Checking PEN continuity in practice — measurement method and the pitfall of a misleadingly low reading

The guide on PEN conductor breakage in TN-C-S covers what goes wrong when the PEN conductor breaks. This article covers the practical side: how a technician actually measures the continuity of protective and bonding conductors, which pitfall can produce a misleadingly favourable reading, and why testing the network's own PEN conductor occupies a separate, more limited position.

The correct test method: not an ordinary ohms reading

An ordinary multimeter in resistance mode uses a small, non-standardised test signal — adequate for finding a gross open connection, but not reliable enough to distinguish a connection with slightly elevated contact resistance (for example due to early corrosion or a loosening terminal) from a good connection. For a continuity measurement of a protective conductor, an instrument should therefore be used that delivers a standardised test circuit: a test voltage between 4 V and 24 V (AC or DC), with a short-circuit current of at least 200 mA. That higher test-current level makes a slight contact resistance far more visible in the measurement than an ordinary multimeter would.

The pitfall: parallel earth connections

The most common mistake in this measurement is not the equipment used, but the test setup: if the conductor under test remains connected at both ends to the rest of the earthing network (for example because main bonding, other PE conductors and the earth electrode are all interconnected — see the guide on the main earthing terminal), the test current does not flow exclusively through the conductor under test, but also via parallel paths through the general mass of earth and the rest of the bonding network. The result is an artificially low, reassuring- looking resistance value, even if the conductor actually being tested contains a break or a poor connection. To prevent this, the conductor under test must actually be disconnected at at least one end from the rest of the network before measuring — precisely why §542.4 requires every connection on the main earthing terminal to be individually disconnectable (see the guide above).

Why the network's own PEN occupies a separate position

The above concerns the continuity measurement of protective and bonding conductors within the installation, to which the installer has full access. The combined PEN conductor upstream of the splitting point (the part belonging to the network, before the transition to separate N and PE — see the guide on PEN conductor breakage) is, however, owned by the network operator and usually not accessible for a direct, isolated continuity measurement by the installer. In practice, a suspected PEN problem on the network side is therefore more often inferred from indirect signals than from a direct measurement:

a voltage between the neutral conductor and an independent reference earth that is higher than expected under normal operating conditions;
an unusually high touch voltage on earthed metal parts without an identifiable internal fault;
RCDs tripping without an identifiable leakage-current cause, which can point to a disturbed neutral-earth relationship.

Given a concrete suspicion of a PEN problem on the network side, notifying the network operator is the next step, not attempting to isolate and measure the network's own PEN conductor.

Practical relevance

At periodic inspection or commissioning, the continuity measurement of protective and bonding conductors should be performed with an instrument meeting the 4-24V/≥200mA requirement, with the conductor under test actually disconnected from parallel paths — not with a quick continuity beep test using an ordinary multimeter, and not with both ends still connected to the rest of the network.

Common mistakes

Using an ordinary multimeter in ohms mode for a continuity measurement of a protective conductor, instead of an instrument with a standardised 4-24V/≥200mA test circuit.
Measuring while the conductor under test is still connected at both ends to the rest of the earthing network — this produces an artificially low, misleading resistance value due to parallel current paths.
Attempting to directly isolate and measure the network's own PEN conductor — this segment is owned by the network operator and normally not accessible to the installer for that specific measurement.
Ignoring indirect signals of a PEN problem (elevated N-earth voltage, unexplained RCD trips) because a direct measurement is not possible — these signals are precisely the indication to notify the network operator.