Domestic installations

The electrolysis protection process using impressed current aluminum anodes allows uncoated and hot-dipped galvanized ferrous materials in domestic installations to be protected from corrosion. If impressed current aluminum anodes are installed in water tanks, the pipework is protected by the formation of a film without affecting the potability of the water. With domestic galvanized steel pipes, a marked retardation of the cathodic partial reaction occurs [15]. Electrolytic treatment alters the electrolytic characteristics of the water, as well as internal cathodic protection of the tank and its inserts (e.g., heating elements). The pipe protection relies on colloidal chemical processes and is applied only to new installations and not to old ones already attacked by corrosion. 

Figure 20.5 LPG storage vessel for a domestic installation. (Courtesy of the Calor Group Pic)...

Stainless steels Thin-walled stainless steel (Fe-18Cr-8Ni) tubes are now frequently used for domestic installations in place of copper pipe . Care is required, however, in the design of stainless steel equipment for use in waters with a high chloride content, or where the concentration can increase, since pitting attack may occur. It may also be susceptible to failure by stress-corrosion cracking under certain conditions. 

Cold-water tanks made from Polythene or GRP are generally available, especially in domestic sizes, and are now often used in domestic installations. 

Bath or shower water is likely to contain bacteria, some of which could be potentially harmful to health, so this gray water should be used Immediately. Gray water filtering systems, which overcome this difficulty, are already available for domestic Installation in some countries, and are currently the focus of much research and development it is hoped that, in the not-too-distant future, every new home will incorporate such technology. 

With respect to future activity in the field of solar distillation, three basic categories of solar stills can be visualized permanent, semipermanent, and expendable. It is not possible to single out any one type as the best, because each has advantages in particular applications which may range from small remote domestic installations to plants covering many acres and serving municipalities, industry, and agriculture. 

FIGURE 1. Bacterial density of biofilms developed on main pipe lines from carbon steel (1,2) or reinforced concrete (3,4) and concrete tank (5,6) in drinking water distribution system Yovkovtsy , domestic installation from galvanized steel (7,8) and test surfaces from stainless (9) or carbon steel (10). 

Metals and alloys are the most common materials in use for domestic installations. To comply with European and national regulations on the quality of water intended for human consumption, it is necessary to take into consideration the interactions between these materials and water. 

Phosphates and silicate corrosion inhibitors have been used with or without pH control, to reduce the metal release and to prolong the service life of distribution systems or domestic installations. When the concentration is limited, the inhibitors may not avert localized corrosion such as pitting or the corrosion of galvanized steel, steel, cast iron, copper, or lead, sufficiently to extend the life of the system beyond 75-100 years. Corrosion inhibitors are useful when concerns about water quality deterioration have to be resolved. Unfortunately, there is no simple solution for balancing water quality, health risks, system reliability, and environmental impact. 

Cartridge fuses to BS 88-3 2010. These are used for a.c. circuits on industrial and domestic installations having a fault capacity of about 30 kA. 

Semi-enclosed fuses to BS 3036. These were previously called rewirable fuses and are used mainly on domestic installations having a maximum fault capacity of about 4 kA. 

This type of fuse is illustrated in Fig. 3.26. The fuse element should consist of a single strand of plain or tinned copper wire having a diameter appropriate to the current rating of the fuse. This type of fuse was very popular in domestic installations, but less so these days because of its disadvantages. 

The supply to a domestic, commercial or small industrial consumer s installation is usually protected at the incoming service cable position with a 100 A high breaking capacity (HBC) fuse. The maximum, that is, worst case value of external earth fault loop impedance outside of the consumer s domestic installation is ... 

Part 5 of the lET Regulations tells us that electrical equipment and materials must be chosen so that they are suitable for the installed conditions, taking into account temperature, the presence of water, comosion, mechanical damage, vibration or exposure to solar radiation. Therefore, PVC insulated and sheathed cables are suitable for domestic installations but, for a cable requiring mechanical protection and suitable for burying underground, a PVC/ SWA cable would be preferable. These two types of cable are shown in Figs 3.38 and 3.39. 

A small, single-point over-sink-type water heater may be considered as a permanently connected appliance and so may be connected to a ring circuit through a fused connection unit. A water heater of the immersion type is usually rated at a maximum of 3 kW, and could be considered as a permanently connected appliance, fed from a fused connection unit. However, many immersion heating systems are connected into storage vessels of about 150 litres in domestic installations, and the On Site Guide states that immersion heaters fitted to vessels in excess of 15 litres should be supplied by their own circuit (OSG Appendix H5). 

A domestic installation usually calls for a PVC insulated and sheathed wiring system. These cables are generally fixed using plastic clips incorporating a masonry nail which means that the cables can be fixed to wood, plaster or brick with almost equal ease. 

An appropriate wiring method for a domestic installation would be a ... 

The use of junction boxes with fixed brass terminals is the method often adopted in domestic installations, since the joint boxes can be made accessible but are out of sight in the loft area and under floorboards. However, every connection must remain accessible for inspection, testing and maintenance (lET Regulation 526.3). 

Socket outlets can be obtained in 15, 13, 5 and 2 A ratings (see IEE Table 55.1), but the 13A flat pin shuttered type complying with BS 1363 is the most popular for domestic installations in the United Kingdom. Each 13A plug top contains a cartridge fuse to give maximum potential protection to the flexible cord and the appliances which it serves. 

In this table, I am assuming a standard 230V domestic installation, having a sheathed earth or PME supply terminated in a 100 A HBC fuse at the mains position. Final circuits are fed from a consumer unit, having Type B, MCB protection and wired in PVC insulated and sheathed cables with copper conductors having a grey thermoplastic PVC outer sheath or a white... 

Almost 100,000 lead connection pipes were present in The Hague, although the number of lead domestic installations is not known. 

The pipelines and components which come into contact with drinking water on their inner surfaces can be briefly described as follows in the sequence following drinking water treatment by the water supply companies (WSC) drinking water tanks, long-distance lines, distribution lines, domestic service lines, domestic installation (consumer). 

In domestic installations, there are alternating periods of static, gently flowing and faster flowing water, depending on what is being drawn off for use. The corrosion conditions are thus less dear, so that no general statements can be made, only material-spedfic statements. 

In the construction of systems for drinking water transport and distribution, connection elements, for example pipe connections, whose design can significantly affect the corrosion phenomena, must be made. This is dear particularly in the case of domestic installation, where pipe connections are made in the form of screwed, soldered or welded joints [11]. 

In a domestic installation, a combination of different metallic materials is unavoidable, that is to say the possibility of contact corrosion must be taken into account. Indications of the contact corrosion risk are contained in [12]. 

Unalloyed ferrous materials are used without additional protective measures to a strictly limited degree. The reason for their limited use is the lack of resistance of these materials to local attack, such as wide or deep pitting. In domestic installations, it is the brown discolouration and change in taste of drinking water (rusty water), above all, which are unacceptable to the public - although they are not a health hazard. 

The corrosion behaviour of unalloyed steels without protective measures is of importance in respect of evaluation of older long-distance and distribution lines. This also applies to older pipelines in domestic installations, especially in cases where the hot-dip galvanised layer is worn away non-uniformly and too rapidly, so that formation of a good surface layer is no longer possible. 

Amongst the stainless steels, ferritic Cr steels and the austenitic CrNi steels with and without added molybdenum must be considered as passivatable materials for domestic installations. These materials are of particular interest for hot water pipes and hot water tanks, as well as for cold water pipes. The stainless steels suitable for domestic installations are summarised in Table 16. 

Table 16 Stainless steels suitable for domestic installations, water heating units and pipes 28]...

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