Cable construction Conductor

Impedance monitors require the trailing cable to have a pilot conductor. The pilot is a separate, small conductor, incorporated in the cable construction. The pilot conductor is used to form a continuous loop with the grounding conductor. The monitor is calibrated to the impedance of the loop formed by the pilot and grounding conductors. The device then monitors the change of impedance from the initial calibration. If the impedance of the loop increases beyond a preset value, the monitor trips its associated circuit breaker. 

Multi-layer insulation constructions are used. With the high-voltage cable, three separate layers may cover the center conductor. The innermost layer will function as an electric screen, the intermediate layer is usually a PE insulation material, and the outer layer serves as an electric screen. The processing technique can be used for primary and secondary coating where the covering is on metallic conductors or coating previously insulated wires. 

Ramped field losses are being measured for both of these conductors and will be correlated with the coil performance and separately reported. Lower losses are anticipated for the configurations which incorporate copper by extrusion, particularly the cable configurations 7 or 9, which are constructed of small, tightly twisted, electrically insulated strands. 

Cables can be considered to be constructed in three parts the conductor, which must be of a suitable cross-section to carry the load current the insulation, which has a colour or number code for identification and the outer sheath, which may contain some means of providing protection from mechanical damage. 

The cable is constructed of stranded aluminium conductors formed around a core of steel-stranded conductors (see Fig. 3.41). The aluminium conductors carry the current and the steel core provides the tensile strength required to suspend the cable between pylons. The cable is not insulated since it is placed out of reach and insulation would only add to the weight of the cable. 

Copper is a red metal, very malleable and ductile and a good conductor of heat and electricity. It tarnishes when exposed to air, slowly forming a green film of basic copper salts called verdigris. Copper is easily fabricated, but care must be taken as it tends to work-harden repeated bending of the metal causes it to become brittle. It is used in the construction of heat exchangers, electrical components and cables, and as a constituent of brass, bronze, and other alloys. 

Portable tools are used extensively on sites and maintaining them and their connecting cables in good repair is a critical factor of their safe use. Electrocution occurs when the body acts as the conductor from a power line and earth, often because the earth connection on the tool has broken. All portable tools must be securely earthed or be of double insulated construction and the plug on the lead must be correctly fused. Unfortunately it is frequently difficult to keep track of every item, so reliance has to be placed on the person using them. 

Coaxial lines use two types of dielectric construction to isolate the inner conductor from the outer conductor. The first is an air dielectric, with the inner conductor supported by a dielectric spacer and the remaining volume filled with air or nitrogen gas. The spacer, which may be constructed of spiral or discrete rings, typically is made of Teflon or polyethylene. Air-dielectric cable offers lower attenuation and higher average power ratings than foam-filled cable but requires pressurization to prevent moisture entry. 

Oceanographers were always keen to have visible and available in situ salinity on-line. The most effective method to achieve this goal was to construct an instrument that measures three basic thermodynamic parameters simultaneously with high precision from a research vessel, transfer the data via a one-conductor cable to the deck, calculate salinity from the three basic parameters, make them visible and store them. The parameters easiest to measure electrically, are pressure P, temperature T and the specific electrical conductivity of sea water C relative to a fixed reference. With the introduction of the PSS78 (see Section 3.3.2), a unique procedure was prescribed to calculate salinity S from these three basic measurements. 

The uniformity of the dielectric material and consistency in spacing of the conductors in the final constmction becomes increasingly evident as the constructions begin to push the dielectric limitations of the materials. These efforts focus on the engineering design of the cable and the quality systems during manufacturing. 

Crimp Tabs. Crimp tabs were originally developed for connections of flat conductor cables however, they are also applied for flexible circuits because of the similar construction. 

Originally, FFC connectors were developed for laminated cable with flat conductors to connect to another circuit board. A similar construction of flexible circuits was developed to attach the connector. At this time, the standard pitch of the connectors was 2.54 mm. Due to increased trace densities of flexible circuits, small-pitch FFC connectors are now required. The newest connector can make 0.3 mm pitch connections for 30 traces. Zero in force (ZIF) mechanisms were introduced for easier handling. Due to hmited height requirements for thin board assembly, a 1.0 mm high connector from the board surface is now available. 

Portable apparatus may be of Class I construction, in which case the metalwork is earthed by a protective conductor which is a separate core in the flexible supply cable, or it may be of Class II construction, having no protective conductor terminal as its metalwork is not earthed. The essential safety feature of Class II apparatus is that the basic insulation is supplemented by additional insulation to provide a further safety barrier and danger arises only if both insulating layers fail. There are two types all insulated where the supplementary insulation is a plastic case, and double insulated where there is a metal case but live parts are separated from it by two layers of insulation. It is not advisable to use enclosed ventilated Class II apparatus in wet environments, because moisture may penetrate and provide a conductive film between the touchable surfaces and internal live conductors. 

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