Conductive locations with restricted movement (§706) — working inside tanks and boilers

The LOTO guide covers how an installation is de-energised before work begins. §706 (based on IEC 60364-7-706) covers a different aspect: which supply voltage for portable tools and lighting is permitted once someone is actually working inside a metal tank, boiler, silo or comparable enclosed conductive space.

What a "conductive location with restricted movement" is

The standard describes this as a location consisting mainly of metallic or other conductive surrounding parts, where a person is (or can come) into contact with a substantial part of their body with that conductive surrounding, and where the ability to quickly break that contact is limited — think of the inside of a steel boiler, tank, silo or comparable metal enclosure in which someone is physically present during inspection, cleaning or maintenance.

Note: this is a fundamentally different risk category from an ATEX explosive zone (see the atex-explosiegevaar guide) — this is about the risk of electric shock through full-body contact with a conductive environment, not an explosive atmosphere. Both risks can occur in the same space at the same time, but require separate assessments.

The core measure: the safety source is located outside the space

For portable tools and hand lamps used inside such a space, an ordinary socket-outlet connected directly to the mains is not permitted. Instead:

• Supply via SELV or PELV, with the safety transformer or source located outside the conductive location — not inside the tank or boiler itself.
• For equipment that cannot use this extra-low voltage, a safety isolating transformer (to the relevant product standard) also installed outside the space, with only one connected item of equipment per isolated circuit.
• An ordinary 230V socket-outlet and a hand lamp or hand tool connected directly to the mains do not belong inside the space itself.

Note: this article gives the principle. The exact permitted voltage values, the requirements on the transformer, and the precise delineation of what qualifies as "restricted movement" follow from the full standard and must be assessed per situation.

Practical relevance

For maintenance, inspection or cleaning inside a steel tank, boiler, silo or comparable metal space (for example in the food industry, with steam boilers or storage tanks), it must be established in advance which supply voltage is used for lighting and hand tools, and — critically — where the safety transformer is placed: outside the space, not inside it. This is a separate check alongside the regular LOTO procedure for the installation being worked on.

Common mistakes

1. Bringing an ordinary 230V extension lead and hand lamp into the tank — not permitted in a conductive location with restricted movement.
2. Placing the safety transformer itself inside the tank or boiler — the source must be located outside the space; otherwise the intended level of protection is lost.
3. Confusing §706 with an ATEX explosive-zone assessment — this concerns electric-shock risk from body contact with a conductive environment, a different risk category from explosion hazard, even though both can coincide in the same space.

Related

• LOTO — 5 steps
• ATEX & explosion hazard
• §414 — SELV, PELV and FELV