Commercial Lightning Protection
The following information describes how to install lightning protection systems on commercial structures. Most of the components used on residential structures are used on commercial structures. Please review the residential section first. We will list some commercial specific requirements in this section. This list is not all-inclusive but will give you a general understanding. Blackbird Lightning Protection provides free designs and assistance nationwide. We will provide you with a drawing and answer any questions on the installation.
Cross Run Conductors- Cross run conductors are coursed over flat or gently sloping roofs that exceed 50’ in width to interconnect air terminals required in these areas. For example, a roof from 50’ to 100’ in width requires one additional run; roofs 100’ to 150’ in width require two runs, etc. These cross run conductors shall be connected to the main perimeter cable at intervals not exceeding 150’.
Dead Ends- An 8’ dead end line can come off the main conductor cable on the highest roof level. This allows you to put an air terminal on a vent for example. The dead end cable has to be main sized conductor cable. On a lower roof level the dead end can be 16’ long.
Down Conductors- Every structure must have at least 2 down conductors. Structures with a perimeter of 250’ or less use two down conductors. Structures exceeding 250’ in perimeter shall have a down conductor for every 100’ of perimeter or fraction thereof. The down conductor on large structures shall be spaced not to exceed an average distance of 100’. Every down conductor connects to a ground rod.
Steel beams must be at least 3/16” thick when used as down conductors. Through roof connections must not exceed 100’ when steel structures are utilized as down conductors. Bonding plates for cable to steel transitions must be at least 8 square inches.
Roof Top Mechanical Units- Roof top mechanical units with continuous metal housings less than 3/16” thick shall be protected by air terminals mounted on bases having a minimum contact area of three square inches. Each base is secured to the bare metal of the housing by drilling and tapping to the unit’s frame (or use nut, washer & bolt). At least two main-size conductors shall be installed with connection made to bare metal at the base or lower edge of the unit. The bonding devices will have a surface contact area of three square inches providing two or more paths to the lightning protection system. The base bonding plates shall be located as far as apart as practicable on the electrically continuous metal housing.
Tanks & Silos- Steel tank walls less than 3/16” thick require air terminals on top of the tank. Steel tank walls at least 3/16” thick just require ground rods. The ground rod cables are attached to the bottom of the tank using bonding plates. Peak or dome-roofed silos shall have at least one air terminal at the peak and additional air terminals as required to create a zone of protection for the silo’s perimeter. Silos standing alone shall be equipped with at least two down conductors for up to 200’ circumference. One additional down conductor shall be added for each additional 100’ of perimeter or fraction thereof.
U and V pockets- Conductors shall maintain a horizontal or downward course, free from “U” or “V” (down and up) pockets. Such pockets, often formed at low-positioned chimneys, dormers, or other elevations on the slope of a roof and at coping walls, shall be provided with a down conductor from the base of the pocket to ground, or to an adjacent downlead.