Protective conductor continuity — the R1+R2 method

The measuring-instruments-and-CAT-guide names the low-ohm meter as the right instrument for earth-connection continuity, and gives the R = ρ·L/A formula for an expected value. The test-sequence guide places continuity testing among the first de-energised measurements (phase 1). This article covers the specific technique used to check that continuity across a complete circuit: the R1+R2 method.

What R1 and R2 actually are

R1 — the resistance of the live conductor (line or neutral) from the origin of the circuit (distribution board) to the furthest connection point.
R2 — the resistance of the protective conductor (PE) over that same run.

By temporarily linking both conductors together at the origin of the circuit with a bridging (wander) lead, and then measuring the resistance between those same two conductors at the furthest connection point, a single measurement captures the combined resistance of the outward and return path: R1+R2.

Why this is more than just "is the PE still there"

A simple continuity beep from an ordinary multimeter only confirms that a connection exists — not its quality. R1+R2 is also not an end in itself: the result is a direct building block for the fault-loop impedance:

Zs = Ze + (R1+R2)

where Ze is the external loop impedance (measured at the origin of the installation). A too-high R1+R2 — from a long cable run, an undersized cross-section, or a poor terminal connection — directly raises Zs, which in turn affects the disconnection time of the overcurrent protective device (see the Zs loop-impedance guide).

Test procedure, step by step

De-energise the installation and prove dead (LOTO, see the test-sequence guide).
At the origin of the circuit (distribution board), temporarily link the live conductor and the protective conductor of that circuit together with a bridging lead.
At the furthest connection point of the circuit (for example the last socket outlet in the run), use a low-ohm meter — test current ≥ 200 mA, see the measuring-instruments-and-CAT-guide — to measure the resistance between those same two conductors.
The reading obtained is R1+R2 for that run.
Remove the bridging lead and restore the circuit to its original connection before re-energising.

Calculating and assessing an expected value

Always compare the measured value against a pre-calculated expected value (R = ρ·L/A per conductor, see the measuring-instruments-and-CAT-guide) rather than judging only whether there is "some" continuity. This distinction matters: a fully broken protective conductor gives an infinite reading and is immediately obvious, but a subtly elevated value — for example from an oxidised terminal or a partially loosened connection — still gives a reading, just a too-high one. Without an expected value as a reference, such a partial defect is easily missed.

Note: on a circuit with multiple branches (for example several socket outlets in a run), the measurement must be taken to the furthest point of each branch separately — the highest measured R1+R2 value in the circuit is the one that governs, not the average.

Practical relevance

For both the initial verification of a new or altered installation (NEN 1010) and the periodic inspection of an existing installation (NEN 3140), the R1+R2 measurement is how you demonstrate that the protective conductor is not only present, but also has a low enough resistance that, combined with Ze, it produces a Zs within the required disconnection time. A report that states only "PE present: yes/no" without the measured value omits the most important information.

Common mistakes

Forgetting to remove the bridging lead before re-energising the circuit — this creates a permanent, direct connection between the live conductor and the protective conductor.
Using an ordinary multimeter instead of a low-ohm meter — the low test current of an ordinary multimeter cannot break through oxidation on a terminal, masking a poor connection.
Judging only "some continuity or none" instead of comparing the actual value against the calculated expected value.
Not feeding the measured R1+R2 value into the Zs assessment — even though it is a direct, measurable building block of it.