structure, steel-frame reinforced concrete structure or reinforced concrete structurecan be utilized as common grounding electrode. The detailed requirements are in accordance with the article 235.

Section 5 EARTHING IN CIRCUITS AND CABLE LINES

Article 237. Earthing of metal covers

This article stipulates that grounding conductors of iron pedestal or metal enclosure can be connected with metallic shielding layer of high-voltage cable in order to reduceground resistance of grounding system. Instead of the grounding method in which each electrical equipment is provided with respective grounding work, grounding conductor of each electrical equipment is connected with each other to form one common grounding system from the viewpoint of reduction groundof resistance effectively. In this case, ground resistance of this grounding system shall satisfy the value stipulated in the relevant standard.

Even if ground resistance is difficult to meet the requirement,ground resistance can be reduced by adopting the above-mentioned grounding method because grounding conductor can be extended.

Article 238. Use of aluminum cover

This article stipulates that the aluminum cover of a cable can be used as a neutral wire. A neutral wire must be hard to corrode, and fault current must flow through it safely. Moreover, it is necessary to have sufficient mechanical strength so that disconnection. shalletc not occur. Therefore, the aluminum cover applied to a neutral wire must satisfy the predetermined valueof stress area, mechanical strength, and ground resistance provided in the design criteria.

Article 239. Terminal with earth wires

Grounding conductors must be connectedfirmly by pressure bonding or welding so that ground resistance does not increase by the contact resistanceat a contact point. Moreover, the tensile strength of the connected grounding conductor should satisfy the value provided in the design criteria.

Article 240. Earthing of flexible links

When a grounding conductor is required to be flexible, an electrical insulated wire or a cable shall be used as the grounding conductor. The grounding conductor must beconnected firmly with a bolt. Welding connection is permitted at the part where connection with a bolt is unsuitable.

Article 241. Use of steel conduits

This article stipulates that grounding system iscomposed by connecting metal ducts for wiring. In other words, this article stipulates the requirements in the case that metal ducts for wiring are usedas a common grounding electrode in grounding system. The requirements are same as these stipulated in Article235. In order to satisfy therequired ground resistance, the metal ducts must have sufficient conductivity. Moreover, ducts andgrounding conductor must beconnected firmly to reduce touch resistance sufficiently.

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Article 242. Lighting grouped grids

In spite ofstipulation in Article 238, the metal or the lead sheath of a cable whichis used for the circuit for lightings shall not be utilized as a neutral conductor. Moreover, when this sheath needs to be grounded, it shall be grounded firmly at two or more grounding points throughout the full length of the cable.

Article 243. Supplying or distribution cubicles

This article stipulates that a metal enclosure of switching/distribution board can be connected to metal pipes or metal sheaths of cables to formone grounding system. In this case, the specification on the kind and thickness of a groundingconductor must satisfy therequirements on ground resistance and tensile strength. In addition to this, a metal enclosure of switching/distribution board shall be connected to metal pipes or metal sheathof cables firmly with bolt or by welding in order to prevent slack of a connection point.

Article 244. Joint of earthwires with metal covers

A metal enclosures or iron pedestals of electrical equipment, a cubicle and a switchboardshall be connected to grounding conductors firmly so that breakage or disconnection of grounding conductors. In addition to this, before connection, the connection surface shall be cleaned up so that the imperfect contact between a metal enclosure or metal pedestal and grounding conductor, or insertion of foreign body into connection surfacedoes not occur and increase of touch resistance or overheat connection surface is not caused. The specifications on the kind, the cross-sectional area and the mechanical strength of the grounding conductor must satisfy what is provided in the design criteria.

1.grounding conductor shall let earth fault current flow safely.

2.grounding conductor shall be the metal wire which is difficult to corrode with its tensile strength of 1.04kN and more or the annealed copper wire of which diameter is diameter 2.6mm and more.

Section 6 METHODS OF PAINTING AND MARKING

Article 245. Protection of grounding wire

When a grounding conductor is laid at the place where a person can touch it easily, it shall be laid as follows. But these requirements are not applied to a power receiving electricity room and an electric room.

1.An electrical insulated wire, a cabtyre cable or a cable shall be used between grounding electrode and 60 cm above ground.

2.As for a grounding conductor between 25cm below ground and 2m above ground, it shall be

covered with a synthetic resin conduit pipe with its thickness of 2mm and more, or the material which has equivalent insulation and mechanical strength to this conduit pipe.

3.When a grounding conductor is laid along a metal object such as a metal pole, a grounding electrode shall be buried apart from the metal object by 1m. However, if the grounding electrode

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is buried in depth of 30cm and more from the bottom of the metal object, this requirement is not applied.

Grounding wire

60cm

25cm

1m

30cm

Grounding electrode

Figure 245 Installation of grounding conductor

Article 246. Painting of earthing system

A grounding conductor shall be marked by black color in order toenable to distinguish a grounding conductor from main conductors easily. But this requirement is not applied in the following cases.

1.Only a grounding conductor is laid alone, and accordingly, the grounding conductor can be distinguished easily

2.One core of a multi-core cable, a multi-core cabtyre cable or a multi-core code which is used as a grounding conductor is a naked wire or is painted by black color.

In case that an electrical insulated wire painted by other than blackcolor is used for a grounding conductor, this wire shall be marked by black tape at every suitable distance including its terminals.

Article 247. Use the bare earthed wires

A bare grounding conductor shall be paintedtwo times and more with an undercoat and a finishing coat respectively.

After cleaning up the parts to be paintedand confirming that there are no objects such as dusts, foreign bodies, etc on the surface, an undercoat shall be carried out immediately.

The finishing coat shall be carried out after confirming that an undercoat is dried completely when 24 hours has passed after completion of an undercoat.

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