Cables adverse conditions

Small size, ruggedness, simple cabling and the ability to operate the equipment under adverse conditions in the field has also been design goals. The system should also conform with the regulations necessary for the CE-marking (i. e. standards and directives for EMC, Electrical Safety and Machine Safety). 

Isolation valves should be easily accessible under adverse conditions or valve should be remotely operable. The isolation valve should be fire rated and the actuator and power cables should be fire proofed. Twenty minutes of fireproofing is required when the design is not "fail closed." Isolation valves can serve a dual function, such as equipment isolation. The isolation valves should be located as close to the outlet flange of the vessel as possible. 

Section 4 is concerned with fire risks consequent on alterations or additions. Among the electrical causations listed are overloading of cables due to changes in the connected load, cables surrounded by thermal insulation applied subsequent to the initial installation, and extra circuits added in conduit and trunking. Some of the non-electrical causations are the subsequent installation of steam pipes close to parts of the electrical installation, and changes in the use of the premises which may introduce adverse conditions inimical to the installation, such as dust, corrosive fumes or vibration. 

Interaction tests should be made on all unprotected structures in the vicinity of a proposed cathodic protection installation, and should be repeated annually or at some other suitable interval to ensure that alterations in the layout of plant or in the electrical conditions are taken into account. It is most convenient if the tests on all unprotected pipes or cables are made at the same time, the potential measurements being synchronised with the regular switching on and off of the protection current. It may then be convenient to continue with further tests to confirm that any remedial measures applied to one installation do not adversely affect other installations. 

Work-reiated fauits. If the work employees will perform in a manhole or vault could cause a fault in a cable, the employer shall deenergize that cable before any employee works in the manhole or vault, except when service-load conditions and a lack of feasible alternatives require that the cable remain energized. In that case, employees may enter the manhole or vault provided the employer protects them from the possible effects of a failure using shields or other devices that are capable of containing the adverse effects of a fault. 

Just as it is immune to EMI from outside sources, fiber produces no electronic emissions and, therefore, is not a concern of the Federal Communications Commission (FCC) or European emissions regulations. Crosstalk does not occur in fiber systems, and there are no shared sheath issues as with multipair UTP cables. Because all-dielectric cables can be used, grounding concerns can be eliminated and lightning effects dramatically reduced. Optical fibers are virtually impossible to tap, making it the most secure media type. Most importantly, optical bandwidth cannot be adversely affected by installation conditions. Compare this to the dramatic effects that an installer can have with crosstalk in a copper system. 

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. 

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