How to protect your link from lightning?

142019 May

Introduction

Lightning is visible discharge of static electricity between clouds or between the earth and a cloud. Most cloud to earth strikes are negative. Negative charge moving downwards to earth creates almost invisible “stepped leader” that produces ionized path in the air. The most visible event is “return stroke” that carries the major part of the lightning discharge and flows along the ionized path. “Return stroke” performs direct contact with earth.

Tower sites are vulnerable by lightning more often than any other site, because tower is higher than the surrounding terrain. Moreover, it is a conductor. Without proper protection and grounding SAF Tehnika equipment will suffer damage. Therefore, it is very important to plan lightning protection and grounding before establishing Integra series equipment on the mast.

This technical guide will lead you through instructions for setting up lightning protection and grounding to have the best protection from harmful effects of lightning and surge. Note that these instructions are recommended and not mandatory. You may build protection system guided by your own beliefs. However, 100% protection is not possible.

Recommended Tower/Mast Installation

SAF Tehnika recommends using Lightning Protection System (LPS) that provides means for avoidance of personnel, electrical equipment and buildings damages. Main components of LPS are as follows:

    • Air Terminal (lightning rod)– intended to intercept lightning flashes. It should be installed at the highest point of the tower and constructed of steel with a pointed tip.
    • Horizontal lightning rods– intended to protect side mounted antennas if these are installed at heights higher than 50m (150 ft).
    • Down conductorpart of LPS that conducts lightning current from the Air Terminal system to the Earth Termination system. It should be installed straight down to the earth in order to provide the shortest and most direct path to earth. Bending must be avoided. Down conductor may be made of Cu, Al or Fe. SAF Tehnika recommends at least 50 mm2 dimension of conductor.
    • FODU grounding all Integra series FODUs are equipped with grounding screw for connections to the grounding system.
    • Earth termination system– part of external LPS that is intended to conduct and disperse lightning current to earth.
    • Lightning protectors (surge arresters)– provide additional protection to Integra equipment embedded protectors in places where lightning danger is elevated. External surge arresters can be installed at strategic points of a site if additional protection is necessary, although Integra series products contain embedded lightning protection.

The recommendations depend on flash density in the area of tower placement. If the density is low (0 - 1) then also risk and protection level is low. It would be enough with built- in protection of equipment and grounding at top and bottom of the tower and at the entrance to ground station shelter. In case of medium flash density (1-4) it is recommended to ground the cable every 60m and place the grounding clamps on the tower every 25m. Also additional indoor surge arresters are recommended. In case of high flash density (4 and above) it is recommended to place additional surge arresters on top of the tower. The highest level risk is considered, when the height of tower exceeds 100m. In this case it is recommended to place surge arresters every 30m on the tower.

Surge Protection and Grounding of Integra FODU

As Integra FODU may have either electrical or optical Ethernet interface to user equipment, required and recommended protection components will differ. Next two sections provide separate description of protection and grounding of electrical (PoE injector solution) and optical (direct DC cable) Integra FODUs.

Surge Protection and Grounding of Integra FODU (electrical) with PoE Injector solution

Picture 1: Surge Protection and Grounding of Integra FODU (electrical) with PoE Injector solution

(!) Power supply should be equipped with fuse. Alternatively, external fuses for both DC wires should be installed near power supply indoors. The nominal current of fuses should correspond to rated current of particular radio model.

Shielded F/UTP or S/UTP outdoor twisted pair cables should be used for Ethernet connection. Any broadly available grounding kit should be used for grounding of Ethernet cable to the tower. Grounding kits (clamps) on the tower should be placed with maximum distance of 25m.

(!) As Integra FODU has embedded surge protection for Ethernet connection, it is optional to install additional surge arresters near Integra FODU (outdoors). However, we recommend installing outdoor Ethernet surge protector in case cable length is larger than 30m. If SAF GE Programmable PoE Injector is used for powering Integra, it plays the role of indoor surge protection. If third party PoE injectors are used, we recommend installing indoor Ethernet surge protector near CPE (indoors) to protect end users equipment.

SAF Tehnika recommends using outdoor surge arrester shown below as outdoor Ethernet connection protection. SAF indoor GE PoE injector can be used as indoor surge arrester for Ethernet connection. Note that each Ethernet connection requires separate surge protection outdoors and indoors.

Left: 10/100/1000 Base-T CAT6 Lightning Surge Protector, P/N I0ALAO03  Right: GE PoE programmable injector with built in surge protector, P/N I0ATPI44

Picture 2: Left: 10/100/1000 Base-T CAT6 Lightning Surge Protector, P/N I0ALAO03 Right: GE PoE programmable injector with built in surge protector, P/N I0ATPI44

Surge Protection and Grounding of Integra FODU (optical) with direct DC cable

Picture 3: Surge Protection and Grounding of Integra FODU (optical) with direct DC cable

(!) Power supply should be equipped with fuse. Alternatively, external fuses for both DC wires should be installed near power supply indoors. The nominal current of fuses should correspond to rated current of particular radio model.

In this case, Integra FODU is equipped with LC port and fiber optical cable that does not require any surge protection and grounding. Only surge arresters for DC power source protection can be placed optionally indoors and outdoors. It is recommended to place indoor surge arrester to protect power supply in case PSU lacks surge protection. The same 48VDC cable surge arresters can be used indoors and outdoors (P/N I0ASP202), please refer to the picture below.

Picture 4: Left: Outdoor 2 x 48V DC Power Line Lightning Surge Protector, P/N: I0ASP202; Right: Outdoor Power adapter cable for Integra, P/N: D0ACPW01

Outdoor Power adapter cable for Integra, P/N D0ACPW01 is intended to interconnect PoE capable Ethernet port of Integra with direct DC power cable used. Terminal block, encapsulated in hermetic connection box, ensures the connection. If optional outdoor DC power line protector, PN I0ASP202 is used, the latter provides connection between DC power cable and outgoing Ethernet cable. Optional outdoor DC power line protector must be grounded directly to Integra FODU grounding screw, as shown in picture 3.

If you have any questions regarding lightning protection or any other technical issue regarding SAF equipment, please contact our techsupport team via email Sorry, no go without enabled JS, pal. :(

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