Suggest checking your state laws. For example, Alaska is pretty clear:
HV lines is anything over 750V
Overhead lines means above ground, energized, and not in "Iron Pipe" - pretty broad definition.
Have to stay 10 feet away or:
The operator (of the HV lines) is require to de-energize, or put up barriers. The outfit requesting the protective barriers is required to pay for the operator's work.
Just not putting up the required sign is up to $500 and up to 6 months in jail - per day
And if they screw up and have actual contact, the violator is liable for all the damage and all the liability of the operator/owner.
The following is the state law (reference):
www.labor.alaska.gov/lss/forms/electrical-stats-regs.pdf
Sec. 18.60.670. Prohibition against placement of equipment near electrical power lines and conductors.
A person individually or through an agent or employee may not
(1) place any type of tool, equipment, machinery, or material that is capable of lateral, vertical, or swinging motion, within 10 feet of a high voltage overhead electrical line or conductor;
(2) store, operate, erect, maintain, move, or transport tools, machinery, equipment, supplies, materials, apparatus, buildings, or other structures within 10 feet of a high voltage overhead electrical line or conductor.
Sec. 18.60.680. Placement of barriers for temporary work.
Before a person is going to temporarily engage in work or other activity in closer proximity to a high voltage line or conductor than is permitted by AS 18.60.670, the person shall immediately notify the operator or owner of the high voltage line or conductor of the work to be performed and make appropriate arrangements, with payment satisfactory to the operator, for the installation of temporary mechanical barriers, temporary deenergization and grounding of the conductors, or a temporary raising of the conductors. Costs incurred by an operator or owner of a high voltage line or conductor in providing barriers, deenergization, and grounding as specified in this section shall be paid by the person engaging in the work that requires these protective measures.
Sec. 18.60.695. Definitions.
In AS 18.60.670 - 18.60.695,
(1) "high voltage" means a voltage in excess of 750 volts between conductors or between any single conductor and the ground;
(2) "overhead lines or overhead conductors" means all bare or insulated electrical conductors installed aboveground except those that are de-energized and grounded or enclosed in iron pipe or other metal covering of equal strength.
And there has to be a Sign:
Sec. 18.60.675. Posting of warning sign before operation.
A person individually or through an agent or employee may not operate a crane, derrick, power shovel, drilling rig, hoisting equipment, or similar apparatus, any part of which is capable of vertical, lateral, or swinging motion, unless the operator or the operator's employer posts and maintains, in plain view of the operator, a durable warning sign legible at 12 feet that reads as follows: "It is unlawful to operate this equipment within 10 feet of high voltage lines."
And they even put a criminal penalty, civil liability on it:
Sec. 18.60.685. Criminal penalty; civil liability for damages.
(a) A person who violates AS 18.60.670 - 18.60.695 is guilty of a misdemeanor, and upon conviction is punishable by a fine of not more than $500, or by imprisonment for not more than six months, or by both.
(b) If a violation of AS 18.60.670 - 18.60.695 results in physical or electrical contact with an overhead high voltage line or conductor, the violator is liable to the owner or operator of the high voltage line or conductor for all damage to the facilities and for all liability incurred by the owner or operator as a result of the unlawful activities.
(c) Each day on which a person fails to post or maintain a sign as required by AS 18.60.675 constitutes a separate and additional violation.
