Earthing Systems
Grounding, also known as earthing, is one of the most important elements of any electrical installation. A well-designed grounding system protects people from electric shock, prevents damage to equipment and keeps the electrical grid stable.
What is grounding (earthing)?
Grounding is the direct electrical connection, without fuses or any other intermediate protection, between certain parts of an installation and one or more electrodes buried in the ground. Thanks to it, fault currents and atmospheric currents (lightning) are dissipated into the soil through a low-resistance path.
In practice, a grounding installation has three functions: to limit the voltage that exposed metal parts can reach, to ensure that protective devices trip when a fault occurs, and to give equipment a stable reference potential.
HOW IT IS BUILT
Earthing network: the parts of a grounding installation
The earthing network is the set of electrodes, conductors and connections that make up the grounding installation. According to ITC-BT-18 of the Spanish REBT and IEC 60364-5-54, it has four parts:
01
Earth electrode
The grounding electrode (rod, plate, buried conductor or special graphite or Picron electrodes) in direct contact with the soil. Its type, number and depth depend on soil resistivity.
02
Earthing conductor
Connects the electrodes to the main earthing terminal. It is sized to carry the fault current and to withstand soil corrosion throughout the life of the installation.
03
Main earthing terminal
The point where the earthing conductor, the protective conductors and the bonding conductors meet. It allows the earth electrode to be disconnected to measure its resistance.
04
Protective and bonding conductors
They take the earth to every exposed metal part and every piece of equipment, and bond conductive parts together so that no dangerous potential differences appear.
EARTHING SYSTEMS
Design and installation service for earthing systems
At Procainsa, we have been designing and installing earthing systems for industrial, energy, and critical infrastructure facilities for over 30 years. Each project starts with a soil resistivity study and adapts to the applicable regulations — REBT, IEC 60364, or sector-specific ones — to guarantee a durable and safe solution.
What does our service include?
From the preliminary study to commissioning, we manage all project phases:
- Soil resistivity study
- System design
- Electrode installation
- Verification and measurement
- Technical documentation
Sectors we work in
We have experience in earthing projects in particularly demanding environments:
- Refineries, tank farms, and petrochemical plants
- Wind farms and photovoltaic plants
- Data centers and telecommunications
- Industrial and tertiary buildings
- Port infrastructure and marine environments
GROUNDING FUNCTIONS
Protective earthing and system (service) earthing
Two grounding functions coexist in an installation. Protective earthing connects exposed metal parts (enclosures, structures, switchboards) to protect people. System or service earthing connects a point of the electrical system itself to earth, usually the transformer neutral, or provides the reference that equipment needs to operate.
In transformer substations they are generally built as separate earths, in line with Spanish regulation ITC-RAT 13. In low voltage they can be independent or combined, depending on the system layout.
Protective earthing
Connects to earth the metal parts that are not live but could become live due to an insulation fault: enclosures, frames, structures and metal pipes. Together with the residual current device or circuit breaker, it prevents anyone from being exposed to a dangerous touch voltage.
System or functional earthing
Connects the transformer or generator neutral to earth and sets the reference potential of the system. As functional earthing, it ensures that sensitive equipment works properly, such as telecommunications facilities and data centers, where stable and uninterrupted operation is vital.
Combined grounding
Brings the protective and system functions together in a single equipotential earthing network. It is the usual solution for installations that need both, such as hospitals, air traffic control centers or industrial plants with electronic equipment, provided the step and touch voltage calculation allows it.
SYSTEMS AND ELECTRODES
Types of grounding
Grounding is classified in two ways: by how the neutral and the exposed parts are connected to earth (the earthing system) and by the type of electrode buried in the ground. Both decisions are made at the design stage and determine the protective devices, the cost and the service life of the installation.
By earthing system: TT, TN and IT
The first letter indicates how the neutral is connected to earth (T: directly; I: isolated or through an impedance) and the second, how the exposed parts are connected (T: to their own earth electrode; N: to the neutral). This is set out in IEC 60364 and in ITC-BT-08 of the Spanish REBT.
| System | Neutral | Exposed parts | Usual protection | Typical use |
|---|---|---|---|---|
| TT | Connected to earth | To their own earth electrode, independent of the neutral earth | Residual current devices | Public low-voltage distribution in Spain: homes, shops and small industry |
| TN (TN-S, TN-C and TN-C-S) | Connected to earth | Connected to the neutral through the protective conductor (separate, combined or mixed) | Circuit breakers or fuses, and residual current devices in TN-S | Industry and buildings with their own transformer substation |
| IT | Isolated from earth or connected through an impedance | Connected to earth | Insulation monitoring: the first fault does not cut the supply | Operating theatres, continuous processes and mining |
By grounding electrode
| Electrode | Strengths | Where it is used |
|---|---|---|
| Star-plates and plates | Acceptable resistance values in high-resistivity soils, which improve as the soil settles and remain stable for 5 to 10 years | High-resistivity soils, with a 2 to 3 m³ pit or trench and soil treatment |
| Rods or stakes | Quick installation by driving and an immediate resistance value; steel corrosion makes it deteriorate quickly | Simple installations in favourable soils |
| Rigid graphite | Not affected by corrosion like metals; values that stay stable over time, similar to or better than plates | High-reliability grounding |
| Zinc stakes | Provide cathodic protection to galvanized steel networks and prevent galvanic couples with copper | Refineries, fuel tank farms and buried steel structures |
| Picron electrodes | Service life of more than 30 years, with minimal degradation by corrosion | Deep grounding, marshy soils, high water tables and marine environments |
| Building slabs (Picron and galvanized steel) | Prevent galvanic couples between copper and the steel mesh | Large buildings with floors below the water table |
REGULATIONS
Grounding regulations: REBT, IEC 60364-5-54 and NFPA 70
The design and installation of a grounding system must comply with the regulations of each country and sector. These are the three standards we work with most often:
SPAIN
REBT (ITC-BT-18)
The Low Voltage Electrotechnical Regulation governs low-voltage installations in Spain. Its ITC-BT-18 sets out how grounding must be carried out, and ITC-BT-08 covers earthing systems.
INTERNATIONAL
IEC 60364-5-54
The international standard for the selection and erection of earthing arrangements and protective conductors in low voltage. It is the basis of many national regulations.
US AND LATIN AMERICA
NFPA 70 (NEC)
The reference electrical code in the United States and much of Latin America. Its Article 250 covers grounding (grounding) and bonding (bonding).
Grounding electrodes: types and applications
Star-plates and plates
Earthing systems using star-plates, plates or similar are installed in artificial pots based on opening a pit or trench of 2 to 3 m³ and filling it with topsoil and other additives to reduce soil resistivity (Ledoux treatment).
The electrical earthing resistance values obtained in these installations can be considered acceptable for high resistivity soils. Due to the lack of soil compaction, these values tend to improve some time after installation, remaining stable for a period ranging from 5 to 10 years.
Conventional rods or stakes
Rods or stakes are the most widespread earthing system due to their easy installation. Considering that their introduction is done by driving, the earthing resistance values are obtained immediately, and are better than those of the plate system. However, these values should be understood as exclusively circumstantial, since due to the effect of corrosion on steel, the rate of loss of initial resistance is very rapid, and even more so when the quality of copper or zinc coatings has been reduced or deteriorates during the driving process.
Rigid graphite electrodes
The configuration of the rigid graphite electrode in the form of an anode, with a filler activator-conductor to improve intimacy with the ground, makes this earthing system highly reliable. Being an electrode made entirely of graphite, it is not intensely affected by corrosion, unlike metals.
Regarding remote earthing resistance values in soils of different resistivities, their behavior is very similar or even better than that of star plates, and much better than conventional rods. In parallel, the evolution of these values over time is unbeatable given their low corrosion wear rate, and therefore their service life is in principle unlimited compared to traditional systems. Thus, the very nature of the electrode, its dimensions, and the surrounding conductive activator mean that it does not require any maintenance (watering or mineralization) as is so frequent in other systems.
Due to all these characteristics, the rigid graphite electrode is ideal for shallow and deep earthing systems as it guarantees long durability and more than acceptable performance.
Zinc stakes
Zinc stakes are an ideal solution for cathodic protection against corrosion of earthing systems when these are made of galvanized steel conductors. They also prevent the galvanic couples so frequent in earthing systems of steel structures (buried tanks, or bases of above-ground tanks) against bare copper conductors.
Recent MIE-ITC-01 and MIE-ITC-02 standards mandate the installation of earthing systems with galvanized steel conductors (or insulated copper) and Zinc stakes in refineries and fuel storage tank farms. These technical considerations are extendable to installations such as gas stations (MIE-ITC-04), chemical plants, etc.
The main characteristics of these stakes are:
- Good performance due to their low electrical resistance.
- Large dispersion surface and good intimacy with the ground as they come with a bag filled with a bentonite-based activator-conductor.
- Easy handling and easy installation by any user.
- Possibility of determining their degradation status without unearthing them.
Picron Electrodes
PICRON electrodes have been designed for high-performance earthing systems, especially for deep or semi-deep earthing, in marshy terrains, with high water tables (deltaic areas) and even in very aggressive waters (marine environments or directly in seawater), for high and low voltage electrical installations, lightning rods, and IT or robotics equipment.
PICRON electrodes can be considered the earthing system with the highest guarantee and stability on the market.
Their main characteristics are:
- Unlimited duration (>30-year life), due to minimal degradation by corrosion.
- They can be used as single electrodes or chain electrodes, for installation in vertical boreholes from 160 x 3000 mm diameters, or they can be installed directly deposited on marine sediments.
Zero maintenance, as they do not require periodic watering to establish their conductivity
Earthing for building slabs
Frequently asked questions about earthing systems
What is the difference between 'puesta a tierra' and 'toma de tierra'?
‘Puesta a tierra’ and ‘toma de tierra’ are two terms that designate the same concept: the electrical connection between an installation and the ground to dissipate fault currents and protect people and equipment. The difference is solely terminological and geographical.
‘Puesta a tierra’ is the predominant term in Spain and is included in the Low Voltage Electrotechnical Regulation (REBT). ‘Toma de tierra’ is used as a synonym in some regulatory contexts and is more frequent in certain Latin American countries.
In practice, both expressions refer to the same system: buried electrodes, protective conductors, and equipotential connections that ensure the safety of the installation.
How often should I inspect my earthing system?
How does weather affect earthing systems?
What to do if the earthing system fails?
Is it expensive to install an earthing system?
What are the risks of not having an adequate earthing system?
Are there home solutions to improve my home's earthing?
What grounding resistance value is acceptable?
It depends on the installation. The Spanish REBT does not set a single value: it requires that no exposed part can reach a touch voltage above 24 V in damp locations or 50 V elsewhere, taking into account the residual current device installed. As a reference, ITC-BT-26 recommends not exceeding 15 Ω in buildings with lightning protection and 37 Ω in buildings without it. In industrial installations, the target value is calculated at the design stage from the soil resistivity.
How is grounding resistance measured?
With an earth resistance tester, usually by the fall-of-potential method: a current is passed between the electrode and an auxiliary rod, and the voltage is measured with a second rod placed at about two thirds (62%) of that distance. The measurement is taken with the electrode disconnected from the installation at the main earthing terminal or, if it cannot be disconnected, with a clamp meter. At Procainsa we measure, record and document the values at every inspection.