An eighteen-inch diameter area of finished hangar floor or apron pavement is marked with concentric rings of yellow and red paint, with the word "GROUND" in one-inch black letters and the test date in half-inch black letters. The flush-mounted assembly consists of a cast bronze housing and cover connected by a number ten brass ball chain, with a three-quarter-inch National Coarse thread receiving a three-quarter-inch grounding rod. The grounding rod extends a minimum of ten feet below the concrete slab and connects via exothermic bonding to a number four-slash-zero American Wire Gauge bare copper grounding cable. Maximum resistance to ground must not exceed twenty-five ohms from any individual ground rod within aircraft hangars.
10' MIN 3/4" 3" 2-3/4" DIA. 2-3/4" HANGARS 3/4" ROD FOR 3/4" N.C. THREAD #10 BRASS BALL CHAIN PLAN FINISHED HANGAR FLOOR OR APRON PAVEMENT PAINT YELLOW DATE GROUND 2" PAINT RED 18" DIA. SECTION GROUND RECEPTACLE SET IN FLOOR 2" INSTALL BELOW CONCRETE SLAB. EXOTHERMIC BONDING. #4/0 AWG BARE COPPER GROUNDING CABLE. IN HANGARS, MAX. RESISTANCE TO GROUND MUST BE 25 OHMS FROM ANY GROUND ROD. PAINT THE WORD "GROUND" IN 1" BLACK LETTERS AND THE DATE TESTED IN 1/2" BLACK LETTERS CAST BRONZE COVER, FRICTION FIT BRASS PIN CAST BRONZE HOUSING
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