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Asia On The Mark Issue 26 (Summer 2008)

General Differences between UL and IEC Standards for Small Household Kitchen Appliance (Part 1)

Small household kitchen appliances are diverse in types and usages. Consumers are typically concerned for the safety of these products when in use. At present, UL and IEC standards for small household kitchen appliances are not yet harmonized as harmonization efforts often involve the difficult task of addressing differences between the standards being harmonized. Differences in national codes, laws and practices may result in national differences from the IEC requirements. As UL standards are maintained and updated, effort is made to avoid creating unintentional national differences to minimize obstacles for future standards harmonization.

In order to help manufacturers of small appliances gain access to global markets smoothly, this article will explain the differences between UL and IEC standards, in terms of description, definitions and testing requirements.

UL and IEC Standards

The Standard IEC 60335-1 published by IEC (International Electrotechnical Commission) addresses general requirements for household and similar electrical appliances — safety. It shall be used with the relevant part 2 of IEC 60335. The part 2 standards are companion documents to the part 1, making reference to the part 1 by affirming, deleting, modifying or adding requirements to part 1. For household kitchen application, there are four part-2 Standards; namely, IEC 60335-2-9, IEC 60335-2-13, IEC 60335-2-14 and IEC 60335-2-15 (see Table 1).

Standards Applicable Products Applicable UL Standards
IEC 60335-2-9 Grills, toasters and similar portable cooking appliances. It also applies to waffle iron, bread makers, ovens, barbecues, griddles, etc.
For these three kinds of product types in the U.S. market, the applicable standards are:
UL 1026 for Electric Household Cooking and Food Serving Appliances
UL 1083 for Household Electric Skillets and Frying-Type Appliances
UL 1082 for Household Electric Coffee Makers and Brewing-Type Appliances
IEC 60335-2-13 Deep fat fryers, frying pans and similar appliances.
IEC 60335-2-15 Appliances for heating liquids, coffee makers, kettles, steam cookers, yoghurt makers, egg boilers, etc.
IEC 60335-2-14 Food processors, grinders, slicing machines, knife sharpeners, centrifugal juicers, etc. For the U.S. market, the applicable standard is UL 982 for Motor-Operated Household Food Preparing Machines
Table 1. Applicable Products of IEC 60335-2 and Applicable UL Standards

1. Definitions

  • Class II (IEC) vs Class 2 (NEC®/UL)

  • “Class II” in IEC standards stands for the appliance construction in which protection against electric shock does not rely on basic insulation only but in which additional safety precautions are provided, such as double insulation or reinforced insulation, and there being no provision for protective earthing or reliance upon installation conditions. Once an appliance is in compliance with all Class II insulation requirements of the relevant IEC end-product standards, the following symbol shall be used to indicate the appliance as Class II equipment.

     

    For UL, this symbol also indicates that the equipment is double insulated. However, once this symbol is marked on appliance, not only the UL end-product standard (e.g. UL 982) is applicable, but also the additional standard, UL 1097, Double Insulation Systems for Use in Electrical Equipment, is applied.

    “Class 2” is a U.S. terminology for isolated electrical power sources having limited voltage and energy capacity so as to reduce the risk of electric shock and fire hazard. Requirements for voltage and energy capacity limitation are indicated in the U.S. National Electrical Code® and numerous UL standards, including UL 1310, Class 2 Power Units. “Class 2” is not related to double insulation at all.

  • Grounding vs Earthing

  • The meaning of the terms “Grounding” and “Earthing” are identical. The former is a U.S. term referenced in the National Electrical Code® and the latter is the IEC term. Similarly, the terms “ungrounded” and “grounded” used in UL standards are equivalent to “live” and “neutral” in IEC standards.

    Per IEC requirements, including those appliances with supply cords to be replaced by qualified technical person, the protective earthing terminal shall be indicated by the following symbol.

     

    This symbol can also be found in UL Listed household appliance, but it is not common, since grounding is not required for these cord-connected products. In both the UL and IEC standards, these products are not required to be grounded or double insulated (Class 0). However, in many countries where the supply source has a potential of more than 150 V to ground, such as in Europe, these products are required to be grounded or double insulated. In addition to the IEC standard, grounded products (Class I) with nonmetallic enclosures must be evaluated for double insulation (Class II Construction).

    2. Leakage Current Test

    The equipment for measuring leakage current for UL and IEC requirements appear to be different based on the specific wording in the standards. However, actual practice is not very different.

    The type of instrument to measure leakage current is clearly defined in standards UL 1026, UL 1082, UL 1083 and UL 982. Leakage current meters suitable for “threshold of perception” leakage current measurements are commercially available, typically described as meeting the requirements of UL standards. The standards do not currently anticipate high frequency and non-sinusoidal leakage current and therefore are silent on making such measurements. Where such leakage current is expected, the measuring instrument must comply with the requirements of UL 101 (Standard for Leakage Current for Appliances).

    In the past, leakage current values have been given in milliamperes (mA), however, the term Measurement Indication Unit (MIU) is being adopted in conformance with the latest edition of the American National Standard for Leakage Current for Appliances, ANSI C101-1992. The term MIU refers to the numerical indication of a defined measurement instrument.

    The MIU coincides numerically with milliamperes only at low frequencies. At high frequencies, the number of milliamperes flowing through the instrument can be significantly higher than the indication in MIUís. Therefore, the term MIU has been selected instead of milliamperes for measurement of leakage current.

    The IEC 60335 requirements are based upon the requirement of IEC 60990, where the leakage current meter shall be capable of responding to peak readings with frequencies of up to 1 M Hz. The test instrument utilized for the UL appliance standards, measuring mA's at low frequencies, does not fulfill IEC 60335, requiring MIU measurements at higher frequencies; however, UL 101 is consistent with IEC 60990 and 60335.

    3. Dielectric Strength Test

     

    For appliances rated 120 V, other than an electric knife, the test potential of the UL Dielectric Voltage Withstand test is typically 1000 Vac for a period of one minute. If this appliance employs a motor rated at more than Ĺ horsepower, the test potential is 1000 V plus twice rated voltage (e.g. 240 Vac for 120 V appliance). The IEC requirement makes no distinction for the test voltage (1000 V for basic insulation) based on the horsepower.

    Before conducting a Dielectric Voltage Withstand test, the test equipment tripping current sensitivity should be set. However, this is a difference between the UL requirements and IEC requirements on how to get it done. Sensitivity is set at UL by using a calibrated resistor of 120 K ohm connected across the output of the unloaded test equipment. For a product subjected to 1000 V potential, the tripping current will thus be 8.3 mA. The tripping current in IEC requirements is not calibrated by an external resistor, but rather, in accordance with Table 5 of IEC 60335-1, it is based on the short circuit and release energies of the test equipment transformer (100 mA tripping current for a 120 V appliance).

    Generally, for small household kitchen appliances, the test voltage applied per the UL Dielectric Voltage Withstand Test is based upon the rated voltage and horsepower while the IEC Electric Strength Test is based upon the rated voltage and the type of insulation.

    4. Impact Test

    The UL and IEC enclosure impact tests have distinct methods.

    There are two types of UL impact tests: drop impact test and ball impact test. The type of test to be applied is dependent on the intended use of appliance. If it is a hand-held appliance, drop impact test is applicable; otherwise ball impact test is applicable. To determine the impact energy for the ball impact, the material of enclosure has to be taken into account first, basically 0.75 ft-lbf (1.0 J) for plastic and 1.5 ft-lbf (2.0 J) for metal enclosures of counter supported appliances. The impact test may be conducted on a single sample or on up to three samples, however, each sample must withstand at least three impacts.

    For IEC requirement, appliance is checked by applying three blows to the appliance by means of the spring hammer with impact energy of 0.5 J according to IEC 60068-2-75. Only one sample is subjected to the impact test.

    (See Part 2 in Issue 27)

    by Cherie Ip, Engineer, Conformity Assessment Services, Hong Kong

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    In this Issue
    On the Cutting Edge — UL research programs address key safety issues
    Global Compliance Strategy Shared in Technical Summit
    UL 61058-1 Appliance Switches (WKKY2) — Frequently asked questions
    Understanding UL Standards for Optical Fiber
    NOM Mark of Mexico issued by UL
    UL’s Management System Registration Business to Merge with Germany’s DQS
    General Differences between UL and IEC Standards for Small Household Kitchen Appliance (Part 1)
    Taking the Mystery Out of UL’s Follow-Up Services
    UL University
    UL Standards
    News Bites


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