Grounding Resistance Measurements - RWS200 - RWCC - AWS310-SITE - AWS310 - FOC201 - AWS430 - RME111

Grounding and Lightning Protection in Vaisala Outdoor Installations Technical Reference

Document code
M211786EN
Revision
B
Language
English (United States)
Product
RWS200
RWCC
AWS310-SITE
AWS310
FOC201
AWS430
RME111
Document type
User guide

Grounding resistance is not the only qualification for good grounding, but a numerical value for electrical safety grounding is sometimes a contractual requirement. To verify whether a contractual requirement is met, for example a maximum of 10 Ω grounding resistance, you need to measure the grounding resistance.

The best time to make the measurement is right after the rainy season.

Soil resistivity measurements do not give correct results in frozen soil. Make the measurements when the soil in not frozen.

The measurement helps you to evaluate and design the required ground electrode for a certain resistance value.

There are several methods and pieces of measurement equipment for measuring grounding resistance:

  • Use a widely preferred method, which is the four-electrode Wenner method (ASTM G57-06), to measure soil resistivity in the intended grounding location.
  • Use soil type tables for rough estimates of the grounding resistance of different electrode sizes.
  • Outsource grounding resistance measurements to a local power utility company.

Multi-meters and clamp-type loop resistance meters can be used to measure one ground electrode at a time in a large system with several interconnected ground electrodes located far from each other. This is very seldom the case on a Vaisala installation site.

For the operational details of measuring equipment, see the user manual of your specific grounding resistance instrument.