Equipotential bonding in a house is a central part of its electrical equipment. It serves to protect the house against the spread of electrical damage in the event of overvoltages, short circuits and lightning strikes. The measure commonly referred to as “grounding” is now planned and carried out as standard when building a house. Due to previously applicable laws, however, numerous houses dating back to the 1960s were equipped with insufficient or no equipotential bonding. In this case, it must be retrofitted today.
Who can install earthing?
This should be said in advance: All work related to the electrical connection to the house power supply and lightning protection is reserved exclusively for certified specialist companies. Any self-tests in this area are prohibited by law and will be punished with a fine. Apart from that, fire protection insurance usually refuses a contract if there is no expert opinion on the existing electrical protection of a house. However, since fire protection insurance is also mandatory for a homeowner, there is a risk of a fine in this area as well. All in all, you save yourself a lot of trouble by leaving this task to a professional service provider.
With a lot of goodwill on the part of the electrician, it may be possible to carry out the individual work steps yourself and have them approved. However, the electrician has to come to the construction site after each work step and give his OK. This can be useful when the electrician is very busy and cannot free up time for small tasks like this. However, since the electricians not only earn their money with this work, but also take responsibility for it with their signature, it is very rarely possible to carry out their own work in this case.
task of grounding
Grounding or equipotential bonding has the task of deriving overvoltages into the ground. For this purpose, the residual current device is connected to the potential equalization.
This can then be connected to the lightning arrester if the design is appropriate. The installation of the foundation earth electrode has been mandatory for every new building since 2007. Compromises were also previously possible in that sewer pipes or other earth-bound metal pipes could be used as grounding. However, since plastic pipes are increasingly being used for this purpose and the metal pipes have proven to be very susceptible to rust due to the electrical stress, the requirements for earthing are particularly strict today. The procedure, execution and permitted personnel are regulated in detail in DIN 18014.
The ring earth
The most common earth electrode in new buildings is the ring earth electrode integrated in the strip foundation or floor slab. It consists of a long sheet of hot-dip galvanized steel. It is laid in the concrete on the outside in a ring around the entire building and laid inwards via a connection cable with a wide cross-section. The ring earth electrode is the cheapest to lay at the moment of building the foundation: The wide metal sheet is simply anchored together with the reinforcement in the casing and concreted over. If the concrete cover is sufficient, galvanized sheet steel is perfectly adequate. A meter of grounding tape costs around 1.30 and is installed at virtually no cost when the reinforcement is brought in.
Ringerders can also be retrofitted. To do this, a 0.5 meter to 1 meter deep ditch is dug around the house. In this case, however, galvanized sheet metal does not have to be used if it should not or cannot be concreted in. Although the standard grounding strap has a 70 micron layer of zinc as a minimum for corrosion protection, this is not sufficient for contact with the permanently damp soil. The tape would rust. In addition, electrical stress is also highly conducive to corrosion. That’s why only the expensive V4A comes into question for a subsequently installed ring earth. This stainless steel is extremely corrosion resistant, making it a permanent solution. However, this has its price: At just under 9 euros per meter, the ring anchor made of stainless steel is almost ten times more expensive than galvanized sheet steel. Added to this are the costs for installation and acceptance by a qualified electrician.
In a house with an edge length of 10 meters and a ring earther of 0.03 meters, there is an area of approx. 3 m² effective contact surface to the ground, from which the current to be discharged is radiated. This large area is the default for any other ground electrode shape.
The deep earther
A deep earth rod is a popular form of ground anchor if the structural conditions do not allow the subsequent installation of a ground anchor. It consists of a long rod, also made of V4A stainless steel. He is rammed at least nine meters deep into the ground. It must be ensured that the earth rod cannot cause any damage to other installations such as power lines or sewage pipes. A prior ground survey is therefore required in order to determine the ideal point of impact for the earth rod.
A ground rod costs about 20 euros per 1.5 meter rod. The rods can be plugged into each other and are permanently connected to each other when they are rammed into place. The ramming of the earth rod is a matter for a professional operation with the appropriate tools. A powerful hammer drill is sufficient for smaller tasks. However, a piling device is required for larger foundation earth electrodes. Setting a ground anchor in a simple family home costs between 200 and 500 euros.
Basically, the only thing that matters with an earth electrode is that there is a sufficient contact surface with the earth. Therefore, instead of a deep earth rod or a ring anchor, there are also:
- Straight Earths
- plate earth or
- Mesh grounders to consider.
Straight earth electrodes are horizontally laid earth straps, cables or rods and are inserted parallel to earth current cables. They are very inexpensive because they cause practically no installation costs, but they must be planned for when building the house.
In order to get the required contact surface to the ground, the straight earth electrodes can also be distributed in a radial or cross-shaped manner. It is only important that all rays meet at a common point and have electrical contact with each other there. A maximum of six individual beams are permitted, which are laid at an angle of 60° to one another.
If you connect the rays of a radiation earther with each other, you get a field with six meshes. This type of earth is called a mesh earth. For the avoidance of doubt, a wire mesh fence is definitely not a buried chain link fence! Also for the mesh earther, only permitted material can be used that has a sufficiently large cross-section.
Finally, earth plates are also permitted as a ground connection of a house. They can be buried horizontally at a depth of 0.5 – 1 meter and driven back vertically into the ground.
However, their use is reserved for telecommunications systems. Earthing plates are rarely used in house construction.
Procedure of a foundation grounding
If you buy a house from before 2007, you should definitely have the grounding and equipotential bonding checked. The costs for this check are very moderate. From the process, the electrician only measures the resistance at the ground. This is already sufficient to be able to make a valid statement about the equipotential bonding. It can also happen that a maintenance technician from the cable connection detects a missing or insufficient equipotential bonding. This requires grounding with a sufficient cross-section to be able to connect the amplifier from the cable connection. If this is missing, you should not try to install your own separate equipotential bonding. The detection of missing or insufficient potential equalization during the installation of the cable connection should definitely be regarded as a warning signal.
The expert opinion is now followed by advice. Which equipotential bonding is necessary and which version is possible? The specialist electrician will advise you comprehensively on the cross-section, process and costs of equipotential bonding. If he cannot do it himself, the electrician will certainly be able to name a company that is well versed in the process of installing the equipotential bonding. Most often this is a construction company. They also have the right equipment in the form of excavators, rams or other equipment, with which the costs for installing the potential equalization are kept within limits.
The next step in the process of retrofitting earthing is the soil survey. In order to keep the costs under control, it is worth visiting the land registry office. All supply and discharge lines around the property should be marked there. The local specialists can also advise on the ideal point for installing the grounding.
With the ground report, the next step is to go from the grounding process back to the construction company. When it is clear at which point or from which area the potential equalization can be installed, the construction work can begin. In any case, real construction work can only be said to be when the trench is being dug. If you dare to do it yourself, you can also lend a hand at this point: A spade-wide trench with a depth of one meter is completely sufficient to place a foundation earth electrode with any cross-section in the ground. This process is additionally accelerated with a mini excavator. The earthworks are not yet part of the process for installing equipotential bonding. So you can safely do it yourself. The cost of a mini excavator is approx.
If you want to lay the grounding strap yourself with the right gauge, you must not fill in the trench until the electrician has given you his blessing. He will check the cross-section again to ensure that the potential equalization will also serve its purpose. A cross-section that is too small would initially burn through the cable with the next lightning strike and set the house on fire with the second lightning strike. Therefore, no costs may be saved on the cross-section of the grounding cable, otherwise there is a risk of serious consequential damage!
Finally, as the last point in the course of the subsequent installation of the grounding, the cable must be connected to the house electrical system. Now, this is definitely a task that cannot be done without the help of an electrician. He will check the resistance to the ground wire again and thus release the subsequent grounding. The cost of this measure is between 100 and 500 euros. In any case, this maximum level of security should be worth it.
Tips for speed readers
- Don’t want to reduce costs by cutting cross-sections
- Earthworks can reduce costs
- Have all work steps approved by a specialist electrician