What Is an Earthing Conductor? Definition, Requirements, Size

Earthing conductor (UK) / Grounding conductor (US): conductor forming a conductive path between a conductive part and an earth electrode [definition: IEC 60050-195-2021]. Included as part of the earthing arrangement.

Example: conductor connected between a main earthing terminal or busbar and an earth electrode.

Earthing arrangement
Figure 1. Example of a earthing arrangement (the figure shows the earthing conductor)

Note: Uninsulated parts of earthing conductors that are in the ground are considered part of the earthing electrode.

Requirements and Cross-Section

Earthing conductors shall comply with 543.1.1 or 543.1.2 [2]. Their cross-sectional area shall be not less than 6 mm2 for copper or 50 mm2 for steel. Where a bare earthing conductor is buried in the soil, its dimensions and characteristics shall also be in accordance with Table 54.1 [2].

For example, for a circular vertical earth electrode made of hot-dip galvanised steel rod, the minimum diameter will be 16 mm. And for horizontal earthing electrode and earthing conductor made in the form of a round wire of the same steel, the minimum diameter will be 10 mm.

Here is the table below:

Table 54.1 – Minimum size of commonly used earth electrodes, embedded in soil or concrete used to prevent corrosion and provide mechanical strength
Material and surface Shape Diameter, mm Cross sectional area, mm2 Thickness, mm Weight of coating, g/m2 Thickness of coating/sheathing, μm
Steel embedded in concrete (bare, hot galvanized or stainless) Round wire 10
Solid tape or strip 75 3
Steel hot-dip galvanizedc Stripb or shaped strip/plate

– Solid plate – Lattice plate

90 3 500 63
Round rod installed vertically 16 350 45
Round wire installed horizontally 10 350 45
Pipe 25 2 350 45
Stranded (embedded in concrete) 70
Cross profile installed vertically (290) 3
Steel copper-sheathed Round rod installed vertically (15) 2000
Steel with electrodeposited copper coating Round rod installed vertically 14 250e
Round wire installed horizontally (8) 70
Strip installed horizontally 90 3 70
Stainless steela Stripb or shaped strip/plate 90 3
Round rod installed vertically 16
Round wire installed horizontally 10
Pipe 25 2
Copper Strip 50 2
Round wire installed horizontally (25)d 50
Solid round rod installed vertically (12) 15
Stranded wire 1,7 for individual strands of wire (25)d 50
Pipe 20 2
Solid plate (1,5) 2
Lattice plate 2
a Chromium ≥16 %, Nickel ≥5 %, Molybdenum ≥2 %, Carbon ≤0,08 %.
b As rolled strip or slit strip with rounded edges.
c The coating shall be smooth, continuous and free from flux stains.
d Where experience shows that the risk of corrosion and mechanical damage is extremely low, 16 mm2 can be used.
e This thickness is provided to withstand mechanical damage of copper coating during the installation process. It may be reduced to not less than 100 μm where special precautions to avoid mechanical damage of copper during the installation process (e.g. drilled holes or special protective tips) are taken according to the manufacturer’s instructions.
NOTE. Values in brackets are applicable for protection against electric shock only, while values not in brackets are applicable for lightning protection and for protection against electric shock.

Where no noticeable fault current is expected to flow through the earth electrode (e.g. in TN systems or IT systems), the earthing conductor may be dimensioned according to 544.1 [2].

Caution: Aluminium conductors shall not be used as earthing conductors.

Note. Where a lightning protection system is connected to the earth electrode, the cross-sectional area of the earthing conductor should be at least 16 mm² for copper (Cu) or 50 mm² for iron (Fe) (see the IEC 62305 series).

The connection of an earthing conductor to an earth electrode shall be soundly made and electrically satisfactory. The connection shall be by exothermic welding, pressure connectors, clamps or other suitable mechanical connectors. Mechanical connectors shall be installed in accordance with the manufacturer’s instructions. Where a clamp is used, it shall not damage the electrode or the earthing conductor.

Connection devices or fittings that depend solely on solder shall not be used independently, as they do not reliably provide adequate mechanical strength.

Note. Where vertical electrodes are installed, means may be provided to allow the inspection of the connection and the replacement of the vertical rod.

In order to measure the resistance of an earthing arrangement, it must be possible to disconnect the earthing conductor at a convenient location. In an electrical installation of building, this is usually the main earthing terminal. Disconnecting the earthing conductor must only be possible with a tool.

An identification symbol must be provided at the point where the earthing conductor enters the house:

Protective earthing symbol

Grounding Conductor in NFPA 70 (USA)

Grounding Conductor: A conductive path (s) that is part of an effective ground-fault current path and connects normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both. [3]

Informational Note No. 1: It is recognized that the equipment grounding conductor also performs bonding.

Informational Note No. 2: See 250.118 for a list of acceptable equipment grounding conductors.

Types of Equipment Grounding Conductors

The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following [3]:

  1. A copper, aluminum, or copper-clad aluminum conductor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
  2. Rigid metal conduit.
  3. Intermediate metal conduit.
  4. Electrical metallic tubing.
  5. Listed flexible metal conduit meeting all the following conditions:
  • a. The conduit is terminated in listed fittings.
  • b. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
  • c. The size of the conduit does not exceed metric designator 35 (trade size 1 1/4).
  • d. The combined length of flexible metal conduit, flexible metallic tubing, and liquidtight flexible metal conduit in the same effective ground-fault current path does not exceed 1.8 m (6 ft).
  • e. If used to connect equipment where flexibility is necessary to minimize the transmission of vibration
    from equipment or to provide flexibility for equipment that requires movement after installation, a wire-type equipment grounding conductor shall be installed.
  1. Listed liquidtight flexible metal conduit meeting all the following conditions:
  • a. The conduit is terminated in listed fittings.
  • b. For metric designators 12 through 16 (trade sizes 3/8 through 1/2), the circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
  • c. For metric designators 21 through 35 (trade sizes 3/4 through 1 1/4) , the circuit conductors contained in the conduit are protected by overcurrent devices rated not more than 60 amperes and there is no flexible metal conduit, flexible metallic tubing, or liquidtight flexible metal conduit in metric designators 12 through 16 (trade sizes 3/8 through 1/2 ) in the effective ground-fault current path.
  • d. The combined length of flexible metal conduit, flexible metallic tubing, and liquidtight flexible metal conduit in the same effective ground-fault current path does not exceed 1.8 m (6 ft).
  • e. If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation, a wire-type equipment grounding conductor shall be installed.
  1. Flexible metallic tubing where the tubing is terminated in listed fittings and meeting the following conditions:
  • a. The circuit conductors contained in the tubing are protected by overcurrent devices rated at 20 amperes or less.
  • b. The combined length of flexible metal conduit, flexible metallic tubing, and liquidtight flexible metal conduit in the same effective ground-fault current path does not exceed 1.8 m (6 ft).
  1. Armor of Type AC cable as provided in 320.108 (NFPA 70).
  2. The copper sheath of mineral-insulated, metal-sheathed cable Type MI.
  3. Type MC cable that provides an effective ground-fault current path in accordance with one or more of the following:
  • a. It contains an insulated or uninsulated equipment grounding conductor in compliance with 250.118 (1) (NFPA 70).
  • b. The combined metallic sheath and uninsulated equipment grounding/bonding conductor of interlocked metal tape-type MC cable that is listed and identified as an equipment grounding conductor.
  • c. The metallic sheath or the combined metallic sheath and equipment grounding conductors of the smooth or corrugated tube-type MG cable that is listed and identified as an equipment grounding conductor.
  1. Cable trays as permitted in 392.10 and 392.60 (NFPA 70).
  2. Cablebus framework as permitted in 370.60 (1) (NFPA 70).
  3. Other listed electrically continuous metal raceways and listed auxiliary gutters.
  4. Surface metal raceways listed for grounding.

FAQ

What Is the Difference Between a Grounding Conductor and a Grounded Conductor?

Grounded Conductor: A system or circuit conductor that is intentionally grounded. Although an equipment grounding conductor is grounded, it is not considered a grounded conductor.

What Type of Wire Is Used for Earthing?

There are a few different types of wire that can be used for earthing, depending on the specific application. The most common type of wire used is copper, as it has good electrical conductivity and resistance to corrosion. Other metals such as aluminum or stainless steel can also be used, but they may not have the same level of performance as copper. In some cases, speciality wires such as silver-coated copper or braided strands may be used to improve earthing performance.

How Do You Calculate Earthing Conductor Size?

There are several ways to calculate the size of an earthing conductor. The most common method is to use the American wire gauge (AWG). This method takes into account the cross-sectional area of the conductor, and is a good way to estimate the size of a conductor for most applications.

Another way to calculate the size of an earthing conductor is to use the International Organization for Standardization (ISO) system. This system uses the diameter of the conductor, and is more accurate for very small conductors.

To calculate the size of an earthing conductor using the AWG system, first determine the cross-sectional area of the conductor. This can be done by measuring the diameter of the conductor with a ruler or caliper. Once the diameter is known, consult a table of AWG sizes to find the corresponding cross-sectional area.

To calculate the size of an earthing conductor using the ISO system, first determine the diameter of the conductor. This can be done by measuring the cross-sectional area of the conductor with a ruler or caliper. Once the cross-sectional area is known, consult a table of ISO conductor sizes to find the corresponding diameter.

Once the size of the earthing conductor has been calculated, it is important to select a material that is compatible with the environment in which it will be used. Copper and aluminum are two common choices for earthing conductors, but other materials may be better suited for specific applications.

References

  1. IEC 60050-195-2021
  2. IEC 60364-5-54-2011
  3. NFPA 70. National Electrical Code, 2020