Technical Guidance Note 7

TOPIC: Class A versus Class B

DRAFT: 5

REVISION DATE: 6.11.98

PREVIOUS REVISION DATE: 22.1.98

BACKGROUND: EN 50081-1:1992 requires that equipment intended for use in the residential, commercial, and light industrial environments complies with the Class B limit of EN 55022, while EN 50081-2:1993 allows equipment for use in the heavy industrial environment to comply with the less stringent Class A limit.

EN 55022 does not rigidly relate the A and B classification to particular environments but states that "Class B ITE is intended primarily for use in the domestic environment".

ISSUE: Which limit, A or B, should a piece of IT equipment comply in order to satisfy the requirements of the EMC Directive ?

GUIDELINES: A product specific standard such as EN 55022 always takes precedence over the corresponding generic standard(s); this is stated explicitly in CENELEC Report R110-001 "Guide to EMC standardisation for product committees"

While EN 55022 does not generally preclude the use of Class A ITE in a domestic environment, such use would give a higher probability of interference being caused than if Class B ITE were used. In the event of interference being caused, the EMC Regulations (Regulation 78) may be invoked to prohibit the user from operating the equipment and/or the manufacturer from manufacturing it. It is recommended that ITE likely to be used in a domestic environment (e.g. a desktop PC) complies with the Class B limit.

ITE used in the office / light industrial environment may in general be Class A. It is less likely to be close enough to susceptible equipment to cause interference. It should be noted, however, that this is not always the case. For example, the office environment might be a high street bank with residential apartments above it. Again, Regulation 78 may be invoked if interference is caused.

For example, a PC used in the office environment may contain an adapter which connects it to a local area network. When the adapter is active, the PC may comply with the Class A limit but not the Class B limit. With the adapter inactive, the PC may comply with the Class B limit. It may disconnected from the local area network and taken home for use with little risk of causing interference. In such a case, the instructions for use must make this distinction clear.

In the above case, if the adapter is sold as an integral part of the PC (i.e. it is not possible to purchase the PC without the adapter), the EC Declaration of Conformity for the PC should indicate that it complies with the Class B limit of EN 550222 with the adapter inactive, and the Class A limit with the adapter active.

SUPPORTING INFORMATION: The text of EN55022: 1994 allows manufacturers to supply Class A products into domestic environments, providing that guidance is given to users to enable them to avoid interference. However, manufacturers should consider whether such an approach might compromise their compliance with the protection requirements of the EMC Directive.

EN 55022 requires Class A ITE to have a warning statement included in its instructions for use. The text of the warning is as follows:

"Warning: 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."

Disclaimer
No responsibility or liability can be accepted by the EMC Test Laboratories Association or any of its officers or members for the contents, specifications and/or advice referred to or contained in this Technical Memorandum and/or action taken as a result of information contained in this Technical Memorandum. Note that:
1. The Association is not by supplying this Technical Memorandum providing professional advice or guidance to any specific party on any specific matter and no legal relationship is created by the provision of this Technical Memorandum.
2. Parties should take specific advice when dealing with specific situations and consult their own professional advisors in this regard.
3. Members are free to deviate from the above guidelines where they think it appropriate, unworkable, or not commercially viable. Under these circumstances, the EMCTLA Secretariat should be informed of the reasons for the deviation so that the matter can be reviewed.