Live-line working

When working on live ( FRoM ) the work is referred to on live electrical equipment with operating voltages above 120 V DC and 50 V AC voltage. Working under tension requires specially trained staff ( in Germany FRoM - trained electricians, Switzerland specially trained electricians ), specific work equipment ( insulating tool ) and in some countries special organizational measures ( in Switzerland: Couple ). FRoM divided into three areas:

Is practiced live working for selected maintenance work mainly in the field of low-voltage networks and in the range of medium voltage networks. Certain activities which do not alter the system electrically, such as cleaning work is carried out, generally under tension. In some countries, working under stress in high and extra high voltage range carried. In this case, due to the high voltages exclusively insulating platforms or aircraft arrive under high voltage overhead lines as helicopter for service work before.

When working in the unstressed state, the 5 safety rules must be observed.


One advantage of working under stress is to avoid interruptions. This justifies, in many cases, especially when no spare capacity exists, the elaborate precautions against the shutdown. Work on energized parts is carried out for the purpose of cleaning by using special insulating executed purification equipment such as special brushes on insulating rods or industrial vacuum cleaners, which are used in compliance with the safety distances.

For certain work, a special protective equipment consisting of insulating clothing ( gloves, shoes ) or appropriate face protection ( visor) is necessary. Working on high voltage lines from 50 kV are generally possible only by insulating platforms. In the field maximum voltage if no external field shielding is possible to wear special conductive full body suits with incorporated metallic fibers. These are derived according to the capacitive currents deriving from the environment and according to the peak discharge ( corona discharge). Despite isolation from contact of the conductors of helicopters or from the insulating platform is a potential equalization necessary. The cause are to the environment capacitive charging currents, similar to occur in aircraft according to atmospheric electricity.


Common and often done in the low voltage range in many countries, including:

  • Exchange of HRC fuses
  • Installation works in the supply line from the house connection box, for example into the house
  • Installation of branch joints in underground cables

In the area of ​​low and medium voltage networks, including:

  • Making the work situation for cleaning and alterations to standing near energized parts of the plant ( covering, fence off )
  • Maintenance and cleaning of transformer stations and substations
  • Maintenance of air-insulated switchgear MS and refilling Nasskabelendverschlüssen
  • Switch maintenance and testing of protective functions such as HRC fuse tripping and Buchholz protection ( industry) using a mobile bridging unit ( MÜE )

In the field of high voltage work is carried out under tension only in exceptional cases and are usually limited to countries like the U.S., where due to lack of spare lines no maintenance even shutdown of the system is possible:

  • Exchange of spacers of bundle conductors in overhead lines, with fitters of helicopters be lowered or raised by means of insulating cables and devices on the mast on the conductors.
  • Installation of cable branches in overhead lines of isolated platforms

Maintenance of in-service transmission towers as broadcasters are also partly to the work under tension. However, the radiations of the antennas and the limits of the power density must be respected and supported special protective suits when needed against microwave radiation here with safety distances in addition.

Rules in Switzerland

Only electricians with federal certificate or persons with equivalent qualification may carry out work on installations that are under tension. You must be for such work in accordance with the latest findings specially trained and equipped. There are always use two people, one of these should be identified as responsible. (SR 734.22, Article 22, para 2-3)