Ask a facility manager for their earth resistance reading and most can produce one — a single number from the last test report, filed away and rarely looked at again. That number, on its own, tells you almost nothing.
An earth electrode’s resistance moves with the seasons, with groundwork nearby, with corrosion at the test link, and with age. A reading of 4 ohms means very little unless you know what it read at commissioning, what it read at the last two inspections, and which direction it is moving.
Building the baseline
The first thing we do on any earthing audit without prior records is establish that baseline properly — locating every test point, confirming continuity to the electrode, and taking a reading that future audits can be measured against. Buildings with a documented trend are cheaper to maintain, because problems get caught while they are still small.
If your last set of readings has gone missing, or nobody can tell you when the earthing system was last tested, that gap is the risk — not the number itself.