Overhead cables

Two-bearing screens, ot which there are rnanv types, have the same screen boclv as the four-bearing type but without the two outer bearings and the base frame. The gyi ating motion is caused bv eccentric weights on the shaft, and the screen itself is supported bv overhead cables or springs on the floor. 

Machinery, including cranes, hoists, and forklifts Public access and perimeter fencing Adjacent facilities Buried cables Overhead cables... 

The existing locomotion rehabilitator designs rely on simple attachment schemes. The MGT attaches to the patient s foot via a foot plate, whereas the Lokomat attaches to the thighs and shanks through padded straps. Skin irritation has been reported with the Lokomat if the exoskeleton is not properly adjusted. For both devices, modified parachute or rock-climbing-type harnesses provide an attachment to the torso that allows partial body weight support through an overhead cable. 

This is the type of supply more often found when the installation is fed from overhead cables. The supply authorities do not provide an earth terminal and the installation s circuit protective conductors (CPCs) must be connected to earth via an earth electrode provided by the consumer. lET Regulation 542.2.3 lists the type of earth rod, earth plate or earth tapes recognized by BS 7671. An effective earth connection is sometimes difficult to obtain and in most cases a residual current device (RCD) is provided when this type of supply is used. The arrangement is shown in Fig. 3.36. 

Suspended from cable towers or pylons, overhead cables must be light, flexible and strong. 

Cables buried on agricultural or horticultural land should be buried at a depth of not less than 600mm, or 1000 mm where the ground may be cultivated, and the cable must have an armour sheath and be further protected by cable tiles. Overhead cables must be insulated and installed so that they are clear of farm machinery or placed at a minimum height of 6m to comply with lET Regulation 705.522. 

Details of underground services and overhead cables and other site obstructions should be obtained for the erection contractor before work commences. Extra care should be taken with long carbon composite members that are lifted near live exposed electrical wires, as these composite plastics, like many metals, will conduct electricity. 

Note The precautions that may be required for this range from the safe placement of cables as overhead cables to formal safe systems of work for high voltage switching where the risk of danger cannot be avoided. 

Collision with other cranes, overhead cables or structures... 

Collision v/ith overhead cables or structures, occasionally involving eccentrically-loaded platforms Operator errors from impaired/restricted visibility, poor eyesight, inadequate training and wrong operating position... 

Operating area - all nearby hazards, including overhead cables and bared power supply conductors, should be identified and removed or re-routed where practicable. Solid support should be available and on fixed site installations the dimensions and strength of support required should be specified. The possibility of striking other cranes or structures should be examined. 

In a simulation of an induced voltage to an overhead control cable from a counterpoise, the control cable and the counterpoise are represented as a distributed-parameter line in the EMTP [35, 36-37]. The parameters of the line models are evaluated by the EMTP Cable Parameters (CP) [37]. First, the model system is evaluated as an overhead line system by the CP with a negative sign of the depth of the counterpoise. Initially, the input data, the CP gives the self-impedance/admittance of the overhead cable and the mutual impedance to the counterpoise. Then, the self-impedance/-admittance of the counterpoise is calculated as an underground cable. Finally, the self-impedance/admittance of the counterpoise in the first calculation is replaced by those in the second. 

Paper insulated lead-covered steel wire armour cables are only used in systems above 11 kV. Very high-voltage cables are only buried underground in special circumstances when overhead cables would be unsuitable, for example, because they might spoil a view of natural beauty. 

Regulation 44 (2) reads as where any electrically charged overhead cable or apparatus is liable to be a source of danger to persons employed during the course of any operations or works to which these regulations apply, whether from the operation of a lifting appliance or otherwise, all practicable precautions shall be taken to prevent such danger either by the provision of adequate and suitable placed barriers or otherwise . 

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