Work on Electrical Installations and in premises presenting a fire or explosion hazard
Definitions and concepts:
20. Technical instructions
20.1 Disconnecting and reconnecting the power supply in an installation
The aim of this Procedure is to establish the guidelines that are to be followed to cut-off and then reconnect the power supply in an electrical installation so as to be able to carry out work in the absence of voltage, compliance with which is mandatory for all ISASTUR Group staff qualified to carry out work with an electrical hazard in accordance with Spanish Royal Decree 614/2001.
General case
Any operation or manoeuvre to disconnect the power supply in an installation before carrying out work in the absence of voltage and subsequent work to reconnect the installation once all the work has been completed is to be carried out by an Authorised Worker, in the case of LV installations, and by a Qualified Worker in NVW/WVLP, in the case of HV installations. Said operations are always to be performed in the presence of a Preventive Resource figure (this could be the same person as the Authorised or Qualified Worker). Prior to starting to cut-off the power supply:
- The person responsible for the planning of jobs (see the definitions for Authorised Worker and Qualified Worker in NVW/WVLP, in the section “Preparation of jobs in the vicinity of installations”) is to precisely identify the area and the elements of the installation where work is to be carried out. In HV work, this operation is to be carried out in the presence of the person in charge, foreman or head of the installation on the part of the Client and in LV work, said presence is recommendable.
- The person in charge of the work is to inform the workers involved in disconnecting and reconnecting the power supply operations and manoeuvres of the risks and preventive and protection measures to apply, as well as the contents of the present Technical Instruction. A written record is to be left of the information given to workers.
The person in charge of the installation must give his permission, preferably in writing.
Cutting-off the power supply (the five golden rules)
Operations are to be performed in the following strict order:
1ª. Disconnect
This consists in isolating the part of the installation where work is to be carried out from all power supplies. To do so, all the switches or automatic switches and circuit-breakers via which said installation may be connected to known power supplies are to be opened. For this purpose, fuses may be removed or bridges used to join different sections of an electrical line or installation may be opened.
To guarantee the aforementioned electrical isolation, the following must be taken into account:
- Disconnection of the neutral conductor, when it exists, must be the last operation to carry out (and the first when connecting).
- The installation may form part of a loop, so both sides have to be disconnected.
- The installation may include condensers; if so, proceed as indicated further on.
- In direct current installations providing electrical traction to motors, these may have a reversible functioning mode, acting as generators during the braking of the traction system.
When the possibility exists that other voltage supplies from centres that use the grid as receptors may be connected to the installation to be disconnected, the company responsible for the power line is to ensure that every one of these companies has knowledge of the need to carry out the disconnection. It is advisable to have at one’s disposal any and all communication in this regard.
