Energize Ensuring lightning protection
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Ensuring lightning protection

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Providing a simpler approach for surge and lightning protection insurance for thatched roofed buildings which combines public and product liability, professional indemnity and the underwriting of electronic equipment insurance is now available. The product is based on use of DEHN components, approved design, approved installation and approved maintenance.

Hano Oelofse, managing director at lightning and surge protection company DEHN Africa, says, “DEHN Africa has been involved in a number of installations on lightning protection systems for thatched roofs, and we are excited to launch a new and exciting initiative, which combines our expertise in lightning protection with a holistic insurance offering. We believe this is a first in South Africa, where vast areas of our country are prone to the high possibility of a lightning strike at different times of the year.” “The DEHN high-voltage-resistant insulated (HVI) lightning protection system, which is compact and neat, removes the need to have a 30+ metre lightning mast installed. This is far less visible to the naked eye than a mast, and therefore more visually pleasing. At the same time, however, the HVI system provides arguably even better protection from a lightning strike than a thirty-metre mast, and it is accepted by leading insurance companies.” he concludes.

Fig. 1:  Lightning protection for standard structures.

Oelofse says that, given the technical expertise offered by the HVI technology, and the company’s confidence in its product, the company is now prepared to offer insurance guarantees linked to its HVI system, through the launch of DEHNinsure.

Fig. 2: Protective cone provided by mast for non standard structure.

The development of this system was preceded by a survey of the thatch lodge market which revealed the following:

  • 81%  had external lightning protection systems (masts)
  • 45% still experienced damage in spite of LPS
  • Only 9% had surge arrestors fitted to the electrical systems
  • 79% are not being maintained

Fig. 3: Existing Lightning protection masts.

There are two types of lightning protection system used for structures.

  • Low risk of ignition or explosion (standard structures). The air termination (AT) is mounted on top of the structure and connected the earth  via a down conductor, which is usually uninsulated (Fig. 1).
  • High risk of ignition (Non-standard structures-typically thatch roofs and inflammables plant). The air termination and uninsulated down conductor cannot be mounted on the structure because of the danger of arcing causing sparks that could ignite flammable material in the structure. Protection is provided by a mast that creates a protective cone extending 45° around the top of the mast. The structure must lie entirely within this cone. (Fig.2)

Fig. 4: Construction of HVI cable (DEHN).

The second solution is problematic for several reasons

  • The high mast is unsightly and spoils the aspect of the building.
  • To limit the height of the mast, it needs to be placed close to the structure. This creates unsafe zones close to the building due to step and touch potentials.
  • The mast requires constant maintenance which often proves difficult and is thus neglected ( The industry estimates that 95% of all masts installed would not meet standards due to poor maintenance).

Fig. 5a and b: Connection of the cable to the AT. Compression sleeve connecting cable semiconductor layer to mounting tube.

The Product introduced by DEHN combines the features of both methods, without the danger of ignition due to arcing , and solves the problems associated with masts  by allowing the protective mast to be mounted on a non standard structure. This provides a protective cone using a much shorter and less obtrusive air termination, and provides a system that can be maintained easily.

The core of the system is the down conductor ( HVI), a high-voltage , insulated down conductor for maintaining the separation distance to electrically conductive parts according to IEC/EN 62305-3.The cable is manufactured with a semiconductor layer on the outside of the sheath, which reduces the stress in the insulation, and hence the risk of insulation breakdown. This is a proven technique used in high voltage power cables. The cross section of the cable is shown in Fig.4.

Fig. 6a and b: Air termination and supporting tube installed on thatch roof. Supporting tube inside thatched roof.

High impulse voltages cause flashover on the surface of insulating material if no additional measures are taken. This effect is also referred to as creeping flashover. If the creeping discharge inception voltage is exceeded, a surface discharge is initiated which can easily flash over a distance of several metres. To prevent creeping discharges, the HVI conductor features a semiconductive outer sheath which allows high lightning impulse voltages to be discharged to a reference potential. For functional reasons, a connection is established in the sealing end range between the semiconductive outer sheath and the building’s equipotential bonding system. This connection to the functional equipotential bonding system can be made at earthed metal roof-mounted structures located in the protected zone of the lightning protection system, earthed parts of the building’s structure that do not carry lightning voltage or the protective conductor of the low-voltage system.

The air terminal installation consists of a supporting tube, which is earthed, and the air termination itself which is mounted on the supporting tube but insulated from it by a resin/ glass fibre tube. The cable is fitted with a head piece that allows connection to the air termination. The outer semiconductor layer is connected to the supporting tube by a compression sleeve. The assembly is shown in Fig.5(a) and (b).

Fig. 6 shows the installed cable and air termination.

The cable, together with the air termination and earth connection, is manufactured to the exact length required and no jointing is normally performed on site. The system has been adopted by the Legacy group and is being installed on the new villas currently under construction at the Bakubung bush lodge.

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