When lightning protection is desired, it is usually achieved by providing a path of low resistance to ground. Copper roofs offer ideal lightning protection where the copper roofing, gutters and rain leaders are electrically interconnected and reliably grounded. The specified thickness of materials, i.e., roof covering sheets, wall claddings, gutters and leaders are usually adequate for lightning protection and in these circumstances additional conductors are unnecessary.
Additional protection may be necessary with lighter gauge copper bonded panels or when some components of the grounding system are made from less conductive materials.
In the absence of adequate grounding through the copper system, additional lightning protection may be required.
It should be pointed out that, due to its excellent electrical conductivity and resistance to corrosion, copper maintains an important role in lightning protection applications. Its use for the grounding of copper roofing overcomes problems associated with mixed metal corrosion. When using copper for grounding in combination with other materials, instructions concerning corrosion protection should be followed.
Those not familiar with lightning protection systems seem to believe that copper components, including roofs, actually attract lightning. Needless to say this assumption is not based on fact.
It is true however, that the high conductivity of copper facilitates the rapid transmission of lightning energy. Lightning takes the path of least resistance and no damage is done to a building if there is a low resistance path to earth. This path can consist of the copper roof, lightning conductor and grounding device.
To ensure proper lightning protection in an installed copper roof system, a separate lightning conductor system should be used including air terminals and intercepting conductors on the roof; a system of ground electrodes; and a system of down conductors connecting the roof and ground components. It is recommended that the copper roof be bonded to the system of conductors. This bonding ensures that the conductors and roof remain at approximately equal potential and reduce side flashing and possible roof damage.
The Copper Development Association makes no representation as to the proper, correct or safe design of any lightning protection system. This information is presented as a guide only and the reader is cautioned that the design of any lightning protection system and devices is the responsibility of the electrical engineer. All such system design should be based on local applicable code requirements and sound engineering practice.