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Detachable power supply systems (Appliance Couplers) according to IEC 60320 provide a great deal of flexibility and efficiency while complying with the strictest safety requirements and responding to the increasing need for user-friendliness and maximum safety.

IEC Appliance Couplers Safe, Simple and Flexible

Detachable power connectors are used in office equipment, in measurement instruments, in IT environments and in medical devices, among many other types of equipment for worldwide distribution. Therefore, each appliance's power system must be adapted to country-specific conditions (e.g. different power plugs in the US, Germany, the UK, etc.). This, in turn, entails differences in the requirements placed on the appliances from the beginning of the life cycle to assembly and testing to logistics and field maintenance. In contrast to hard-wired power components, detachable power systems make it easier to comply with these diverse requirements, thereby minimizing cost and expenses in each phase of the product's life. These trends toward power harmonization are reasons why the need for appliance couplers continues to grow.

Figure 1 illustrates the great variety of detachable power systems (appliance couplers) and the different components. Appliance coupler means a device for connecting a flexible power cord to an appliance or another type of installation. An appliance coupler consists of an appliance inlet and a connector. The figures below show the fundamental differences between the various plug and socket components as defined by the standards on appliance couplers (IEC 60320-1) and interconnection couplers (IEC 60320-2-2), using components rated for 10 A, Protection Class I, pin temperature.

Power supply cord means a flexible cord fitted with a power (mains) plug and a connector, used for connecting an electrical appliance to the power supply (mains).

Interconnection cord means a structural unit consisting of a flexible cord fitted with a plug and a connector built for interconnecting or disconnecting any appliance or installation with/from any other appliance or installation using a power supply cord.

PEM (short for 'Power Entry Module') means a component that integrates other functional components with the actual appliance coupler such as:

• a switch including integrated or remote bowden cable actuation
• a circuit breaker for equipment including overload and overcurrent protection, undercurrent protection and remote triggering
• an appliance fuseholder
• a voltage selector
• an EMC filter for standard and medical applications

Manufacturer such as Schurter, distinguishes between Power Entry Modules with and without filters.

Advantages of PEM over Individual Components:

• Compact dimensions
• Only one product with pre-wired individual components
• Efficient mounting
• Alternative designs with similar dimensions
• Protected, pre-wired and tested power components

Ditribution unit means a housing fitted with multiple appliance outlets to form a component designed to distribute power. A typical application area could be a mobile measurement station, where several devices can be supplied with power from a single distribution unit.

Cord retaining clamp means a mechanical device preventing an appliance coupler from inadvertently being pulled or shaken loose. Typical application areas with stricter safety requirements include medical technology, stage and lighting technology as well as IT.

Advantages of Appliance Couplers over the Entire Life Cycle

An appliance becomes universally compatible with country-specific power requirements when using appliance couplers. A country-specific power supply cord is simply included in the packaging. Model variations are thus minimized. Mounting and hardwiring a power supply cord is labor-intensive and subject to errors. On the other hand, when using appliance couplers all that needs to be mounted is the appliance inlet. In many cases, there is no need for internal wiring, as the appliance's PCB already comes fitted with an appliance inlet. There are no connection wires dangling from the housing exterior. Assembly and handling become easier as a result. Detachable power solutions help eliminate errors while increasing process security; hence enhancing the quality of the finished product.

Further economies of scale can be realized during systems testing. No country-specific test setups are required. The appliances can be connected to slot-in test ports which test appliance functionality and safety in one go using the predefined testing procedures.

Parts procurement, manufacturing and inventory costs are reduced, as appliance manufacturers need only keep a small number of appliances in their inventory. When ready to ship, the appliance is packaged according to its destination country, and includes a country-specific power supply cord as well as operating instructions in the respective language.

Evidence of the consistent and steadfast implementation of this optimized production principle can be seen in the fact that in many instances the software's country-specific basic settings, too, are determined by the end users themselves instead of being set at the factory.

After initial use, appliances can be easily transferred to and used in another country, with a simple change of the power supply cord including an IEC 60320 connector and a country-specific power plug. Even when the power supply cord is damaged, it can be replaced easily, because it is a standardized part that can simply be unplugged and re-inserted. Safety hazards, maintenance expenditure and repairs are thus minimized.

Below is a summary of the advantages of power supply systems fitted with IEC appliance couplers in each phase of an appliance's lifecycle (Figure 3):

Standards Overview

Power supply safety is crucial from the users' perspective. The IEC 60320 standards as well as its substandards create a binding agreement, defining the mechanical, electrical and thermal requirements and safety goals of a detachable power system (appliance couplers) and by establishing a common base for combining components with different origins, thus eliminating the potential safety hazards involved when adding an additional, separate component, i.e. power supply cord. The standard scope is limited to appliance couplers rated at 250 VAC, up to 16A (20A 125/250 VAC UL respectively). Figure 4 shows an overview of the standardized appliance couplers with their relevant names as described in IEC 60320. IEC 60320-1 deals with appliance couplers including appliance inlets and appliance outlets. IEC 60320-2-2 describes interconnection couplers including connectors and plugs. Power supply cords are fitted with these appliance couplers (dotted lines). In addition to these two central standards, there are further substandards of IEC 60320 focus on special topics such as IP protection and appliance specific requirements.

Safety through Coding

The standards establish the fundamental criteria governing protection class, nominal current and pin temperature as well as define various plug outlines. The purpose of plug outlines is to code the appropriate connections in a manner that: the part of an appliance coupler or interconnection coupler to be supplied with power defines the relevant safety limits. In other words, an appliance inlet can be fed only by a connector of identical or higher valency. It is impossible, for instance, to connect a Protection Class II connector to a Protection Class I appliance inlet, while the opposite, i.e. connecting a Protection Class I connector to a Protection Class II appliance inlet, is very well possible. The same applies to the nominal current and the pin temperature. This coding plays a significant role in the safe operation of appliances and the protection against improper use.

Table 1 shows the various main criteria and their specific values according to the standard's definition.

Nominal current: The standard, instead of 'nominal current', uses the term 'rated current'. It defines the current for which the manufacturer has designed the appliance coupler.

Pin temperature TP is measured where the pin projects from the engagement surface (Figure 5). The maximum permitted pin temperatures, according to the standard, are 70°C, 120°C and 155°C, respectively. The appliance's normal ambient temperature TA1 during operation, according to IEC 60320, is 25°C and may occasionally reach 35°C. In other words, the pin temperature is determined essentially by the design of the respective appliance, i.e. its interior temperature TA2, rather than by its ambient temperature. Typical applications with increased pin temperatures include appliances with heating coils such as ovens or electric grills.

Protection classes are defined in IEC 61140. The IEC 60320 standard defines, for appliance couplers, protection class 1 and 2 types, i.e. types for appliances equipped with a protective conductor and special insulation.

In addition to the limiting values described, the standards define further general criteria such as withdrawal forces, testing procedures, the minimum number of insertion cycles and the number of flections in flexible cords. IEC 60320-1 codes the various plug outlines using a combination of letters and numbers (e.g. 'C14'), while IEC 60320-2-2 uses a single letter (e.g. 'F').

Tables 2, 3 and 4 describe the individual plug outlines in detail, i.e. their relevant nominal/rated current, pin temperature and protection class parameters. They also show which combination the standard defines. Each possible combination in the matrix is denoted with a dot. The columns list the components with the pins, while the lines show the sockets.

Normally the parameter of inlet and outlet are similar (e.g. protection class 1 -> 1). It is generally possible to match a connector with a higher rated temperature with a lower rated inlet.

In addition to the connections within the standards, as mentioned, there are possible combinations between IEC 60320-1 and IEC 60320-2-2. Fitted with a flexible cord, the components become interconnection cords to be used for connecting appliances or for extending other interconnection cords or power supply cords.