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
5ª Protect against elements in the vicinity of live parts and establish safety signposting to demarcate the work area
The aim of this last rule is to prevent workers from entering into Contact with other live elements by placing barriers or demarcating and signposting the work area.
Signposting and demarcating may be done using fences, tape (securely fastened) or insulating chains and signs indicating danger (electrical hazard), prohibition (access for authorised personnel only) and obligation.
Additional protective measures are to be adopted before commencing work when there are elements in an installation in the vicinity of the work area that must remain live. For such cases, there are 3 solutions:
- 1. Consider the work as “proximity work”: in this case, it will have to be performed in accordance with the stipulations in the Technical Instruction “Work in the vicinity of live parts”.
- 2. Consider the work as “live work”: in this case, it will have to be performed in accordance with the corresponding Technical Instruction on LW on HV. LW CANNOT BE CARRIED OUT on HV installations, except for the maintenance of circuit-breakers by the “remote” working method.
- 3. Place protective elements, such as screens, insulation and obstacles that allow the work areas to be seen outside all danger or proximity zones. If the positioning of these elements involves live work on low voltage (LW on LV) or work in the vicinity of live parts (WVLP), it will have to be carried out adopting the measures indicated in the previous sections.
In the case of in-service High Voltage substations, the Technical Instruction “Signposting of the work area in HV substations and accesses to the same. Licences” is to be followed.
The solution to adopt must be decided on and applied before commencing work; i.e. during the planning phase.
Reconnecting the power supply
Reconnection of the power supply is only to commence once work has finished, after all those workers who are not essential have left the area and all the tools and equipment that have been used have been cleared away.
Prior considerations to reconnecting the power supply
Before starting to reconnecting the power supply:
- Notify all the workers involved that the power supply is about to be re-established.
- Check that all workers have left the area, except those who are to take part in reconnecting the power supply.
- Inform the person in charge of the installation that it is about to be connected.
During operations:
- Ensure that all short-circuiting to ground equipment has been removed.
- Actuate the corresponding manoeuvre devices.
Sequence of operations to re-establish the power supply
In general, the sequence of operation to re-establish the power supply is the inverse of that required to carry out disconnection; the precautions and safety measures to take are also the same in each of the steps:
- 1. Removal of additional protections and signs that indicate the limits of the work area, should they exist.
- 2. Removal of the short-circuit to ground, should this exist.
- 3. Unlocking and/or removal of the signs for cut-off devices.
- 4. Closing of the circuits to re-establish the power supply.
From the moment when one of the measures initially adopted to carry out work in the absence of voltage under safety conditions is suppressed, the part of the installation affected is to be considered live.
Particular cases:
Replacing fuses
With respect to the 4th step described for disconnecting the power supply, when replacing fuses:
- It will not be necessary to short-circuit to ground if the disconnection devices on both sides of the fuse are visible to the worker, the cut-off is visible or the device provides equivalent safety guarantees and the possibility of untimely closure does not exist.
If the fuses are connected directly to the primary winding of a transformer, it will be sufficient to short-circuit to ground on the HV side, between the fuses and the transformer.
