Posted by: GLeung in on 11 6 月, 2010

Technical Commentary


Part A – The use of *E.F.* Lightning Terminal (Early Streamer Emission (ESE) air terminal) and *E.F.* Lightning Carrier in the context of BE EN 62305 lightning protection standard

BS EN 62305-3:2006 deals with the protection, in and around a structure, against physical damage and injury to living beings due to touch and step voltages.

BS EN 62305-3:2006 is applicable to:
– design, installation, inspection and maintenance of an lightning protection system (LPS) for structures without limitation of their height
– establishment of measures for protection against injury to living beings due to touch and step voltages

Together with BS EN 62305-1:2006, BS EN 62305-2:2006 and BS EN 62305-4:2006, BS EN 62305-3 supersedes BS 6651:1999 which has become obsolete since 31 August 2008.

Besides, BS EN 62305-3 also replaces previous IEC 61024-1 (1990), or IEC 61024-1-2 (1998).

With reference to the terms and definition of IEC 62305-3, the component of an external lightning protection system (LPS) shall consist of a) air-termination system, b) down-conductor system and c) earth-termination system (see attached Page 19 of IEC 62305-3).

a.) Air-termination system (part of an external LPS using metallic rod, mesh conductors or catenary wires intended to intercept lightning flashes):

Although not of a conventional type, *E.F.* Lightning Terminal can be used in the context of BS EN 62305-3 as it is a well established form of air terminal know as Early Streamer Emission (ESE) air terminal governed by an international product standard – French Standard NFC 17-102.

By virtue of its ESE property, the *E.F.* Lightning Terminal offers a comparatively larger protection radius based on the electrogeometric model than a conventional air terminal.

*E.F.* Lightning Terminal has been type-tested in accordance with French Standard NFC 17-102 by Korea Electrotechnology Research Institute (KERI) accredited by Korea Laboratory Accreditation Scheme (KOLAS) which is the government accreditation body established on December 8, 1992 and administered by the Koren Agency of Technology and Standards (KATS). KOLAS signed Mutual Recognition Arrangement with Asia-Pacific Laboratory Cooperation (APLAC) in 1998 and with International Laboratory Accreditation Cooperation (ILAC) in 2000. In fact, *E.F.* Lightning Terminal attained an advance time (DT) of 68.7ms – one of the highest values attained in the lightning protection industry

Therefore, the proposed *E.F.* Lightning Terminal which belongs to the class of ESE air terminals can be used as an alternative to or in conjunction with conventional air termination system comprising metallic rod(s), mesh conductors or catenary wires as proposed by IEC 62305-3.

b.) Down-conductor system (part of an external LPS intended to conduct lightning current from the air-termination system to the earth-termination system).

*E.F.* Lightning Carrier is a proven downconductor well positioned to deal with and suppress the risks of sideflashing as well as the risks of touch voltage and step voltage the new BS EN62305-3 aims to address in particular. The advantages in using *E.F.* Lightning Carrier are briefly explained below:

With the use of double heavy high voltage insulating materials in the *E.F.* Lightning Carrier, dangerous touch potential risk is made negligible during lightning interception as the lightning carrier is type-tested to a lightning impulse withstand strength of 250kV 1.2/50ms waveshape which is well in excess of the BS EN lightning impulse withstand requirement of 100kV 1.2/50ms impulse waveshape for negligible touch potential risk (see attached).
Due to the significantly low impedance path offered by the *E.F.* Lightning Carrier, for instance its inductance is only 1/20 that of a 1/C 70mm2 PVC insulated copper cable, the magnitude of temporary overvoltage due to lightning interception as experienced in *E.F.* Lightning Carrier is substantially less than that experienced in a conventional downconductor. Hence, side-flashing risk during lightning interception is eliminated or significantly reduced.

Besides, the polarity of the charge induced on the outer conductors during lightning interception of the *E.F.* Lightning Carrier is of the SAME TYPE as that induced on the objects at ground (or any grounded objects) by the thundercloud above, the potential difference between the *E.F.* Lightning Carrier and the grounded objects is substantially reduced thereby minimizing the side-flashing risk compared to that a generated normal mono-core copper cable or copper tape which carries OPPOSITE CHARGE with respect to grounded objects.

Additionally, the Transient Absorption Technology of the *E.F.* Lightning Carrier, as realized by its high capacitance formed by the concentric arrangement of its Inner Conductors and Outer Conductors, enables that the lightning energy is temporarily stored in the *E.F.* Carrier System of Lightning Protection which is subsequently released after the lightning current peak in a steadier filtered manner. The lightning current conducted in the *E.F.* Lightning Carrier instead of the conventional downconductor is therefore regulated, filtered and less impulsive. Any undesirable effects caused by the passage of the impulsive lightning current are reduced to a minimum.

Furthermore, the *E.F.* Lightning Carrier can be suitably positioned and installed away from sensitive electronic/electrical equipment in most applications. Inverse Square Law can be effectively exploited to minimize magnetic coupling of lightning current thereby significantly reducing potential surge problems to the sensitive equipment.

Regarding the possibility of reduction in step potential (subject to project conditions and site boundary), the high voltage insulated *E.F.* Lightning Carrier easily permits diversion and grounding of lightning current at a remote location away from building structure and/or places people would gather therefore minimizing the momentary hazardous ground potential rise at these locations.

c.) Earth termination system (part of an external LPS which is intended to conduct and disperse lightning current into the earth).

For a high rise building, natural foundation earthing should be employed.

In practice, minimum two interconnected lightning earth pit c/w supplementary earth electrodes and connection to re-bars below ground should be added with one of them acting as inspection and testing earth pit. The *E.F.* Lightning Carrier shall be terminated at the designated inspection and testing earth pit

The lightning earthing system should be connected to the “electrical earth” indirectly via the reinforced rods of the foundation and the buried walls.

In conclusion, we are pleased to confirm that the case of both the *E.F.* Lightning Terminal and *E.F.* Lightning Carrier will comply with or exceed the requirements of BS EN 62305-3.

Part B – Recommended Surge Protection for Electrical Installation / Equipment within the Building Structure

Typically, the resulting recommendations of a risk assessment for a high-rise building performed in accordance with BS EN 62305-2 will necessitate the application of the following surge protection measures:

1. To install power line surge protectors at the LV main switchboards(s) to divert lightning current away from electrical installation and to suppress the common-mode overvoltages that appear on G-N and G-L.
2. To install data line surge protectors on incoming and outgoing telecom services system.
3. To install power line surge protector(s) at the MCB distribution board which feeds power to the electrical equipment located at building roof top to suppress and divert induced electrical surges that may enter from exposed equipment cables installed at building roof.
4. To install data line surge protectors at both ends of the satellite/TV coaxial cables to protect the CABD equipment.