Cable sheaths

Fine Powder Resins. Fine powder PTFE resins are extremely sensitive to shear. They must be handled gendy to avoid shear, which prevents processing. However, fine powder is suitable for the manufacture of tubing and wire insulation for which compression molding is not suitable. A paste-extmsion process may be appHed to the fabrication of tubes with diameters from fractions of a millimeter to about a meter, walls from thicknesses of 100—400 )J.m, thin rods with up to 50-mm diameters, and cable sheathing. Calendering unsintered extmded soHd rods produces thread-sealant tape and gaskets. 

The principal types of scrap are battery plates and paste, drosses, skimmings, and industrial scrap such as solders, babbitts, cable sheathing, etc. 

Only lead alloys containing copper below 0.08% have practical appHcations. Lead sheet, pipe, cable sheathing, wine, and fabricated products are produced from lead—copper alloys having copper contents near the eutectic composition. Lead—copper alloys in the range 0.03—0.08 wt % copper are covered by many specifications ASTM B29-92 (7), QQL 171 (United States), BS 334, HP2 Type 11 (Canada), DIN 1719 (Germany), and AS 1812 (Austraha). 

Lead—copper alloys are the primary material used in the continuous extmsion of cable coverings for the electrical power cable industry in the United States. Other alloys, containing tin and arsenic as well as copper, have also been developed for cable sheathing in the United States to provide higher fatigue strength. 

Lead—tin (1.8—2.5 wt %) is used both as a cable sheathing ahoy (BS 801 ahoy A and DIN 17640) and as a battery connector ahoy ia sealed lead—calcium—tin batteries (15). Tia is generahy added to lead—arsenic cable ahoys ia smah amounts. The arsenic ahoys have excehent creep resistance and mechanical properties, but are unstable and lose arsenic readily by oxidation. The addition of smah amounts of tin (0.10—0.20 wt %) eliminates arsenic loss. Lead ahoys having 0.4 wt % tin and 0.15 % cadmium, which are used for cable sheathing, do not age harden, show excehent corrosion and creep resistance, and are very ductile. 

Copper is a galvanic metal and causes corrosion, in the presence of moisture, in nearby metals, such as cable sheathes, steel structure and water, gas or drain pipes, buried in its vicinity. With all such metafs. it forms a complete electrolytic circuit and corrodes them. Tinning may give protection against its galvanic effects but this is ati expensive proposition... 

The header cable between anode bed and rectifier must be particularly well insulated. For this reason cables with double plastic sheathing of type NYY-O are used. The cable sheath must not be damaged during installation because the copper core at the defects will be anodically attacked in a very short time and the connection to the rectifier broken. Damage to the cable sheath is not so serious if a multicored cable is used. Usually not all the core insulation is damaged so that the operation of the anode bed is not interrupted. In addition, measurement of resistance and detection of defects is easier. 

Since copper-sheathed cables are also coated with plastic, the ratio of cathode/anode area (SJSJ is very small so that there is not an increased risk of corrosion of the lead-sheathed cable by the electrical connection between the cable sheathings according to Eq. (2-44). 

Aluminum-sheathed cables should not be connected to other cables because aluminum has the most negative rest potential of all applicable cable sheathing materials. Every defect in the protective sheath is therefore anodically endangered (see Fig. 2-5). The very high surface ratio SJS leads to rapid destruction of the aluminum sheathing according to Eq. (2-44). Aluminum can also suffer cathodic corrosion (see Fig. 2-11). The cathodic protection of aluminum is therefore a problem. Care must be taken that the protection criterion of Eq. (2-48) with the data in Section 2.4 is fulfilled (see also Table 13-1). Aluminum-sheathed cables are used only in exceptional cases. They should not be laid in stray current areas or in soils with a high concentration of salt. 

Measurement of the cable sheathing/soil potential can be used to assess the corrosion danger from stray current interference (see Section 15.5.1). Since the measured values vary widely and the stray currents cannot be switched off, IR-free potential measurements are only possible with great effort. In order to keep the IR term of the potential measurement low, the reference electrode must be placed as close as possible to the measured object. With measurements in cable ducts (e.g., underneath tramway tracks), the reference electrodes can be introduced in an open duct. 

Fig. 13-1 Resistance load R of cable sheathing as a function of cable diameter d and sheathing material.

Extruded applications of nylon, other than film and monofilcunent, are less commonly encountered because of the low melt viscosity of the polymers. Uses include cable sheathing which requires resistance to abrasion and/or chemical attack, flexible tubing for conveying petrol and other liquids, piping for chemical... 

Business machinery applications include keys for keyboards, typewriter ribbon guides, plug and socket connectors and optical cable sheathing. 

Cable sheathings for special heavy-duty cables Marine cables and drill-lock cables for deep wells... 

Cable sheath. Additional overhead line conductor Protective multiple earthing fP.M.E.) Buried Strip/rod/plate Earth-leakage circuit breaker, Voltage-operated Earth-leakage circuit breaker, Current-operated... 

The major uses of lead in the UK are in batteries, and in sheet and pipe of which the vast majority is sheet for building purposes. These applications account for about one third each of lead used. This situation is unique, since in all other countries batteries account for most of the lead market. A small but very important application is sheet and pipe for the chemical industry. Lead is no longer installed for water services. Lead cable sheathing which accounts for 5% is in general decline, but is valued in niche applications such as on oil rigs where resistance to hydrocarbons is important. The use of lead for anodes accounts for a very small tonnage, but is still of great importance to the industries which use them. 

Electrolytic corrosion may also occur on the inside of cable sheaths by the passage of current from the cable sheath to the wire . 

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