Delta C2000 Series User Manual page 679

Electrical Cabinet Design
In a high frequency electric field, shielding can be achieved by painting a thin layer of conductive
metal on the enclosure or on the internal lining material. However, the coating must be thorough and all
parts should be properly covered without any seams or gaps (just like a Faraday cage). That is only the
ideal. Making a seamless shielding shell is practically impossible since the cage is composed of metal
parts. In some conditions, it is necessary to drill holes in the shielding enclosure for installation of
accessories (like optional cards and other devices).
1. If the metallic components are properly welded using sophisticated welding technology to form an
electrical cabinet, deformation during usage is unlikely to occur. But if the electrical cabinet is
assembled with screws, the protective insulating layer under the screw must be properly removed
before assembly to achieve the greatest conductivity and best shielding.
2. Drilling holes for the installation of wires in the electrical cabinet lowers the shielding effectiveness
and increases the chance of electric waves leaking through the openings and emitting interference.
We recommend that the drilled holes are as narrow as possible. When the wiring holes are not used,
properly cover the holes with metal plates or metal covers. The paint or the coating of the metal plate
and metal cover should be thoroughly removed to ensure a metal-to-metal contact or a conductive
gasket should be installed.
3. Install industrial conductive gaskets to completely seal the electrical cabinet and the cabinet door
without gaps. If conductive gaskets are too costly, please screw the cabinet door to the electrical
cabinet with a short distance between the screws.
4. Reserve a grounding terminal on the electrical cabinet door. This grounding terminal shall not be
painted. If the paint already exists, please remove the paint before grounding.
Electrical wires and cables
Shielded Twisted Pair (STP) is a type of cable where two insulated copper wires are twisted
together with a metal mesh surrounding the twisted pair that forms the electromagnetic shielding and can
also be used for grounding.
The individual electrical wires and complete cable are surrounded by (synthetic) rubber, that
provides insulation and also protects against damage.
There are two types of electrical cables: high voltage and low voltage. The high voltage cable
differs from the low voltage cable in that it has an additional insulation layer called the dielectric insulator
within the plastic sleeve. The dielectric insulator is the most important component in insulation. The low
voltage cable is usually only filled with a soft polymer material for keeping the internal copper wire in
place.
The shield has two functions.
1. To shield the electrical wire and cable.
A. Electric currents increase as power flows through the power cable and generate an electrical field.
Such interference can be suppressed inside the cable by shielding the power cables or the electrical
wires.
B. To form a protective earthing. When the cable core is damaged, the leakage current will flow via
the shield to ground
2. To protect the cable. A power cable used for the computer control purpose generates only relatively
low amount of current inside the cable. Such power cable will not become the source of interferences
but has great possibility to be interfered by the surrounding electrical devices.
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