LIGHTNING PROTECTION 2

[pristava]

Steel Structure Telecommunication Tower is provided to be protected from the Lightning.
Is it true that Lightning Rod ( Air Terminal) is not necessary to be specified because Telecommunication Tower is Air Terminal ? Where to install a ground wire connected to the Grounding ?
Is there any Article describing that problem ?

 

[RonShap]

Underwriters laboratory 96A and NFPA 780 will help you work this out.
A telecom tower (5/16" thick steel) will provide protection for the building if the tower is large and the building is small and close by, but it is of any real size, then you need additional air terminals.
The tower gets bonded per to the lightning protection system per the standards listed at the top.

 

[alehman]

It's not necessary if the antennas on the tower are within the protected zone (defined in NFPA 780) created by the highest point of the tower structure. A pointed air terminal may be beneficial. A downlead conductor is not typically necessary as long as the tower structure is electrically continuous, at least 3/16" thick, and connected to an appropriate grounding electrode system.

 

[pristava]

I didn't understand last answar. My antenna is a highest point in that area, but I am informed that air terminal is not necessary to be installed because tower is air terminal by itself.

 

[GerH]

No need to have a lightning down conductor.

No need to have an air termination if the top of the tower is high enough to shield the uppermost antennae or they are a type that have integral lightning conductors.

Connect the very bottom of the tower to the lightning ground e.g. where the holding-down bolts fix the plates at the concrete.

Route the coax cables off a sharp right angles some distance up from grond level e.g. 2.5 meters. this si so that stroke current will proceed down tower and not tend to turn the sharp bend with the coaxial cables.

You must bond the outer screen conductor of the coax cables at the top and at the lower point where they depart the tower. Otherwise you can have a side flash that will damage the cables.

 

[busbar]

Coaxial surge protection may be applicable in this situation. Although written to promote their own products, there may be some more universal information at URLs like

http://www.polyphaser.com/ppc_technical.asp

 

[alehman]

A pointed air terminal may serve to improve the odds of directing leaders away from the antennas. It is not a requirement of NFPA 780.

 

[CJFlatters]

Both BS 5839 and IEC 1024 also cover lightning protection of towers and masts such as yours. These are generally consider to be self-protecting structures, though clearly the integrity and impedance of the earth termination network is critical.

Bonding to prevent side flashing is important (as previously mentioned), similarly care must also be taken to prevent re-entrant loops.

You may find IEC 1024 useful, though in my experience (back in 2000) it is not as comprehensive as the BS.


_______________________________________
Regards -

Colin J Flatters
Consulting Engineer & Project Manager

 

[jbartos]

Comment: The galvanic connection of the transmitter/receiver to the telecommunication tower needs to be protected against lightning. The following article recommends unplugging antennas:

http://www.sundayobserver.lk/2003/05/18/new25.html

however, if the transmitter is supposed to be in service, lightning arresters will be needed. Therefore, there is a need for the lightning protection system of the tower. The article also states that some "ball" falling away from the lightning strike to the tower may materialize.