Air Force Regulation 91-43

1. AFM 91-3 Exterior Electrical Distribution which includes equipment, fencing, pole grounds and neutrals. Frequency is every 2 years and as required.
2. AFR 91-4 General Facilities to include continuity and resistance checks of facility grounds every 5 years. Resistance maximum is 25 ohms.
3. AFM 85-16 POL Facilities (Petroleum, Oil & Lubricants) should check static ground as needed. Resistance at 10,000 ohms unless connected to facility ground where 25 ohms is common.
4. MIL STD 188-124A & MIL HNBK 419 Communication Facilities including Tempest should read resistance maximum of 10 ohms and be checked every 21 months.
5. AFR 91-4 Communication Facilities Non Tempest , frequency of testing to be determined by user.
6. AFP 91-28 Air Field Lighting, frequency of testing is 2 years. Resistance maximum is 25 ohms.
7. NFPA #78 Medical Facilities, frequency of testing is 5 years. Resistance maximum is 10 ohms.

STATIC GROUNDING AFR 91-43 Page 5 Section 6
NFPA #77 contains the minimum acceptable static grounding and bonding requirements for the USAF activities except as modified in the AFR 91-43.

1. The minimum size #8AWG braided ground wire for flexibility of moveable equipment - #6 AWG is preferred for repair.
2. Static bus bars are to be 2" x ¼" and bonded to the down conductor of the lightning protection system. Do not connect telephone grounds, electrical conduit or intrusion systems to this bus. If these systems require bonding and grounding, do so at the down conductor or ground loop conductor.
3. Static current resistance of 10,000 ohms is adequate but since these are connected to facility ground systems, 25 ohms resistance is common.

LIGHTNING PROTECTION SYSTEMS AFR 91-43 Page 5/6 Section 8
Modifications:

8.a.(1) New connections must be of the high compression or exothermic weld type. Replace existing bolted connectors which need repairing with these type of new connectors.

9. Surge Protection: All incoming metallic power, intrusion detection, and communication and instrumentation lines require lightning arresters to reduce transient voltages to a harmless level. Install low pass filters if desired for additional protection or if the user needs it for specific critical electronics loads.

BONDING STANDARDS AFR 91-43 Page 6 Section 10
Adequate bonding is more important than grounding. Bonding makes sure that all metallic objects are at equal potentials, preventing dangerous sparkovers. NFPA #78 and AFR 91-43 contain the minimum acceptable lightning system bonding requirements for USAF facilities. Do not paint wires, connectors of bonds, or the lightning protection system. Bond metal ventilators, steel doors, metal doorframes and steel reinforcing bars to the structure grounding system. Bond to the facility grounding system any metallic fences or RR tracks that are within 6 feet of the protection system. Bonding straps should not exceed 1 ohm resistance.

GROUNDING RESISTANCE AFR 91-43 Page 6 Section 11
11.a. Low resistance is desirable, but not essential for lightning protection. Rock foundation: Lay extensive wire network on the rock surrounding the structure. Bury the wire network if there is enough soil. At locations where the soil is of high resistivity but also deep, drive rods as deeply as possible. Interconnect ground rods with a ground loop conductor.

11.b. For most facilities, resistance to ground should be less than 10 ohms. If this reading is not possible at existing facilities that have only ground rods, install a ground loop conductor. The resistance to ground of a ground loop system is acceptable even if it is greater than 10 ohms.

Additional information and site survey information can be obtained by contacting

POC: Mike Helms mike@lightningmike.com