Air Force Instruction  32-1065

1 October 1998

Civil Engineering

Grounding Systems

Overview

1.        Compliance with this publication is mandatory.

2.        This instruction implements AFPD 32-10, Installations and Facilities.

3.        This instruction also implements DOD 6055.9 STD, Ammunition Explosives Safety Standards

4.        This instruction assigns maintenance responsibilities

5.        Base Civil Engineers are responsible for Ground Resistance Tests and for 29 of the 34 listed items.

General Facility             Resistance Check                 25 ohms max                          every 5 years

 

POL Facilities                Resistance Check                 10,000 ohms max                   when damaged

                                        Tightness on ground conductors                                     quarterly

 

Communication

Facilities                        Resistance Check                 10 ohms max                          every 21 months

 

 

Explosive Area             Conductive Floor                 AFMAN 91-201                    every 6 months

Hazardous

       

Explosive Area             Resistance Check                 25 ohms max except loop    every 24 months

Non Hazardous            Continuity Check                 1 ohm                                     every 24 months

                                        Static Bar Check                   1 ohm                                     every 24 months

 

Protective Aircraft

Shelter (PAS)                Resistance Check                                                                 every 24 months

 

Medical Facilities         Resistance Check                 25 ohms max                          every 5 years

 

Airfield Lighting           Resistance Check                 25 ohms max                          every 2 years

 

PMEL                             Resistance Check                 25 ohms max                          every 2 years

 

6.        Users are responsible for seven of the 34 listed items but no Ground Resistance Tests.

Communication

Facilities                        In House Electronic Ground                                               by user

 

Explosive Area             Visual Check                                                                                        

Hazardous                     Static Ground Check            1 ohm                                     by user each day

Continuity Check

From Equipment to

Static bar                               1 ohm                                     every 3 months

                                                                                                                                        Or by T.O,

 

Explosive Area             Visual Check                                                                         Quarterly

Non Hazardous            Static Ground Check            1 ohm                                     every 24 months

 

Fuel Labs                       Visual Check                                                                         Monthly

                                        Of ground wires

 

Fuel Labs                       Visual Check                                                                         Monthly

                                        Facility Grounds

 

7.        Records keeping:  Sketch of the grounding system, test points, date, tester’s name, general condition of air terminals, conductors, other components, corrosion  protection measures, security of attachments, resistance measurements, variations from requirements, discrepancies noted and corrective action, date of repairs.  Keep these records for a minimum of 6 inspection cycles.

8.        Visual inspection of the lightning protection system: The system is in good repair, no loose connections, no excessive corrosion, conductors are in tact, no excessively frayed wires, no mower damaged wires or masts, components are securely fastened, surge suppression devices installed and operational.

9.        Visual inspection of facility grounds:  The system is in good repair, no loose connections, system neutral is grounded at the service entrance including connection to the grounding electrode, separately derived systems are properly grounded, flashover protection is installed, grounding systems within the facility are bonded together at ground level or below.

10.     Static Protection:  13.1.2  Static grounding system must be connected to the facility grounding system.

11.     Lightning Protection Systems: 14.1 General, streamer emission systems or charge dissipation systems are not permitted.  14.2  Adequate bonding is more important than grounding.  14.3  Low resistance is desirable but not essential for lightning protection.  For most facilities, resistance to ground should be less than 25 ohms.  If this cannot be achieved where only ground rods are used, install a ground loop conductor.  The resistance to ground of a ground loop is acceptable even if greater than 25 ohms.

12.     Surge Protection: Metallic power lines, intrusion detection, communication antenna and instrumentation lines must have surge protection sized for lightning surges to reduce the transient voltages to a harmless level.  These lines must enter the facility in shielded cables or metallic conduits run underground for at least 50 feet from the facility.  The antenna leads from antennae on the facility and within the zone of protection do not have to go underground.

13.     Definition of Facility Ground System: The electrically interconnected system of conductors and conductive elements that provides multiple current paths to earth.  The facility ground system can include the earth electrode subsystem, lightning protection subsystem, signal reference protection subsystem, fault protection subsystem, static ground subsystem, as well as the building structure, equipment racks, cabinets, conduit, junction boxes, raceways, duct work, pipes, and other normally non-current-carrying metal elements.

14.     Definition of Lightning Protection System: A complete system consisting of components such as air terminals, interconnecting conductors, ground terminals, surge suppression devices, and other connectors or fittings and subsystems required to assure a lightning discharge will be safely conducted to earth.

15.     Attachment 2: Basic Requirements for Grounding Systems.  A2.1.6  Static Grounds, Equipment Grounds, Electrical System Grounds, Lightning Grounds, Signal Reference Grounds are the five basic types of grounding systems.  Each of the grounding systems may be a subsystem of a total facility grounding system.  All grounds and subsystem grounds must be bonded together according to NFPA 780.

16.     A2.2.1 Ground rods must be at least 8 feet in length and no closer than 6 feet from other rods or plates.

17.     A2.3.2. Methods of Obtaining Better Grounds:  Deeper Rod, Parallel Ground Rods spaced the distance of the rod as a minimum, Soil Replacement, Concrete Encapsulation, Extensive Wire Networks, Ground Loop Conductor.

18.     A3.6.4 Fences and railroad tracks within 6 feet of a structure’s lightning protection system must be bonded to the structure grounding system.

19.     A4.1.1 Air terminals must extend at least 10 inches above the object to be protected.

20.     A4.1.4 Lightning protection down conductors must present the lease impedance to ground.

21.     A4.1.5 Down conductors must not have sharp bends or loops.  All bends must have a radius of 8 inches or greater and measure not less than 90 degrees from the inside of the bend.

22.     A4.1.8 If a down conductor runs through a ferrous metal tube of pipe usually for mechanical protection, the conductor must be bonded to both ends of the tube.

23.     A4.1.9 Do not paint down conductor connectors unless they are the high-compression or exothermic welded type.  Conductors on roots must be bare.

24.     A4.1.11 Ground rods for lightning protection must be at least 10 feet in length and ¾” diameter.  Stainless steel ground rods may not be used.  Ground rods must be at least 3 feet from the building walls or footings and must penetrate 10 feet into soil. Ground rods should be buried at least 1 foot below grade.

25.     A4.1.15 Ground loop conductors (cable) must not be less than AWG No. 1/0 copper.

26.     A6.1  Grounding System Resistance Test.  Resistance should be less than 25 ohms (10 ohms for communication facilities).