Atch 2 - Roof Projects Lightning Protection Guidance and Design.pdf

Briefing Paper: Major Elements of Lightning Protection for Terminal Roof Projects

Reference: FAA-STD-019G

FAA facilities require higher LPGBS performance than standard commercial codes. The LPGBS program sets FAA-STD-019 (latest version) as the minimum standard for all new installations, sustainment projects, and facility upgrades.

Due to unique structures and the modern air traffic equipment in FAA facilities, LPGBS practices in the FAA have a higher performance standard than the commercial code requires. This is especially true since the agency is moving toward more commercial off-the-shelf (COTS) products containing increasingly faster processors with low logic voltages that are sensitive to electrical irregularity or power system disturbance.

Commercial codes contain requirements to protect building structures from fire. FAA requires performance standards that protect people, structures, and equipment, and ensure the equipment operates during adverse conditions. One LPGBS key document is FAA-STD-019 (latest version) Lightning and Surge Protection, Grounding, Bonding, and Shielding Requirements for Facilities and Electronic Equipment. It serves as a performance document for those implementing new projects or conducting operations and maintenance in FAA facilities. The requirements contained in FAA-STD-019 (latest version) reflect investigations and resolutions of malfunctions and failures experienced at field locations. The requirements in FAA-STD-019 (latest version) are considered the minimum necessary to reduce or preclude outages and to enhance personnel safety.

Further, the requirements have been coordinated with industry standards, and in some cases exceed the industry standards to meet the FAA mission.

Objective:

This document summarizes some of the basic guidance and design considerations for implementing compliant lightning protection systems on FAA Terminal roof projects, in accordance with the latest version of FAA-STD-019, NFPA 780, and Handbook 010A.

Refer to FAA-STD-019 latest version for additional information as needed.

1. Core Lightning Protection Components

- Air Terminals

- Main and Down Conductors

- Metallic objects within 6-ft of the lightning protection system.

- Equalization Loop

- Earth Electrode System (EES)

2. Air Terminal Placement and Impalement Risk

- Air terminals must be located per NFPA 780, extending at least 10" above the object.

- Maximum spacing between 12” air terminals is 20’ and for 24” air terminals is 25’ apart on a roof. If near walkways, they must be at least 5 ft above the surface or otherwise mitigated.

(Ref: Handbook 010A Section 2.2.8.2, Page 35).

- Air terminals are to be pointed or blunt-tipped.

- Horizontal air terminals are not required on ATCT tower shafts for equalization loops on intermediate levels where there is no personnel access or electronic equipment.

(Ref: FAA-STD-019G Section 5.2.2.2.1, Page 65).

3. Down Conductor Configuration

Minimum Quantity:

- At least (2) class II down conductors for buildings located on opposite corners <

60 ft high.

- Additional conductors for perimeters > 250 ft (one per additional 100 ft).

(Ref: FAA-STD-019G Section 4.3.4.1, Page 25).

- All ATCTs shall have (4) class II down conductors on structures up to 180 ft in height.

- Additional conductor for heights > 180 ft (one per additional 60 ft).

(Ref: FAA-STD-019G Section 5.2.2.3, Page 66).

Routing:

- Must follow a direct downward path, minimal bends, and no bends less than an

8-in radius.

- 6-ft clearance from signal/power lines or shielded in RGS conduit.

(Ref: FAA-STD-019G Section 4.3.5, Page 25).

- Class II down conductors are to be secured every 3’ and transition to a 4/0 AWG copper conductor not less than 18-in above finished grade.

- The 4/0 AWG copper conductor must be exothermically welded to the EES.

4. Bonding of Metallic Objects

- All metallic objects (e.g., HVAC, antenna masts, access doors, stairs, roof drains, handrails, exhaust stacks, and ladders) within 6-ft of the lightning protection system should be bonded with a class II conductor.

(Ref: Handbook 010A Section 2.2.6.1, Page 25).

5. Equalization Loop Location on Roof or Roof Parapet

- A continuous bonding loop is required within 24-in of the roof edge.

(Ref: FAA-STD-019G Section 5.2.2.2a, Page 65).

- ATCT tower shafts are to have an equalization loop installed at intervals no greater than every 60 ft measured from the roof equalization loop.

(Ref: FAA-STD-019G Section 5.2.2.2c, Page 65).

- Air terminals are to be bonded to the equalization loop and have two paths to ground.

- Cable holders that do not have mechanical support such as products with fold-over or break-away tabs shall not be used. (Ref: FAA-STD-019G Section 4.3.7.1).

6. Earth Electrode System (EES)

- All connections from class II down conductors are to transition to a 4/0 AWG before being exothermically welded to the EES.

- All ground rods are to be at least 1 foot below the finished grade level or 1 foot below the frost depth to suit climatic conditions.

(Ref: Handbook 010A Section 2.3.7.4, Page 65).

7. Material Requirements

- Cables: Class II copper or tinned copper; aluminum permitted only with aluminum/galvanized surfaces.

- Fittings: UL-96 listed and refer to Table 1 to prevent galvanic corrosion if dissimilar metals are being used.

- Exothermic welds are preferred over mechanical pressure bonds (Ref: FAA- STD-019G Sections 4.3.2, 4.3.7.2, Pages 24 and 29).

- At manned facilities, bonds above grade are required to be irreversible c-crimp or other hydraulically crimped terminations using a 12-ton minimum force applied with a tool using matching dies. With regards to the use of exothermic welds and its applications at manned facilities refer to the following section:

(Ref: FAA-STD-019G Sections 4.2.3.1 and 4.3.5.1).

8. Protective Guards and Conduit

- Down conductors must be shielded using 1-in Schedule 40 PVC or bonded metal guards.

- PVC is to extend 6-ft above the finished grade and 1-ft below the finished grade and be secured every 3-ft.

(Ref: FAA-STD-019G Section 4.3.7.3, Page 29).