Bare-hand, or potential working involves placing the worker in direct electrical contact with an energized overhead line. The worker might work alongside the lines, from a platform that is suspended from them, or may sit or stand directly on the line itself. In all cases, the worker’s body is maintained at the same voltage as the line. It is imperative that the worker maintain appropriate and adequate limits of approach to any part at a different potential.
The first procedures for barehand working were developed in 1960 by Harold L. Rorden, a high-voltage engineer for American Electric Power. Techniques were further refined following field and laboratory tests.
There are a number of ways in which the worker can access the live parts:
The worker can access from a specialist type of mobile elevating work platform (MEWP) termed an insulating aerial device (IAD) which has a boom of insulating material and which all conductive parts at the platform end are bonded together. There are other requirements for safe working such as gradient control devices, a means of preventing a vacuum in the hydraulic lines, etc.
The worker can stand on an insulating ladder which is maneuvered to the line by means of non-conductive rope.
The worker is lowered from a helicopter and transfers himself to the line.
The worker is brought alongside the wire in a hovering helicopter and works from that position.
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. 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.