Grounding system for electrical equipment and that for lightning protection system shall be separated.

Chapter 6-10 Alternatives to Earthing Conductors

Article 586. Alternatives to Earthing Conductors

(1) When, in ferroconcrete building or steel framed building, the steel frame or reinforcing steel in this building is used as a grounding conductor or a grounding electrode, the part of such steel shall be buried underground and all the steels shall be connected each other firmly in order to equalize the voltage on the steels. In this case, the following conditions shall be satisfied.

-The touch voltage on conductive part of thebuilding shall not exceed 50V in case that one-phase earth current flows through the grounding systemTherefore,. steel frames or reinforcing steels shall be connected each other.

-In addition to the above, the touch voltage on metal parts of electrical machine installed in the building shall not exceed 50V.

-Moreover, the touch voltage on the metal parts of external wall of the buildingadjacent to the above-mentioned building shall not exceed 50V.

(2)the steel frame or reinforcingsteel in the building of which ground resistance is not more than 2ohm, can be used as grounding electrode of the grounding system for the powerwithgird isolated neutral point.

(3)If the following conditions are satisfied, embedded metal water pipeline with ground resistance no more than 3ohm, can be used as a grounding electrode.

-Grounding conductor shall be connected to metal water pipe at the point where the diameter of the water pipe is more than 75mm or equal

-If there is the connection point betweengrounding conductor and metal water pipe at the water consumer side from the water meter, bypass conductor shall connect the both sides of the water meter.

-If the connection point between groundingconductor and metal water pipe is exposedto the public, this connection point shall be protected by appropriate cover.

-The metal used to connect grounding conductor and metal water pipe shall have performance of keeping the connecting part from electrical corrosion.

Article 587. Priority of Natural Objects as Earthing Conductors

Natural conductors made of conductive materials, which will always remain in/on the structure and will not be modified (e.g. interconnected steel-reinforcement, metal framework of the structure) may be used as parts of grounding system

Other natural components can only be considered as being additional to grounding system.

Steelwork within reinforced concrete structure is considered to be electrically continuous provided that the major parts of interconnections of vertical and horizontal bars are welded or otherwise

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security connected. Connections of vertical bars shall bewelded, clamped or overlapped a minimum of 20 times their diameters and bound or otherwise securely connected.

Steel conduits for electrical conductors, box and other structures which are used as ground conductor or protection neutral conductor shall be connected with each other tightly.

-In case that the steel conduits are arranged without cover, the sleeves can be used to connect on minimum paint layer or other tight connectors can be used.

-In case that the steel conduits are arranged with cover, onlysleeves for tight connection can be used on minimum paint layer.

-In case that long screw joint is applied for connection, lock nuts are applied to the both sides of the joint part.

In both cases such as with cover and without cover in the power line with earthed neutral point, the conduit shall be connected to the sleeve or the connector at two points on the both sides of it by welding

Interconnected reinforcing steel in concrete foundations or other suitable underground metal structures should preferably be used as a grounding electrode. When the metallic reinforcement in concrete is used as a grounding electrode, special care shall be exercised at the interconnections to prevent mechanical splitting of the concrete. In case that the conduit is arrangedwithout cover, lock

nuts cannot be adopted.

Chapter 6-11 Earthing of Mobile Electrical Equipment

Article 588. Earthing of Mobile Electrical Equipment

The enclosure of mobile generator shall be grounded.

The neutral point of the generator shall be grounded in order toavoid danger such as electrical shock and damage to the electrical equipment caused by earth fault current.Moreover, the protective device such as earth leakage breaker or earth fault protective relay shall be installed at the generator in order to detect earth fault and interrupt the earth fault current.

Article 589. Earthing of Enclosures of Mobile Electrical Equipment

The enclosure of mobile electrical equipment shall be grounded.

Flexible conductor shall be used as a grounding conductorThe. grounding conductorshall be connected to the enclosure of the mobile electrical equipment firmly in order to avoid disconnection of the grounding conductor.

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Figure 589 Connecting method of grounding conductor

Article 590. Alternatives to Earthing

Refer to Article 564 – Article 568.

Article 591. Conditions not Requiring Earthing

As for generator and motor, connection between the metal enclosure and metal base can be considered as grounding. In this case, at the contact surface between its metal enclosure and the metal base, paint

shall be removed from the surface and the surface shall be cleaned and fattened in order to ensure electrical good connection.

Base

Figure 591 Connection between metal enclosure and metal base

Article 592. Earthing Conductors for Mobile Electrical Equipment

The following conductors can beused as conductor which connects enclosures of power supply source to the enclosure of the mobile electrical equipment.

a)The fifth core of cable cores in 3-phase power network with neutral conductor.

b)The fourth core of cable cores in 3-phase power network with neutral conductor

c)The third core of cable cores in single-phase power network

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