§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

1. Complete disconnection.
2. Secure against re-energization.
3. Verify absence of voltage.
4. Earth and short-circuit (mandatory for high voltage; where necessary for low voltage).
5. 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).

Load-break switch versus isolator — what may be operated under load?

Not every switching device may be operated under load:

• Load-break switch — may be switched under load and has a guaranteed, visible or verifiable isolating distance in the open position. Suitable for carrying out step 1 (disconnection), even while current is still flowing.
• Isolator (e.g. a fuse-carrier or knife-blade isolator) — may only be operated de-energized/unloaded. Opening it under load can cause an arc that damages the isolator and the user.

Always check the type before switching: only a load-break switch (or a circuit breaker/power switch, which by design may also switch under load) is suitable for interrupting a loaded circuit.

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:

1. Before the measurement: test on a known live point (≥ U_n) to verify that the tester is functioning correctly.
2. Measurement on all conductors in the work area: L1–N, L2–N, L3–N, L1–L2, L2–L3, L1–L3, L–PE.
3. 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!):

1. First attach the earth clip to the earth electrode or earthed rail.
2. 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

1. Workers leave the area and report their work as completed.
2. Step 5: shields are removed.
3. Step 4: earthing set removed (phases first, earth last).
4. Step 3: measurement not required, but a visual check is performed to ensure no tools have been left behind.
5. Step 2: locks and signs removed by each worker individually.
6. Step 1: installation switched on again by or on the order of the WV, in a fixed sequence: first the main switch, then the RCDs, and only after that the final circuits one by one. This keeps the inrush current limited and immediately makes clear which group has a fault, should a defect occur.

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.

Can you work alone?

• Live working (WOS) may never be done alone — a second person must always be present who can intervene or raise the alarm.
• De-energised work: whether working alone is permitted is determined by the company's RI&E. Even when it is formally permitted, having a second person nearby a switch cabinet is always advisable — among other things, to be able to raise the alarm quickly in the event of an incident.

What if the diagram doesn't match what you see in the cabinet?

Always work from the physical component, never from a diagram whose accuracy you haven't verified. In the event of a discrepancy: stop, touch nothing, and report the discrepancy immediately to the Work Supervisor so the diagram can be corrected. Carrying out a switching action based on an incorrect diagram — for example, assuming a group is de-energised because the diagram says so — is life-threatening.

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

1. 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.
2. No pre- and post-testing of the voltage tester. Defective tester → technician "sees" 0 V while 230 V is present.
3. Screwdriver phase tester as the only instrument. Not IEC 61243-3 compliant; gives false security.
4. Earthing set connected to phases first, then to earth. Incorrect sequence; with induced charge, the technician becomes the path for voltage discharge.
5. PV panel supply forgotten. Sunlight = voltage on the inverter DC, even if the AC mains is off. → Manually open DC isolator + shield.
6. One lock, shared by multiple workers. One way → everyone "gone", while a second is still working. Each worker their own lock.
7. 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.

Further reading

• NEN 3140:2024 §6.3
• NEN-EN 50110-1:2023
• Arbo-portal SZW — Working on electrical installations