Taking over Andy's role here ;o)

The term EMC is often misused in the way Erik does in his above post. What is called "EMC", electromagnetic compatibility is actually "EMI", electromagnetic interference.

EMI can be any electrical disturbance; from DC to microwaves, coupled through the air or through wires. It also includes ESD, transients and surges.

EMC, on the other hand, is defined(*) as: "The ability of a device, unit of equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment."
In other words: An electrical or electronic system should be designed in such a way that:
1. Its intended operation is not affected by EMI from nearby other systems.
2. Its own, emitted, EMI does not interfere with the intended operation of nearby other systems.
The key phrase in the above is "in its electromagnetic environment", which means that the acceptable limits for EMI emissions and susceptibility for a given system are related to its intended use.
So Erik's devices, for example, operate in an 'EMI hostile' environment in terms of susceptibility, eventhough their own emissions are relatively harmless.

More specifically the term EMC, especially when talking about "EMC compliance", is often used to signify the European EMC Directive, 89/336/EEC.


Rob.

* IEC50: "Glossary of electrotechnical, power, telecomunication, electronics, lighting and colour terms."