Hello,
Unfortunately, I am not an expert and have never dealt with this before.
Aunt Google could have been helpful - as usual
Equipotential bonding means measures to reduce or eliminate potential differences, electrical voltage differences between conductive pipe systems such as water, gas, or heating pipes, or between pipe systems and the protective conductor. For this, the conductive pipe systems are connected to each other by a so-called equipotential bonding conductor.
Such equipotential bonding is required for every newly installed electrical consumer system and according to DIN VDE 100, part 410 ff, a distinction must be made between the main equipotential bonding and an additional, local equipotential bonding.
The building's technical equipment consists, in addition to the electrical installation, of more or less extensive piping systems for the heating system, gas and water supply, which together form an extensive network of conductive systems that extend throughout the entire building. These pipe systems are partially interconnected but often separated. Therefore, faults or defects in one piping system can adversely affect another system. If, for example, an insulation fault occurs in the electrical system such that the metal pipe comes into contact with a live phase, a dangerous touch voltage arises. This is schematically shown in Figure 1, where it is clear that a touch voltage occurs between pipe system 1 and pipe system 2, which can be bridged by a person. To largely prevent this dangerous condition, it is required to connect all metal systems conductively to each other. Then no voltage differences, no potential differences as the experts say, and thus no dangerous touch voltages can occur. This is called "equipotential bonding," and the conductor that connects the system parts with each other is called the "equipotential bonding conductor."
The DIN VDE regulations for low-voltage electrical installation require equipotential bonding at every house connection or main distribution board. This is why it is called the main equipotential bonding, and all metallic pipe systems of the building, the main protective conductor of the electrical network, the main earthing conductor, as well as all other possibly existing grounding and piping systems including antenna, telephone, or lightning protection systems must be connected together. All these conductors are collected and connected via the main equipotential bonding conductor at the main equipotential bonding busbar. This is connected via a terminal to the foundation earth electrode. Such a foundation earth electrode is mandatory because plastic pipes are often used for water networks and therefore cannot be used as an earth electrode. However, it is not necessary to provide every piping system with its own equipotential bonding conductor. Several systems can also be interconnected and connected via a common main equipotential bonding conductor. Main equipotential bonding conductors may be continuously marked green-yellow like protective conductors. However, this is not mandatory, so the conductors can also be bare or installed in any other color. At the connection points, however, a permanent green-yellow marking must be present. This does not apply to special electrical installations, such as those used medically - here continuous green-yellow marking is required. The dimensioning of the main equipotential bonding conductor is determined by the cross-section of the main protective conductor of a system; it must be at least half the cross-section of the largest protective conductor of the system. The minimum cross-section, however, is 6 mm2 Cu, and the possible upper limit is 25 mm2 Cu or equivalent conductor - these details are summarized in Table 1. The largest protective conductor of the system in this sense is the protective conductor leaving the main distribution board with the largest cross-section. Metal piping can be included in the equipotential bonding, e.g., over partial lengths, if they meet the requirements for equipotential bonding conductors. Here, care must be taken – for example, with screwed water pipes – that the transition resistance of the screw connections is not too high. However, no clear resistance value is specified, so the assessment is left to the experience and discretion of the installer. If necessary, one can orient oneself on the resistance of an equivalent copper conductor. However, it must be known that
internal gas pipes must not be used as equipotential bonding conductors. The reason is that if a fault current occurs, heat development can arise at the resistance-causing connections due to the current flow, which can lead to leaks or worse. The gas pipe itself must naturally be included in the main equipotential bonding.
In areas of special hazard due to environmental conditions (e.g., moisture), an additional, local equipotential bonding is required. This supplements the main equipotential bonding and prevents the occurrence of dangerous touch voltages. This is required, among other things, for rooms with bathtubs or showers – specifically for areas 1, 2, and 3 – as well as for covered swimming pools. Metallic parts such as pipes, drain connections on bathtubs and shower tubs must be connected by an equipotential bonding conductor – with a minimum cross-section of 4 mm2 Cu – and connected to the protective conductor. Galvanized steel strips of at least 20 mm x 2.5 mm are also permitted; however, in practice, copper conductors are preferred for installation reasons.
The connection to the protective conductor can be made at a central point in the electrical system, such as the circuit distributor, the main equipotential bonding busbar, or even at the water consumption pipe if it is conductively connected throughout to the main equipotential bonding. In medically used rooms, an additional, special equipotential bonding must also be carried out and where uncontrolled stray or compensation currents could cause an explosion hazard. The additional equipotential bonding must also be executed if there are no electrical installations in the respective rooms. The reason is that dangerous touch voltages could be introduced into these rooms via conductive pipe systems.
After installation, the effectiveness of the equipotential bonding must be checked before commissioning the electrical system. This is done by initially inspecting at the main equipotential bonding whether all main equipotential bonding conductors, protective conductors, earth electrodes, metallic pipes, and building constructions are connected conductively as required to the equipotential bonding busbar. All parts of the equipotential bonding must be protected against damage, and all connections must provide good and lasting contact. The same applies to the additional equipotential bonding, and it must be verified whether all simultaneously touchable metallic parts, protective conductor connections, and other conductive bodies are interconnected.
Furthermore, the continuity resistance of the conducting connections must be measured. How this is done is shown in Figure 5, where the resistance between the equipotential bonding busbar and the end of the pipe systems included in the equipotential bonding is measured. The equipotential bonding is considered effective if a resistance of no more than 3 Ω (ohms) is measured at a test current of at least 5 A (amperes). For safety reasons, a lower value, e.g., 1 Ω, should be aimed for in practice. The measurement is easier if a potential bonding tester is used, as offered by industry.
Rhenish regards