Table of Contents
What Is Equipotential Bonding?
Equipotential bonding means establishing electrical connections between conductive parts in order to reduce or completely prevent dangerous potential differences. This is also how DIN VDE 0100-200 defines the term.
Typical conductive parts include, for example:
- protective conductors of the power supply system
- metal pipe systems, such as water, heating and gas pipes with insulating sections
- larger metallic structural parts, such as supporting structures or ventilation ducts
- lightning protection systems and foundation earth electrodes
Protective equipotential bonding, formerly referred to as “main equipotential bonding”, connects these parts to the earthing system via a main earthing terminal or equipotential bonding bar. The objective is to limit touch voltage in the event of a fault, such as a fault to exposed conductive parts, and to enable protective devices to trip.
In simple terms, equipotential bonding means: all essential conductive parts of a building or installation are electrically connected so that no dangerously high voltage differences can occur between them.
Normative Framework - Where Is It Defined?
For planning, installation and equipotential bonding measurement, the following standards are particularly relevant in German-speaking countries:
- DIN VDE 0100-410 - protection against electric shock; among other things, it requires protective equipotential bonding in every building.
- DIN VDE 0100-540 - earthing systems and protective conductors; regulates the design and cross-sections of earthing conductors and protective equipotential bonding conductors.
- DIN VDE 0100-600 - initial verification; among other things, it requires the measurement of continuity of protective conductors and protective equipotential bonding conductors.
- For equipment testing, DIN VDE 0701-0702 is also relevant, for example for protective conductor resistance and protective conductor current.
Important: VDE 0100-600 requires testing, but does not specify the exact measurement method for continuity. In practice, low-resistance or continuity measurements using a sufficiently high test current have become established.
Technical Background: Why Equipotential Bonding?
Without equipotential bonding, the following can occur in installations and buildings:
- touch voltages between different contact points
- bonding currents flowing via pipework or cable shields
- EMC problems, such as interference voltages in measurement and communication systems
- very high potential differences between parts of the installation in the event of lightning or overvoltage
Equipotential bonding provides several effects at the same time:
- Safety
- Limitation of touch voltages in the event of a fault
- Support for the protective measure “automatic disconnection of supply” through low loop impedance
- System protection and EMC
- Reduction of interference voltages and stray currents
- Improved reference conditions for measurement, control and communication technology
- Lightning and overvoltage protection
- Integration of the earthing system and lightning protection system into a coordinated equipotential bonding system
What Does “Measuring Equipotential Bonding” Mean in Practice?
When practitioners talk about “measuring equipotential bonding” or “measuring protective equipotential bonding”, they usually refer to two aspects:
- Equipotential bonding measurement in the narrower sense
→ Low-resistance measurement / continuity testing of protective equipotential bonding conductors and connections:- Is every installed conductor electrically continuous?
- Are the resistance values within a low and technically plausible range?
- Verification of the effectiveness of protective measures
→ for example loop impedance measurement, RCD testing and similar tests to prove that sufficient fault current flows in the event of a fault and that automatic disconnection functions reliably.
Important:
- VDE 0100-600 does not define a fixed limit value for the resistance of an equipotential bonding conductor.
- Technical literature often mentions typical reference values of around < 0.1 Ω for protective conductors and, for example, < 1 Ω for equipotential bonding conductors. Older installations may have higher values, but these must be assessed in context.
The decisive factor is always the system effect:
- sufficient conductor cross-sections,
- safe connection technology,
- permanently low contact resistance,
- and an overall system that fulfils the disconnection conditions.
Practical Procedure:
Equipotential Bonding Measurement Step by Step
Clarify the Measurement Objective
Before any equipotential bonding measurement, the objective should be clear:
- Am I testing a new installation, as part of initial verification according to DIN VDE 0100-600?
- Am I testing as part of a periodic inspection or revision?
- Is there a specific suspected fault, such as corrosion, modification work, recurring faults, or acceptance testing after a retrofit, for example a PV system or charging infrastructure?
Measurement Methods
The following methods have proven effective in practice:
a) Low-resistance measurement / continuity testing
- Test current typically ≥ 200 mA, AC or DC, as recommended in many guidance documents and technical articles.
- Measurement between:
- main earthing terminal / equipotential bonding bar and
- the connected conductive parts, such as pipes, protective conductors or metallic structures.
- If necessary, use a 4-wire Kelvin measurement method, especially for very long cables or very low resistances, to compensate for lead and contact resistances of the test leads.
b) Assessment of measured values
- Comparison with internal reference values or company standards
- Plausibility check:
- Are deviations between conductors routed in parallel plausible?
- Do conspicuously high values occur on specific branches or terminal points?
Typical Pitfalls
- Contact problems: dirty or painted parts → prepare the contact point before measurement.
- Parallel paths: In meshed protective conductor systems, the measured resistance can appear very low; in such cases, values that are “too high” are usually the critical issue.
- Conductive parts not included in bonding: for example subsequently installed pipework, metal structures or ventilation ducts.
Measuring Protective Equipotential Bonding - Typical Scenarios
New Construction of a Building or Substation
During initial verification, the following must be checked, among other things:
- continuity of all protective equipotential bonding conductors between:
- main earthing terminal
- water, heating and gas pipes
- metallic parts of the building structure
- cross-sections and execution according to DIN VDE 0100-540, for example a minimum cross-section of 6 mm² Cu for protective equipotential bonding conductors.
Retrofitting PV Systems or Charging Infrastructure
In PV systems and charging infrastructure, classic protective equipotential bonding is often supplemented by functional equipotential bonding and lightning protection equipotential bonding:
- integration of module frames or mounting structures into the equipotential bonding system
- connection of surge protective devices, or SPDs, to the equipotential bonding system
- avoidance of potential rise between parts of a building during lightning current discharge
In these cases, clean documentation and re-measurement of the equipotential bonding system are particularly important to avoid later EMC and protection problems.
Existing Installations, Modifications and Corrosion
Typical reasons for targeted equipotential bonding measurement include:
- recurring nuisance tripping of protective devices
- corrosion damage to pipework where earthing or bonding currents are suspected
- changes to the earthing system or network system, such as conversion from TN-C to TN-S
Importance for Power Quality, Measurement and Control Technology
Functional equipotential bonding is more than “just” personal protection:
- Grid quality and power quality
- unbalanced or stray currents can flow via unfavourable equipotential bonding paths and distort measurements
- EMC interference affecting power quality measurements, control lines and digital signals
- Automation and protection technology
- incorrect reference potentials can lead to malfunctions of protection devices
- communication disturbances in station control technology, protection devices and automation devices
Especially in complex distribution grids, industrial installations or systems with a high level of decentralized feed-in, equipotential bonding becomes a system-relevant component for reliable measurement, analysis and control concepts. Companies such as A. Eberle, which specialize in grid monitoring and power quality, regularly encounter the effects of faulty equipotential bonding connections in grid operation.
Power quality analyzers do not perform low-resistance or continuity measurements of equipotential bonding conductors. However, they make it possible to analyze indirect effects such as increased neutral conductor currents, unbalances or stray currents.
Equipotential Bonding vs. Earthing vs. Other Bonding Measures
For classification:
Earthing
- Connection of a conductive part to the earth, for example via an earth electrode, foundation earth electrode or ring earth electrode.
Equipotential bonding / protective equipotential bonding
- Connection of conductive parts to each other and to the earthing system in order to minimize potential differences and support protective measures.
Functional equipotential bonding
- Serves less for personal protection and more for functional reliability, such as EMC, measurement, control and communication technology.
Lightning protection equipotential bonding
- Interconnects the lightning protection system, earthing system and relevant conductive parts so that dangerous potential differences are reduced in the event of lightning.
In practice, these functions often overlap. Nevertheless, the distinction helps to perform measurements and assessments in a targeted manner.
Benefits of Systematic Equipotential Bonding Measurement
A regularly and methodically performed equipotential bonding measurement supports:
higher operational safety
- Proof of effective protective measures
- Early detection of contact problems, loose terminals and corrosion
better basis for decision-making
- Assessment of whether extensions, such as PV systems, charging infrastructure or new production systems, fit into the existing earthing and equipotential bonding concept
- Prioritization of remediation measures
improved transparency in grid operation
- clearly documented equipotential bonding structures
- more comprehensible measurement and power quality results
Verifying Equipotential Bonding by Measurement
Analysis of residual currents, unbalances and unwanted current paths in the low-voltage grid
The Role of System and Solution Expertise
Equipotential bonding cannot be considered in isolation. For planners and industrial users, the following is important:
an integrated view of:
- network type, such as TN, TT or IT
- earthing system
- protection and automation technology
- EMC and lightning protection concept
measurement and analysis expertise:
- how faulty equipotential bonding connections appear in measured values and in power quality
- how measurement results, such as low-resistance, loop impedance and insulation measurements as well as power quality analyses, are considered together
The decisive factor is not a single measured value, but the understanding of the overall system and how it actually functions in real grid operation with all boundary conditions.
FAQ on Equipotential Bonding and Its Measurement
1. What is equipotential bonding in one sentence?
Equipotential bonding is the electrical connection of all important conductive parts of an installation so that no dangerously high voltage differences can occur between them and protective measures remain effective.
2. How does equipotential bonding differ from the protective conductor?
- The protective conductor (PE) is part of the power supply system and carries the fault current in the event of a fault.
- Protective equipotential bonding additionally connects extraneous conductive parts, such as pipework and metal structures, to the earthing system and the protective conductor system in order to minimize potential differences.
3. How often should protective equipotential bonding be measured?
The VDE standards do not define universal test intervals. Instead, they refer to a risk assessment and company-specific definitions, for example according to DGUV Regulation 3 and DIN VDE 0105-100. Typical cases include:
- initial verification of every new or significantly modified installation, which is mandatory
- periodic inspections at defined intervals, depending on the installation, use and environmental conditions
4. Is there a fixed limit value for the resistance of an equipotential bonding conductor?
No. DIN VDE 0100-600 does not specify a fixed limit value for equipotential bonding conductors. Technical articles refer to guide values, for example < 1 Ω, but the decisive factors are that:
- the connection remains permanently low-resistance and
- the disconnection conditions, such as loop impedance and RCD tripping, are fulfilled.
5. How should I proceed in large, meshed installations?
In large industrial installations or transformer stations with meshed protective conductor systems:
- measure continuity with a sufficiently high test current and, where necessary, with reverse potential injection
- evaluate measured values in the context of the entire mesh, not only individual routes
- closely coordinate the assessment with the earthing design, lightning protection and EMC concept
Conclusion
- Equipotential bonding is a central element of personal and system protection and also affects power quality, EMC and measurement and control technology.
- Equipotential bonding measurement, especially measuring protective equipotential bonding, primarily serves to verify a low-resistance, continuous connection of all relevant conductive parts.
- Standards such as DIN VDE 0100-410, -540 and -600 define the requirements for execution and testing, but deliberately leave room for technically appropriate measurement and assessment methods.
- For grid operators, planners and industrial users, it is therefore important to always consider equipotential bonding in the system context, including the earthing system, protection concept, power quality and automation.
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