5　Lightning Protection of Outdoor Units

5.1　Furnace Area

5.1.1　For furnace chamber supported by steel structure，its structure shall be connected to earthtermination system via connectors.

5.1.2　For furnace chamber supported by concrete structure，earth lugs shall be welded on the attachment such as reinforcing pad（rib）of furnace chamber，and the exposed metal conductor run along column or the main longitudinal reinforcement in column in diameter not less than 10mm shall be served as downconductor.

5.1.3　For small-size furnace directly installed on grade，earth lugs shall be welded on the reinforcing pad（rib）of furnace chamber.After the earthterminal is connected to earth lugs，it shall be down led along the structure and connected to earth-termination system.

5.1.4　No fewer than two earthing points shall be provided for each furnace，spacing between earthing points shall not be larger than 18m，and impulse earth resistance of each down-conductor shall not be larger than 10Ω.

5.1.5　Earth lugs for furnace shall be installed on the column of structure at a location in height not lower than 450mm above grade.

5.1.6　Metal components on furnace shall be all bonded with the furnace frame.