Installation
Early streamer emission lightning conductor (E.S.E.L.C.) External lightning protection system
Air terminal
PREVECTRON® Early Streamer Emission lightning rod (ref. 1202 to 1243). The PREVECTRON® should always represent the highest point of the construction (including antennae) it is intended to protect. The air terminal should be positioned at least two metres above the area it is intended to protect. It is usually placed at the top of an elevation pole, the height of which is determined by the area to be protected. (2 m to 6.50 m before guy wires are required) (refs. 2001,...). When deciding on the siting for the pole and the PREVECTRON®, obvious vantage points (i.e. high points) should be taken into consideration.
- outbuildings on the roof
- the building’s gables
- metallic or brick chimneys
The PREVECTRON® can either be fixed on top of a self-standing tower (refs. 2061, ...) in order to provide protection for an open area on the ground. In this instance it should be bolted to the uppermost tube on the mast (supplied). If more than one PREVECTRON® is needed to protect a single construction they should be interconnected by a conductor which conforms to standards. This interconnection can be possibly avoided in the case of a height variation of more than 1.5 m along the length of the connection.
The down conductors
Each PREVECTRON® is connected to earth by at least one down conductor.
Two down conductors are necessary if :
- the horizontal length of the conductor is 1 greater than the vertical drop (see Fig. 1)
- the height of the construction to be protected is greater than 28 m
The down conductors should be positioned on the outside of the building. If this cannot be avoided, the down conductor may pass through the building using a special jacket tube or fire proof isolating sheath with a cross section of 2000 mm2 minimum.
The down conductor can be positioned behind a metal cladding, a stone or glass curtain wall or a permanent covering such as a double strap web joint, for example. The cross section of the down conductors (refs. 5001 - 5010) must conform to French Standard NF C 17 - 102. See Tables 2-3-4. A tinned copper strip 30x2 mm is recommended. On aluminium surfaces a 30x3 aluminium strip is used and, in certain corrosive atmospheres such as by the sea, a 30x2 stainless steel strip is preferred.
Figure 1
The following recommendations should be observed when installing the down conductor :
- use the shortest route down to the earthing point
- follow a straight line, avoiding sharp angles (radius of curvature > 20 cm - Fig. 2)
- avoid upward turns (except when passing over obstacles lower than 40 cm where a 45° maximum incline is tolerated (Fig. 3)
- avoid passing close to any electric lines. If crossing cannot be avoided, the electric lines should be metal-shielded 1 m either side of where the down conductor passes and the cladding then connected to the down conductor
A test clamp (ref. 7001B) should be positioned at a height of two metres from the ground and the lightning flash counter (refs. 8010 & 8012), if required, should be placed just below the test clamp. The down conductor should be protected from the test clamp down to the ground by a stainless steel sheath (ref. 7014). This sheath is fixed to the support by three stainless steel clamping collars (supplied).
Fig. 3
Fig. 2
Earthing
Each down conductor should be connected to its own earthing point which conforms to NF C 17 - 102 (see Tables 4 - 6, p.26). In normal circumstances, however, the 30x2 tinned copper strip (ref. 5001) along with the copper plated steel earth rods (refs. 7030,...) are used.
The minimal configuration for each individual earthing point is as follows : (see Fig. 4).
Three 2-metre ground rods (refs. 7030,...) set out in a triangular formation and interconnected by 2 m of conductor buried in a trench at least 50 cm deep.
Each individually isolated earthing point must carry a resistance of 10 ohms or less. Should this prove difficult to achieve, it is possible to improve the earthing points by :
- adding top soil around the conductors
- adding extra earthing rods (refs. 7030,...) to the crows feet or to the existing earthing rods
- treating the ground artificially so as to lower the soilts impedance
- where burial is not possible, horizontal earthing grills can be added
Each earthing point is connected to the mains earth supply by an earth clamp.
Certain precautions are to be observed concerning the positioning of the lightning conductor’s earthing points close to any underground low- or high-voltage cables or metallic gas pipes. (see NF C 17 - 102 - Tables 4 & 5).
Figure 4a
Figure 4b
Figure 4c