In electrical engineering, live-line working, also known as hotline maintenance, is the maintenance of electrical equipment, often operating at high voltage, while the equipment is energised. Although this is more hazardous for personnel than working on electrical equipment with the power off, live-line maintenance techniques are used in the electric power distribution industry to avoid the disruption and high economic costs of having to turn off power to customers to perform essential periodic maintenance on transmission lines and other equipment.

The first techniques for live-line working were developed in the early years of the 20th century, and both equipment and work methods were later refined to deal with increasingly higher voltages. In the 1960s, methods were developed in the laboratory to enable field workers to come into direct contact with high voltage lines. Such methods can be applied to enable safe work at the highest transmission voltages.

As the lineman approaches the wire, an arc will form between them as the worker is charged. This arc can be debilitating, and the worker must immediately bond himself electrically to the line to prevent further arcing. A worker may use a conducting wand during the approach to first make the connection. Once on the line, the worker is safe from shock as both the lineman and the wire are at the same electric potential, and no current passes through his body. This is the same principle that allows birds to safely alight on power lines.

When the work is completed, the process is reversed to remove the worker safely from the wire. Barehand working provides the lineman with greater dexterity than the hot stick method, and may be the preferred option if conditions permit it. With this technique, insulator strings, conductor spacers and vibration dampers can be replaced, or lines spliced, without any loss of supply.

The strong electric field surrounding charged equipment is enough to drive a current of approximately 15 μA for each kV·m−1 through a human body.[5] To prevent this, hot-hand workers are usually required to wear a Faraday suit. This is a set of overalls made from or woven throughout with conducting fibers. The suit is in effect a wearable Faraday cage, which equalizes the potential over the body, and ensures there is no through-tissue current. Conducting gloves, even conducting socks, are also necessary, leaving only the face uncovered.

There is little practical upper voltage limit for hot-hand working, and it has been successfully performed at some of the highest transmission operating voltages in the world, such as the Russian 1150 kV system.

Helicopter
A lineman wearing a Faraday suit can work on live, high-power lines by being transported to the lines in a helicopter. The worker can perform maintenance sitting on an outrigger platform attached to the helicopter while the aircraft hovers next to the line. When approaching the line a long wand is touched to the line to equalize the potential of the aircraft to that of the line, then a breakaway bonding wire connected to the helicopter's frame is attached to the line during work. Alternatively the worker can transfer to the wires from the helicopter and crawl down the wires, then be picked up by the helicopter after the work is completed.