Safe Clearances

State and federal safety standards state the minimum safe working clearance from any overhead line is 10 feet. Greater clearances are required for overhead lines operating at voltages exceeding 50,000 volts to ground.

Diggers Hotline operators ask whether the equipment being used can extend to more than 14 feet above ground. If the answer to this question is "yes," the operator will ask if this equipment will be used within 25 feet of any overhead lines. If the answer to both questions is "yes," members with overhead lines that require working clearances greater than 10 feet will call or arrange to meet regarding safe working clearances from their overhead lines.

From OSHA Construction Safety Standard 1926.451 paragraph (f)(6)

INSULATED LINES
Voltage Minimum distance Alternatives
Less than 300 volts 3 feet (0.9 m)  
300 volts to 50 kV 10 feet (3.1 m)  
More than 50 kV 10 feet (3.1 m) plus 0.4 inches (1.0 cm) for each 1 kV over 50 kV 2 times the length of the line insulator, but never less than 10 feet (3.1 m)
UNINSULATED LINES
Voltage Minimum distance Alternatives
Less than 50 kV 10 feet (3.1 m)  
More than 50 kV 10 feet (3.1 m) plus 0.4 inches (1.0 cm) for each 1 kV over 50 kV 2 times the length of the line insulator, but never less than 10 feet (3.1 m)

Exception to paragraph (b)(6)

Scaffolds and materials may be closer to power lines than specified above where such clearance is necessary for performance of work, and only after the utility company, or electrical system operator, has been notified of the need to work closer and the utility company, or electrical system operator, has de-energized the lines, relocated the lines, or installed protective coverings to prevent accidental contact with the lines.

From OSHA Construction Safety Standard 1926.550 paragraph (a)(15)

1926.550(a)(15)

Except where electrical distribution and transmission lines have been de-energized and visibly grounded at point of work or where insulating barriers, not a part of or an attachment to the equipment or machinery, have been erected to prevent physical contact with the lines, equipment or machines shall be operated proximate to power lines only in accordance with the following:

1926.550(a)(15)(i)

For lines rated 50 kV or below, minimum clearance between the lines and any part of the crane or load shall be 10 feet;

1926.550(a)(15)(ii)

For lines rated over 50 kV, minimum clearance between the lines and any part of the crane or load shall be 10 feet plus 0.4 inch for each 1 kV over 50 kV, or twice the length of the line insulator, but never less than 10 feet;

1926.550(a)(15)(iii)

In transit with no load and boom lowered, the equipment clearance shall be a minimum of 4 feet for voltages less than 50 kV, and 10 feet for voltages over 50 kV, up to and including 345 kV and 16 feet for voltages up to and including 750 kV;

1926.550(a)(15)(iv)

A person shall be designated to observe clearance of the equipment and give timely warning for all operations where it is difficult for the operator to maintain the desired clearance by visual means;

Cage-type boom guards, insulating links, or proximity warning devices may be used on cranes, but the use of such devices shall not alter the requirements of any other regulation of this part even if such device is required by law or regulation;

1926.550(a)(15)(vi)

Any overhead wire shall be considered to be an energized line unless and until the person owning such line or the electrical utility authorities indicate that it is not an energized line and it has been visibly grounded;

1926.550(a)(15)(vii)

Prior to work near transmitter towers where an electrical charge can be induced in the equipment or materials being handled, the transmitter shall be de-energized or tests shall be made to determine if electrical charge is induced on the crane. The following precautions shall be taken when necessary to dissipate induced voltages:

1926.550(a)(15)(vii)(a)

The equipment shall be provided with an electrical ground directly to the upper rotating structure supporting the boom; and

1926.550(a)(15)(vii)(b)

Ground jumper cables shall be attached to materials being handled by boom equipment when electrical charge is induced while working near energized transmitters. Crews shall be provided with nonconductive poles having large alligator clips or other similar protection to attach the ground cable to the load.

1926.550(a)(15)(vii)(c)

Combustible and flammable materials shall be removed from the immediate area prior to operations.