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It is a common practice to measure grounding only in AC here in Brazil. I’ve told, since I was at university, that DC currents cannot be used to measure grounding because of the ionic recombination of salts dissolved in the soil, which in turn would cause the resistance to increase. Please explain.

Hi Camilo,

Thank you for your question regarding Direct-Current (DC) versus Alternating-Current (AC) measurements for earth readings.  It is our pleasure to help.

When measuring resistance, you technically can only use a Direct-Current (DC) signal.  When you use an Alternating-Current (AC) signal you are actually measuring impedance. 

Now to your soil measurement question.  We have never heard that the “ionic recombination of salts” presents a special issue for Direct-Current(DC) measurements.  But, the resistance that the salts present would be something that we would want to measure.  While we are not Geologists, I can tell you that every single manufacturer of ground measuring equipment advertises Direct-Current (DC) gear for a reason.  Even when their gear actually uses AC signals.

Often you will see lower-cost ground measurement meters that claim to use 128 Hz “pulsed DC” signals.  “Pulsed DC” is a less-than-honest way of saying that the meter uses a Square-Wave AC Signal.  The reason for the misrepresentation is clear, the manufacturers of this gear want you to think that they use the better Direct-Current (DC) measurement method.

E&S Grounding Solutions does NOT recommend the use of Alternating-Current (AC) for earth measurements.

We hope you find this information useful.  If you should have any further questions, please feel free to call us at 310-318-7151 to further discuss how we can assist you.

Best regards,

The Engineering Team at E&S Grounding Solutions

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