Photo courtesy Boston Lightning Rod Company
Penetrations
Locations where conductors pass through roofs, walls, structural members, and other building materials require the A/E’s attention to ensure the function of the penetrated construction is not compromised. For example, the integrity of fire-rated assemblies, water-resistant barriers, and air barriers must be maintained.** A preinstallation meeting can help with trade co-ordination and scheduling.
Roof penetrations can be made with various types of boots, pitch pockets, and flashings—the selection and installation must be co-ordinated with the roofing supplier to make certain the roof warranty is not voided. It may be possible to avoid roof penetrations altogether. For example, the owner of a computer server farm prohibited roof penetrations as a way to reduce the likelihood of roof leaks. Since the building’s walls were tilt-up concrete panels, down conductors were located in the gaps between panels and became concealed when the joints were sealed.
Photo courtesy East Coast Lightning Equipment, Inc.
Through-structure assemblies for wall penetrations are typically made with metal rods that can be cast or built into the walls floor and roof decks or installed through drilled holes or in conduit.
Fittings and connectors
Hundreds of configurations of fittings and connectors are required to satisfy myriad construction conditions.
Whether fabricated from stamped metal or solid castings, they must be selected for galvanic compatibility with adjacent materials; special bi-metallic parts are available for when transitions between aluminum and copper conductors are necessary. Fittings and connectors are mounted with approved mechanical fasteners or construction-grade adhesives.
Bonding
Lightning ‘does not care’ what path it takes between sky and ground, and will sideflash (arc) from components of the lightning protection system to other building components not designed to handle the current. Therefore, the lightning protection system must be connected (bonded) to grounded metal structural elements, piping, ductwork, wiring, equipment, antennae, and other equipment and building components within approximately 2 m (6 ft) of a conductor.
The importance of bonding is demonstrated in the following case study by the BC Safety Authority.
Photo courtesy Dobbyn Lightning Protection
Lightning struck the ground near an underground natural gas distribution line, and energized the tracer wire used to locate underground gas lines. This created an electrical arc that shorted from the tracer wire (serving the individual gas service to the home) to the gas service riser. This arc created a hole in corrugated stainless steel tubing (CSST). The resulting gas leak and sources of ignition started a fire in the home. During the investigation, it was found the home’s gas lines were not bonded as required by CSA B149-10 Natural gas and Propane installation and Handling Code (CSA B149-10) and the CSST manufacturer’s certified installation instructions.
However, even with bonding the thin walls of CSST are still susceptible to perforation when exposed to a lightning side flash. A research report states:
The underlying issue…is whether or [not] CSST is as safe as conventional black pipe. In this regard, reported fire losses indicate it is not as safe as black pipe in regards to the issue of lightning. While we cannot state black pipe will never fail from lightning, we have yet to see such a fire.
Ground electrode
The conductivity of soil at a building site affects its suitability as a ground for lightning protection. Wet clay may not be desirable from a structural perspective, yet it is highly conductive and performs well as a ground. Dry sand, gravel, and rock have more resistance and will require more extensive methods to ground. If an owner obtains a soil investigation report, it can be made available to lightning system designers and installers; contractual provisions, however, should spell out what happens if conditions onsite differ from those in the report.
In conductive soil, a copper rod, located at least 0.1 m (2 ft) outside the building perimeter and driven 3 m (10 ft) vertically into the earth, may provide sufficient ground. In non-conductive soils or where rocky conditions, such as the Canadian Shield, make it difficult to drive a ground rod, a shallow ground plate or ground ring will help to distribute charges over a wider area. A ground ring, also known as a counterpoise, can be more economical than installing separate ground rods at each down conductor and is required at tall buildings.
A test well is recommended to simplify inspection of a ground. The well selected should have a cover suitable for traffic loads that may be applied.
