Work on live systems in the low-voltage area up to 1,000 volts has meanwhile become an inherent part of work in the energy supply sector. These jobs are undertaken to ensure uninterrupted electrical power supply. Both power utilities as well as industrial companies carry out work on live systems. The fundamental preconditions for carrying out these kinds of jobs are, on the one hand, the professional qualification and training of the staff involved and, on the other hand, the use of special tools and protective clothing.
Work on live systems may only be carried out by professionally qualified staff with special tools and protective clothing. This is immediately recognisable through the bell symbol or the double triangle.
In the sector of public energy supply, it is mainly cable fitting work that is carried out under voltage. This includes the assembly of end sleeves, connecting sleeves, transitions sleeves and branch tee couplings (see Figure 1). An end sleeve ensures a secure cable end connection that is both waterproof as well as safe in that any sharp edges can no longer do any harm. The connecting sleeve is used whenever two cables out of the same material need to be joined. By contrast, the transition sleeve is applied when two cables out of different materials have to be connected. The branching cable joint allows three cables to be connected with one another. Moreover, assembly work on transmission lines, street lighting systems and metre devices can also be carried out under voltage. Work on live systems in industrial switching systems is mainly carried out on terminal strips and extension elements as well as when cleaning work needs to be done.
Figure 1 - End sleeve, connecting sleeve and branching cable joints (from left to right):
Depending on the respective application and type of cable, tap connectors are generally used as a connecting material for branch tee couplings and screw connectors or compression joints for transition sleeves.
The compact tap connector (see Figure 2) allows all phases of a cable to be branched off. To enable this, it is simply positioned on the main conductor. Previously, however, the outer sheath insulation needs to be properly removed with due attention paid to the provisions applying to work on live systems. Insulation-penetrating teeth, cuts or screws ensure contact with the main conductors. A contact screw connects the tap conductor with the respective main conductors.
By contrast to when tap connectors are used, the main conductors need to be severed when screw connectors or compression joints (see Figure 3) are deployed. Moreover, the entire insulation has to be removed at the contact points for the connecting screws. There are various types of screw connectors. They normally have two or four screws depending on the type of cable and its diameter. In the case of so-called screw connectors with breakaway bolts, the bolt head breaks off at a specific torque during tightening. This serves as an indicator for the fitter that the connector has been tightened to the right degree of torque.
Figure 2 - Compact tap connectors by Klauke:
Figure 3 - Screw connectors and compression joints by Klauke:
Similar to the connecting materials, there are also differences between the sleeves. Generally-speaking, a distinction is made between cast resin sleeves and heat-shrink sleeves. In the case of the heat-shrink sleeves (see Figure 4), an “inner sleeve” – similar to a heat-shrink tube – is slid over every connection of the conductors. It insulates the contact points of the cable connections against each other. The “outer sleeve” is then pulled over this. This is likewise a kind of heat-shrink tube. It shrinks when correspondingly heated, for instance with the help of a gas burner. The outer sleeve protects the joint against mechanical influences and water and offers outstanding electrical insulation values.
The so-called cast resin sleeves are mainly used for branching cable joints (see Figure 5). In this respect, a plastic housing is attached around the finished contact. The cast resin comes in a double-cell bag which may only be mixed together by the fitter. Subsequently, the fitter fills the material into the housing through the envisaged opening. As soon as the mass has hardened out, it protects the connection against dirt and moisture.
Figure 4 - GT GmbH, pre-assembled cable connection with screw connector and heat-shrink sleeves:
Figure 5 - Pre-assembled branching cable joint with clamping ring:
To be able to work on live systems, the fitter needs to be specially trained for this task. The basic preconditions for taking part in a so-called “Work on Live Systems Training” are to be a qualified electrician, to have a first-aid training certificate and to be physically fit for the job – as proven in a G 25 medical examination for instance.
An exception is defined in Section 3.2 (Training) of the BGR A3 (employers’ liability insurance association [BG] rules on safety and health at work). Here it is stated: “In addition, persons that have not had an electro-technical vocational training may be suitable to take part insofar as they have acquired sufficient expertise and experience through their many years of work in this sector to be able to assess the work assigned and recognise any possible hazards.” Please consult “Gesetze/Vorschriften BGR A3, 3.2.1 Voraussetzungen” for more detailed information on the qualification preconditions.
The basic training both in the energy supply as well as in the industrial sector is split into a theoretical and a practical part. The professional content in the theoretical basic training comprises e.g. fundamentals, laws and requirements in the area or industrial safety, operational management, legal consequences, organisational measures and the use of personal protective clothing. The latter includes, in particular, the selection, care and inspection of the personal protective clothing as well as the tools and auxiliary components required to do the job.
In the practical part of the qualification, the different types or work on live systems are trained i.e. those elements that the participants will need later in their everyday work.
More details on the theoretical and practical training modules can be found in the BGR A3.
The selection of the right tools and materials depends on the work to be carried out. However, as a matter of principle, only tools and auxiliary components should be used that are designed and approved for work on live systems. A marking on the tool as well as a verification as per EN/IEC 60900 (VDE 0682 Part 201) is mandatory. The certification as per EN/IEC 60900 is based on a cold impact test (at -25˚C); a test of the adherence of the insulating material (with 500 N) as well as an individual voltage test in a water bath (V/AC 10,000). The marking may take the form of a bell-shaped insulator and/or a double triangle. The marking often stands together with other symbols e.g. the VDE sign or an indication of the voltage up to 1,000 V (see Figures 7, 8 and 9)
Some pliers also have an enhanced hand protection feature against spark discharge (see Figure 10). However, on account of the regular use and a natural aging process, the tools and auxiliary components are subject to wear and tear. Damage to tools with a 2-colour dipped insulation (Figures 9 + 10) is immediately evident since the substrate layer is in a different colour (mostly yellow) to the upper one (mostly orange or red). It is therefore important to check these tools and auxiliary components before use for any external signs of damage or deficiencies and to exchange them if need be.
Figure 7 - The bell-shaped symbol and VDE sign on the rubber covering cloths by Klauke document the approval:
Figure 8 - The double triangle on the Klauke safety gloves ensures safe working on live systems:
Figure 9 - The fully-insulated tool set from the Klauke range offers the 1,000 V needed for work on live systems: the 2-colour dipped insulation can be easily recognised – orange outside, yellow inside.
Figure 10 - Klauke pliers with enhanced hand protection against spark discharge:
Be careful, act responsibly, work safely and securely. Nothing is more important than safety when working on live systems! A qualified training is just as essential as it is to work with approved, safety tools. You will always be on the safe side with the certified VDE tools by Klauke: after all, these tools have been manufactured and tested – without exception –in accordance with the latest guidelines for safety standards pursuant to EN/IEC 60900 (VDE 0682 Part 201). They are thus approved for work on alternating current up to 1,000 V and direct current up to 1,500 V.
Klauke also offers safe solutions for the medium and high voltage ranges such as the BG-approved safety cutters to sever live cables should anything have gone wrong (see Figure 11).
Figure 11 - ASSG - BG-approved safety cutter from Klauke: