Soil resistivity, a single rod, rods in parallel, a buried ring or a plate. Free, works with no signal, and every number names where it came from.
Four pins in a straight line, equal spacing a. This is the soil value you feed into every formula below.
ρ = 2 · π · a · R. Repeat at several spacings (1, 2, 4, 8 m) and at a few spots: the reading changes with depth and season, so test where and when the job matters.
Rough sizing only. Measure the actual electrode with a fall-of-potential or clamp test before you sign it off.
R = (ρ / 2πL) × (ln(4L/r) − 1). Deeper beats thicker: doubling L cuts R far more than doubling the diameter. The N-rods figure assumes they are spaced well apart.
n rods give one rod divided by n only when they are spaced far apart. Closer than that they rob each other.
Planning estimate: a spacing factor is applied on top of R1 / n (1,0 at ≥4L, 1,15 at 2–4L, 1,45 at 1–2L, 1,9 under L). Measure the grid before you sign it off.
A bare conductor buried as a loop or a run.
R ≈ 2ρ / L (Schneider Electrical Installation Guide). The ring must sit in real soil, not gravel or hardcore, below the foundation base. Deeper is better for a reason that has nothing to do with the conductor.
A plate buried on edge, centre at least 1 m down. Rare on a domestic job; rods or a ring are the normal SA route.
R ≈ 0,8ρ / L (Schneider Electrical Installation Guide).
Where SANS 10142-1 sets no value it says so. Nobody should hand you a magic number and call it the book.
Test at 4–24 V, ≥ 0,2 A. SANS 10142-1 8.6.2.
Table 8.1, by the rated current of the protective device.
10142-1 8.6.7 sets no single value, and on a TN supply (supplier earth terminal) the test is optional.
Recommended overall value (SANS 62305-3 / 10313). A hard "less than 10 Ω" applies to explosive structures (10313 12.3.2). Do not measure while the soil is wet.
SANS 10142-1 8.6.6, main switch off. Draft wording is ambiguous on the exact step; check your licensed copy.
The rest: 34 fault entries that get you to the cause, a CoC test report that does the maths, invoices and quotes offline, 8 setup guides with drawings, and a solar suite. One file, your phone, no signal needed.
Try the free demo Own the full app — R699