Earthing System
Introduction
The earthing system of the ULP system architectures must be designed and installed in power switchgear and controlgear assemblies in accordance with IEC 61439-2 standard.
The types of earthing are as follows (conforming to standard IEC 60050-826):
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Protective earthing:
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Earthing a point or points in a system or in an installation or in equipment for purposes of electrical protection.
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Functional earthing:
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Earthing a point or points in a system or in an installation or in equipment for purposes other than electrical protection.
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Mounting Devices in the Electrical Enclosure
The following rules for mounting devices in the enclosure must be followed:
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The enclosure can be used to connect devices to the earth, in particular auxiliary power supply, PLC, and ULP modules, when the resistance between the protective conductor (PE) and all the metallic parts of the enclosure is 0.1 Ω maximum (conforming to IEC 61439-2 standard).
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All metallic parts of the enclosure must be connected together. The contact between parts must be metal on metal: paint and other isolating material must be removed. A special grease or paint must be applied on the connection to avoid corrosion in harsh environmental conditions (for example, relative humidity >65%, outdoor applications, atmosphere where corrosive agents, such as Hydrogen Sulfide (H2S, are present).
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The connection to the protective earth terminal block in the enclosure must be as short as possible.
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Each DIN rail must be connected to the protective earth of the enclosure. A stainless steel DIN rail is recommended rather than an aluminum one in order to provide the most consistent earthing.
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A |
DIN rail connected to the protective earth of the enclosure |
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B |
Connection as short as possible |
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C |
Protective earth terminal block |
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D |
Power supply |
Functional Earthing
The Enerlin'X modules (IFE, EIFE, and IFM interfaces, IO module, and FDM121 display) have a functional earth. The functional earth is provided by the metallic parts of the assembly (enclosure with metallic DIN rails) having a resistance equal to 0.1 Ω maximum with the main protective earth conductor (PE).
If the devices are mounted on the door of the enclosure, check the earth continuity between the door and the PE conductor. The door must be connected to the enclosure frame with at least one PE cable. It is recommended to use PE cable with copper braids.
Examples:
