All regulations constituting the local law are obligatory. For semi-permanent parts of the site installation, such as site offices and ancillary buildings, the local regulations, if they exist, shall be adhered to. In absence of local regulations generally accepted standards, e.g [IEC 364] or the [IEE wiring regulations] shall be followed.
F.2 Protection of circuits
Appropriate protection shall be provided for all main and sub-apparatus and this shall be capable of interrupting without damage any short circuit current that may occur. To this end consideration shall always be given to the fault level of the supply.
The ratings of fuses and circuit breakers used for this purpose shall be coordinated so as to afford discrimination in operation where necessary.
F.3 Power transformers
Power transformers needed for the mains supply shall be surrounded by a fence with locked gates.
F.4 LV distribution boards
Each distribution board shall be provided with one or more incoming ‘on-off’ switching devices, which shall be accessible at all times.
Each outgoing feeder shall be provided with a switching device in combination with a short circuit protection device, e.g. fuse, circuit breaker.
Switching devices shall be padlockable in the ‘off’ position. Switchgear and all its components shall be capable of withstanding the thermal and dynamic stresses resulting from the prospective short circuit currents.
Busbars and other conductors shall be suitably sized to carry continuously the maximum expectable currents in the rated service.
Each distribution board shall be provided with an earth bar suitably sized to carry with the fault current and fault clearing time under the prospective short circuit conditions for a solidly earthed system.
The distribution board shall be suitable for outdoor use, enclosure protection IP 56, and be protected at least by a weather canopy.
The distribution board shall consist of metal or of an all-insulated material and shall be suitable for heavy-duty requirements.
Opening of enclosures or removing of parts of enclosures giving access to live parts (doors, covers, etc.) shall be possible only when one of the following conditions is fulfilled : -
• All ‘live’ parts may be touched after opening the door or enclosure only after the supply is disconnected and made safe at its source. By interlocking the door or doors with an isolating switch such that they can be opened only if the isolating switch is open and only if it is not possible to close the isolator if the door or doors are open except by releasing the lock or by means of a tool.
• If the distribution board is fitted with a device allowing authorized persons to obtain access to live parts while the equipment is live, the interlock shall be automatically restored when the door or doors are re-closed.
• The distribution board shall include an internal barrier or shutter protecting all live parts in such a way that they cannot be touched accidentally when the door is open. This screen or shutter shall conform to a degree of protection of at least IP20. The screen or shutter shall either be fixed in place or shall slide into place on its own as soon as the door, or the enclosure, is opened. It shall not be possible to remove this screen or shutter except by the use of a tool.
Such screens, shutters or barriers to live parts shall preferably be made of rigid transparent insulating material and provided with a warning label.
Fuses shall be accessible only if they are offering a degree of protection of at least IP20, or when fully isolated.
All outgoing circuits shall have sensitive earth fault type cut-out devices installed in the distribution board. These shall include outgoing circuits feeding lighting equipment, socket outlets or other electrical apparatus.
The sensitivity of the earth fault type cut-out devices shall be as follows : -
• 30 mA for circuits up to 63A.
• 300 mA for circuits 63A and higher.
F.5 Cabling
F.5.1 Underground temporary cables
Temporary cables buried directly in the ground shall be of a type incorporating a galvanized steel wire armouring or braiding which is continuous and effectively earthed.
Such cables shall be buried at a sufficient depth to avoid being damaged by any disturbance of the ground reasonably likely to occur during the construction period. Cable armouring shall be bonded to the earth bar in the distribution board.
Underground temporary cables shall be provided along the routing with the marking 'Temporary cable’, this marking shall also indicate the applicable project number.
For cable marking purposes normally non-corroding strips shall be used, each having ample length to be wrapped twice around the cable and in which the text has been indelibly
imprinted. In addition, routing markers shall be provided at each change of direction in the routing and at crossings.
F.5.2 Aboveground temporary cables
Above ground temporary cables shall be fixed on site so that they are clear of building operations or engineering construction work and so that they are not a hazard. Where possible they are to be installed clear of passageways, walkways, ladders, stairs and the like. The use of overhead cables on sites is deprecated but, where their use is unavoidable, overhead cables crossing roads or routes where cranes or other mobile plant are likely to pass shall be erected so that there is a minimum clear height of 5.8m. In areas where motor transport and mobile plant are prohibited, cabling shall be fixed at any height above 3.5m.
Overhead cables when crossing passages, shall be bound with yellow and black-coloured tapes. Alternatively freely moving strips of fabric or plastic may be attached to attract attention. In some circumstances protective barriers may be required.
All cables shall be installed in such a way that they are at least 150mm clear of piped services such as steam, gas and water. Apparatus and accessories other than lamp holders shall not be suspended from electric cables.
All cables which are likely to be frequently moved in normal use shall be flexible, of the heavy-duty neoprene rubber type or equivalent.
F.6. Earthing
For the purpose of earthing of the electrical system and equipment the installation shall have one common earthing grid connected to at least two earth electrodes.
The requirements for Permanent Installations shall apply, see (19) in the main text together [section (10.4) in ES.2.03.0001].
The resistance to earth of this common earthing resistance grid shall be as low as practicable but at least such that in the case of earth faults the electrical protective devices shall prevent shock hazard potentials on any part of the equipment which is not part of the electrical circuits. For portable and mobile equipment, with exposed conductive parts likely to be held in the hand, the following correlation between duration and voltage shall not be exceeded : -
For AC For DC Continuous Less than 50 V 110 V
5 seconds 50 V 110 V 1 second 75 V 110 V 0.5 seconds 90 V 110 V 0.2 seconds 110 V 110 V 0.1 seconds 150 V 110 V 0.05 seconds 220V 110 V 0.03 seconds 280V 110 V
Earth wires shall be of the standard copper green/yellow PVC covered type, suitably sized to cope with fault current level and fault clearing time. For mechanical reasons main earth wires shall be at least 50 sq mm., branch earth wires 10 sq mm., unless adequate mechanical protection is provided by other means, e.g. wire installations in conduit, or earth conductors forming part of a cable, allowing a smaller size.
The connections between earth electrode and conductors shall be so executed that easy inspection and testing of the earth resistance of each individual electrode, without disconnecting any part of the earthing system, is possible.
The earth bar in the distribution board shall be connected with two earth wires each suitable for 100% duty to the above-mentioned common earthing grid.
F.7 Selection of components
The components shall be suitable for their particular application as regards their rated voltages, rated currents, service life, making and breaking capacities, short circuit strength, etc.
The components having a short circuit strength and/or a breaking capacity insufficient to withstand the stresses likely to occur at the place of installation shall be protected by means of current-limiting devices, for example fuses or circuit breakers. When selecting current-limiting devices for built-in switching devices, account shall be taken of the maximum admissible values specified by the manufacturer of the apparatus, having due regard to coordination. Components incorporated in the distribution board shall, in their design and construction, comply with the corresponding IEC standards.
Plugs of different rated currents or voltages shall not be interchangeable, so as to avoid errors in connection., see [IEC 309 Part 2].
Connections for three-phase plugs shall be made in such a way as to retain the same order of phases.
The socket outlets and plugs used outdoors shall have a degree of protection at least IP56, both when the plug is removed or fully inserted.