Test sequence for initial verification — why dead tests come before live tests

The insulation resistance testing guide, the loop impedance (Zs) testing guide and the RCD trip-time testing guide each cover a single test. This article covers something none of those guides addresses separately: the order in which all these tests must be carried out during initial verification — and why that order is not a matter of preference.

Two phases: dead first, then live

NEN 1010 chapter 6 (initial verification, based on IEC 60364-6) splits the tests into two phases, with a strict order between them.

Phase 1 — tests without voltage (installation fully de-energised)

Continuity of protective conductors and of main and supplementary bonding conductors.
Insulation resistance test — see the separate insulation resistance testing guide for the test procedure and the limit values per test voltage.
Polarity check (where applicable) — verifying that switches and fuses are actually located in the line conductor and not in the neutral.

Phase 2 — tests under voltage (after energising)

Loop impedance Zs / prospective fault current — see the loop impedance (Zs) testing guide.
RCD operation (trip time) — see the RCD trip-time testing guide.
Functional testing — verifying that switches, relays and other control functions actually do what they are supposed to do.

Phase 2 may only begin after the results of phase 1 have been assessed and found acceptable.

Why this order is not arbitrary

Safety of the technician and the instrument: an insulation resistance test is carried out with a test voltage of 250, 500 or 1000 V DC (depending on the circuit's nominal voltage) on a de-energised installation. Combining that test voltage with an installation that is simultaneously live is not the intent of the test and can create danger or damage the instrument.
Validity of the result: if an insulation fault were only to come to light during phase 2 — because phase 1 was skipped — the installation would already have been energised with that fault still present. A loop impedance test or RCD test on an installation with an unnoticed insulation fault can, moreover, give a misleading result.
Order of correction: a failed phase-1 test must be remedied before the installation is energised for the first time — there is no meaningful reason to start phase 2 on an installation that has already failed phase 1.

Note: this is the same underlying logic as in the two-pole voltage tester guide: first establish that the starting situation is safe and correct, before carrying out a further, more advanced step.

Practical relevance

When commissioning a new installation, or after a major modification, this order must be followed consistently: first fully complete and assess the dead tests, only then energise for the live tests. This prevents not only danger, but also a report in which it is no longer possible to tell which test was carried out dead and which under voltage.

Common mistakes

Starting straight away with loop impedance or RCD tests without first checking continuity and insulation resistance — a habitual shortcut that bypasses the fixed order.
Energising the installation despite a failed insulation resistance test, on the assumption that the fault will still be found later.
Mixing up phase-1 and phase-2 results in the report without clearly stating which test was carried out dead and which under voltage — making the report difficult to trace later.
Forgetting to check polarity before energising — a reversed line/neutral connection that only comes to light during functional testing should already have been caught during the dead tests.