An earthing system’s entire job is to give fault current somewhere safe to go. If the surrounding soil can’t conduct that current away quickly enough, voltages can rise to dangerous levels at exactly the point where people are most likely to be standing — around substations, switchyards and electrical infrastructure. That’s why soil resistivity testing sits at the centre of earthing design, not as a formality but as the number the whole safety case is built on.
What Earthing Resistivity Testing Measures
Soil electrical resistivity testing measures how strongly the ground resists the flow of electrical current. A lower resistivity means current disperses more easily through the soil; a higher resistivity means the earthing system needs to work harder — typically through a larger or deeper earth grid — to achieve the same level of protection.
The Safety Case
Earthing design in Australia is governed by requirements referenced in AS/NZS 3000 and the broader framework set out by Energy Networks Australia and individual network operators. These frameworks exist because an undersized or poorly understood earthing system can allow step and touch voltages to exceed safe limits during a fault — a real risk to anyone nearby, not just a compliance figure on a drawing.
What Happens Without It
Skipping resistivity testing means designing an earth grid on assumed or generic soil data. Since resistivity can vary by an order of magnitude between soil types — and even across one site — an assumed figure can be badly wrong in either direction: an oversized, unnecessarily expensive grid, or worse, an undersized one that doesn’t meet its safety margin when a fault actually occurs.
When It’s Required
Resistivity testing is typically called for wherever a fault needs somewhere defined to go: substations, switchyards, solar and wind farm inverter stations, large civil and infrastructure projects, and any site where a new or upgraded earthing system is being designed. It’s standard practice ahead of detailed earthing design, not an afterthought once construction has started.
Our soil thermal & electrical resistivity testing service measures ground resistivity on-site and reports it in a form your earthing designer can use directly, in line with current Australian requirements.