Safety and Compatibility in “Hot” Appliance Couplers

Heat-generating appliances place special demands on the products’ power supplies. Couplers can guarantee safety and compatibility.



Appliance couplersElectric grills, heating devices, powerful projectors, data servers, or lighting systems – all these appliances generate a high degree of heat during operation and place special demands on the power supply. Inherent risks such as overheating, short circuits, burns, or electric shocks must be reliably prevented for safe operation. Hot appliance inlets, according to the IEC 60320-1 component standard, guarantee this safety as well as the compatibility of products from one manufacturer to the next.

The IEC 60320-1 component standard is a worldwide specification for appliance inlets and connectors, covering various current ranges, protection classes, maximum pin temperatures, and ambient temperature for the connectors. Until the introduction of this standard, appliance couplers were covered under the DIN 49491 standard and were commonly called “waffle iron plugs,” since they were frequently used in electric irons and waffle irons. A porcelain insulator with a steel tongue to establish the safety contact was installed in the appliance. The coupler was surrounded by a Duroplast (Bakelite) housing and was typically fabricated using low-quality cords with a fabric or rubber sheath. This type of hot appliance inlet design concealed serious safety risks:

  • Short circuits inside the socket due to a lack of heat-resistant insulation on the cord
  • Charring caused by overheating of the plug components
  • Electric shocks due to insufficiently recessed conductive contacts on the plug

With products manufactured according to the IEC 60320-1 standard, these risks can be eliminated, for the most part, with proper use – meaning users and appliances are properly protected as are the equipment and surroundings. An additional advantage of IEC 60320-1 is the complete compatibility of products from a wide range of manufacturers.


High-temperature appliance inlets are used universally for the operation of appliances with high heat generation, such as electric grills, table grills, raclette makers, or electric heaters. Hot appliance inlets are also frequently used in other applications such as IT equipment (e.g., high-powered computers, data servers), powerful projectors, lighting systems, medical devices, measurement instruments, power supplies, or other industrial types of equipment.


From the user’s perspective, power supply safety is crucial. The IEC 60320 set of standards establishes basic criteria for protection class, rated current, and pin temperature, and provides specific measurements for the different coupler shapes. Based on the maximum permitted pin temperature, the IEC 60320-1 component standard distinguishes three main categories:

  • Appliance couplers for cold conditions with maximum pin temperature of +70°C
  • Appliance couplers for warm conditions with maximum pin temperature of +120°C
  • Appliance couplers for hot conditions with maximum pin temperature of +155°C

These three temperature categories (cold, warm, and hot appliances) are established only for the 10A inlet styles. The remaining styles have only one or two temperature categories (see Table 1).

Coupler categories

Table 1: Coupler categories (source: SCHURTER AG)

Protection classes I and II are another criterion for distinction. Protection class I describes appliance couplers with a protective ground conductor. Protection class II (also called protective insulation II) is distinguished by increased or doubled insulation. In IEC 60320-1, nominal current values of 2.5A, 6A, 10A, and 16A are referred to as rated current, thereby defining the current rating according to that which the manufacturer has conformed to for the appliance coupler design.

Besides the limit values described above, the standard defines added general criteria such as pull-out forces, test procedures, minimum number of insertion cycles with and without an electrical load, and the number of flexions in the attached cords. The standard’s scope is limited to appliance couplers from 250VAC to a maximum 16A.

In the IEC 60320-1 standard, the different connectors and appliance inlets are categorized and labeled with the letter C followed by a number (e.g., C14). The outlets (female contact-protected appliance outlets) receive an uneven number (e.g., C21); the mating inlets (male) receive the following even number (e.g., C22).

Pin Temperature

Appliance inlet diagram

Lateral section view of an appliance inlet and its relevant temperatures (source: SCHURTER AG)

The classification according to cold, warm, and hot appliance couplers results from the maximum pin temperature (PT), which is the maximum that can occur during nominal current operation. The ambient temperature (AT1) provided for standard operation of the appliance is +25°C. On occasion, a temperature may reach +35°C according to the standard 1. The pin temperature is measured where the pin projects from the plastic surface. However, besides the ambient temperature, the temperature reached in the interior of the appliance (AT2) during operation also has an effect on the pin temperature. This again depends on the type and design of the appliance.


Different coupler contours encode the matching couplers, to ensure the appliances are safely operated and improper use is prevented. Normally, the appliance inlet and outlet parameters match, as defined in the IEC 60320-1 standard. This solution is preferred if possible. An inlet, however, can also be supplied with current from an outlet with a higher rated value. So an appliance inlet from protection class II can be connected to an appliance outlet from protection class I, but not vice-versa. The higher value principle also applies to the pin temperature: It is possible to connect outlets with a greater temperature resistance to inlets with a lower temperature resistance without affecting the safety of both appliance and user in the process.

This article was contributed by SCHURTER.


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