Circuit Separation

The IEC or International Electrotechnical Commission standard 61010-1 has provided examples of circuit types that can be used to determine when basic, reinforced or double insulation is needed.

The definitions below are the same as other international standards except that functional insulation is not specified (although a note is provided that basic insulation may serve for functional purposes). As such, there is no minimum spacing specified between line and neutral conductors on a PC board.

FUNCTIONAL, BASIC, AND SUPPLEMENTARY INSULATION

Linear interpolation is permitted between the nearest two points, the calculated spacing being rounded to the next higher 0.1-mm increment

Table IV. Table 2L of the standard provides minimum creepage distances (creepage distances in millimeters)

The use of these tables is explained in sections 2.10.3–2.10.4 of EN 60950. Measurements should be accurate and repeatable and should also consider the end application.

POLLUTION DEGREES AND OVER-VOLTAGES

Pollution degree is divided into four categories. The following definitions are based on those in IEC 60664.3, which define the degree of pollution that could be expected where the electrical equipment is being installed:

• • Pollution degree 1. No pollution or only dry, nonconductive pollution occurs. The pollution has no influence (example: sealed or potted products).
• • Pollution degree 2. Normally only nonconductive pollution occurs. Occasionally a temporary conductivity caused by condensation must be expected (example: product used in typical office environment).
• • Pollution degree 3. Conductive pollution occurs, or dry, nonconductive pollution occurs that becomes conductive due to expected condensation (example: products used in heavy industrial environments that are typically exposed to pollution such as dust).
• • Pollution degree 4. Pollution generates persistent conductivity caused, for instance, by conductive dust or by rain or snow.

The over-voltage — also known as installation — category, is also divided into four categories according to IEC 60664, with each definition below:

• • Over-voltage category I. Signal level (special equipment or parts of equipment), with smaller transient over-voltages than over-voltage category II.
• • Over-voltage category II. Local level (appliances and portable equipment), with smaller transient over-voltages than over-voltage category III.
• • Over-voltage category III. Distribution level (fixed installations) with smaller transient over-voltages than over-voltage category IV.
• • Over-voltage category IV. Primary supply level (overhead lines, cable systems, etc.). This category is not relevant to most product standards.

Typically, most standards are based on conditions being pollution degree 2 and over-voltage category II. It is important to note that as working voltage, pollution degree, over-voltage category, and altitude increase, the creepage and clearance distances also increase. The altitude is particularly important when testing to EN 61010.4.

CREEPAGE AND CLEARANCE IN PRACTICE

Each part of a circuit must be studied to determine the necessary insulation grade. Table 2G in EN 60950 describes common applications of insulation. For example, establishing the required creepage and clearance between a primary circuit and an ungrounded safety extra low voltage (SELV) circuit requires reinforced insulation. By measuring and establishing both the working voltage and the pollution degree, the appropriate row and column in Table 2H (and if necessary, Table 2J) determine the minimum clearance distance needed. For one test, the internal components and parts in both primary and secondary circuits are subjected to a steady force of 10 N, and certain minimum clearance distances must be maintained during the test.

Because the primary circuit is an internal circuit connected directly to the external supply mains, this circuit typically contains hazardous voltage. A secondary circuit, which has no direct connection to primary power, may or may not be hazardous. Non-hazardous circuits are classified as SELV.

DC input products, however, can be treated in one of two ways. They can be considered as being fed by an extra-low-voltage circuit, or as hazardous secondary voltages. This would mean that the clearances could be calculated using Table III rather than Table I, requiring slightly smaller clearance distances. DC input products can also be considered as being fed by SELV secondary circuits, depending upon the end application. If isolation is needed, then Table III of the standard is used. However, if isolation is not required in the end application, then clearances are waived, and only operational insulation is required.

SIMPLE DESIGN TIPS

As IT products continue to get smaller, it is more important than ever to have a good and calculated Printed Circuit Board (PCB) design that not only reduces electromagnetic interference emissions, but that also reduces creepage and clearance problems. Where shortage of space on a PCB is an issue, especially between primary and SELV circuits, techniques such as slots or grooves can be used to attain desired creepage distance. Slots must be wider than 1 mm; otherwise, they are not considered acceptable. For a groove (>1 mm wide) the only depth requirement is that the existing creepage plus the width of the groove and twice the depth of the groove must equal or exceed the required creepage distance. The slot or groove should not weaken the substrate to a point that it fails to meet mechanical test requirements.

Another solution is to design the PCB so that components are mounted flat on the board rather than positioned vertically. This layout overcomes problems that might arise from the 10- N push test required in EN 60950. A minimum of 8 mm separation between primary and secondary circuits also prevents problems. When semiconductors operating at hazardous voltages are mounted on grounded or floating heat sinks, certain precautions must be taken to ensure compliance with EN 60950. If heat sinks happen to be live (and they can be), they should be marked accordingly to warn service personnel. Generally, a semiconductor's plastic enclosure is considered as operational (necessary for correct operation of the equipment) or, in some cases, as only basic insulation. Therefore, depending on the heat sink's grounding arrangement, the semiconductor requires either basic or reinforced insulation.

It is equally important to consider creepage and clearance even when using UL-recognized power-switching semiconductors. Although these products carry a recognition mark, the manufacturer's data sheets must be examined to ensure that the components are suitable for the intended application.

The working voltages of the circuit must be considered. Transistors with built-in reinforced insulation (body thicker than 0.4 mm) must also still meet the spacing requirements at their legs. Some designers mistakenly assume that UL certification eliminates the need for further examination.

ELECTROMAGNETIC COMPATIBILITY

EMC stands for electromagnetic compatibility — and is defined as the ability of equipment to function satisfactorily in its electromagnetic environment without introducing intolerable disturbances to anything in that environment. EMC requirements concern two basic concepts: emissions and immunity or susceptibility.

Electromagnetic disturbance is any phenomenon that may degrade the performance of a device, equipment, or system — or adversely affect living or inert matter.

Electromagnetic interference (EMI) is the degradation of the performance of a device, transmission channel, or system caused by an electromagnetic disturbance. In certain parts of the world, "EMI" is used to characterize emissions. This may lead to confusion when it comes to the characterization of immunity, which is sometimes called EMC.

Electromagnetic disturbances can be conducted or radiated — and the emissions and immunity requirements are referred to in military standards (MIL-STD 461/462), either as CE/RE (conducted emission/radiated emission) and CS/RS (conducted susceptibility/radiated susceptibility), respectively.

Disturbances may represent low-frequency (LF) and/or high-frequency (HF) phenomena, as well as broadband and/or narrowband. Broadband disturbances can originate from commutator motors, ignition systems, arc welding equipment, etc.; narrowband from digital electronic circuitry, switched-mode power supplies, and radio communication equipment. Computers have often been reported to cause interference with radio services, including police, aeronautical and broadcast services. On the other hand, radio transmission by a high-frequency carrier, such as a 900 MHz cellular or a 1.8 GHz DCS, can cause problems in computers and all electrical circuits. This is because the carriers are easily picked up by cables and apertures functioning as antennas; and are demodulated in electronic circuits by different nonlinear electromagnetic phenomena.

To really understand how electromagnetic disturbances emanate, propagate, and influence electrical systems, one must have a thorough knowledge of electromagnetic field theory and high-frequency phenomena. EMC represents a broad field of technology; and may represent a new subject for many manufacturers of electrical products. However, if one follows certain rules of thumb regarding wiring, PCB layout, grounding and shielding — and usage of RFI suppression components — it is not difficult to cope with different EMC standards and regulations. In industry, it is assumed that electronic control systems can be used in conjunction with interfering switching operations, motor drives, high-frequency ovens, welding equipment, etc. In a car, electronic automatic systems must function when we use our mobile phone or meet other vehicles (with interfering ignition systems). An electronically controlled wheelchair is presumed to function normally even when the person sitting in the chair uses a mobile phone or a portable PC. We demand that life-supporting electromedical apparatus in a hospital function safely even near high-frequency — radiating surgical equipment.

U.S. REQUIREMENTS

The general EMC requirements in the U.S. are set by the Federal Communications Commission (FCC), while the Food and Drug Administration (FDA) regulates medical products. Mandatory FCC requirements primarily concern computing devices, defined as any electronic device or system that generates and uses timing pulses at a rate in excess of 9000 cycles per second and uses digital techniques. FCC Part 15 covers radio frequency devices capable of emitting RF energy in the range of 9 kHz—200 GHz. Testing should be done according to ANSI C63.4-1992. Part 18 covers industrial, scientific, and medical (ISM) equipment (Figure 1), defined as any device that uses radio waves for industrial, scientific, or medical purposes — and is not intended for radio communications. While most FCC regulations only concern emissions, FDA also requires immunity for certain life-support equipment. FCC Parts 15 and 18 include regulations, as well as technical aspects and limits. FCC Part 68, which governs the technical requirements for registration of telecom terminal equipment, includes lightning surge tests (surge immunity).

Figure 1. Required frequency range for regulationsd frequency range of radiated measurements—ISM

FCC Part 15 currently has three different procedures for showing conformance:

• • Verification, where the manufacturer or the importer files a test report showing compliance.
• • Certification, which requires a review of the application by the FCC, and the use of a unique FCC identification number.
• • Declaration of Conformity (DoC), which requires that tests are performed by a test lab accredited by A2LA or NVLAP (other accredited labs may also be accepted).

The following represents an example of the FCC's classification system, where the correct administrative procedure is listed according to product type (Class A refers to non-consumer products, Class B to consumer products):

• • Personal computers and peripherals (Class B): Certification or DoC.
• • CPU boards and internal power supplies used with personal computers (Class B): Certification or DoC.
• • External switching power supplies (Class A and B): Verification.

EU REQUIREMENTS

The European EMC Directive, 2014/30/EU, sets out the legal requirements on EMC for principally all electric/electronic equipment to be placed or used in the Common Market/ European Economic Area. It replaces EMC Directive 2004/108/EC, which replaced the original 89/336/EEC. The European legislation covers emissions as well as immunity. The EMC requirements are valid for apparatus and systems placed on the market as complete units. Components such as resistors, transistors, or display units are not included. However, components with a direct function to the end-user, like plug-in PC boards, are regarded as equivalent to apparatus and must follow the same rules (see Table I).

New EEC Directives only set out essential requirements and legal aspects (New Approach). Technical aspects are dealt with in specific standards, the application of which is voluntary. These standards are developed by specific bodies, such as CENELEC or ETSI, and are harmonized to the directives by the action of the European Commission. The EMC Directive itself, however, is based on a presumption principle, which means that a product that meets the requirements of the harmonized standards is also presumed to meet the essential requirements of the EMC Directive.

STANDARDIZATION

Under the General Agreement on Tariffs and Trade (GATT) and its successor, the World Trade Organization (WTO), member countries are obliged to adopt international standards for national use wherever possible. International standards concerning EMC are primarily developed by the International Electrotechnical Commission (IEC) and the International Special Committee on Radio Interference (CISPR). The extensive series developed by IEC includes:

• • IEC 61000-1 — Introduction, terms, and conditions, with general definitions and terms for EMC.
• • IEC 61000-2 — Classification of electromagnetic environments, particularly low-frequency conducted disturbances and signaling in public power supply systems.
• • IEC 61000-3 — Limits and disturbance levels for harmonic current emissions.
• • IEC 61000-4 — Testing and measurement techniques.
• • IEC 61000-5 — Installation and mitigation guidelines, with protection of electronic equipment from lightning surges.
• • IEC 61000-6 — Generic standards with immunity for industrial environments.
• • IEC 61000-7 — Generic standards with immunity for residential, commercial, and light-industrial environments.
• • IEC 61000-8 — Power frequency magnetic field immunity test
• • IEC 61000-9 — Electromagnetic compatibility (EMC) measurement procedure for conducted disturbances and immunity
• • IEC 61000-10 — Electromagnetic compatibility (EMC) with the description of the High-Altitude Electromagnetic Pulse (HEMP) environment

The International Organization for Standardization (ISO) is one group involved with EMC standards. North American EMC standards are published by the FCC, the American National Standards Institute (ANSI), and the Institute of Electrical and Electronics Engineers (IEEE). Private standards are submitted by the International Electrotechnical Commission (IEC), Telecommunications Industry Association (TIA), the Alliance for Telecommunications Industry Solutions (ATIS), the Society of Automotive Engineers (SAE) and automotive manufacturers, and the U.S. Department of Defense.

European EN standards concerning EMC are developed by the European Committee for Electrotechnical Standardization (CENELEC).

Regulations and standards concerning telecom and radio transmitting equipment are published by the International Telecommunications Union (ITU) and the European Telecommunications Standards Institute (ETSI).

International and European EMC standards are to a great extent becoming harmonized, because many EN standards are based on IEC and/or International Special Committee on Radio Interference (CISPR) standards. There are also similarities between international and U.S. standards, though they are not equivalent. Figure 2 shows some intercompatibility problems between similar emission standards (FCC Part 15 J and CISPR 22 limits, respectively, measured at 10 m). The FCC, however, accepts conformity to CISPR 22:2016 (formerly CISPR 22:1985).

Figure 2. Emission limits compared at a measuring distance of 10 m

Figure 3. Required frequency range of conducted measurements

STANDARD REQUIREMENTS

Standards are principally divided into the following main groups:

GENERIC/GENERAL STANDARDS

Generic standards refer to the electromagnetic environment in which the apparatus/system is to be used. General standards concern groups of equipment used for general applications in a specific environment, like general telecom equipment and medical and laboratory equipment.

BASIC STANDARDS

Basic standards describe measuring methods and, in some cases, interference levels as well as limits. One of these is the standard series IEC 801-X for process industrial applications, which has been converted into a general series of basic standards, IEC 61000-4-X, which were then translated into European standards as EN 61000-4-X.

PRODUCT AND PRODUCT FAMILY STANDARDS

These are applicable for specific product types, which are specified within the scope of the standard. In addition to these standard documents, there are also standards offering guidance on installation techniques, or a code of practice, for example the IEC 61000 series, Part 5 (IEC 61000-5-X).

EMC STANDARDS CLASSIFICATION

Generic standards have two environmental classes:

1. Residential, commercial, and light industrial environments, including domestic, office, laboratory, and light industrial environments where the apparatus or system is connected to the public mains.
2. Industrial environments, meaning "heavy" industrial environments with separate transformer stations for mains supply, usually with equipment spread over some distance.

This simplified view of the world as one of two categories does not hold true in all cases. There are so-called gray zones such as laboratory or hospital environments where equipment may be connected either to the public mains or to an in-house power net, through a separate transformer station.

CISPR standards concerning emissions, and to some extent corresponding EN standards, have a classification according to the following:

CLASS B/CISPR 22

Information Technology Equipment (ITE) intended primarily for use in domestic environments and may include portable equipment, telecommunications terminal equipment, personal computers, and auxiliary connected equipment.

CLASS A/CISPR 22

ITE, which satisfies Class A but not Class B limits.

The following warning shall be included in the instructions for use: This is a Class A product. In a domestic environment this product may cause radio interference, in which case the user may be required to take adequate measures.

CLASS B/CISPR 11

ISM equipment suitable for use in domestic establishments and in establishments directly connected to a low-voltage power supply network.

CLASS A/CISPR 11

ISM equipment suitable for use in all establishments other than domestic and those directly connected to a low-voltage power supply network. The emission limits differ 10 dB between Class A and Class B equipment, as well as between the generic emissions standards for the "light" and "heavy" environments, respectively, when referred to the same measuring distance. When recalculated from 10 to 3 meters distance, there is a difference in radiated emissions of 9.5 dB. It should also be noted that the classification of computing devices according to FCC 15, and ISM equipment to FCC 18, is very similar to that of CISPR 22 and CISPR 11 Group 2.

WHICH STANDARDS APPLY?

A product standard is one that covers all EMC requirements for a certain product type. In some cases, product standards also cover electrical safety requirements. A product standard takes preference over all other standards. Once it is determined that a product is within the scope of an applicable product family standard concerning emissions and/or immunity, then that standard should be followed. Some examples of family standards include:

• • CISPR 11/EN 55011 Emission standard for industrial, scientific, and medical (ISM) radio RF equipment (see Figure 3).
• • CISPR 12 Emission standard for vehicles, motorboats, and spark-ignited engine-driven devices.
• • CISPR 13/EN 55013 Emission standard for broadcasting equipment like radio, television, etc.
• • CISPR 14/EN 55014 Emission standard for household apparatus and portable tools.
• • CISPR 15/EN 55015 Emission standards for electrical lighting and similar equipment.
• • CISPR 16/EN 55016 Emission standards for radio frequency interference (EFI)
• • CISPR 20/EN 55020 Immunity standard for broadcasting equipment, such as radio and television.
• • CISPR 22/EN 55022 Emission standard for information technology equipment (ITE).
• • CISPR 24/EN 55024 Immunity standard series for IT, including personal computers, printers, and servers.
• • CISPR 32/EN 55032 Emission standard for ITE, such as personal computers, printers, and servers.

Newer product family standards also tend to appear as complementary emissions and immunity standards:

• • EN 55014-1 (household appliances), EN 55014-2 (industrial, scientific, and medical equipment), EN 55014-3 (outdoor equipment and any other not covered by EN 55014-1 or EN 55014-2).
• • EN 55103-1 (2009), EN 55103-2 (2009), 55103-2 (2012), 55103-2 (2016), 55103-2 (2021), 55103-3 (2009), 55103-2 (2012), 55103-3 (2016), and 55103-3 (2021). Emissions and immunity requirements for professional audio, video, and similar electronic equipment.

Specific types of product family standards transferred into general standards include:

• • IEC 555-2/EN 60555-2 LF emissions standard concerning harmonics for household products, etc.
• • IEC 555-3/EN 60555-3 LF emissions standard concerning flicker and voltage variations for household products, etc.
• • IEC 61000-3-2/EN 61000-3-2 General LF emissions standard concerning harmonics.
• • IEC 61000-3-3/EN 61000-3-3 General LF emissions standard concerning flicker and voltage variations.

Today, however, very few pure product standards exist that cover all requirements. Therefore, one must look for an applicable product family standard. An additional complication is that — for the time being — a product can sometimes belong to different product family standards. For example, most household devices must fulfill emissions requirements according to EN 55014-1, as well as EN 60555-2 and EN 60555-3 or EN 61000-3-2 and EN 61000-3-3.

GENERIC/GENERAL STANDARDS

If no product family standard is applicable, one must follow the suitable generic or general standard, which in turn refers to different basic standards. Some of the product family standards are also referred to in other standards, which consequently gives them characteristics of basic standards. The generic standards include:

• • EN 55081-1 Emissions standard for residential, commercial, and light industrial environments.
• • EN 55081-2 Emissions standard for industrial environments.
• • EN 55082-1 Immunity standard for residential, commercial, and light industrial environments.
• • EN 55082-2 Immunity standard for industrial environments.

The IEC also developed corresponding generic standards, ranging from IEC 61000-6-1 through IEC 61000-6-23, known as IEC 61000-6-X before the standard’s development. A general EMC standard that covers emissions and immunity for medical equipment is EN 60601-1-2, the collateral standard for medical equipment. In addition to this collateral standard, there are several product standards covering safety and EMC for specific medical equipment, like EN 60601-2-24, which covers infusion pumps and controllers.

A general EMC standard that covers emissions and immunity for TTE equipment is ETS 300 339 (general standard for radio transmitting equipment). In addition to this standard, there are several ETS/prETS standards covering EMC for different telecom and radio transmitting equipment.

As far as the emissions requirements are concerned, the generic standard is more rigorous regarding light industrial environments than on heavy industry, which as a rule is already rather electromagnetically contaminated. As far as the immunity requirements are concerned, the situation is the opposite. Interference immunity must be hardier in heavy industrial environments.

What then is applicable in mixed or special environments? When using the generic standards, it is recommended to begin with the strictest requirements, which means that the equipment should be classified according to the "worst" combination, such as EN 50081-1/EN 50082-2. This scenario has sometimes been used for equipment in hospital environments.

BASIC IMMUNITY STANDARDS

The IEC standardization committee for industrial processing techniques, TC 65, drafted the first basic standards for immunity to electrical disturbances. This responsibility has been taken over by the committee that works with general EMC standards, TC77 (IEC) and TC 210 (CLC). With this, the publication numbers changed from IEC 801 to IEC 1000/61000 and EN 61000, and thus far the disturbance types that have been dealt with have gone through the following changes:

1. Electrostatic discharges (ESD).
   • • IEC 801-2, ed. 1.
   • • IEC 801-2, ed. 2=IEC 61000-4-2=EN 61000-4-2.
2. Radiated, radio frequency electromagnetic fields (RF fields).
   • • IEC 801-3.
   • • ENV 50140~IEC 61000-4-3=EN 61000-4-3.
3. Electrical fast transients/burst (EFT).
   • • IEC 801-4.
   • • IEC 61000-4-4=EN 61000-4-4.
4. Surges (1, 2 µs/50 µs).
   • • ENV 50142~IEC 61000-4-5=EN 61000-4-5.
5. Immunity to conducted disturbances induced by radio frequency fields.
   • • ENV 50141~IEC 61000-4-6=EN 61000-4-6.
6. Immunity to magnetic fields.
   • • IEC 61000-4-8, IEC 61000-4-9, and IEC 61000-4-10= EN 61000-4-8, IEC 61000-4-9, and IEC 61000-4-10.
7. Voltage dips, short interruptions, and voltage variations.
   • • IEC 61000-4-11=EN 61000-4-11.

Some generic standards and some product standards were published at the same time as the revised standards. There will be references to new — as well as old — basic standard versions for some time.

CONCLUSION

EMC regulations will continue to be successively refined and amended in the future. In many cases, new standards will mean increased testing requirements. And while these testing requirements might not be welcomed by all manufacturers, they will benefit the end-users of electrical equipment.

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