What is tested during EMC?

The two sides of EMC

The EMC Directive 2014/30/EU requires that equipment does not interfere with its environment and is itself resistant to external interference. These two requirements are called emission and immunity. A product that fails on either one does not comply, even if it otherwise functions perfectly.

The underlying logic is simple. In a home or office, dozens of devices are placed next to each other. If every device were allowed to interfere freely, eventually nothing would work reliably. The directive therefore divides the space, with limit values per frequency band.

Both sides are measured in a shielded room so that the environment does not influence the measurement. What you measure is therefore what your product does, not what the building does.

What is measured during emission

Emission is measured in two ways. Conducted emission is the interference your product sends back into the grid via the power cable. Radiated emission is the interference it emits through the air. Both are compared against a limit value per frequency.

For radiated emission, the product runs on a table in the shielded room while an antenna measures all around it. The setup is varied. The antenna moves up and down, the product rotates, and the cables are rearranged. The latter is not a formality, as a cable acts as an antenna.

Therefore, the conclusion of an emission test is always linked to a specific setup. If you change the supplied cable or the placement of the power supply, the result may change as well.

What is done during immunity testing

During immunity testing, the product is intentionally subjected to interference. This includes electrostatic discharge on the housing and connections, a strong radio field around it, fast voltage peaks on the power cable, and short interruptions in the mains voltage. It is then checked whether the product still functions properly.

You define what ‘functioning properly’ means before the test begins. You describe which functions are essential and what behavior you find acceptable. A device that restarts during a voltage dip but then continues normally may pass. A device that freezes fails.

Which standard for which product

For multimedia equipment, EN 55032 generally applies for emission and EN 55035 for immunity. Household appliances and electric tools follow the EN 55014 series. Measurement and control equipment falls under EN 61326-1. If no product standard exists for your type of device, generic standards apply.

• EN 55032 and EN 55035 for multimedia equipment, meaning emission and immunity are separate.
• EN 55014-1 and EN 55014-2 for household appliances and electric tools.
• EN 61326-1 for measurement, control, and laboratory equipment.
• The EN 61000-6 series as a generic standard, when no product-specific standard exists.

The choice between a product standard and a generic standard is not optional. If a product standard exists for your type of device, it takes precedence. A report based on a generic standard when a product standard was available is a weak point in your technical file.

Why products fail

In practice, most findings stem from a handful of known causes. A switching power supply without sufficient filtering. A long cable without shielding. A poor ground connection in the metal housing. Or a firmware update that has unnoticedly changed the switching behavior.

• The power supply. Cheap switching power supplies are the most common cause of excessive conducted emission.
• Cables. A cable radiates. Length, shielding, and the placement of the ferrite help determine whether you pass.
• Grounding and shielding. A metal housing without proper bonding does not function as shielding.
• Software changes. A changed switching frequency can cause a previously passed product to fail.

What falls outside the directive

The EMC Directive does not apply to equipment falling under the Radio Equipment Directive. If your product has Wi-Fi or Bluetooth on board, the EMC requirements are handled via that directive. Aeronautical equipment and equipment used by radio amateurs also fall outside the scope of this directive.

Additionally, equipment that, due to its physical characteristics, cannot cause relevant emissions and cannot be interfered with is excluded. This is a narrow exception, so ensure it is well-substantiated if you rely on it.

Fixed installations have their own regime. They are assembled at a predetermined location for permanent use. Different regulations apply to them than to devices that circulate freely.

What you need to arrange

First, determine if your product has a radio function, as EMC then proceeds via the Radio Equipment Directive. Next, choose the correct product standard and document in writing what constitutes acceptable behavior. Finally, ensure that the tested setup matches what you actually deliver.

1. Check if there is a radio function. If so, EMC is handled via the Radio Equipment Directive.
2. Find the product standard for your type of device. Use a generic standard only in the absence of one.
3. Describe the essential functions and acceptable behavior before the test starts.
4. Have the testing performed with the cables and power supply you actually supply, in the same length.
5. Document that a change in power supply, cable, or firmware may require a retest.