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
4ª. Short-circuit to ground
The aim of this rule is to guarantee that the safety situation is maintained for the duration of the work. To do so, the parts of the installation where work is to be carried out must be short-circuited to ground:
- a. In HV installations.
- b. In LV installations which, due to induction or other reasons, may accidentally become live.
Should the latter situation not be possible, the grounding connections must be placed as near to the work area as possible, keeping a watch on them.
The grounds must be placed at both ends of the work area so that work is always carried out surrounded by grounding conductors. Use appropriate grounding conductors in accordance with the installation voltage (Low or High Voltage).
If in the course of work the conductors must be cut-off or connected and the danger exists of potential differences appearing in the installation, protection measures are to be taken, such as bridging or grounding in the work area, before proceeding to cut-off or connect these conductors.
The conductors used for grounding, short-circuiting and, if applicable, bridging are to be suitable and have a sufficient cross-section for the short-circuit current of the installation where they are installed.
Precautions are to be taken to ensure that the grounding conductors remain properly connected for the duration of the work. When they have to be disconnected to carry out measurements or trials, suitable additional preventive measures are to be adopted.
Remote-control devices used to short-circuit an installation to ground are to be failsafe and their position in the remote control must be clearly indicated.
Sequence of operations for installing a short-circuit to ground in HV installations:
- Visually check that the short-circuit to ground equipment is in good condition.
- Check that the absence of voltage tester is suitable for the job.
- Visually check that PPE is in good conditions, especially insulating gloves for HV work, checking that the equipment has passed the corresponding revision.
- Check that the absence of voltage tester is functioning properly, paying special attention to the rated voltage or voltage range and to the status of the batteries.
- Connect the ground clip or clamp to the ground electrode (spike, fixed point, metallic structure, etc.).
- Put on Nomex clothing or the like, fireproof gloves, insulating gloves, goggles and a visor. The usual helmet and safety footwear are also to be worn. If work is to be carried out at a height, put on a fall-arrest harness.
- Stand on an insulating mat or stool.
- Verify the absence of voltage in each of the phases.
- Check once more that the absence of voltage tester is functioning properly.
- Check once more that the absence of voltage tester is functioning properly.
- Connect the short-circuit to earth clamps on each of the phases using an insulating pole.
Sequence of operations for placing a short-circuit to ground in LV installations:
- Check that the absence of voltage tester is suitable for the job.
- Visually check that the short-circuit to ground equipment is in good condition.
- Visually check that PPE is in good conditions, especially insulating gloves for LV work.
- Put on gloves, goggles and a visor. The usual helmet and safety footwear are also to be worn. If work is to be carried out at a height, put on a fall-arrest harness.
- Stand on an insulating mat or bench.
- Verify the absence of voltage between phases and between each phase and neutral by means of a voltage tester or voltmeter (previously check that it is functioning properly).
- Check again that the absence of voltage tester or voltmeter is functioning properly.
- Connect the ground clamp to the protection conductor or to the earth of the LV board.
- Connect the device clamps to neutral and to each of the three phases using suitable poles for LV work if working on overhead lines, or using the appropriate terminals if working on LV boards. In the latter case, the connection may also be made using the cartridges designed for inserting into the fuse-holders, once the fuses have been removed from the board.
