Earthing System
Introduction
The grounding system of the ULP system architectures must be designed and installed in power switchgear and controlgear assemblies in accordance with ANSI C37.20.1 and UL 1558, UL 845, and UL 891 standards.
The types of grounding are as follows:
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Protective grounding:
Grounding a point or points in a system or in an installation or in equipment for purposes of electrical protection.
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Functional grounding:
Grounding a point or points in a system or in an installation or in equipment for purposes other than electrical protection.
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 ground, 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 ANSI C37.20.1 and UL 1558, UL 845, and UL 891 standards).
NOTE: The PE wire of devices having power (for example, mains, circuit breakers, feeders, and variable speed drives) must be directly connected to the PE bar. -
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 ground terminal block in the enclosure must be as short as possible.
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Each DIN rail must be connected to the protective ground of the enclosure. A galvanized steel DIN rail is recommended rather than an aluminum one in order to provide the most consistent grounding.
|
A |
DIN rail connected to the protective earth of the enclosure |
|
B |
Connection as short as possible |
|
C |
Protective earth terminal block |
|
D |
Power supply |
Functional Grounding
The Enerlin'X devices (IFE, EIFE, and IFM interfaces, IO module, and FDM121 display) have a functional ground. The functional ground 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 ground conductor (PE).
If the devices are mounted on the door of the enclosure, check the ground 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:
