What is EMC?
EMC, electromagnetic compatibility, is the ability of electrical equipment to function correctly in its electromagnetic environment without causing interference that disturbs other equipment. EMC therefore has two sides: emission (how much a device interferes) and immunity (how much interference a device can tolerate). In industry EMC is essential, because sensitive measurement and control signals, such as 4-20 mA and industrial Ethernet, run alongside powerful sources of interference such as variable frequency drives, welding equipment and switching contactors.
🗓️ Which legislation and standards apply to EMC?
| Rule or standard | Content |
|---|---|
| EMC Directive 2014/30/EU | European law: equipment must meet EMC requirements for CE marking |
| EN IEC 61000-6-2 | Generic immunity requirements for industrial environments |
| EN IEC 61000-6-4 | Generic emission requirements for industrial environments |
| EN IEC 61000-4-x | Test methods, such as ESD (-4-2), radiated field (-4-3), burst (-4-4) and surge (-4-5) |
| EN IEC 61800-3 | EMC requirements for adjustable speed electrical drives |
| IEC 60204-1 | Electrical equipment of machines, with a section on EMC |
A fixed installation, such as a production line or plant, does not need CE marking for EMC, but under the directive it must be built according to good engineering practice, with documented measures.
🧠 How does EMC interference arise?
| Coupling path | Mechanism | Example |
|---|---|---|
| Conducted | Interference via power or signal cables | A drive sends high-frequency currents back into the supply |
| Capacitive | Electric field between parallel cables | Motor cable next to a sensor cable in the same tray |
| Inductive | Magnetic field around current-carrying conductors | Large currents induce voltages in signal loops |
| Radiated | Electromagnetic waves | Two-way radios or wireless transmitters close to a controller |
| Via earth | Potential differences and ground loops | Shield connected at both ends to different earth potentials |
In practice the consequences are fluctuating measurements, unexplained communication errors on ProfiNET or Profibus, spontaneous PLC resets and damaged input cards.
🛠️ Which EMC measures do you take in a control cabinet?
- Zoning in the cabinet — separate power sections (drives, power supplies) from signal sections (PLC, I/O)
- Cable separation — run power and signal cables in separate trays or at least 20–30 cm apart; cross at right angles
- Shielded cables — for drive motor cables and for analogue and data signals
- 360° shield termination — terminate the cable shield all round with EMC glands or clamps on an earthed mounting plate, not with a loose wire (pigtail)
- Common reference plane — a galvanised mounting plate as reference and a meshed earthing network
- Filters and ferrites — mains filters and motor chokes on drives, ferrite cores on sensitive cables
- Surge protection — against lightning and switching surges on power and field cables
🔐 Does EMC have anything to do with security?
EMC is mainly a reliability topic, but it also touches on security. Intentional electromagnetic interference (IEMI) can disrupt or disable equipment; wireless links such as Wi-Fi and WirelessHART can be disrupted with a jammer. In addition, unexplained communication failures may be caused by poor EMC, but also by an attack. Good EMC practice therefore makes it easier to recognise genuine incidents.
❓ Frequently asked questions
What does EMC stand for?
EMC stands for electromagnetic compatibility: the ability of electrical equipment to work properly in its electromagnetic environment without itself causing unacceptable interference. A device meets EMC requirements if its emissions stay below the limits and it withstands the level of interference expected in its environment.
Why do variable frequency drives cause EMC problems?
Variable frequency drives switch the motor voltage with fast transistors thousands of times per second. These steep switching edges cause high-frequency interference that leaks via the motor cable, the supply and the earthing to other equipment. Shielded motor cables with 360° termination, mains filters and good earthing limit that interference.
Must a machine comply with the EMC Directive?
Yes, a machine placed on the EU market as apparatus must comply with the EMC Directive 2014/30/EU, alongside the Machinery Directive or Machinery Regulation. The manufacturer demonstrates this with EMC standards such as EN IEC 61000-6-2 and 61000-6-4 and states it in the EU declaration of conformity. Separate rules apply to fixed installations.
What is the difference between emission and immunity?
Emission is the amount of electromagnetic interference a device itself emits, through cables or through the air. Immunity is a device’s ability to keep working correctly despite external interference. EMC standards set limits on emission and minimum requirements for immunity, depending on the environment: residential or industrial.
How do you terminate a cable shield?
A cable shield is preferably terminated all round (360°) to an earthed metal surface, using an EMC gland or shield clamp, and for high-frequency interference at both ends of the cable. A loose wire (pigtail) performs poorly at high frequencies. Where there are large potential differences between the two ends, good equipotential bonding is needed to prevent ground loops.
How do you track down an EMC problem?
You track down an EMC problem by looking for a link between the fault and the switching of other equipment, such as a motor or variable frequency drive starting. Then check cable separation, shield terminations and earthing. An oscilloscope or a current clamp on the shield makes interference currents and ground loops visible.
📌 In summary
EMC (electromagnetic compatibility) ensures that equipment does not cause excessive interference and can withstand interference itself; in the EU it is governed by the EMC Directive 2014/30/EU and the EN IEC 61000 series. In control cabinets, cable separation, shielding with 360° termination and a good earthing network determine whether measurement and communication signals remain reliable.