Thank you for your question regarding Lightning Protection Systems (LPS), it is our pleasure to help.
The NFPA 780 Standard for the Installation of Lightning Protection Systems refers to “rain gutters” as eave troughs and downspouts in its texts. In NFPA 780 184.108.40.206 it states:
220.127.116.11 “Ancillary metal parts of a structure, such as eave troughs, downspouts, ladders, chutes, or other metal parts except as permitted in 4.16.1, shall not be substituted for the main conductor.”
As you can see, rain gutters are not allowed for use as part of the Lighting Protection System (LPS) according to NFPA 780. The article above references section 4.16.1 of the code which states:
4.16.1 General “The structural steel framework of a structure shall be permitted to be utilized as the main conductor of a lightning protection system if it is electrically continuous or is made electrically continuous.”
As you can see, the structural steel frame may be used (but it is not recommended) as part of the LPS, but rain gutters may not be used.
While we are far more familiar with the American NFPA 780 than the European IEC 62305-3 lighting protection code, the use of rain gutters seemed odd to us so we did a little checking for you. In the IEC 62305-3, they do use the term “rain gutter” instead of “eave trough”, however we did not come to the same conclusion.
IEC 62305-3 Section E.18.104.22.168 (page 235) states:
E.22.214.171.124 “If it is not possible to make a straight connection because of large roof overhangs etc. the connection of the air-termination system and the down-conductor should be a dedicated one and not through natural components like rain gutters etc.”
The reason we found it odd, is that rain gutter should not be used as part of the Lightning Protection System under any circumstance. While the NFPA 780 does a satisfactory job at providing a basic lightning protection system, the European 62305-3 code is a far more detailed and advanced document that requires actual scientific analysis and engineering of systems specifically for a given building. The NFPA 780 is more of a one-size-fits-all code that requires no scientific analysis of your building at all. By definition, any Lightning Protection System built to 62305 standards would exceed any requirements found in the NFPA 780. Here is a link you may want to review:
In conclusion, neither the NFPA 780 nor the IEC 62305 standards allow the use of rain gutters as part of the Lighting Protection System. Metal rain gutters must be bonded to the system, but they may not be used as a conductor.
We hope this has answered your question. Please feel free to call us at 310-318-7151 California time, we will be glad to speak with you in regards to your project, free of charge.
The Engineering Team at E&S Grounding Solutions
Photo credit: http://www.flickr.com/photos/theogeo/2228332175/sizes/o/in/photostream/