Cable avoidance tool

This important topic will be introduced by reference to the manufacture of a case for electrical equipment used in civil engineering (Figure 2.16). The cable avoidance tool (CAT) enables the underground track of power cables to be traced, and hence there are fewer accidents when excavating. Several produc-... 

Figure 2.16 The Cable Avoidance Tool is made by Electrolocation Ltd., Bristol. It was designed by B.I.P. Ltd., Streetly, West Midlands, and is moulded by Brettel and Shaw Ltd., Oldbury...

Where plugs and sockets are used for portable tools, sufficient sockets must be provided for all the equipment and adaptors should not be used. Many accidents are caused by faulty flexible cables, extension leads, plugs and sockets, particularly when these items become damp or worn. Accidents often occur when contact is made with some part of the tool which has become live (probably at mains voltage), while the user is standing on, or in contact with, an earthed conducting surface. If the electrical supply is at more than 50 volts ac, then the electric shock that a person may receive from such defective equipment is potentially lethal. In adverse environmental conditions, such as humid or damp atmospheres, even lower voltages can be dangerous. Portable electrical equipment should not be used in flammable atmospheres if it can be avoided and it must also comply with any standard relevant to the particular environment. Air operated equipment should also be used as an alternative whenever it is practical. 

Where a substantial amount of excavation is required in the danger zone, it is advisable to dig one or more trial holes to find the cable and then work along it from the trial holes to expose it. Careful manual methods should be used to avoid damage to the cable. Surface construction may require the use of power tools to break up the surface for removal, in whieh ease it is advisable to fit the bit with a collar to prevent deep penetration and no drilling should be done immediately above the cable. Sharp-pointed tools sueh as pieks should not be used immediately adjacent to the cable even if it is armoured, as the pick points are capable of penetrating between the strands of wire armour and through badly corroded steel tape. 

Quite often, a problem appears unexpectedly for a user but not for the developers of a simulation tool it is hard for developers to predict such problems at the development stage. These problems are caused quite often by the misuse of the tool by the user. Therefore, reliability and severity tests of simulation tools are very important. For example, it took nearly 10 years to carry out reliability and severity tests on tens of thousands of cases with EMTP cable constants. It should be noted that the reliability of a tool (that is, the probability of a problem occurring) is proportional to the number of elements (that is, the number of subroutines and options) although each individual element has very high reliability. Input data often cause numerical instability when the data physically do not exist this problem is related to the assumption of formulas adopted in the simulation tool as explained in Section 8.1. To avoid such a problem, a KILL CODE is prepared in the EMTP. The kill code judges whether the input data are beyond the limits of assumption. It may be noteworthy that nearly half of the EMTP codes are kill codes. This may be considered by developers in another simulation tool. 

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