When it comes to electrical measuring instruments, precision and reliability are essential, but they’re not the only considerations. In an electrical panel, industrial plant, or distribution network, the instrument may be connected to circuits affected by high voltages, transient overvoltages, and potentially dangerous currents. The safety of measuring instruments therefore becomes as essential a requirement as the quality of the measurement.
Electrical insulation, distances between active parts, protection against overcurrents and overvoltages, correct separation between primary and secondary circuits and the choice of components suitable for the system conditions are elements that must be considered already in the design phase.
These aspects are complemented by the regulatory framework. The CEI, EN, and IEC standards define specific technical requirements and criteria for numerous categories of electrical and measuring equipment. For this reason, choosing an instrument solely based on its measurement range or accuracy class may not be sufficient: it is also necessary to evaluate where it will be installed, which electrical quantities it will need to manage, and what insulation and protection conditions are required by the application.
Why safety is crucial in electrical measuring instruments
Measuring an electrical quantity means, in many cases, creating an interaction between the instrument and the circuit to be analyzed.
This interaction can be direct, such as when a voltmeter is connected to a circuit, or indirect, as occurs through current transformers and voltage transformers.
In both cases, a sizing error or the use of an unsuitable component can lead to dangerous situations.
The risk doesn’t stem exclusively from the system’s nominal voltage. Pulse surges, insulation failures, short circuits, overloads, or transient conditions significantly different from normal operating conditions can also occur.
For this reason, the design of measuring instruments and systems must consider not only what happens during normal operation, but also reasonably foreseeable abnormal conditions.
The IEC 61010 series was developed specifically for the safety of electrical measurement, control, and laboratory equipment. IEC 61010-1 establishes the general safety requirements for this type of equipment, while specific standards address specific configurations and measurement circuits.
Electrical insulation: the first safety barrier
One of the fundamental principles of electrical safety is to prevent parts that may be at dangerous potential from becoming accessible to the operator or from transferring that potential to circuits that should remain protected.
Insulation therefore plays an essential function.
However, it shouldn’t be considered simply as the insulating material surrounding a conductor. In electrical design, the concept encompasses several elements: material characteristics, creepage and clearance distances, insulation voltage, environmental conditions, and the system’s ability to withstand specific electrical stresses.
Depending on the equipment, functional insulation, basic insulation or additional levels of protection may also be provided.
The goal is to prevent a single failure from turning a normal measurement operation into a dangerous condition.
This principle takes on particular importance in instruments intended for industrial plants, where the quantities involved can be significantly higher than those encountered in low-power electronics.
Measuring transformers and separation between primary and secondary circuits
A particularly significant example is represented by current transformers and voltage transformers.
Current transformers allow the secondary circuit to reproduce, according to a specific transformation ratio, a current proportional to that present in the primary circuit. This allows measuring instruments, supervision systems, and protection devices to operate with more easily manageable quantities.
The same general principle of separation and adaptation of the measured quantity applies to voltage transformers.
In these devices, insulation, nominal characteristics and correct choice of device are crucial because the transformer constitutes an interface between the electrical system and the measuring or protection devices.
For instrument transformers, a fundamental regulatory reference today is represented by the IEC 61869 series. IEC 61869-2 concerns inductive current transformers in particular, while IEC 61869-3 regulates the additional requirements for inductive voltage transformers.
In Italy, these references are incorporated into the IEC regulatory system. IEC EN 61869-2, for example, concerns the additional requirements for current transformers, while IEC EN 61869-1 contains the general requirements for instrument transformers.
An important aspect is the evolution of the standards: the IEC 61869 series has progressively replaced several previous references of the IEC 60044 family. For this reason, when designing a new system or selecting equipment, it is always advisable to check the version and validity status of the standard applicable to the specific product.
Protection against surges and transients
An electrical circuit does not always operate under perfectly stable conditions.
Switching, switching, faults and other phenomena can cause transient overvoltages much higher than the voltage normally present in the circuit.
An instrument designed to measure a specific voltage must therefore be chosen by considering not only the nominal value of the quantity to be measured, but also the possible stresses present at the point of the system where it will be installed.
This principle is particularly important because two circuits with the same nominal voltage can present very different risks depending on their position in the system and the potentially available energy.
Safety therefore arises from a combination of several factors: adequate insulation, correct circuit design, protection against abnormal conditions and selection of components consistent with the actual electrical environment.
Measurement categories: why the location of the system makes the difference
In the case of portable equipment and instruments used directly for electrical tests, the concept of measurement category also takes on particular importance.
In practical terms, it’s not enough to verify that an instrument can read, for example, a certain voltage. It’s necessary to understand where in the system that measurement will be taken and what level of transient overvoltage could occur.
Measurement categories allow you to distinguish between different conditions of use and the energy level associated with the measurement point.
This is why the maximum voltage indicated on the nameplate should not be interpreted in isolation: the instrument’s ability to operate safely also depends on the electrical environment for which it was designed.
The IEC/CEI EN 61010 series standards specifically address these aspects. For portable current sensors, for example, the IEC 61010-2-032 specification covers devices used to measure current without physically interrupting the circuit, while the related IEC standard also contains specific requirements regarding measurement categories and the risks associated with the circuits being tested.
IEC 61010: the reference for many measuring equipment
The IEC 61010 family represents one of the main references when dealing with the safety of electrical equipment intended for measurement, control and laboratory use.
IEC 61010-1 contains general requirements and defines the framework from which numerous specific sections derive. The standard covers electrical test and measurement equipment, industrial process control equipment, and certain laboratory equipment.
For equipment with externally connected circuits for measurement or testing, IEC 61010-2-030 is particularly relevant. This standard establishes specific requirements for equipment with test or measurement circuits connected to external devices or circuits, providing additional means of protection between the circuit and the operator.
Therefore, there is no single standard that applies to all instruments. The correct reference depends on the type of device, its intended use, the circuit involved, and the application characteristics.
IEC 61869 and instrument transformers
For a company operating in the field of electrical instruments and instrument transformers, the IEC 61869 series plays a particularly important role.
The structure of the series allows for the general requirements and specific characteristics of the different transformer families to be addressed separately.
IEC 61869-2 covers inductive current transformers used in conjunction with electrical measuring instruments and protective devices. IEC 61869-3 covers inductive voltage transformers intended for the same applications.
IEC 61869-1 defines the general requirements for instrument transformers intended for the applications specified by their respective scopes. The standard also distinguishes the requirements for high- and medium-voltage systems from those specific to low-voltage applications.
FC Misure operates in the electrical measurement sector, with solutions that include indicating instruments and measuring transformers for various applications.
CEI, IEC standards and CE marking: they are not the same thing
In everyday language, terms such as CEI, IEC and CE are often used together, but they indicate different concepts.
The IEC – International Electrotechnical Commission develops international standards in the electrical and electronic sectors.
The CEI – Italian Electrotechnical Committee is the Italian standards body in the electrical engineering sector and implements, publishes, and manages numerous European and international standards at a national level.
The CE marking, however, belongs to the legislative framework of the European Union and indicates that the manufacturer declares the conformity of the product with the applicable requirements established by the relevant European legislation.
For certain electrical equipment, Directive 2014/35/EU, known as the Low Voltage Directive, also falls within the legislative framework. This Directive applies to equipment designed to operate within specific voltage ranges.
Technical standards and European legislation therefore play different but complementary roles: the former define technical criteria and verification methods, while the legislative framework establishes the obligations for placing products on the European market.
Accuracy and safety must be evaluated together
When choosing a measuring instrument, it is natural to focus first on metrological performance: measuring range, transformation ratio, accuracy class, operating frequency or signal type.
For a professional system, however, this assessment must be accompanied by an analysis of the electrical and safety characteristics.
A very precise instrument that is not suited to the voltage, insulation, or conditions of the circuit in which it is installed is not a good choice.
Likewise, a standard-compliant component must be selected and installed consistently with the manufacturer’s specified ratings.
Safety therefore arises from the entire system: instrument design, quality of materials, insulation, protections, correct selection, installation and operating conditions must be consistent with each other.
The importance of choosing the right tools for the application
In the electrical field there is no universally suitable tool for any system.
A measurement inside an automation panel, a current measurement on an industrial circuit and the monitoring of a medium voltage line pose very different requirements.
For this reason, the selection should always start from the real application.
It is necessary to know the quantity to be measured, the nominal values of the system, the required insulation conditions, the type of installation, any expected electrical stresses and the applicable standards.
Only subsequently can the characteristics of the most suitable instrument be defined.
It is precisely in this balance between measurement precision, electrical reliability and safety that the correct design of measurement systems fits.
FC Misure develops and supplies indicator instruments, current transformers, voltage transformers, and solutions dedicated to measuring electrical quantities, with products designed for control panels, industrial plants, energy systems, and specialized applications. Choosing the right solution therefore means not limiting yourself to the value to be measured, but considering the entire electrical context in which the device will operate.
