are broad definitions to classify whether a material is an insulator, static dissipative or conductive. Specific material requirements are provided in product specifications. Both conductive and dissipative materials are classified as antistatic.
  Surface Resistivity, Ωm
Antistatic materials Below 1012
  • Conductive
Below 106
  • Static Dissipative
106 to 1012
Insulative materials 1012 to 1020

What is electrical resistivity testing?

Resistivity is characterised as surface resistivity or volume resistivity. It should be noted, however, that a combination of surface and volume resistivity can be measured depending on the electrode system.

Surface resistivity testing assesses the resistance to leakage of an electrical current across the surface of an electrically insulating material.

Volume resistivity testing analyses the resistance to leakage of an electrical current through the body of an electrically insulating material.
Surface resistivity testing Volume resistivity testing

Factors influencing the results include the applied voltage, electrification time and environmental factors. For example:
  • High humidity levels create lower resistivity therefore the environmental conditions have a large impact on the potential results.
  • For most materials, the resistivity tends to increase with a rise in temperature.

Electrical resistivity standards that Smithers can test to:

Insulating materials 
  • ASTM D257
  • BS 6233:1982, IEC 60093:1980
  • BS EN IEC 62631-3-1
  • BS EN IEC 62631-3-2 
  • BS EN IEC 62631-3-3
  • BS EN ISO 8031:2020
  • BS ISO 14309:2019
  • BS ISO 2951:2019
Antistatic polymer materials (conductive and dissipative)
  • ASTM D991
  • BS EN ISO 3915
  • BS ISO 2878
  • BS ISO 1853
  • BS EN 60079-32-2
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