The electrical installation

However, electrical apparatus and wiring that has to be in the flammable zones must be explosion protected to avoid the ignition hazard. Two examples are provided in the following sections. 

The example in Fig. 15.1 shows the classified zones in the vicinity of a tank of flammable liquid which emits a heavier-than-air vapour. The space above the tank liquid is normally classed as Zone 0 because sufficient air may be drawn in through the vent and the float switch tube when the liquid level falls or the vapour condenses on a fall in the ambient temperature, to form an explosive mixture. The level sensor would normally be intrinsically safe type EEx ia. 

The float switch is on the edge of the Zone 1 boundary, but it is doubtful whether the expense of an EEx d switch is justified. A weatherproof, hermetically sealed, mercury-in-glass, type Ex s switch would be a suitably economic alternative. 

The emission from the tap-operated dispenser is dependent on the surfaee area of the exposed liquid when filling containers and the area of the eon-tainer orifice. Again, it would be reasonable to assume that the vapour plume is blown in one downward sloping direction and disperses until the LEL is reached. The container orifice to this position is the radius of the Zone 1 area. The slope of the zone boundary is a function of the vapour density. The heavier the vapour, the steeper the slope. 

The pump motor is partly within Zone 1 so it would probably be advisable to use a weatherproof EEx e rather than an EEx N motor. 

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Each plant or laboratory should adopt definite rules and procedures for electrical installations and work. All installations should be in accordance with the National Electrical Code (NEC) for the type of hazard, eg, Class I flammable gas or vapor Class II organic, metallic, or conductive dusts and Class III combustible fibers and the degree of process containment, eg, Division 1 open and Division 2 closed (67). Regardless of the flammability of the materials in the installed operations, changes in procedure involving use of such materials often occur, sometimes without concurrent alteration of the electrical installation. 

The people going to be gassed and those in the gas chamber damaged the electrical installations, tearing the cables out and damaging the ventilation equipment. ... 

The electrical installation consists of four major components, namely, power wiring, lighting, transformation and service, and instrument and control wiring. Table 9 shows these component costs as ratios of the total electrical cost... 

When the electrical installation is subcontracted, the subcontractor frequently supplies the bulk materials. If that s the case, the materials should still be shown in the materials column to permit the analysis of the Material/Labor ratio. 

Various technologies employing an electric arc have been used to improve the Huls process, by trying to reduce the cost of the electrical installations er to improve the heat transfer to the gas to be pyrolysed. 

Also defined in the standard are many terms and expressions that are used to describe individual parts and components as well as combinations of them, e.g. assembly, functional unit, barrier. The standard states what is to be achieved but not how and with what materials. An annex has been issued in the UK that expands the general principles. In June 1996 The Electrical Installation Equipment Manufacturer s Association (EIEMA) published Reference 1. The four forms were sub-divided as follows -... 

Guide to forms of separation. The Electrical Installation Equipment Manufacturer s Association. (June 1996)... 

Before expecting a change in safety culture, the physical workplace must be put in order. This includes the guarding of all machinery, the erection of handrails where necessary, and any other modification or repair required to bring the workplace up to compliance with safety legislation. The electrical installation must be safe, and all electrical switches and circuit breakers must be clearly labeled in a standardized... 

The electrical installation is usually in the focus of considerations. Normal switches and sockets are not allowed in an explosion risk area. If possible, electrical components should be avoided at all and replaced by different ones. For example, pneumatic valves may be used instead of solenoid valves. 

Electrical sparks are not only generated in the electrical installation, but also by discharge of static electricity. These sparks can ignite just as well. Expert grounding of all relevant parts of the installation is an important part of this chapter. This is true not only for the gas containing parts of the facility but also for e.g. radiators, water and gas pipes and other metallic parts. Also conductive floors can be very useful. 

The provision of a safe eiectrical system is fundamental to the whole concept of using eiectricity in and around buildings safely. The electrical installation as a whoie must be protected against overload and short-circuit damage, and the peopie using the instaiiation must be protected against electric shock. 

Exposed conductive parts are the metalwork of the electrical installation the conduit, trunking, metal boxes and equipment that make up the electrical installation. 

Extraneous conductive parts are the other metal parts which do not form a part of the electrical installation the structural steelwork of the building, gas, water and central heating pipes and radiators,... 

Functional switching is for the user of the electrical installation or equipment. 

Flexible conduit is used for the final connection to motors so that the vibrations of the motor are not transmitted throughout the electrical installation and to allow for modifications to be made to the final motor position and drive belt adjustments. 

It is important that the wiring systems and fixing methods are appropriate for the particular type of installation and compatible with the structural materials used in the building construction. The electrical installation must be compatible with the installed conditions, must not damage the fabric of the building, or weaken load-bearing girders or joists. 

Will the electrical installation interfere with other supplies and services ... 

Will the materials being used for the electrical installation be compatible with the intended use of the building ... 

Because of the mobile nature of caravans it is recommended that the electrical installation be tested and inspected at intervals considered appropriate, preferably not less than once every three years and annually if the caravan is used frequently (lET Regulation 721.514.1). 

The protection provided by insulating the live parts of the electrical installation is called ... 

The electrical installation in a building is often carried out alongside other trades. It makes sound sense to help other trades where possible and to develop good working relationships with other employees. 

To complete the contract in the specified time the electrical contractor must use the management skills required by any business to ensure that men and materials are on site as and when they are required. If alterations or modifications are made to the electrical installation as the work proceeds which are outside the original specification, then a variation order must be issued so that the electrical contractor can be paid for the additional work. 

The 3rd Amendment to the 17th Edition of the lET Regulations at 134.1.1 makes the following comment good workmanship by skilled (electrically) or Instructed (electrically) persons and proper materials shall be used in the erection of the electrical installation. ... 

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