Why is EMC protection important?
Nowadays it’s difficult to find or create a product or industrial plant without modern cabling technology. Industry 4.0, Big Data and fully automated processes are on everybody’s lips.
Parts of these processes are managed or controlled by frequency converters, transformers, electrical switches and communication devices. However, these kinds of switching processes always involve the risk of interference. Precision and the selection of the right components are needed to keep the machine running perfectly.
The aim is for all processes to function smoothly and without errors. This is because something that’s just a bit disruptive like interference on the radio can have far more dramatic consequences in the context of medical technology if the system fails.
This is why industrial environments need ever greater safety against electromagnetic interference. Electromagnetic compatibility (EMC).
How does EMC work?
An electromagnetic interference always originates from an interference source. This can be an item of equipment that carries a high current, such as a frequency controlled motor or a cable.
The source of interference corresponds to a disrupted piece of equipment, known as the interference sink. The interference sink can be a sensor or data cable, for example.
The coupling mechanism in between causes the interference. This can be divided into four different types of coupling:
- Galvanic coupling: The interference source and interference sink are linked with one another, for example by means of a common grounding conductor. An interference current via the common grounding conductor causes electromagnetic interference.
- Capacitive coupling: The interference source and interference sink are close to one another, but not physically connected. With capacitive coupling, the electromagnetic interference (EMI) is produced by the electric field.
- Inductive coupling: With inductive coupling, the interference source and interference sink are also close to each other, but are not connected to one another. However, the interference is caused by the magnetic field.
- Radiation coupling: Radiation coupling generally occurs when the interference source and interference sink are far apart and the conductors ultimately act as antennae and cause the interference from electromagnetic radiation.
In practice, this is usually a mixture of these 4 coupling mechanisms, which must be eliminated, for example by using shielded cables.
What is the EMC directive?
In EMC Directive 2014/30/EU, Article 3, electromagnetic compatibility is defined as:
“[…] the ability of a piece of equipment to operate satisfactorily in its electromagnetic environment without causing electromagnetic interference, which would be unacceptable for other equipment in this environment.”
According to this definition, EMC has two main aspects:
- The equipment must not cause electromagnetic interference.
- The equipment must not be electromagnetically disrupted by its surroundings.
How is EMC protection measured?
EMC protection is measured and specified using coupling resistance [mΩ/m] and/or shielding attenuation [dB]. The coupling resistance of cables and wires is normally specified at a defined frequency of 30 MHz. By contrast, shielding attenuation is used for high frequencies from 50 MHz.
Coupling resistance and shielding attenuation cannot be calculated. This means that the values can only be determined using measurements. The triaxial measuring tube method defined in EN 50289-1-6 is used to determine the values.
How are shielded power and control cables constructed?
There are four different shielding types for power and control cables. Three of these shielding types are particularly suited to use with EMC protection:
Tin-plated copper braiding
A common method of shielding cables is braided copper between the conductors and the jackets. With a degree of coverage of around 80 percent, the copper braiding forms an effective barrier against electromagnetic fields. These cables can be identified by the abbreviation "C" in the LAPP product designation, e.g. ÖLFLEX® Classic 110 CY or ÖLFLEX® Servo 719 CY . Copper braiding can be done in different ways, with one of the crucial parameters being the angle of twist. In highly dynamic applications, such as the installation of the cable in a cable chain, the copper wire is routed around the conductors at a more obtuse angle, so that it creates a full 360-degree wind around the conductors over a shorter distance. In robot cables that need to withstand millions of torsions, braiding is not ideal because gaps occur over time.
Copper wire wrapping
For moving cables in robotics, where the shielding must withstand torsion, copper wire wrapping is often used. As the copper wires in a wrapping are all positioned parallel to each other, there is no problem with the cable torsion. However, the protection against electromagnetic interference from wrapped cables is often worse as the shield wires do not overlap. These cables can be identified by the abbreviation "D" in the LAPP product designation, e.g. ÖLFLEX® Robot 900 DP.
Aluminum-laminated plastic foil
Individual conductors or all conductors in the cable can be wrapped with aluminum-laminated plastic foil. The plastic foil shielding protects your cables and wires, especially at higher frequencies. Cables often also have several shielding types, e.g. the ÖLFLEX® SERVO 2XSLCH-J with aluminum-laminated plastic foil and tin-plated copper braiding.
How are shielded data cables constructed?
Data cables have essentially the same shielding as power and control cables, but other abbreviations are common in product designations:
- Tin-plated copper braiding: “S” (Shielded)
- Aluminum-laminated plastic foil: “F” (Foiled)
There are also two special features for data cables in terms of their shielding rating for EMC protection:
Data transmissions are particularly susceptible to interference, which is why data cables are generally always shielded. For certain areas of application for signal transmission, there are unshielded data cables specially marked with the abbreviation "U" (unshielded), such as the Cat.6 network cableETHERLINE® LAN Cat.6 U/UTP 4x2xAWG24 LSZH , the Cat.5e Ethernet cable ETHERLINE LAN Cat.5e SF/UTP 4x2xAWG24 or our UNITRONIC® BUS ASI cables for networking systems in the field.
Another design for data cables is twisted pair cables. Individual data pairs are twisted here. The twisting ensures that field effects compensate each other. These cables can be identified by the abbreviation “TP” (Twisted Pair).
For instance, the ETHERLINE Cat 6a H 4x2xAWG22/1 SF/UTP cable is divided up as follows: ShieldedFoiled/UnshieldedTwistedPair. This network cable is shielded around all conductors with a wire braid and an aluminum-laminated plastic foil underneath (shielded/foiled). The conductor pairs are twisted in pairs and are not equipped with additional conductor pair shielding (UnshieldedTwistedPair).
How can cables and wires be connected in accordance with EMC?
Did you know that shielding has no effect if it is not grounded? The electrical resistance between the cable shield and ground potential must be as low as possible. The largest possible contact surface of the shield to the EMC component of the cable conduit or connector housing is required for this purpose. The connection between the shield and the EMC component, when installed correctly and, above all, as completely as possible, generates no impedances or only very low ones, even over long distances. The main advantage is that their connection is particularly electromagnetically compatible.
Requirements at a glance:
- The copper braided shielding is positioned all around (large area) at the transition to the housing and without any gaps.
- The cable conduit has a low-impedance connection to the metallic housing wall.
- It must be possible to assemble and disassemble the cable quickly, easily and without damaging the copper braided shielding.
- Optimum shield contact is ensured at both ends of the cable and is based on the ground potential.
A common method is to fit the shield all around and without gaps, e.g. at the transition from the cable conduit to the connector, or when the cable is inserted into a housing using an EMC screw connection. Only then can the connection housing act as a Faraday cage and keep external interfering signals at bay. It is also important that this optimum shield contact takes place on both ends of the cable and is connected to the ground potential.
Our SKINTOP® BRUSH series
Why are connectors important for EMC protection?
Every system is only as good as its weakest point. LAPP connector systems have the advantage of using all the aforementioned shielding connection concepts. Very often, EMC cable conduits are already integrated into the connector, offer the option of connecting a protective conduit and enable the cable shielding to be contacted with the working or PE contact of the connector system.
The enclosure is powder-coated with a non-conductive seal between the housing parts, which insulates them from one another. EPIC® EMC connectors offer 360-degree shielding and vibration-proof shielded connection. The EMC connectors can be identified by their metallically conductive, usually nickel-plated surface. The seals are designed to ensure that the two housing parts pressed or screwed together are in low-resistance contact with metal on metal. The same principle applies to both cable conduits and the mounting wall.
Rectangular connectors have an integrated SKINTOP® MS-M BRUSH cable conduit . The EPIC® ULTRA H-A3 and the EPIC® ULTRA H-B6-24 are therefore easy to assemble and designed for a wide cable clamping range in shielded cables.
If you need a space-saving design, for example for use in servo drives, actuators and sensors, we recommend the POWER and SIGNAL circular connectors from LAPP. These are equipped with a specially coordinated EMC cable conduit for servo and data cables.
EPIC® POWER M17 , EPIC® POWER LS1 , EPIC® POWER LS1.5 or EPIC® POWER LS3 circular connectors with integrated EMC cable conduit are particularly suited to vibration-proof connections for power supply.
For example, LAPP offers EPIC® SIGNAL M17 or EPIC® SIGNAL M23 connectors for sensor, fieldbus, resolver and encoder cables.
How can unshielded cables be shielded afterwards?
If an unshielded cable is not possible in the system for various reasons, or if cables only need to be electromagnetically shielded in certain sections of the system, our SILVYN ® protective cable conduits can also be equipped with copper braids or wrapped in the 3M Scotch 1183 shielding tape.
To ensure that these systems can be reliably grounded, it is best to rely on our one-part or two-part SHIELD-KON® connector for connecting the copper braid to a grounded housing wall or other grounded connection points.
How can EMC protection be improved?
To ensure optimum shielding, cables can be fitted with double shielding or installed in a copper or steel pipe. From an EMC perspective, these shields are completely sealed. Our helically wound SILVYN® metal protective cable conduits with copper braiding, such as the EMC AS-CU offer you complete EMC protection and, at the same time, outstanding flexibility compared to a pipe. It is suitable for particularly harsh environments with high electromagnetic requirements. Our SILVYN® MSK-M BRUSH conduit connector with EMC protection and integrated strain relief will round off your EMC-shielded system.
Are there pre-assembled power, control and data cables with EMC shielding?
Poor EMC is often the cause of installation errors. For a long time, it was customary in industry to buy cables and connectors separately and only connect them when installing them in a machine or production plant, for example.
There are a few disadvantages to greater flexibility: processing quality often leaves a lot to be desired. For instance if the installer cuts too deep when stripping and damages the conductor insulation or only partially connects the shielding to the housing of the connector, causing EMC problems.
This is why the trend is towards ready-assembled cables, which we at LAPP sell under the name ÖLFLEX® CONNECT. The cable and connector are already connected ex works. Customers even receive cable chains fully equipped with cables and hoses, and LAPP also takes over the engineering work. Customers are therefore guaranteed to always receive optimal quality from a single source and can also concentrate on their own work, namely building machinery.