Grounding and shielding

You can connect SCC shield clamps single-handedly and without using any tools.
Thanks to the convenient clamping bracket and the non-pressurized contact spring, a simple and low-fatigue shield connection can be made. At the same time, the design of the contact spring guarantees a reproducible and long-term stable contact quality and compensates any conductor settling effects.

The shield connection is flexible, with clamps available for direct mounting, neutral bus bar mounting, and for DIN rail mounting.
For a clearer overview and assignment of the individual shield clamps, the clamps feature large marking areas on the clamping bracket. This simplifies assigning the cable in accordance with the circuit diagram.

The SK shield clamps clamp the conductors using a knurled screw. To ensure ideal shielding, the clamps feature a spring-loaded and large-area pressure plate. Shield clamps are available for direct mounting and busbar mounting for mounting in the control cabinet.

As components, it is not possible to certify shield connections in accordance with the requirements of the directive and standards for electrical equipment in potentially explosive areas. As such, shield connection clamps can be used in the Ex area even without an appropriate approval or marking.

Voltage differences arise between the conductors of electronic devices, which lead to each electronic device emitting electromagnetic interference. The superimposition of these various electromagnetic interferences increases the overall level of interference. As a result of this, the shielding of devices against electromagnetic interference is incredibly important.
The effects of electromagnetic interference can cause a great deal of damage, especially in industrial process and production technology systems. A particularly high level of immunity is therefore needed for electrical MCR (measurement and control technology) equipment. Device manufacturers must issue a declaration of conformity for their products to guarantee this immunity. Devices may only be brought to market if they comply with the EMC standard.

Field interferences arise as a result of the voltage differences between positive and negative conductors.
For example, a consumer is supplied by a voltage source. Here, voltage differences arise between the positive and negative conductors, which generates an electrical field between the conductors. Furthermore, a magnetic field is generated by the current-carrying conductors. Due to it being current-dependent, this magnetic field is subject to temporal fluctuations. Because a time-constant current is only present in a very small number of applications, this leads to irregular, alternating magnetic fields. These fields become electromagnetic signals, a type of “mini-transmitter”, and receivers at the same time. Each conductor is therefore capable of negatively influencing the function of other electrical and electronic devices.

In practice, several interference mechanisms usually occur at the same time. Furthermore, in addition to the devices, connecting conductors are also affected. A distinction is made between five different types of interference:

• Galvanic interference
  When two circuits use a common conductive part.
• Capacitive interference
  When two conductors laid in parallel over a longer path behave as two opposing capacitor plates and, in this role, act as a short circuit for high-frequency signals.
• Inductive interference
  When a change in current causes a change in the magnetic field, which then induces a voltage in the adjacent conductors.
• Wave interference
  When conductor-bound waves or pulses overlap onto adjacent data transmission or measurement and control technology conductors, as well as the overlap from one conductor circuit to another circuit within a cable.
• Radiation interference
  When conductor-free electromagnetic waves from a source of interference affect systems and conductors. The free wave is the disruptor.

The type of shield connection used depends mainly on the type of interference to be expected.
For the suppression of electrical fields, it is necessary to ground (1) the shield at one end. Interferences caused by an alternating magnetic field, however, are only suppressed when the shield is grounded at both ends. Connecting the shield at both ends (2), however, creates a ground loop, bringing with it the associated well-known drawbacks. Galvanic interferences along the reference potential in particular influence the useful signal, and the shielding effect is reduced. Here, the use of tri-axial cables (4), in which the inner shield is connected at one end and the outer shield at both ends, is a solution. To reduce galvanic interferences when the conductor shield is connected at both ends, one end is often also connected to the reference potential via a capacitor (3). This interrupts the ground loop, at least for direct and low-frequency currents.

Ground loop:
A ground loop is an arrangement in which the reference potential is closed to form a ring.