The ability to sell power supplies, either built-in or external types, around the world depends on meeting the relevant safety standards that apply in those territories. These standards are defined and administered by national or international agencies with various government-recognized testing laboratories able to certify compliance with such statutory regulations.
The primary goal of safety standards for power supplies used in electrical equipment is to protect against fire, electric shock and injury. Products meeting these requirements may be identified by a safety mark from the associated standards organization or by a mark indicating compliance with local legislation, within a defined economic area or trading zone.
Understanding the complexities and subtle differences between various standards and marking schemes can be daunting. This application note aims to identify the major standards that relate to power supply safety, the agencies that administer them and/or provide certification, and the marking schemes that can be used to show compliance.
Safety Standard Terminology
Classes of Equipment
Safety standards identify different classes of equipment depending on how their power supplies, especially mains units, isolate secondary circuits and accessible parts from dangerous ac mains voltages:
Class I
Equipment achieves electric shock protection through
basic insulation and protective
earth grounding. This requires all conductive parts that could assume a hazardous voltage in the event of basic
insulation failure to be connected to a protective earth conductor.
Class II
Equipment provides protection using double or
reinforced insulation and hence no
ground is required.
Class III
Equipment operates from a SELV (Safety Extra Low
Voltage) supply circuit, which
means it inherently protects against electric shock, as it is impossible for hazardous voltages to be generated
within the equipment.
Understanding safety standards and the above classes of equipment requires a clear understanding of circuit definitions, types of insulation and other terminology used in relation to power supplies.
Insulation and Isolation
There are five types of insulation to shield live components with hazardous voltages from other components and circuits as follows:
- Operational / Functional Insulation
Is only necessary for the correct functioning of the equipment and does not provide any protection against electric shock. - Basic Insulation
Insulation applied to live parts to provide basic protection against electric shock. - Supplementary Insulation
Independent insulation applied in addition to basic insulation in order to provide protection against electric shock in the event of a failure of basic insulation. - Double Insulation
Comprising both basic insulation and supplementary insulation. - Reinforced Insulation
Single insulation system applied to live parts which provides a degree of protection against electric shock equivalent to double insulation.
For power supplies, the minimum insulation requirements are:
- Primary to secondary: Reinforced insulation with a minimum dielectric strength of Vrms.
- Primary to ground: Basic insulation with a minimum dielectric strength of Vrms.
Major Safety Standards
The International Electrotechnical Commission (IEC) and the associated International Organization for Standardization (ISO) are the principle agencies responsible for electrical safety standards. Agencies such as Underwriters Laboratories (UL) and Canadian Standards Association (CSA) provide certification in North America, while similar bodies in Europe are Verband der Elektrotechnik (VDE), Technischer überwachungs-Verein (TUV) and British Standards Institution (BSI). A product meeting an IEC standard such as IEC or the newer -1 standard may be identified with the standard’s number prefixed instead by UL, CSA or EN (European Norm) to indicate the country where it is certified e.g. UL or EN -1. Standards like these with the same numbers but different prefixes are sometimes referred to as “harmonized standards”. But while the IEC continues to pursue harmonization, regional differences remain and consequently products intended for multiple markets will need to show all of the required certifications.
IEC -1
Audio/Video, Information and Communication Technology Equipment
The IEC -1 safety standards represent an important transition from the IEC and -1 standards that currently govern companies marketing audio-visual products or computing/communications equipment in North America and the EU. As the distinctions between AV and ICT equipment become increasingly blurred with new technologies and markets, IEC -1 is a unified replacement for the previous two standards. However, this transition is more significant than a simple merger or name change as IEC -1 adopts fundamentally different engineering principles and terminologies, but like its predecessors, -1 applies to both the end-user as well as to components and subsystems such as power supplies.
IEC -1 ultimately aims to give designers more flexibility in product design and evaluation by implementing Hazard Based Safety Engineering (HBSE) principles that replace the traditional prescriptive approach. These HBSE principles seek to identify potential hazards as energy sources capable of causing pain or injury to others, while finding ways to prevent such energy transfer. This will support the introduction of new and innovative technologies without the standards first needing to be amended, and at the same time minimizing differences between national/regional variations of the standard.
The 2nd edition of IEC -1 is the latest revision that has been accepted by the US, Canada, and EU. This new standard currently coexists with -1 and to aid designers in the transition and includes several clauses to help companies manage legacy inventory of subsystems and components. However, the official adoption of -1 remains on an uncertain timeline as the EU recently pushed its go live date from June to December . As a result, UL has also pushed back its adoption timeline to December to harmonize with the EU. These changing timelines make it imperative for companies to continue to monitor the latest updates and news surrounding -1, while beginning to familiarize themselves with the subtleties and differences between the new and legacy standards. By certifying products to -1 now, companies can further their understanding of the current voluntary standards and avoid the rush to certify their products as the deadline inches closer.
IEC -1
Safety of Information Technology Equipment
IEC -1 consolidates the 2nd edition of this standard with its first and second amendments (from and respectively). The standard is applicable to mains, or battery-powered information technology (IT) equipment and office machines with a rated voltage not exceeding 600 V. It is intended to prevent injury and damage to persons and property from such hazards as electric shock, fire, dangerous temperatures and mechanical instability. Note that in Germany this standard is also referenced as DIN EN -1 and as VDE .
IEC
Safety of Audio, Video and Similar Electronic Apparatus
IEC is intended to protect against fire, electric shock and injury, this time in respect to audio, video and similar equipment, including such examples as video projectors and electronic flash units for photographic purposes. As with the standards already discussed, not all of the protective measures are applicable to power supplies but those that relate to shock and fire require similar precautions with respect to insulation, isolation, limiting voltage and/or current, and measures to increase resistance to fire. IEC references other standards such as: IEC -1 for SELV voltage limits, TNV (Telecommunication Network Voltages) for equipment that is not connected to the mains and IEC -11-10 for component flammability categories.
IEC -1
Safety of Medical Electrical Equipment
IEC -1, which covers the basic safety and essential performance applicable to medical electrical equipment including surgical, monitoring and hospital devices, has a long history with a number of revisions. The standards follow the same general requirements established in IEC -1, but with increased levels of protection for insulation/isolation, creepage, clearance, and leakage current.
Introduced in , the 2nd edition of IEC -1 focused on safety within a 6-foot radius of the patient known as "patient vicinity" and developed three guidelines of increasing severity. This was followed by the 3rd edition in which looked at different "means of protection" (MOP) for patients and equipment operators. Edition 3.1, introduced in , made over 500 changes and clarifications to the 3rd edition to address ambiguities arising from evolving medical technology. Most recently, in , the 4th edition of collateral standard IEC -1-2, "Electromagnetic disturbances - Requirements and tests," was published.
Editions 2, 3, and 3.1
The changes in power supply classification from 2nd edition to 3rd edition dealt with definition, not performance. Both the 2nd and 3rd revisions required two mechanisms for guarding each in the event of a failure. For the area of basic electrical safety and avoiding shock hazard, the 3rd edition further divided means of protection into operator protection and patient protection. This is because the potential hazards seen by each can be quite different; an operator has access to a control panel, for example, while the patient may be "connected" via probes.
Patient leakage currents for various equipment categories were defined in the 2nd edition as follows:
Instead of these classifications, the 3rd edition required medical device manufacturers to define the classification in terms of "Means of Operator Protection" (MOOP) and "Means of Patient Protection" (MOPP) as determined by an ISO- Risk Analysis / Management process. The table below summarizes these classifications and the type of power supply solution that would be appropriate, depending on whether one or two levels of protection were required.
As mentioned earlier, Edition 3.1 then implemented a number of changes to address issues identified as unclear in the 3rd edition. These changes covered subjects such as essential performance, risk management, mechanical testing, temperature testing, and humidity as well as new specifications for mechanical and electrical hazards.
IEC -1-2: 4th Edition EMC Standards
Due to the growing use of devices like smart phones, laptops, and tablets that communicate wirelessly, the new IEC -1-2 collateral standard was introduced to address a reciprocal concern about electromagnetic compatibility (EMC) affecting both the medical device in question and other devices in the vicinity. In the past, it may have been possible to exclude these sources of interference from sensitive medical environments, such as hospitals, but with more and more medical equipment now intended to operate in the home and other environments, EMC concerns had to be taken into account. These "intended use environments" introduced in the 4th edition are specifically defined in three categories: professional healthcare facilities with attending medical staff such as hospitals, home healthcare defined in collateral standard IEC -1-11, and "special" environments that contain high levels of electromagnetic disturbance (e.g. radio-therapy equipment).
The US, Canada, and member countries of the European Union have officially adopted the new 4th edition EMC standards as of December 31, . However, outside of these major countries adoption of the various revisions of IEC -1 is a mixed picture, with transition to the 4th edition being unclear. This means products shipping internationally may require designs meeting more than one revision of the IEC medical standards or multiple versions of the same design to comply.
IEC
Safety of Electrical/Electronic Household Appliances and Similar Applications
IEC -1 is part 1 of an international standard that covers the safety requirements for devices with rated voltages up to 250 V for single phase and up to 480 V for multi-phase, that are intended for household appliances and similar applications. In addition to the general requirements of part 1, there is a part 2 of the standard which sets additional requirements for some specific device types. Due to the variety of appliances that may be found in a household, over 100 device types have been called out in part 2.
In North America, IEC -1 has been used as the basis for a tri-national standard between the United States (UL -1), Canada (CAN/CSA-C22.2 No. -1), and Mexico (NMX-J-521/1-ANCE). In the US, UL -1, which is in its 6th edition, is harmonized to IEC -1 as part of its participation in the HOUS category of the IECEE CB Scheme. However, the United States does not recognize all of the part 2 standards. The part 2 requirements take precedence over the general requirements laid out in part 1.
The European standard is EN -1 and defines how appliances may comply with European directives, such as the low voltage directive. Unlike the United States, the EU recognizes most, if not all, of the 100+ part 2 standards related to specific products.
IEC -1
Safety of Measurement, Control, and Laboratory Equipment
IEC -1 is another safety standard along similar lines to the above IEC and IEC standards, but reflecting requirements in this instance for measurement, control and laboratory equipment, including instruments such as meter and oscilloscopes but also extending to x-ray equipment. Protecting against electrical shock, fire and mechanical or burn injury, IEC also addresses hazards related to fluids, lasers and UV light as well as those that may arise from the measuring circuit. Not all of these hazards are directly relevant to the equipment’s power supply, but fortunately the latest 3rd edition of the standard separates the general equipment requirements from the more specific measurement circuits, which are now covered by IEC -2.
The 3rd edition also defines more stringent requirements in respect to shock and fire hazards:
UL
Safety Requirements for Class 2 Power Units
UL specifies requirements covering indoor and outdoor use Class 2 power supplies and battery chargers in applications such as lighting systems, machinery and other appliances installed in residential and industrial environments. These units utilize an isolating transformer and other components to provide either ac or dc outputs, subject to a maximum rating of 42.4 Vac peak or 60 Vdc. The standard is aimed at products that primarily power low voltage, electrically operated devices including:
- Portable or semi-permanent direct plug-in units with 15 A blade connections for use on nominal 120 or 240 Vac mains circuits.
- Cord and plug-connected units with a 15 or 20 A plug for 120/240 Vac mains supply.
- Units permanently connected to an input supply nominally of 600 Vac or less.
Direct plug-in and cord-connected units also include dc powered supplies operating from a vehicle battery via a cigarette lighter or equivalent dc connector or from a data port associated with information technology equipment. These units are also limited to a maximum input power of 600 W.
The safety requirements of UL are defined in terms of:
- Enclosure strength and rigidity to resist likely abuses.
- Built-in over current and over-temperature protection devices.
- A maximum potential of 42.4 Vac peak / 60 Vdc for exposed wires / terminals.
- Protection from “backfeed” voltage.
Other aspects covered by the standard include: packaging, corrosion, switches, weight, dc cabling, mounting, connections, strain relief, operating temperature, humidity and environment (indoor and outdoor).
UL
Explosive Atmospheres
UL and its IEC and other equivalent standards cover general requirements for the construction, testing and marking of electrical equipment intended for use in explosive atmospheres. Such environments include explosive gas and combustible dust atmospheres (either separately or together). The standard covers the temperatures and pressures under which equipment should be designed to operate safely, taking account of the various potential ignition sources and appropriate protective measures.
Major Safety Agencies and Product Conformance Marks Worldwide
The previous section identified many of the national and international bodies that either define regulatory requirements for product safety or provide testing and certification to assure users that the device or equipment complies with the relevant standard(s). Consequently, conformance marking of products to show this compliance is a necessary prerequisite for their sale in most industrialized countries and may be a legal or contractual obligation.
Product marking may simply show compliance with specific standards but increasingly more general marks are used to indicate compliance with all essential or legally imposed safety requirements. CE and UL marks are two of the most widely implemented conformance marks, while there are a number of other safety marks that may be applied in different regions. These are described more fully below. To ease the issue of regional differences, the Certification Body (CB) scheme allows manufacturers who have been issued a CB test certificate by one National Certification Body (NCB) to obtain certification marks from other participating NCBs.
Regional Safety Marks
Americas, Europe Asia
The maps in the following section highlight some of the more notable safety marking schemes but is not all-inclusive. In addition, in Europe there are other marks applicable in the Nordic countries and other central and eastern European countries such as Denmark, Switzerland, Hungary, Ukraine and Belarus. In Asia, countries including Hong Kong and India operate their own safety marks.
Summary
Despite efforts within Europe, North America and elsewhere to bring about harmonization of safety standards for electrical equipment including power supplies, there are still many different regulations, testing and certification procedures that may need to be taken into account in order to meet legislative requirements in the various territories where such equipment will be sold. Understanding all of these is a challenge and this application note, while it tries to present a fairly comprehensive overview of the various standards, agencies and safety marks, is certainly not a definitive guide.
CUI follows best practices to ensure its power supplies meet the highest levels of safety and performance, offering products approved to standards such as UL, ENEC, TUV and GS while also providing quality solutions that utilize the latest in efficient green power technology.
For more information on regulatory and compliance topics, see our technical papers on EMC Considerations for Switching Power Supplies and Efficiency Standards for External Power Supplies.
Power plug adapters are some of the important gadgets that help to connect electrical appliances of one region to another region where the sockets may vary in shape, size, and voltage system. Here’s a detailed look at the various power plug types:
1. Type A (NEMA 1-15)
Type A, also known as NEMA 1-15, is a two-pinned power plug types appropriate to North America and Japan. It has two flat parallel pins on the side and does not feature a grounding pin. This type of plug is normally used in devices that cannot draw a large amount of power, like lamps and small appliances. It is suitable for Type A and Type B sockets.
2. Type B (NEMA 5-15)
Type B (NEMA 5-15) are power plug types widely distributed in North America. It has two flat parallel conducting tongues and a cylindrical earthen connection pin. The plug is of 15A, 125V, which indicates that the more common electrical appliances’ and electronics’ power requirements can be met by the plug. Its grounding pin makes it safe for use, especially from electrical shocks, as compared to headphones.
3. Type C (Europlug)
Type C, also known as Europlug, is a universal power adapter with two pins that is used preferably in Europe. It has two round pins 4. 0 to 4. The diameter of the electrode is 8 mm, and the distance between the electrodes is 19 mm. The Europlug does not have an earth pin and may only be used at up to 250 voltages. It is meant to fit all those sockets that accept 4. 0 - 4. 8 mm round contacts on 19 mm centers, requirements making it versatile in many countries.
4. Type D
Type D AC adapter plug types are commonly used in India and some African countries. They have three round pins in a triangular pattern, with one larger pin at the top. The voltage typically ranges from 220 to 240 volts. If you are traveling to a country that uses Type D outlets, you will need a Type D adapter to connect your devices safely.
5. Type E
Type E power cord adapter types are mainly used in countries like France, Belgium, Poland, Slovakia, Czech Republic, Tunisia, and Morocco. They are smaller round tapered pins having two and a hole for the socket male earthing pin. This type of plug can be plugged into Type C sockets, although its earthing is better than the plugs. Type E adapters are especially suitable when tourists want to connect their electric items to the outlets present in such countries.
6. Type F (Schuko)
Schuko or Type F is a universal power adapter that has been adopted mostly in the European region. It has rounded twin sharp freelance prongs and twin side earth clips for security. This plug type is best suited to operate up to a capacity of 16 amperes and 250 volts. Also known as the round plug socket, the Type F plugs are used in countries such as Germany, France, and Spain, where they are inserted into round sockets with recessed contacts to avoid electrocution incidents.
Power Adapter Types By Country
Different countries use different power plug types. Therefore, it is important for travelers to know which kind is suitable for use in that particular region.
The most prevalent types, popularly known as types A and B, are found in North America and Japan. Type A has flat parallel pins, while type B adds a central grounding pin.
Type C is used across Europe and is characterized by two round contacts, whereas the UK's popular Type G with three rectangular contacts.
Australia and New Zealand use Type I sockets and plugs, which have two flat pins in the V-form with one for the earth.
One of the most common types is Type D, which has three round pins in a triangular form. Type D is found in India and some African nations.
Namibia and, to some extent, South Africa employ Type M which differs from Type D only in size.
Brazil has a somewhat complex system in which they employ Types C, N, and a Type A, which have slight differences from the original.
Therefore, for an individual who intends to visit different countries, universal adapters or converters will be required to enable the use of electronic products safely and efficiently.
Is It Safe To Use Plug Adapters?
Traveling with the best plug adapters is not dangerous if you take these certain measures. Choose the right adapter to match of your device's voltage and current ratings to ensure it does not overheat.
It is advisable to purchase better quality adapters from reputable brands to avoid using cheap adapters with safety concerns. Look for labels like UL or CE, for example, which ensures the gadget has complied with safety measures.
Do not use adapters for a long time or power high-powered appliances, as this increases the risk of an electrical fire.
Periodically check the state of the adapters and change them if something is wrong in order to ensure safe operation.
Final Words
All in all, it is crucial to navigate power cord adapter types to ensure the safe utilization of electric appliances internationally.
Understanding the types of adapters and their uses thus allows one to have their devices charged without any interference. When traveling, checking the voltage and the type of plugs needed by the appliance to avoid damage or failure is recommended. Furthermore, surge protection, considered a safety measure, would reduce the incidence of accidents among electronics and increase their life expectancy.
Paying more for adapters means purchasing better quality, which will last longer without the same problems as cheaper versions. Remember, however it is extremely important to use the correct power plug adapter types and ensure they are well-maintained to avoid any complications in your travels.
