Earthing Systems: What You Need to Know - LPI Group

Earthing Systems: What You Need to Know

Earthing Systems: What You Need to Know - LPI Group

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:

  1. 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. 
  2. 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.
  3. Certain bonding schemes between metal exposed parts of energized equipment.
  4. 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

Important Note:

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 1

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.

Figure 2


Sample Applications

Sample Application 1 – Protective Earthing and Bonding System

Indirect Contact Without Earthing Connection of the Stove (Figure 3).

Figure 3

Performing a return Earthing Conductor connected to the metal body of Equipment (CPC) (Figure 4).

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.

 

Figure 5

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.

Figure 6

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.

Figure 7

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.

Figure 8

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.

Figure 9

Sample Application 1.7

Protection measures by utilising isolating material and equipotential bonding is demonstrated in figure 10.

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.

Figure 11

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:

  •       Shielding
  •       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

Sample 3.1

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 12

 Sample 3.2

Figure 13 represents a sample connection of DC-I earthing connection between equipment and their power supply.

Figure 13 (*DCEG – DC Equipment Ground Conductor)

Sample 3.3

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 14

Sample 3.4

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.

Figure 15

Sample 3.5

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.

Figure 16

 

Sample 3.6

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.

Figure 17

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.

Figure 18


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.

Equipotentiality- LPI Group

Equipotentiality

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.

Earth (ground)- LPI Group

Earth (ground)

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

Conclusion:

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 info@lpigroup.com and our team will get back to you promptly.

By Hadi Beik Daraei, Technical Designer at LPI Group

Strike Risk Assessments: Importance to Reduce Risks and the Probability of Damage

Strike Risk Assessments: Importance to Reduce Risks and the Probability of Damage

Strike Risk Assessments: Importance to Reduce Risks and the Probability of Damage

This week in the second edition of our technical blog we will demystify the theory of a strike risk assessment and highlight the importance of this study in the design phase of a building development to reduce risks and probability of damage associated with lightning strikes.

What is a Strike Risk Assessment 
A lightning protection system is an important component in protecting human life, the building structure, electrical systems and critical business processes. In the design stage of any given project, when it comes to lightning protection, a strike risk assessment is the first fundamental step that must be undertaken by your chosen lightning protection specialist. This study determines the number of risks and the protection measures needed to reduce these risks to acceptable limits. These findings then enable the designer to establish the parameters that must be considered during the design of the lightning protection system for any building or structure.

Theory of a Strike Risk Assessment
Lightning protection design requirements are closely related to the extent of risk reduction, while the risk amount is directly related to the amount of loss. Risks and losses can be related to human life, service to the public, cultural heritage and economic value.

The amount of Risk (R) associated with a project is established during a strike risk assessment by multiplying the following three key parameters:

  1. Dangerous events? (N): How many events could be considered dangerous?
  2. Probability of damage (P): What percentage of the threats (N) will lead to damage (P)?
  3. Loss Amount (L): What percentage of damage (P) will lead to a loss(L)?

These parameters must be closely considered by a certified lightning protection system specialist using reliable strike risk assessment software.

The general formula used within the strike risk assessment software: R = N x P x L

Reducing Threats
In order to reduce the number of threats on a building, lightning protection specialists will aim to reduce the number of dangerous events (N).

To highlight this in practice figures 1 and 2 outline where top installed earth wires on a building can reduce the number of strikes that may travel and reach the bottom installed power and signal cables. This demonstrates how earth wires act as a protective barrier to any destructive currents that threaten the building and its contents.


Figure 1 

  Figure 2

If we can diminish the possibility of damage (P) at the first exposure points of lightning strikes, then the number of threats will be decreased. For example, by employing overvoltage protective devices along the length of the telecommunication system network, the probability of damage will be reduced.

As shown in figure 3, in a sample facility with a certain value of tolerable frequency of damage (FT), and an expected number of direct flashes (ND), by installing surge protective devices compatible with a level 1 lightning protection systems. This will decrease the threat of a direct flash to approx. 0.01 of the base value.

The standard formula commonly referenced in the design of telecommunication facilities is ITU-TK. 97: ND X PSPD = FT


Figure 3

Reducing Risks Associated with a Lightning Strike
In the initial communication stage between the client and the lightning protection designer, it is established whether any form of lightning protection is already present on the building/structure or on a surrounding building nearby (zone of protection). As outlined above, there are several various risks associated with lightning strikes, which makes it the ultimate aim of the lightning protection specialist to deliver a system design and solution that reduces the risks associated with a lightning strike. These will be decreased, once either one or all of; Dangerous Events (N), Probability of Damage (P) or Loss Amount (L) are reduced.

Dangerous Events (N)
When considering a direct lightning strike to a building, the number of Dangerous Events (N) can be controlled once an external lightning protection system is considered for the building. In other words, the number of dangerous events depends on the dimension of the Collection Area (A1) and the Geographic Condition (Ng) of the structure’s location.

In the case of a direct strike to the power supply lines entering the building, if a Medium Voltage (MV)/ Low Voltage (LV) Transformer is included on the power supply line at its point of entry to the facility, the number of dangerous events will be reduced to 0.2 of its base value (see figure 4).


Figure 4

Probability of Damage (P)
The Probability of Damage (P) can be reduced through various lightning protection standard methods, such as bonding, shielding and the use of overvoltage protection devices. As stipulated above, these types of protection measures can reduce the number of threats to the building, even if no strike risk assessment study has been conducted.

In buildings, such as telecommunications, where an antenna tower situated, at the beginning of the strike risk assessment study some protection measures are required to reduce the number of threats and ensure compliance with lightning protection standard requirements. This is due to the high vulnerability nature of the facility. For example, in standard ITUTK.56 part 6.2, some bonding obligations have been introduced due to the vulnerability level of the waveguide cable and connected equipment found within telecommunication facilities.

Loss Amount (L)
Generally, the loss amount is related to the number of humans and their presence time and duration within an area of a building. There are several lightning protection standard methods used to reduce the loss amount (L), such as utilising a certain type of surface soil or floors, or a fire extinguisher. In addition, as outlined in the lightning protection standard IEC62793, a thunderstorm warning system can be used to reduce the loss amount. In the event of a thunderstorm, this convenient alarm system can prevent the presence of individuals from being exposed to harmful lighting strikes.

Summary
Through close collaboration with your lightning protection system provider and the undertaking of a strike risk assessment study, by reducing one or all of;
1) Number of Threats, 2) Number of Dangerous Events (N), 3) Probability of Damage (P), or 4) Loss Amount (L), the overall risk associated with a lightning strike can be successfully reduced.

Types of Risks a Lightning Strike Can Produce
As stipulated in the standards IEC62305-2, the following describes the risks associated with a lightning strike:

R 1: Risk associated with the loss of life or injury.
R 2: Risk associated with the loss of service.
R 3:  Risk associated with the loss of historical significance.
R 4: Risk associated with the loss of economic value.

In every project there is an accepted value of risk, for instance, the following figure 5 presents the allowable risk limits that are mentioned in lightning protection standards as a typical value.


Figure 5

The above-listed risk values are the typically referenced values, however, in some vital circumstances, lightning protection designers may use different risk values. For example, in vital network and telecommunication buildings, the tolerable loss of service to the public may be considered 10-4 .

In some lightning protection standards and guidelines related to telecommunication buildings, the tolerable frequency of damage value should be defined by the network operator. For example, FT = 0.05 means that on average, 1 damage in 20 years (1/20) is acceptable.

As referenced in IEC62305-2, the following are definitions of different types of loss:

  •       L1 (Loss of human life, including permanent injury): the endangered number of (victims).
  •       L2 (loss of public service): the number of users not served.
  •       L3 (loss of cultural heritage): the endangered economic value of structure and content.
  •       L4 (Loss of economic values): the endangered economic value of animals, the structure (including its activities), content and internal systems.

There are typical loss amounts as shown in following figures 6 and 7:


Figure 6: General typical value of loss based on standard NFPA780.


Figure 7: Typical value of loss used in the calculation of the risks related to the loss of human life based on standard IEC62305-2.


Figure 8: Typical value of loss used in the calculation of the risks related to the loss of service to the public based on standard IEC62305-2.


Figure 9: Typical value of loss used in the calculation of the risks related to the loss of economic value based on standard IEC62305-2.

Risks and Probable Strike Points
Each risk could be caused by different kinds of probable strike points as shown in figure 10.


Figure 10

We can conclude that each area on a building exposed to a lightning strike is at risk. Therefore, to assess the overall risk, we need to establish what kind of strike will cause which type of risk (figure 11). The strike risk assessment software is important for lightning protection specialists to understand the various strike types and determine the appropriate protection measures to reduce the risks.

It is important to note, that before conducting a strike risk assessment, the tables shown in figure 11 and the area defined in figure 12 will be closely considered by your designer.


Figure 11


Figure 12

Conclusion:
Lightning affects European territory on an average of 350 days per year, meaning that there is at least one lightning strike somewhere in Europe every day. Given this stark figure, it is more important to understand the need to conduct a strike risk assessment at the earliest possible design phase. This determines the appropriate level of lightning protection to protect the full building envelope from potential risks and losses caused by lightning strikes.

The LPI Group team of technical design experts located globally can actively assist our clients in establishing their lightning protection requirements by utilising the latest, innovative software to reduce risks and losses and deliver a bespoke code-compliant lightning protection design.

If you have any questions on the topics covered in this week’s technical blog or would like to discuss lightning protection for an upcoming project, please leave a comment below or email technical@lpigroup.com and our team will get back to you promptly.

By Hadi Beik Daraei, Technical Designer at LPI Group

An Introduction to Lightning Protection System Design

An Introduction to Lightning Protection System Design

An Introduction to Lightning Protection System Design

LPI Group are launching our technical blog section with an introduction to lightning protection system design. This will clearly outline over 3 steps the series of considerations, parameters and data required to ensure a system is designed to code compliant standards and meets the client’s project requirements and design criteria.

Step 1

Establish whether there are any project requirements issued from the client or if there is a project specification and design criteria document.

If yes, seek the project documentation, learn about the client’s requirements and conduct a strike risk assessment should it be required. Following this, then examine the following factors:

  • If the level of protection has been specified.
  • If any general diagrams exist for locating the Surge Protection Devices (SPD) in different Lightning Protection Zone (LPZ 1,2,..).
  • Whether an isolated system is a requirement, if there are any restrictions to use isolated cable and whether the client is happy to use cable as an option within the design. Furthermore, if a non-isolated system is a requirement, identify the type of bonding network that is needed for the project.
  • If electronic equipment is going to be employed within the building and if the client has any requirements to use Part 4 of standard IEC 62305?
  • If there are any three-dimensional types of bonding networks required to provide shielding effects against electromagnetic interference.
  • All the above-stated factors shall be specified in accordance with standard guidelines and requirements.

If no, conduct a strike risk assessment study and examine the following factors:

  • The level of lightning protection is required.
  • The best type of system (isolated/non-isolated) for the structure.
  • The most appropriate shielding level for the project based on Part 4 of IEC 62305.

Findings from Step 1:

  • The level of protection required.
  • The type of lightning protection system (isolated/non-isolated).
  • The districts of LPZ.
  • The protection measures needed for each LPZ.
  • If additional requirements of shielding and the three-dimensional bonding network are required based on Part 4 of IEC 62305.

Step 2

Important Investigations and Considerations

Investigation 1:

If there are any telecommunication buildings in adjacent to the telecommunication tower?

Key Considerations 1:

  • Refer to ITUT.K standards to find out the requirements for the typical factors accounted for in the risk assessment study, the bonding requirements of waveguide conductor, the direct lightning protection of the antennas and the best solution for the earthing system at the telecommunication tower.
  • The SPD requirements for the entrance waveguide to the telecommunication building.

Investigation 2:

Are there any hazardous classification areas?

Key Considerations 2:

  • The hazardous classification drawing shall be reviewed to identify.
  • Strike risk assessment to be completed for each zone of different explosive material.
  • The lightning exposure level of all the tanks containing explosive material shall be calculated.
  • All the vents on the tank roof shall be detected and assessed.
  • The safety standards for the hazardous areas shall be used in line with lightning protection design standards.
  • The pipe rack locations shall be identified and protection measures for direct exposure on pipes shall be considered.
  • The SPD requirements shall be investigated for insulating gasket, cathodic protection systems etc.

Investigation 3:

Foundation earth electrode.

Key Considerations 3:

  • If the foundation electrode is a part of an integrated electrode system and is going to conduct the lightning discharge current, all requirements stated in the standard DIN18014 shall be respected.

Investigation 4: 

The architectural drawing shall be reviewed.

Key Considerations 4:

  • Identify the restrictions surrounding the installation of the LPS.
  • The equipment locations on the roof shall be investigated.
  • The feasibility of the lightning current distribution network shall be reviewed.
  • The building facades, parapet structure and it’s material shall be investigated.

Investigation 5:

If there are any lighting poles or CCTV equipment located at the concerned site.

Key Considerations 4:

  • Identify the solution for the protection of direct strike to CCTV and Lightning fixture.
  • Investigate the SPD requirements for the CCTV.

Findings from Step 2:

  • The points and areas that are going to be protected against a direct strike.
  • The restrictions for the installation of the LPS components at roof level and on the wall are ascertained.
  • All the locations that require SPD.

Step 3

Perform the Calculations

  • Zonal coverage study by software (XGSlab – SES Shield – AUTOCAD – Dehn Support, etc.)
  • Consider different types of air termination networks (air rod, mesh, catenary wire, etc.)
  • Choose the most appropriate and cost-effective air termination network.
  • Calculate the separation distance manually or by software such as XGSLAB, Dehn Support, MAT Lab, PSpice, etc.
  • Conduct the surge study to detect the locations of the SPDs in power, data and telecommunication circuits manually or with the manufacturer’s software.Result Outcome for SES Shield Software

Complete the Drawing and Issue the Technical Drawings

Generate 2D/3D DWG drawings and include the following information:

  • Installation locations of the air terminals.
  • The distance between all the air terminals.
  • Side view of all the sections of the buildings to highlight the LPS component on it.
  • Issue all the technical and installation notes (Maximum bending radius of the conductor or tape, separation distances to be maintained, corrosion prevention treatment, the location of polarization cells, bonding requirements, etc.)

Produce Typical Installation Details

  • The standard detail for the down conductor connection on the roof and walls.
  • The installation drawing for the spacer and holder.
  • The installation detail for the air terminal and the down conductor connection to the earthing system.
  • The detail for the inspection chambers.
  • The installation drawing for bonding the embedded concrete rebars to the LPS components.
  • The installation drawing for the SPD installation.

Generate the Technical Submittal

  • The technical submittal should the following subjects; calculation reports consisting of the zonal protection study, all assumptions made, strike-risk assessment study, separation distance study, AUTO-CAD drawing and surge study calculation.

By Hadi Beik Daraei, Technical Designer at LPI Group