Lecture 10 Grounding Electrode

Shop Practice with Electrical Code: Grounding Electrode Jayson Bryan E. Mutuc, REE, RME BSEE-PUP MSEE, Major in Power Systems -MIT (candidate)

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2.50.3 Grounding Electrode System and Grounding Electrode Conductor (p.214) 2.50.3.3 Grounding Electrodes (a) Electrodes Permitted for Grounding (1) Metal Underground Water Pipe. A metal underground water pipe in direct contact with earth for 3000 mm or more (including any metal well casing effectively bonded to the pipe). Interior metal water piping located more than 1500 mm from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system

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2.50.3 Grounding Electrode System and Grounding Electrode Conductor (p.214) (2) Metal Frame of the Building Structure. The metal frame of the building or structure, where any of the following methods are used to make an earth connection. a. 3000 mm or more of a single structural metal member in direct contact with earth or encased in concrete that is in direct contact with the earth b. The structural metal frame is bonded to one or more of the grounding electrodes d. Other approved means of establishing a connection to earth. 3

2.50.3 Grounding Electrode System and Grounding Electrode Conductor (p.214) (3) Concrete-Encased Electrode. An electrode encased by at least 50 mm of concrete, located within and near bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6000 mm of one or more bare or rods of not less than 13 mm in diameter, or consisting of at least 6000 mm of bare copper conductor not smaller than 22 mm2. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. 4

2.50.3 Grounding Electrode System and Grounding Electrode Conductor (p.214) (5) Rod and Pipe Electrode. Rod and pipe electrodes shall not be less than 2400 mm in length and shall consist of the following materials. a. Electrodes of pipe or conduit shall not be smaller than 20 mm raceway size and, where of iron or steel, shall have the outer surface galvanized or otherwise metalcoated for corrosion protection. b. Electrodes of rods of iron or steel shall be at least 16 mm in diameter. Stainless steel rod less than 16 mm in diameter, nonferrous rods, or their equivalent shall be listed and shall not be less than 13 mm in diameter 5

2.50.3 Grounding Electrode System and Grounding Electrode Conductor (p.214) (4) Ground Ring. A ground ring encircling the building or structure, in direct contact with the earth, consisting of a least 6000 mm of bare copper conductor smaller than 30mm2 (6) Plate Electrodes. Each plate electrode shall expose not less than 0.186 m2 (2 ft2) to surface to exterior soil. Electrodes of iron or steel plates shall be at least 6 mm in thickness. Electrodes of nonferrous metal shall be at least 1.5 mm in thickness.

(7) Other Local Metal Underground Systems or Structures. Other local metal underground systems or structures such as piping systems, underground tanks, and underground metal well casing that are not effectively bonded to a metal water pipe

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2.50.3 Grounding Electrode System and Grounding Electrode Conductor (p.214) (b) Electrodes Not Permitted for Grounding. The following shall not be used as grounding electrodes: (1) Metal underground gas piping system (2) Aluminum electrodes

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2.50.3.4 Grounding Electrode System Installation (p.216) (a) Rod, Pipe, and Plate Electrodes. Where practicable, rod,

pipe, and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel. (b) Electrode Spacing. Where more than one of the electrodes are used, each electrode of one grounding system shall not be less than 1800 mm from any other electrode of another grounding system. 8

2.50.3.4 Grounding Electrode System Installation (p.216) (d) Metal Underground Water Pipe. Where used as a grounding electrode, metal underground water pipe shall meet the requirements (1) Continuity. Continuity of the grounding path or the bonding connection to interior piping shall not rely on water meters or filtering devices or similar equipment.

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2.50.3.4 Grounding Electrode System Installation (p.216) (d) Metal Underground Water Pipe. (2) Supplemental Electrode Required. A metal underground water pipe shall be supplemented by an additional electrode of a type specified in 2.50.3.3(a)(2) through (a)(7).

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2.50.3.4 Grounding Electrode System Installation (p.216) (5) Rod and Pipe Electrode. The electrode shall be installed such that at least 2400 mm of length is in contact with the soil. It shall be driven to a depth of not less than 2400 mm except that, where rock bottom is encountered, the electrode shall be driven at an oblique angle not to exceed 45 degrees from the vertical or, where rock bottom is encountered at an angle up to 45 degrees, the electrode shall be permitted to be buried in a trench that is at least 750 mm deep. The upper end of the electrode shall be flush with or below ground level unless the aboveground end and the grounding electrode conductor attachment are protected against physical damage. 11

2.50.3.7 Resistance of Rod, Pipe, and Plate Electrodes(p.218) A single electrode consisting of a rod, pipe or plate electrode that does not have a resistance to ground of 25 ohms or less shall be augmented by one of additional electrode of any types specified by 2.50.3.3 (a)(2) through (a)(7). They shall not be less than 1800 mm apart

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