CSA B72:20 Installation code for lightning protection systems.
4 General requirements
4.1 Classifications
In this Standard, lightning protection installations are classified as follows:
a) Class I—an installation, not included in another class, that protects a building or a construction of less than 23 m (75 ft) in height;
b) Class II—an installation, not included in another class, that protects a building or a construction of 23 m (75 ft) or more in height;
c) Class III—an installation that protects a smoke or a vent stack whose smallest cross-sectional area is equal to or greater than 0.3 m 2 (500 in 2 ) and whose height is greater than 23 m (75 ft);
d) Class IV—an installation that protects miscellaneous structures such as towers, silos, non- hazardous tanks, stages, outdoor pools, terraces, fences, trees, wires, antennas, masts, construction cranes, solar arrays, etc.; and
e) Class V—an installation that protects structures with explosive or highly flammable contents.
4.2 Materials, general
Only copper, copper alloys, aluminum, aluminum alloys, or stainless steel shall be used in an installation, except that
a) copper-clad steel rods may be used as ground electrodes;
b) galvanized steel may be used for air-terminal supports, nails, screws, and bolts, or as part of an overhead ground wire protection system;
c) lead may be used as anchors or to protect other materials from corrosion; and
Copper lightning protection materials shall not be installed on or in contact with aluminum surfaces, or on exterior galvanized or painted steel surfaces.
Note: This requirement is not intended to preclude the use of exothermic weld connections between copper conductors and exterior steel surfaces.
Aluminum shall be installed in accordance with other applicable clauses and with the following:
a) Aluminum lightning protection equipment shall not be installed on copper surfaces, or where exposed to runoff from copper surfaces.
b) Aluminum materials shall not be used within 450 mm (18 in) of where the lightning protection  down conductor enters the earth.
c) Fittings used to connect aluminum lightning protection components to copper or copper-alloy components shall be bimetallic and suitable for the purpose.
d) An aluminum conductor shall not be attached to a surface coated with alkaline-base paint; embedded in concrete, masonry, or soil (e.g., on green roofs); or installed in any location subject to excessive moisture.CSA B72 pdf download.