Depending on the system and intended use, a receptacle for grounding or an electrically conductive (metallic) hook is permanently attached to the upper end . With the earthing rod is in the context of installation or maintenance work on de-energized high voltage equipment a short circuit of a technically used electric conductor, such as an overhead line or catenary , produced by electrical accidents to be prevented by electrical voltages.
The grounding rod is a red or yellow rod made of glass fiber reinforced plastic (GRP) or other insulating materials. Depending on the intended use, the rod can be designed as a telescopic rod or can be assembled from several individual parts. It is easier to transport and can be stored in bags protected from the weather. By putting together individual elements, lengths of several meters can be achieved. The earthing rod is to be assembled to such a length that the system part to be earthed is reached and safety clearances are not exceeded.
At the upper end of the rod is the head, which is used to hold the earth . This head is usually designed so that the earthing rod can be removed when the earth or euk is installed. Systems that function according to the bayonet system or systems that initially fix the earth using spring force are common. This makes it possible to install several earths with just one earthing rod. The earth to be installed is selected according to the necessary terminal for the part of the system to be earthed (busbar, conductor cable, earthing point) and the required length and cross-section. The earth is first connected to the earth potential using a clamp, the other end of the earth is installed on the system part to be earthed using an earthing rod. The earthing rod can be removed with a strong jerk or a corresponding twisting movement with the bayonet system .
In the low and medium voltage range as well as in the railway, earthing rods are used that are permanently connected to the earthing cable. There is z. B. a V-shaped, conductive suspension device at the track at the top of the grounding rod. This hooks the rod to the electrical overhead line. From there, a copper grounding cable runs a little way inside the pole and emerges from the pole above a hand guard - coated with insulation. The grounding cable ends in two clamps that must be grounded before use . In the railway sector, the ends are attached to the rails in order to establish the earth fault.
The correct procedure for earthing with earthing rods is an adapted sequence as with the five safety rules :
- Activation of the overhead line or overhead line at the railway.
- Secure against being switched on again: This can be done with suitable blocking elements.
- Verify the absence of voltage on all poles: This can be done using an appropriate test rod and high- voltage indicator .
- Ground the grounding rod at the lower end using a clamp connection. (For railways: attach to the rail foot, in single-rail insulated sections on the earth rail)
- Earth and short-circuit. For earthing rods with hooks: The overhead line should be approached with the rear of the suspension device. This is to ensure, to the grounding rod that when an error occurs or existing charging led by the then resulting arc can not inadvertently impose on the line. Turn the earthing rod by 180 degrees and hang it in the cable using the suspension device. Tighten the grounding clamp on the conductor. If the track beneath the earthed contact line is to remain accessible for railways, then the earthing rod connected to the earthing clamp via a bayonet lock is released and the earth wire is then suspended profile-free. In this case, it is advisable to ground at a support point.
In railway operations ground rods are used to temporarily switched off sections of the overhead line - to keep energized - for example, in construction or loading work. This ensures that people are not endangered by any creep voltages that may occur or even by accidentally switching on the catenary. Electric traction vehicles , construction vehicles and train stations are usually equipped with earthing rods so that the contact line can be quickly earthed in the event of a fault .
Electrical energy networks
In the area of outdoor switchgears, substations and overhead lines , earthing rods are used to establish a safe and visible earthing connection when working in the area of the workplace. They also serve to avoid atmospheric charging due to the influence of disconnected and isolated overhead lines or overhead line sections during assembly .
- Günter Springer (editing): Electrical engineering. 18th edition 1989 Verlag - Europa - Lehrmittel ISBN 3-8085-3018-9
- Employer's liability insurance association information BGI / GUV-I 781 Safety instructions for work in the track area of railways , Chapter 4 Work in the vicinity of contact line systems (online on the BG Bau website)
- Description of the rail grounding on the website of the Nittendorf Volunteer Fire Brigade