Reasons for the classification

In an industrial environment, signals are classified in four categories according to their EMC performance. This classification is required for the application of cabling rules.

Classification of signals

The following table shows the classification of signals according to their EMC performance:

Classification

EMC performance

Example of a circuit or device with cables in this class

Class 1

Sensitive

Signal is very sensitive.

  • Low level circuits with analog output, instrument transformer ...

  • Measuring circuit (probes, instrument transformer ...)

Class 2

Slightly sensitive

Signal is sensitive.

Can disturb class 1 cables.

  • Low-level digital circuits (bus ...)

  • Low-level circuits with digital output, (instrument transformer ...)

  • Control circuit for resistive load

  • Low-level d.c. power supplies

Class 3

Slightly interfering

Signal disturbs class 1 and 2 cables

  • Control circuit for inductive loads (relay, contactor, coils, inverters ...) with corresponding protection

  • A.C. power supplies

  • Main power supplies for high power devices

Class 4

Interfering

Signal disturbs other classes signals

  • Welding machine

  • Power circuits in general

  • Electronic speed controller, switching power supplies ...