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
2ª. Foresee any possible renewal of power
The aim of this rule is to impede the installation from being reconnected due to fortuitous errors or faults. For this purpose, the manipulation devices used to disconnect the installation must be ensured against any possible reconnection, preferably via a manoeuvre lockout mechanism, and a sign must be placed, whenever possible, prohibiting the manoeuvre.
When using remote-control devices, erroneous manipulation of these devices from the remote control must be impeded.
Many manoeuvre devices, above all those used in HV installations, use auxiliary energy sources to actuate them (electric motors, compressed air or accumulated energy via springs). All these auxiliary energy sources must be deactivated.
3ª. Verify the absence of voltage
The aim of this verification is to check that the installation is, at that moment in time, dead and that it allows certain operations to be performed on it, including its short-circuiting to ground.
The absence of voltage must be checked in all the active elements of the electrical installation in the work area, or as close as possible to this, immediately before short-circuiting to ground, so as to reduce to the minimum the possibility of the installation being connected to a power supply by mistake or due to a fault in the interval of time that passes between verifying the absence of voltage and short-circuiting to ground.
The proper functioning of the devices for verifying the absence of voltage must be checked before and after said verification.
Voltage detectors may indicate the “absence of voltage” even though a certain induced voltage exists in the installation, provided this does not reach the threshold voltage of the detector. This voltage is only suppressed when the installation is grounded. This is yet another reason for always carrying out these operations using the appropriate auxiliary and protection means and equipment.
Before using a voltage detector, it is important to check its rated working voltage or voltage range, as well as the state of the test probes and of the batteries, should they be used.
To verify the absence of voltage in insulated wires or conductors that may be confused with others existing in the work area, devices are to be used that act directly on the conductors (basic voltage testers or similar).
Remote-control devices used to verify that an installation is dead are to be failsafe and their position in the remote control must be clearly indicated.
