§6.3 — Working de-energized: the five steps

NEN 3140 is the Dutch implementation of NEN-EN 50110-1 (Operation of electrical installations) and specifies how work on or near electrical installations must be carried out safely. The cornerstone of this is the so-called five-step rule for working de-energized — internationally known as LOTO (Lockout / Tagout). If the technician skips one step, he is no longer working de-energized; he thinks he is.

The five steps — in order

Complete disconnection.
Secure against re-energization.
Verify absence of voltage.
Earth and short-circuit (mandatory for high voltage; where necessary for low voltage).
Shield or barricade adjacent live parts.

Only when all five steps have been completed is the work area "declared de-energized" and may work commence. The Work Supervisor (WV) issues the work permit; the Competent Person (CP) carries out the work.

Step 1 — Complete disconnection

Interrupt all voltage sources that can supply the work area, in a manner that is visible or via a switchable switch with mechanical position indication.

Practical:

Main switch or circuit breaker in the distribution board switched off.
Power switch in the switchgear open (position visible in the viewing port / on the control panel).
Welding floor knife switch in the "open" position with visual inspection.
Not sufficient: only a software-based shutdown of a PLC or magnetic contactor. This can be inadvertently reactivated by a glitch in the control system.

Do not forget the secondary power supplies:

Emergency power battery (UPS) in the same cabinet.
PV panel installation that can provide backfeed (see §722).
Generator set with automatic start (ATS).
Neighbor supply via double-ended cable (rare but possible).

Step 2 — Securing against re-energization

Make it physically impossible for anyone else to switch the installation back on while work is in progress.

Methods, from weakest to strongest:

Warning sign — minimum, but insufficient as the only measure. Fits on the switch: "Do not switch on — work in progress — name — telephone".
Switch handle removed — for older switching installations with removable controls.
Padlock (LOTO padlock) on the switch with a hasp that allows multiple locks. Each worker hangs their own lock — only when everyone has left can all locks be removed and the installation be switched on again.
Control removed from the switch cabinet and stored in a lockable box.
Mechanical lockout on the drive (no electrical start possible).

Requirement: one person cannot open another person's lock. A common key box (group lock) keeps the master key away as long as individual locks are in place.

Step 3 — Establishing voltage-free condition

Using a suitable voltage tester, functionally tested before and after use, on all active conductors (including N) against earth and against each other, prove that no voltage is present.

Three-point test with voltage detector / multimeter:

Before the measurement: test on a known live point (≥ U_n) to verify that the tester is functioning correctly.
Measurement on all conductors in the work area: L1–N, L2–N, L3–N, L1–L2, L2–L3, L1–L3, L–PE.
After the measurement: re-test on a known point to prove that the tester has not failed during the measurement.

Voltage detector: two-pole, compliant with IEC 61243-3 — not a "phase tester screwdriver" (LED-type), which is not recognized as a reliable instrument by NEN 3140.

For high voltage: use a voltage detector with an insulated rod, category appropriate for U_n, tested within the inspection cycle.

Step 4 — Earthing and short-circuiting

Connect all active conductors, including N, to the earth electrode and short-circuit them to each other using suitable earthing hardware.

Voltage	Mandatory?
HV > 1 kV	Always mandatory (NEN 3140 §6.3 + EN 50110-1)
LV in outdoor / overhead lines	Mandatory
LV in installations with risk of backfeed (PV, UPS, generator)	Mandatory
LV domestic indoor	Exempt provided that all supplies are demonstrably off and no induced field

Objective: in the event of an unexpected reclosing or inductive coupling of parallel lines, the current flows to earth instead of through the technician. The earthing set typically has a cross-section of ≥ 35 mm² Cu with crocodile clips and must be able to carry its rated short-circuit current for 1 s without melting.

Connection sequence (critical!):

First attach the earth clip to the earth electrode or earthed rail.
Then attach the phase and N clips to the conductors.

Removal sequence is the reverse: first disconnect phases, then earth. Otherwise, any remaining inductive charge may flow through the technician via the earth connection.

Step 5 — Shield off or fence off adjacent parts

If live parts remain in the work environment at a distance less than the DV-distance, shield them off with suitable material (insulating blanket, rigid insulating plate, fencing).

Practical examples:

Working on busbar A in the switchgear; busbar B remains live behind a cover. → Insulating blanket over busbar B with clear "LIVE" marking.
Working on a cable above a live group at the bottom of the cabinet → rigid insulating partition placed between positions, so that falling tools cannot cause a short circuit.
Working on a lighting circuit on a ladder above a live busbar in the ceiling → marking + storage of PPE (PPE) for minor incidents.

Requirement: the shielding must effectively increase the DV-distance so that the worker never needs to enter the danger zone.

Completion of work — reverse order

Workers leave the area and report their work as completed.
Step 5: shields are removed.
Step 4: earthing set removed (phases first, earth last).
Step 3: measurement not required, but a visual check is performed to ensure no tools have been left behind.
Step 2: locks and signs removed by each worker individually.
Step 1: installation switched on again by or on the order of the WV.

Switching on may only take place once the WV has confirmed that all lock holders have been removed. A common practical problem: one technician still working somewhere upstairs in the building whose lock is forgotten — the WV is personally responsible for this.

Documentation

NEN 3140 §6.3.5 stipulates:

Work permit (Permit-to-Work, PTW) with: permit number, date, location, description of the work, responsible party, executing personnel, designated leaders if applicable, agreed voltage-free interval, used earthing sets.
Work schedule / lock-out log in the switch room: who hung which lock when, and who removed it again.
Key custody: controlled issuance; keys for high-voltage rooms under seal.

Keep documentation for ≥ 5 years (NEN 3140 §6.3.5.4); in case of an incident, it forms the basis for the inspection report to the Labour Inspection.

Common mistakes

Step 3 skipped because "I just saw it turned off". Between switching and touching lies the time in which a colleague can switch on — hence step 2 and step 3.
No pre- and post-testing of the voltage tester. Defective tester → technician "sees" 0 V while 230 V is present.
Screwdriver phase tester as the only instrument. Not IEC 61243-3 compliant; gives false security.
Earthing set connected to phases first, then to earth. Incorrect sequence; with induced charge, the technician becomes the path for voltage discharge.
PV panel supply forgotten. Sunlight = voltage on the inverter DC, even if the AC mains is off. → Manually open DC isolator + shield.
One lock, shared by multiple workers. One way → everyone "gone", while a second is still working. Each worker their own lock.
WV and VP are the same person without written designation. Not compliant with §3.2; historically the basis for criminal liability in the event of an incident.

Exam tip

This rule always appears in the VP test, usually as "arrange in the correct order." Mnemonic: "S-B-V-A-A" — Switching, Protecting, Verifying, Earthing, Shielding. Anyone who can recite and explain this acronym will score full marks for the entire section on working dead.

Working De-energized — The 5 Steps (LOTO)