Grounding underground cable

In certain locales, power transmission is made by means of underground cables. In one example an 8.0-cm-diameter cable is buried at a depth of 1.3 m, and the resistance of the cable is 1.1 x 10 4 ft/m. The surface temperature of the ground is 25°C, and k = 1.2 W/m °C for earth. Calculate the maximum allowable current if the outside temperature of the cable cannot exceed 110°C. 

The arrangement form used in the electrode cables buried inside seam roof, electrical meter installed in the tunnel behind, linked ground monitoring station through the underground cable. 

Electrocution from striking an underground cable can be spectacular when it occurs and the most effective precaution is to obtain clearance from the local Electricity Board or the factory electrical engineer that the ground is clear of cables. If doubt exists, instruments are available that enable underground cables to be traced. 

Another responsibility of the plant layout designer is to establish the location of the instrument cable trays and analyzer houses. Both items are coordinated with the instrument engineer during the early phase of the job. The main instrument cable runs are located either in elevated trays, generally in the pipe rack, or below ground in cable trenches. These requirements are dis-cu.ssed in Chapters 11 (Pipe Racks) and 13 (Underground Piping). 

Test condition A (100 °Cfor 42 days) is applicable for cable insulations and installations under moderate conditions, generally below 50°C, e.g., for underground cable, ducts, and suspension cable or above ground cable in moderate climatic zones. 

The most usual forms of buried metal structures are pipelines, piles, tanks and power and telephone cables. Power cables must usually have some metal protection, covered by expensive continuous factory-applied sheathings of considerable thickness. Since water, gas and petroleum pipelines provide the greatest area of metal surfaces to be protected below ground, a detailed discussion of the protection given to them would appear to be the best means of dealing with coatings for underground use. 

The electric current is induced into the ground by means of alternating anodes and cathodes. Anodes as well as cathodes are integrated into separate closed-loop pump systems, wherein electrolytes are circulated. Via these electrolytes, pH is controlled at a predetermined level, and the pollutants, transported by the groundwater, are captured by the electrodes under the influence of the applied potential (Fig. 17.1). Conditioning of the electrolytes as well as periodical removal of the contaminants from the electrolytes is effectuated in a special containerized installation. If necessary, electricity cables and extraction ducts and pipes can be installed underground. 

Blue stake- Another phrase for Utility Notification. This is when a utility company (telephone, gas, electric, cable TV, sewer and water, etc) comes to the job site and locates and spray paints the ground and/or installs little flags to show where their service is located underground. 

Install critical power, control, instrument, and alarm wiring and pneumatic tubing outside the fire-exposed envelope. Cable trays and conduit banks should be routed underground or on the upper levels of elevated pipe racks at least 30 feet above the ground and outside the drainage path of hydrocarbon spills. Install fire proofing of critical systems and equipment if they are inside the fire-exposed envelope. 

Later that morning the excavation crew broke ground. Five minutes later, in the area that Diego wasn t able to get checked, they struck a fiber optic cable. Two minutes after that the utility crew arrived to identify and mark the underground installations. 

CFR Part 56, Subpart K and Part 57, Subpart K address the use of electricity at surface metal and nonmetal mines and underground metal and nonmetal mines, respectively. These subparts address adequacy of cable conductors, circuit and traiUng cable overload protection, performance of work on electric equipment and electric power circuits, grounding system requirements and testing of grounding systems, handheld electric tools, fuse removal and replacement, protection of trading cables from physical damage, installation of troUey wires and track, isolation of communication circuits from power circuits, and so forth. 

Cathodic protection is a proven corrosion control method for protection of underground and undersea metallic structures, such as oil and gas pipelines, cables, utility lines and structural foundations. Cathodic protection is now widely applied in the protection of oil drilling platforms, dockyards, jetties, ships, submarines, condenser tubes in heat exchangers, bridges and decks, civil and military aircraft and ground transportation systems. 

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