This week in the third edition of the LPI Group technical blog, we will outline and explore the different types of earthing systems that are required for various protection and functional purposes. We will also discuss important definitions associated with earthing systems, highlight examples of sample earthing applications and introduce the various meanings behind earthing symbols that can be encountered during earthing and bonding system applications.
Before delving further into the technicalities of all you need to know about earthing systems, it is important to consider them as a critical system to mitigate any safety risks and adverse effects that IT and electrical equipment may encounter due to potentional differences, stray currents or a lightning strike.
Different Types of Earthing Systems
There are three different types of earthing systems that are employed to achieve different protection and functional goals, including:
- Safety earthing systems
- Functional bonding and earthing systems
- Lightning protection system earthing
The Safety Earthing System
These systems are related to the technical concepts of protective earthing and bonding, and earthing schemes of power and distribution.
These technical concepts can be broken down into the following topics:
- The LV Earthing Distribution Network (TN, TT & IT) for AC and DC System – Note: The main attribution to the LV distribution network is to provide protection against indirect contact with voltage (Fault Protection). For this purpose, protection shall be provided against dangers that may arise from contact with exposed conductive parts of the installation by people or livestock.
- The MV/HV Earthing Distribution Network (Directly earthed, unearthed, resistance earthed, inductance earthed, petersen coil, etc). – Note: Some schemes of earthing in this regard are not solely for safety reasons. The system is also used to avoid Arc Energy, extra voltage stress on the equipment insulation and to provide conditions for the efficient operation of the protection device.
- Certain bonding schemes between metal exposed parts of energized equipment.
- Electrostatic bonding and earthing.
Functional Bonding and Earthing
This type of earthing system is defined as an earthing point or points in a system, in an installation, or within equipment for purposes other than electrical safety.
Functional bonding and earthing concepts can be broken down into the following topics:
- EMC Earthing
- DC System Special Configuration –(dc-I and dC-C)
- Data Centre and Telecommunication Equipment Bonding Infrastructure
- Logical / Reference Voltage Earthing termination
- Signal Reference Connection and Networks
In some technical guidelines, the EMC Earthing is introduced as a separate main topic and is not associated with a functional earthing system. In this case, the different types of earthing systems can be categorised as follows:
- Safety Earthing
- Functional Earthing
- EMC Earthing
- Lightning Protection System Earthing
Lightning Protection System Earthing
Figure 1 shows a sample configuration of an earthing electrode system at a telecommunication tower that is situated adjacent to the telecommunication building.
The electrode system is composed of rods, a ring and a radial earthing electrode. The reason for this particular shape and the number of electrodes is to distribute the lightning current adequately, and in such a way that the resulting voltage gradient emerges far enough from the side of the building (See Figure 2).
Figure 2 shows the sample of the voltage gradient zone on the ground surface upon the lightning strike at the top of the Telecommunication Tower.
Sample Application 1 – Protective Earthing and Bonding System
Indirect Contact Without Earthing Connection of the Stove (Figure 3).
Performing a return Earthing Conductor connected to the metal body of Equipment (CPC) (Figure 4).
Sample Application 1.2
As shown in figure 5, the implementing bonding connection will reduce the touch voltage to the UC =RP x IF.inc, in other words, the amount of touch voltage depends on the resistance of the bonding conductor which could be less enough to avoid a high level of touch voltage.
Then what will happen if the bonding conductor does not exist?
Definitely, dangerous touch voltage can occur as in such case the touch voltage is not dependent on a conductor resistance. The voltage is directly imposed from the power system fault circuit.
Sample Application 1.3
A fault current and voltage in a TN system is demonstrated in figure 6. Here the PE Conductor connects the metal body of the equipment to the neutral point of its upstream supply, which is itself connected to earth electrodes.
Sample Application 1.4
A fault current and voltage in a TN system is also demonstrated in figure 7. In this configuration, the metallic is directly connected to the local earth electrode.
Sample Application 1.5
A fault current and voltage in an IT system at the first fault is demonstrated in figure 8. In this configuration, the metal body of equipment is directly connected to the earth electrode and none of the supply circuit is directly connected to the earthing electrode.
Sample Application 1.6
A fault current and voltage in an IT system at a second fault is shown in figure 9. In this configuration, the existence of PE conductors which connect two metal bodies of equipment provides indirect contact when the second fault happens and while the first fault still exists. And ultimately control the exposed touch voltage.
Sample Application 1.7
Protection measures by utilising isolating material and equipotential bonding is demonstrated in figure 10.
Sample Application 1.8
This figure shows the three accepted configurations to control static discharge that could accumulate on different parts of a system and build hazardous voltage differences.
Sample Application 2: Functional Earthing and Bonding System
Sample Application 2.1 EMC Earthing
EMC earthing refers to all bonding, shielding or earthing methods that are implemented for IT or Electronic Equipment and their connected circuits to reduce or eliminate the probable damage and inference to electrical equipment.
EMC can be divided into the categories of:
- The particular configuration of earthing and bonding networks
- Low transfer impedance earthing
Note: For EMC purposes, we can distinguish three almost hierarchical definitions of the earth:
- An equipotential area or plan used as a system reference
- A low impedance path for currents to return to their source
- A low transfer impedance path to prevent common-mode currents from converting to differential mode.
Sample Application 2.3 – Logical or Reference Voltage Earthing
- Some electronic equipment requires a reference voltage at about earth potential in order to function correctly.
Sample Application 2.3 – DC-I / DC-C Earthing Configuration of DC system
Sample Application 2.4 – Signal Reference Earthing Plan
Figure 12 represents a sample of the infrastructure at a telecommunication bonding network. As shown, some earth bars and conductors are connected in a certain way to build a standardised bonding backbone which is introduced in standards TIA607-C, BICSI 002, and BSEN50310. This backbone ensures that the exceeded amount of voltage difference does not occur for two of the interconnected IT equipment.
Figure 13 represents a sample connection of DC-I earthing connection between equipment and their power supply.
Figure 13 (*DCEG – DC Equipment Ground Conductor)
Figure 14 is another key example of a DC earthing system. As seen in this example, there are two AC/DC power supplies that are located inside one storage cabinet for the electrical panel. These power sources are going to supply electrical equipment with DC power.
As shown, the DC return conductor of each source has been connected to the same earth bar which itself is connected to the main earthing bar for the entire facility.
Figure 15 excellently illustrates two interconnected equipment which uses bonding and earthing as a reference signal plan.
This figure shows typical single-ended and differential interfaces.
- A single-ended interface uses a single signal conductor and an earth return path. Clearly, any potential difference between the local ‘earth’ at the transmitter and receiver appears in series with the signal and is likely to cause data corruption. The apparently simple solution of adding another signal conductor between the two earth points is not feasible a large and undefined current will flow causing interference and possibly damage
- A differential interface uses two signal conductors and data is sent as a voltage difference between them. Ideally, the receiver is sensitive only to the differential voltage between the signal lines and insensitive to the common-mode voltage
- In summary, unlike single-ended transmission wiring which is highly vulnerable to the different potential that may be created by bonding and earthing reference plan, differential transmission wiring shows the reference plan connection that is considerably less vulnerable to earthing connection quality.
As shown in figure 16, a typical signal reference plan can be seen in the form of a mesh (500mmx500mm) network. This mesh has also been used for equipotential bonding purposes.
It is important to note that in some circumstances we can have a separated bonding network and signal reference plan.
Shown in figure 17 is a sample of an earthing termination which is used as a reference point voltage for communication purposes of two electrical types of equipment.
Sample Application 4.1 – Common Bonding Network
A Common Bonding Network (CBN) is the default bonding system at the building and enlarges any intentional equipment multipoint bonding topology.
- The primary example of the CBN is the multi grounding and bonding which normally occurs when the ac power system is installed into the building. Other connections to the ac power system grounding conductors and other grounded entities (such as a water pipe and rack work) serve to augment and enlarge the CBN.
- The grounding electrode system, although a separate entity, becomes a part of the CBN (because the CBN must always be grounded). For example exposed beams and columns of building steel that are utilised for the grounding electrode system are also bonded to the chosen topology for the CBN These include metallic parts of the building such as I-beams and concrete reinforcement where accessible, and cable supports, trays, racks, raceways, and ac power conduit. Indeed, the CBN always exists at the building.
CBN is an Equipotential bonding system providing both protective-equipotential-bonding and functional-equipotential-bonding.
Important Symbols Associated with Earthing
Protective Earth (ground)
To identify any terminal which is intended for connection to an external conductor for protection against electric shock in case of fault, or the terminal of a protective earth(ground) electrode.
To identify the terminals which, when connected together, bring the various parts of equipment or of a system to the same potential, not necessarily being the (ground) protentional, e.g. for local bonding.
To identify an earth (ground) terminal.
Noiseless (clean) earth (ground)
To identify a noiseless (clean) earth (ground) terminal, e.g. of a specially designed earthing (grounding) system to avoid causing malfunction of the equipment.
Frame or chassis
To identify the frame or chassis terminal.
Sample of Different Earthing Symbols
In conclusion, this blog has discussed three critical earthing systems: safety earthing systems, functional bonding and earthing systems, and lightning protection system earthing. As always, we urge our readers to consult a registered/certified earthing specialist to ensure the proper design, installation, and ongoing maintenance and management of their earthing system is accomplished safely. It is critical to always maintain the highest level of safety standards around these installations.
LPI Group has a global network of certified technical design experts who can assist you with your upcoming earthing project. By utilising cutting-edge, innovative software, LPI Group is able to mitigate any safety risks and adverse effects that IT and electrical equipment may be exposed to.
If you have any questions on the topics covered in this week’s technical blog or would like to discuss your earthing requirements for an upcoming project, please leave a comment below or email firstname.lastname@example.org and our team will get back to you promptly.
By Hadi Beik Daraei, Technical Designer at LPI Group