HG/T 20513-2014Design code of instrument grounding (English PDF)

3.1 Safety grounding

3.1.1 The metal casing of electrical instruments and the normally non-energized metal

parts of automatic control equipment may carry dangerous voltage due to various reasons (such as insulation damage). The safety grounding shall be implemented for the following electrical instruments and automatic control equipment.

3.1.3 For field instruments, transmitters and local switches with a power supply lower

than 36 V, safety grounding is not required unless there are special needs.

3.1.4 Automatic control equipment that has safety grounding can be considered to have electrostatic grounding. When using an anti-static raised floor in the control room, electrostatic grounding shall be done. Electrostatic grounding shall share the grounding system with safety grounding.

3.2 Working grounding

3.2.1 Working grounding shall include signal loop grounding and shielding grounding.

3.3 Intrinsically safe grounding

3.3.1 For components of intrinsically safe instruments that need to be grounded for

safety functions, the intrinsically safe grounding shall be implemented according to the requirements of the instrument manufacturer.

3.3.2 The bus bar of the Zener safety barrier shall be connected to the common terminal of the DC power supply, and the bus bar (or guide rail) of the Zener safety barrier shall be intrinsically safe grounded.

3.3.3 The isolation safety barrier does not need to be grounded.

3.4 Electrostatic protective earthing

3.4.1 Control rooms, cabinet rooms, and process control computer rooms where

automatic control systems and other equipment are installed shall be grounded against static electricity. These indoor static conductive floors, anti-static raised floors, workbenches, etc. shall be anti-static grounded.

3.4.2 Instruments and equipment, for which the safety grounding and working

grounding are implemented, do not need to be grounded against static electricity.

5.1 Field instrument bonding method

5.1.1 For the safety grounding of field instrument cable troughs, instrument cable

protective tubes and instrument shells above 36 V, bonding wires shall be connected to nearby grounded metal components every 30 m, and the reliability and electrical continuity of the grounding shall be ensured. Metal equipment and pipelines for storing or transporting flammable media as well as related metal components shall not be used for grounding.

5.1.3 For field instruments that require or need to be grounded on site, they shall be grounded on the field side (see Figure 5.1.3).

5.2 Fieldbus instrument cable shielding grounding method

5.2.1 The signals of the fieldbus instrument system are transmitted by digital communication. The grounding of the shielding layer of the bus signal cable is different from that of the analog signal cable. Both ends of the shielding layer of the bus cable should be grounded (see Figure 5.2.1).

5.2.2 When it is not certain that there is a good equipotential grounding system between the control room and the field, it is advisable to directly ground the shielding layer at the field end of the bus signal cable shielding layer, and the other end of the cable shielding layer is connected to the grounding system through a capacitor. In places with explosive hazards, the capacitor connection grounding end of the cable shielding layer shall be set in a non-explosive safe place (see Figure 5.2.2).

5.2.3 The metal housings of all fieldbus instruments shall be connected to the equipotential grounding system.

5.2.4 For bonding of digital communication cable shields between systems, it is advisable to use a capacitor to connect to the grounding system at one end of the communication cable shielding layer, and the other end is directly grounded. The capacitor connection grounding end of the cable shielding layer shall be set up in a non- explosive safe place (see Figure 5.2.4).

Figure 5.2.4 -- Shielding grounding of communication cables between equipotential bonding control systems

5.3 Bonding method for instruments in the control room/field cabinet room

6.1 Bonding specifications

6.1.1 The conductors of the grounding system shall be multi-stranded copper core insulated wires or cables.

6.1.2 The cross-section of the grounding system connecting wire should be selected according to the type of bonding and the following values.

Bonding wire. 1 mm2~2.5 mm2; grounding branch trunk wire. 4 mm2~16 mm2; bonding trunk wire. 10 mm2~25 mm2; grounding main line. 16 mm2~50 mm2.

6.2 Bonding bar and bonding terminal bar specifications

6.2.1 The bonding bar should be made of 25 mm×6 mm copper strips, or it can be formed by the combination of connecting terminals.

6.2.2 The bonding terminal bar and main grounding plate should be made of copper plates. The thickness of the copper plate shall not be less than 6 mm, and the length and width dimensions shall be determined as needed.

6.3 Requirements for bonding structure

6.3.1 All bonding wires shall be well insulated before being connected to the bonding bar; all grounding branch trunk wires shall be well insulated before being connected to the bonding terminal bar; all bonding trunk wires shall be well insulated before being connected to the main grounding plate.

6.3.2 The bonding bar (bus bar), bonding terminal bar, and main grounding plate shall be fixed with insulating brackets.

6.3.3 Various connections of the grounding system shall ensure good electrical conductivity.

6.3.4 The grounding system shall be marked with durability. The color of identification shall comply with the provisions of Table 6.3.4.