Correct design of earthing and shielding is essential for both personnel safety and the reliability of your installation. In modern environments, full of power electronics and sensitive control systems, a traditional "50Hz look" at earthing is no longer sufficient. Errors in earthing or incorrect shielding lead directly to EMI (Electromagnetic Interference), unexplained machine failure and even physical damage to bearings and components.
On this page, you can read how to correctly apply earthing and shielding, how to recognise common mistakes such as ground loops and what steps to take to ensure the electromagnetic compatibility(EMC) of your installation.
Short on time? These are the key points you need to know about earthing and shielding:
Safety and functionality: Earthing serves two purposes: protection against electric shock (safety earth) and fault elimination (functional earth).
EMC foundation: Good earthing and shielding, together with potential equalisation, form the basis for electromagnetic compatibility (EMC). Without this foundation, filters or other solutions do not work optimally.
High-frequency behaviour: Modern faults are often high-frequency. A ground connection that measures well with a multimeter (low resistance) can be an open connection for high frequencies.
The weakest link: Most problems arise at the finish. An expensive shielded cable connected incorrectly (e.g. via a 'pigtail') loses its performance.
This information is specifically prepared for professionals responsible for critical electrical installations:
Do you work with variable speed drives, LED lighting, PLC controls or sensitive measuring equipment? Then the quality of your earthing and shielding directly affects your operational reliability.
To solve problems, we need to keep terms pure. In practice, these terms are often used interchangeably, but they have different functions.
Connecting to earth.
Safety earth (PE): Intended to dissipate the current in the event of a fault (short circuit) so that the protective device trips. This is low-frequency (50Hz) and focuses on human safety.
Functional earth: Meant to ensure fault-free operation of the installation. It acts as a reference point for signal voltages and dissipates high-frequency currents.
Connecting all conductive parts (cabinets, lines, structures) together to prevent voltage differences.
Comparison: Think of this as a boat. If everyone is on the same level, nobody falls over, even if the boat (the voltage level) goes up and down on the waves.
Wrapping cables or equipment in conductive material (such as a copper braid or foil). This works both ways: it prevents a cable from radiating interference to its surroundings and it prevents the cable from picking up interference from outside (Faraday cage principle).
Nuance - Low-frequency vs high-frequency: A yellow-green wire is fine for safety earth (50Hz). But for high-frequency disturbances (kHz/MHz range, coming from switching electronics), a round wire has too high an impedance. High-frequency currents flow on the outside of the conductor (skin effect). Therefore, for functional earth we prefer to use flat wires, which have a larger surface area.
Poor earthing or shielding is rarely immediately visible, but the consequences are. Often the software or components are unfairly pointed at, while the cause lies in the cabling.
Typical symptoms in practice:
Impact on the organisation: The impact goes beyond a technical failure. It leads to unexpected production stops, loss of data and unsafe situations for technicians. In addition, manufacturers can reject warranty if it is found that EMC installation regulations have not been followed.
A food manufacturing company was suffering from random stops of a packaging line. The PLC gave several error messages, but after a reset, everything was running properly again for hours. Replacing the sensors and the PLC board solved nothing.
The analysis: Engineers from HyTEPS performed measurements on the potential equalisation and currents through the shielding. What emerged? The main motor's variable frequency drive (VFD) was connected with a shielded cable, but the shield was not correctly connected all around (360 degrees) on the motor side, but twisted together to form a long 'pig-tail'.
The conclusion: The 'pig-tail' created a high impedance for the high-frequency disturbances generated by the inverter. The interference could not dissipate through the shield and sought another path: through the sensor cables that were in the same duct. This disturbed the 0-10V signal to the PLC.
The solution: The glands were replaced with EMC glands where the shield makes contact with the enclosure all around. The faults disappeared immediately and did not recur.
Improving earthing and shielding requires a combination of correct design, proper use of materials and craftsmanship during installation.
Use the right system (TN-S)
In modern installations, a TN-S system (where Zero and Earth are strictly separated from the transformer) is the norm. In old TN-C systems, Zero and Earth are combined (PEN conductor). This ensures that return currents can also flow over equipment enclosures, which is disastrous for EMC.
Create a meshed earthing network (MESH)
We used to work with a tree (star) structure. For high-frequency currents, a meshed structure (MESH) works much better. This involves connecting as many metal parts together as possible to lower the impedance.
Correct connection of shielding
Separation of cables
Keep power cables (which cause interference) physically separated from signal cables (which are sensitive). Preferably use metal cable trays with a partition.
Even experienced installers unintentionally make mistakes in this area, often because training focused on 50Hz safety and not high-frequency EMC.
Do you suspect a problem with earthing or shielding? Follow these steps:
Basic checks you can often perform yourself. However, EMC problems are complex and often invisible without sophisticated equipment. Call in a specialist when:
Our engineers not only analyse your installation for standards, but look at the actual physics behind the failure.
Delve further into the subject matter via these related pages:
Do not hesitate in case of unexplained failures. Speak to a HyTEPS engineer about your situation or request a Power Quality survey. We will help you find the cause and restore operational reliability.
HyTEPS
Beemdstraat 3
5653 MA Eindhoven
