Lightning protection for guyed tower 2

[Lutfi]

I am structural engineer and I need to gain some knowledge on how to protect a steel tower, triangular in cross section, it is 30 foot high, it has three guy cables that are equally spaced around the tower. The cables are connected to a steel frame/collar and clamped to the tower frame. The other end of the cables is connected to a guy connector which is embedded into a concrete footing.

Near all three cables ground area, I have placed three (3) 0.75 inch diameter rods by 20 foot long. The three rods are in triangular configurations with 10 foot spacing.

Is this adequate? Do I need to bond the tower itself to the grounding system as well?

Please let me know.

 

[rbulsara]

You need to ground the tower too.

The three rod grounding electrode (also known as counterpoise grounding electrode) should be provided at EACH of the three guy wires PLUS the steel tower. More importantly at the towers base then the guy wires as the tower is the the path of least resistance to the lightning currents.

You also must interconnect all the grounding electrodes, in this case all four 'electrodes', using a buried copper conductor no less than #2/0 in size.

Sounds like this is already built. HOwever, best (and almost free) grounding electrode is obtained when you use the concerete foundation with re-bars (for the steel tower if applicable) as the grounding electrode. In that case need to bond the steel tower to the rebars. You can also bury a bare copper conductor at the bottom of the foundation and bond it to the steel tower. Use min. of #2/0 or #4/0 copper conductors.

 

[jbartos]

Suggestion: Adhere to NFPA 780-2004 Lightning Protection System.
Visit

http://www.lightningsafety.com/nlsi_bus/nfpa-780-2004.html

http://www.nfpa.org/Codes/NFPA_Codes_and_Standards/List_of_NFPA_documents/NFPA_780.asp

http://tis.eh.doe.gov/techstds/meeting/NRCDOELightningStandardsPresentation.pdf

http://www.lightningsafety.com/nlsi_lhm/magic.pdf

etc. for more info

 

[Lutfi]

Excellent feed back and my thanks to both of you. Our company has all of the NFPA codes including 780. I read it and I usually rely on my EE; however, he is on vacation and was trying to educate myself.

The tower is not built yet and the design will be completed and reviewed by EE. This was mostly for me to understand.

Once again, I am much obliged to both of you.