The general rule is that any work with electrical risk on or near an installation is done with the power off (article 4.2). The guide points out that ignoring this has caused serious accidents. It is done by authorised workers (qualified ones on high voltage), following five steps in order:
- Disconnect that part of the installation from all its supply sources.
- Prevent any reconnection: lock the switch (preferably with a padlock) and put up a sign not to touch it.
- Verify that there is no voltage on all live parts, at the work area or as close to it as possible.
- Earth and short-circuit (compulsory on high voltage, and on low voltage if it could become live through induction or other causes).
- Protect against nearby live parts and mark out the work area.
Until all five are complete, the installation is treated as live. To restore power at the end: remove signs and protections, remove the earthing, unlock and close the circuit, and only once workers who are not needed have left and the tools have been collected (part A.2).
Source: Real Decreto 614/2001, sobre protección frente al riesgo eléctrico (Royal Decree on protection against electrical risk; consolidated text, in Spanish), article 4.2 and annex II, parts A.1 and A.2 · INSST, Guía técnica para la evaluación y prevención del riesgo eléctrico (technical guide, 2020, in Spanish), comments on annex II