The Federal Aviation Administration (FAA) is the national aviation authority of the United States, with powers to regulate all aspects of American civil aviation. These include the construction and operation of airports, the management of air traffic, the certification of personnel and aircraft, and the protection of US assets during the launch or reentry of commercial space vehicles.
The FAA's roles include:
- Regulating U.S. commercial space transportation.
- Regulating air navigation facilities' geometric and flight inspection standards.
- Encouraging and developing civil aeronautics, including new aviation technology.
- Issuing, suspending, or revoking pilot certificates.
- Regulating civil aviation to promote safety, especially through local offices called Flight Standards District Offices.
- Developing and operating a system of air traffic control and navigation for both civil and military aircraft.
- Researching and developing the National Airspace System and civil aeronautics.
- Developing and carrying out programs to control aircraft noise and other environmental effects of civil aviation.
If you have some questions, you can reference to http://www.faa.gov.
We excerpt some provisions from FAA AC 70/7460-1 L - Obstruction Marking and Lighting as following:
2.7.4
Spherical Markers.
It is also recommended that high-visibility aviation orange spherical marker (or cable) balls be attached to the guy wires. Spherical markers should be installed and displayed in accordance to Chapter 3, paragraph 3.5. The FAA, however, recognizes various weather conditions and manufacturing placement standards may affect the placement and use of high-visibility sleeves and/or spherical markers. Thus, some flexibility is allowed when determining sleeve length and marker placement on METs.
3.5
Unlighted Markers.
Unlighted markers are used to identify structures and to make them more conspicuous when it is impractical to paint them. Unlighted markers may also be used in addition to aviation orange and white paint when additional conspicuity is necessary for aviation safety. Unlighted markers should be displayed in conspicuous positions on or adjacent to the structures so as to retain the general definition of the structure. They should be recognizable in clear, daytime visibility from a distance of at least 4,000 feet (1,219 m) and in all directions from which aircraft are likely to approach. Unlighted markers should be distinctively shaped, i.e., spherical or cylindrical, so that they are not mistaken for items that are used to convey other information. They should be replaced when faded or otherwise deteriorated.
3.5.1
Spherical Markers.
Spherical markers are used to identify overhead wires and catenary transmission lines that are less than 69 kV. Markers may be of another shape, i.e., cylindrical, provided the projected area of such markers is not less than that presented by a spherical marker.
- Size and Color.
The diameter of the markers used on extensive catenary wires (catenary wires that cross canyons, lakes, rivers, etc.) should not be less than 36 inches (91 cm). Smaller 20-inch (51-cm) spheres are permitted on less extensive catenary wires or on power lines below 50 feet (15 m) AGL and within 1,500 feet (458 m) of an airport runway end. Each marker should be a solid color, specifically aviation orange, white, or yellow. - Installations.
- Spacing. Unlighted markers should be spaced equally along the wire at approximately 200-foot (61-m) intervals, or fraction thereof. There should be less space between markers in critical areas near runway ends [i.e., 30 feet to 50 feet (10 m to 15 m)]. They should be displayed on the highest wire or by another means at the same height as the highest wire. Where there is more than one wire at the highest point, the markers may be installed alternately along each wire if the distance between adjacent markers meets the spacing standard of 200 feet or less. This method distributes the weight and wind-loading factors. (See Figure A-1 in Appendix A.)
- Pattern. An alternating color scheme provides the most conspicuity against all backgrounds. Unlighted markers should be installed by alternating solid-colored markers of aviation orange, white, and yellow. Normally, an orange marker is placed at each end of a line and the spacing is adjusted [not to exceed 200 feet (61 m)] to accommodate the rest of the markers. When less than four markers are used, they should all be aviation orange. (See Figure A-1 in Appendix A.)
- Wire Sag. Wire Sag, or droop, will occur due to temperature, wire weight, wind, etc. Twenty-five (25) feet (7.62 m) is the maximum allowable distance between the highest wire installed with marker balls and the highest wire without marker balls, and shall not violate the sag requirements of the transmission line design.
- Adjacent Lines. Catenary crossings with multiple transmission lines require appropriate markers when the adjacent catenary structure's outside lines are greater than 200 feet (61 m) away from the center of the primary structure. (See Figure A-2 in Appendix A.) If the outside lines of the adjacent catenary structure are within 200 feet (61 m) or less from the center of the primary structure, markers are not required on the adjacent lines. (See Figure A-3 in Appendix A.)
Catenary unlighted markers
Required for transmission lines less than 69 kV
Recognizable from a minimum distance of 4,000 ft (1219 m)
Wire markers may be staggered over the catenary to enable better wind load distribution

Extensive catenary wires: min 36-inch- (91-cm-) diameter markers; less extensive catenary wires: 20-inch- (51-cm) or 12-inch- (30.48-cm-) diameter markers.
Evenly spaced along the wire at approximately 200-ft (61-m) intervals.
Lighted markers should be a solid color, such as aviation orange, white or yellow.
Lighted markers should be alternate aviation orange, white, yellow with aviation orange markers position at each end.
If less than four lighted markers are on the line, all markers should be aviation orange.
Figure A-1. Catenary Unlighted markers
Catenary markers - line spacing
Adjacent lines greater than 200 ft (61 m) away
Required for transmission lines 69 kV or greater
Recognizable from a minimum distance of 4,000 ft (1,219 m)
Wire markers may be staggered over the catenary to enable better wind load distribution

Extensive catenary wires: min 36-inch- (91-cm-) diameter markers; less extensive catenary wires: 20-inch- (51-cm) or 12-inch- (30.48-cm-) diameter markers.
Evenly spaced along the wire at approximately 200-ft (61-m) intervals.
Unlighted markers should alternate aviation orange, white, yellow, with aviation orange markers positioned at each end.
If less than four markers (lighted or unlighted) are on the line, all markers should be aviation orange.
Catenary crossings with multiple transmission lines require additional line markers when the outside lines on the adjacent structure are more than 200-ft (61-m) from the center of the primary structure.
Figure A-2. Catenary markers - line spacing (Adjacent lines greater than 200 ft (61 m) away)
Catenary markers - line spacing
Adjacent lines with in 200 ft (61 m) or less
Required for transmission lines less than 69 kV
Recognizable from a minimum distance of 4,000 ft (1,219 m)
Wire markers may be staggered over the catenary to enable better wind load distribution

Extensive catenary wires: min 36-inch- (91-cm-) diameter markers; less extensive catenary wires: 20-inch- (51-cm) or 12-inch- (30.48-cm-) diameter markers.
Evenly spaced along the wire at approximately 200-ft (61-m) intervals.
Unlighted markers should alternate aviation orange, white, red, with aviation orange markers positioned at each end.
If less than four markers (lighted or unlighted) are on the line, all markers should be aviation orange.
Catenary crossings with multiple transmission lines require additional line markers when the outside lines on the adjacent structure are more than 200-ft (61-m) from the center of the primary structure.
Figure A3. Catenary markers - line spacing (Adjacent lines within 200 ft (61 m) or less)
More information please browse the full version of the PDF of FAA AC 70/7460-1L, obstruction Marking and Lighting.