Summary
Resistance and resistivity sound similar in everyday language, but they answer different questions. One measures the condition of an installed system; the other describes the electrical behavior of the soil.
What resistance measures
Grounding resistance represents the opposition of the installed system to current flow toward remote earth.
It is useful for verifying an existing grid, electrode or system, always considering the measurement method and actual configuration.
What resistivity measures
Soil resistivity expresses the ability of the soil to conduct electrical current and is normally measured in ohm meter.
Its value changes with humidity, compaction, temperature, layers, salts, rocks and fills.
Why they do not replace each other
A new grid should not be designed only by measuring the resistance of an existing ground, because that measurement does not characterize the full soil.
Knowing resistivity is also not enough if the finished installation is not verified with inspection and measurements.
How they are used in projects
Resistivity feeds grid design and calculation. Installed resistance helps validate the condition, maintenance and performance of the built system.
In substations, step and touch voltage, fault current and clearing time criteria are also added.
Frequently asked questions
Which one is measured first in a new project?
Soil resistivity is normally measured before design.
Is installed resistance useful for acceptance?
Yes, when it is interpreted together with the method, scope and applicable criteria.
Does a ground with few ohms always comply?
Not necessarily; safety, continuity and equipotential bonding must be verified.
Can both be measured in the same campaign?
Yes, if the scope requires design and verification of existing systems.
If you need technical support applied to this topic, review our industrial grounding service.