Section 5 Water and Electrical Materials

The power consumption of a medical laboratory is very large, and the laying of wires and circuits is therefore rather complex.

Wires and cables are wire-rod products used to transmit electrical (magnetic) energy and information and to realize the conversion of electromagnetic energy. In the broad sense, wires and cables are also abbreviated as cables; in the narrow sense, a cable means an insulated cable, which can be defined as an assembly consisting of the following parts: one or more insulated cores, together with their respective possible coatings, an overall protective layer, and an outer sheath; a cable may also have additional conductors without insulation.

By application they can be divided into bare conductors, insulated wires, heat-resistant wires, shielded wires, power cables, control cables, communication cables, radio-frequency cables, and so on.

By material they can be divided into polyvinyl chloride insulated wires, polyvinyl chloride insulated flexible wires, butyryl polyvinyl chloride mixture insulated flexible wires, rubber-insulated wires, plastic-insulated aluminum-core wires for direct underground burial in agriculture, rubber-insulated cotton-yarn braided flexible wires, polyvinyl chloride insulated nylon-sheathed wires, polyvinyl chloride insulated flexible wires for power and lighting, and so on.

Cable trays are suitable for the overhead laying of power cables and control cables indoors and outdoors in ordinary industrial and mining enterprises, and may also be used indoors and outdoors by departments such as telecommunications, radio, and television.

Wire and cable products are mainly divided into the following three major categories.

I. Insulated Conductors

A wire in which a layer of non-conductive material, such as resin, plastic, silicone rubber, PVC, etc., is uniformly and hermetically wrapped around the outside of the conductor to form an insulating layer that prevents the conductor from contacting the outside world and causing accidents such as electric leakage, short circuits, and electric shock is called an insulated conductor, as shown in Fig. 8-49.

Common wires for electrical equipment include plastic wires (BV, BLV, BVR, BVVB, BLVVB, etc.).

1. The following are several commonly used types of insulated conductors

1.1 Rubber-insulated conductor model designations: BLX—aluminum-core rubber-insulated wire; BX—copper-core rubber-insulated wire.

1.2 Polyvinyl chloride insulated conductors (plastic wires) model designations: BLV—aluminum-core plastic wire; BV—copper-core plastic wire.

1.3 Rubber cable model designations: YHC—heavy-duty rubber-sheathed cable; NYHF—neoprene-sheathed trailing cable for agricultural use.

Rubber-insulated conductors come with copper cores or aluminum cores, and in single-core, twin-core, or multicore versions. They are used for indoor wiring, and the working voltage generally does not exceed 500 V.

2. Model designations and uses

2.1 R stands for soft copper wire, V for polyvinyl chloride insulation, S for twisted pair, B for flat type, and P for shielding.

2.2 RV—polyvinyl chloride insulated single-core flexible wire, maximum operating temperature 65 ℃, minimum operating temperature -15 ℃, working voltage AC 250 V, DC 500 V; used as the internal wiring of instruments and equipment.

2.3 RVB: parallel stranded flexible wire (flat), just like the bare telephone wire often used in homes, except that its core wires are the same as RVV core wires; the two core wires are wrapped in parallel within a sheath, usually two cores per sheath. 2.4 RVS: pair-twisted stranded flexible wire, made simply by splitting the soft cores of an RVB and twisting them together in pairs. Usually two wires are twisted together.

2.5 RVSP: twisted-pair shielded wire.

2.6 RVVB: polyvinyl chloride sheathed flexible wire (flat type), standard GB/T 5023.5-2008/IEC 60227-5:2003.

2.7 RVV: stranded flexible wire, i.e., the core wires consist of multiple strands of copper wire. The RVV wire is the most commonly used cable in weak-current systems; the number of its core wires is not fixed—there may be a single wire or multiple wires—and there is also a sheath on the outside. However, there is no special requirement for the arrangement of the core wires.

2.8 RVVP: copper-core polyvinyl chloride insulated shielded polyvinyl chloride sheathed flexible cable, also called anti-interference flexible cable for electrical connections, rated voltage 250 V/450 V.

2.9 BVVR is a copper-core polyvinyl chloride insulated polyvinyl chloride sheathed flexible wire with an outer protective layer; BVR is a copper-core polyvinyl chloride insulated flexible wire with only an insulating layer and no outer protective layer. The commonly called double-plastic wire refers to the BVV series—the first V denotes polyvinyl chloride insulation and the second V denotes the polyvinyl chloride sheath—whereas the BV series refers to single-plastic wires.

Fig. 8-49 Insulated conductor

II. Power Cables

The main characteristic of this category of products is that an insulating layer is extruded (wrapped) outside the conductor, as in overhead insulated cables, or several cores are twisted together (corresponding to the phase wire, neutral wire, and ground wire of the power system), as in overhead insulated cables with more than two cores, or a sheath layer is added, as in plastic/rubber-sheathed wires and cables. The main process technologies include drawing, stranding, insulation extrusion (wrapping), cabling, armoring, and protective-layer extrusion; the combinations of process steps differ to a certain extent among the various products. The products are mainly used for the transmission of strong-current electrical energy in power generation, distribution, transmission, transformation, and supply lines, with large currents passing through (from several tens of amperes to several thousand amperes) and high voltages (220 V to 500 kV and above).

1. Classification by voltage class

By voltage class they can be divided into medium- and low-voltage power cables (35 kV and below), high-voltage cables (above 110 kV), extra-high-voltage cables (275–800 kV), and ultra-high-voltage cables (1000 kV and above). In addition, they can be divided by current type into AC cables and DC cables.

2. Classification by insulating material

2.1 Oil-impregnated paper-insulated power cables: power cables insulated with oil-impregnated paper. They have the longest application history. They are safe and reliable, have a long service life, and are inexpensive. Their main disadvantage is that laying is restricted by the height difference. Since the development of non-draining impregnated-paper insulation, the height-difference restriction problem has been solved, allowing oil-impregnated paper-insulated cables to continue to be widely used.

2.2 Plastic-insulated power cables: power cables whose insulating layer is extruded plastic. Commonly used plastics include polyvinyl chloride, polyethylene, and cross-linked polyethylene. Plastic cables have a simple structure, are convenient to manufacture and process, are light in weight, are easy to lay and install, and are not subject to laying height-difference restrictions. They are therefore widely used in medium- and low-voltage cables and show a tendency to replace viscous-impregnated oil-paper cables. Their greatest disadvantage is the existence of the treeing breakdown phenomenon, which limits their use at higher voltages.

2.3 Rubber-insulated power cables: the insulating layer consists of rubber mixed with various compounding agents; after thorough mastication it is extruded onto the conducting wire core and formed by heating and vulcanization. It is soft and elastic, and is suited to occasions with frequent movement and small laying bend radii.

Rubber compounds commonly used for insulation include natural-rubber–styrene-butadiene-rubber blends, ethylene propylene rubber, butyl rubber, and so on.

3. Classification by voltage class

3.1 Low-voltage cables: suitable for fixed laying on power transmission and distribution lines with AC 50 Hz and rated voltage 3 kV and below, for the purpose of conveying electrical energy.

3.2 Medium- and low-voltage cables (generally 35 kV and below): polyvinyl chloride insulated cables, polyethylene insulated cables, cross-linked polyethylene insulated cables, and so on.

Fig. 8-50 Power cable

3.3 High-voltage cables (generally 110 kV and above): polyethylene cables and cross-linked polyethylene insulated cables, and so on.

3.4 Extra-high-voltage cables (275–800 kV).

3.5 Ultra-high-voltage cables (1000 kV and above).

III. Wires and Cables for Electrical Equipment

The main characteristics of this category of products are: a great variety of types and specifications, a wide range of applications, and an operating voltage mostly at 1 kV and below; for special occasions new products are constantly being derived, such as fire-resistant cables, flame-retardant cables, low-smoke halogen-free/low-smoke low-halogen cables, termite-proof and rat-proof cables, oil-resistant, cold-resistant, temperature-resistant and wear-resistant cables, medical, agricultural, and mining cables, and thin-wall wires.

New derivative products of wires and cables arise mainly from the requirements of different application occasions and application requirements, equipment convenience, and reduction of equipment cost, by adopting new or special materials, changing the product structure, raising process requirements, or combining products of different varieties, as shown in Fig. 8-51.

Adopting different materials, such as flame-retardant cables, low-smoke halogen-free and low-smoke low-halogen cables, termite-proof and rat-proof cables, oil-resistant, cold-resistant, and temperature-resistant cables, etc.;

Changing the product structure, as with fire-resistant cables, etc.;

Raising process requirements, as with medical cables, etc.;

Combined products, such as OPGW, etc.;

Convenient installation and reduced equipment cost, such as prefabricated branch cables, etc.

Common power cables include plastic power cables (including four types: VV, VLV, VV22, VLV22) and high-, medium-, and low-voltage cross-linked cables (including four types: YJV, YJLV, JYV22, YJLV22, with voltages of 0.6/1 kV, 8.7/10 kV, 26/35 kV, 66/110 kV, etc.). Advantages: large cross section, supporting long-distance high-voltage and extra-high-voltage power transmission.

Fig. 8-51 Cable for electrical equipment

In accordance with the relevant provisions of the national Code for Electrical Design of Civil Buildings and other regulations, all wires must be run through conduit; the two types of conduit currently in common use are as follows.

IV. PVC Conduit

Its full name is "insulating electrical conduit for building use," with implementation standard JG 3050-1998. In plain terms, it is a kind of white rigid PVC plastic pipe, a corrosion-proof, leakage-proof tube used for running electric wires. PE corrugated pipe is now commonly used as the "electrical conduit"; it is of good quality and low price, attractive, and convenient.

If the national requirements were followed strictly, carbon steel conduit would have to be used. However, the cost would then be too high. Therefore, in actual projects, interior decoration works mostly use PVC conduit; doing so saves cost on the one hand, and on the other hand PVC conduit is relatively convenient to construct, as shown in Fig. 8-52.

Fig. 8-52 PVC conduit

V. Carbon Steel Conduit

A protective tube for wires and cables manufactured from welded steel pipe of Q235 material, usually an R=6D product. The larger R is, the gentler the bend, and the easier the wires are to pull through during threading. When carbon steel conduit is connected to a straight pipe, a coupling sleeve protects the joint, and then the pipe and the conduit are joined by welding; the purpose is to keep the joint from being damaged by electric welding and thereby protect the wires and cables inside. The common specifications are DN20–DN150. It is used in normal indoor environments and in places with high temperature, much dust, vibration, and fire hazard. It may also be used in damp places. It must not be used in especially damp places, in places corroded by acids, alkalis, or salts, or in places with explosion hazard. The operating ambient temperature is -15 ℃ to +40 ℃. The conduit has excellent mechanical properties and excellent corrosion resistance, high pressure resistance, with a working pressure exceeding 2.5 MPa. The conduit surface is smooth, fluid resistance is small, it does not form scale and is not prone to breeding microorganisms. The thermal expansion coefficient is small, and it does not shrink or deform. It uses the traditional installation and connection method. The epoxy plastic-coated layer of the conduit more effectively solves the corrosion of metal pipelines by water conveyance, burial, and acids, alkalis, and salts, and its service life can reach more than 50 years, as shown in Fig. 8-53.

Fig. 8-53 Carbon steel conduit

VI. Water-Supply Pipes

In the decoration engineering of a medical laboratory, the laboratory water supply and drainage belongs to indoor concealed works and occupies a significant part of the entire project; moreover, it places high demands on construction quality, because once a problem occurs it may well cause a whole series of rework. Therefore, the requirements for water supply and drainage materials are given particular emphasis.

1. PVC-U Pipe

UPVC, also called rigid PVC or PVCU, is composed of an amorphous thermoplastic resin made by the polymerization of vinyl chloride monomers together with certain additives (such as stabilizers, lubricants, fillers, etc.). Besides using additives, the method of blending and modifying it with other resins is also adopted to give it clear practical value. These resins include CPVC, PE, ABS, EVA, MBS, and so on. UPVC has high melt viscosity and poor flowability; even if the injection pressure and melt temperature are raised, the change in flowability is not great. In addition, the molding temperature of the resin is very close to its thermal decomposition temperature, and the temperature range within which molding can be carried out is very narrow, making it a difficult-to-mold material. In medical laboratory decoration engineering, PVC-U pipe can be used as tap water conduit, as shown in Fig. 8-54.

Fig. 8-54 PVC-U pipe

Properties of PVC-U pipe:

1.1 Light weight, convenient to transport, load, and unload

PVC-U pipe material is very light, convenient to transport and construct, and can save labor.

1.2 Excellent chemical resistance

PVC-U pipe has outstanding resistance to acids, alkalis, and corrosion, and is very suitable for use in the chemical industry.

1.3 Small fluid resistance

The wall surface of PVC-U pipe is smooth and offers little resistance to fluids; its roughness coefficient is only 0.009, lower than that of other pipe materials, so at the same flow rate the pipe diameter can be reduced.

1.4 Great mechanical strength

PVC-U pipe has very good hydrostatic pressure resistance, external pressure resistance, and impact resistance, and is suitable for piping works under all kinds of conditions.

2. PP-R Pipe

PP-R (polypropylene random) pipe is also called type-III polypropylene pipe, random-copolymer polypropylene pipe, or PPR pipe. PP-R pipe is made from random-copolymer polypropylene by extrusion into pipe material and injection molding into pipe fittings.

Compared with traditional pipes such as cast iron pipes, galvanized steel pipes, and cement pipes, PPR pipe material has the advantages of energy and material saving, environmental protection, light weight and high strength, corrosion resistance, smooth inner walls that do not form scale, simple construction and maintenance, and long service life. It is widely used in building water supply and drainage, urban and rural water supply and drainage, city gas, power and optical-cable sheathing, and industrial fluid transportation, as shown in Fig. 8-55.

Fig. 8-55 PPR pipe

3. Stainless Steel Water Pipes

In a laboratory, several room groups need to use purified water. At present, many laboratories, with cost saving in mind, mostly substitute PPR pipe for purified-water pipe during construction; strictly speaking, however, this does not meet the standard—according to the relevant national specifications, stainless steel water pipe must be used as the conduit for purified water. Stainless steel water pipe is the best pipe material for conveying direct drinking water. It has the feature of a low water-leakage rate, which can save precious water resources. For water-supply pipes, choosing stainless steel pipe is the most beneficial to health. In immersion-water tests, all indicators meet the requirements of the relevant national drinking-water standards. The inner wall of stainless steel pipe is smooth; with long-term use it does not accumulate scale and is not easily contaminated by bacteria, so there is no need to worry about the water quality being affected, and secondary pollution of the water can be eliminated. The thin, dense chromium-rich oxide film on the stainless steel surface gives stainless steel water pipes good corrosion resistance in all water qualities, including soft water; even when buried underground they have excellent corrosion resistance. Field corrosion test data show that the service life of stainless steel water pipes can reach 100 years, with almost no maintenance needed during the life cycle, avoiding the expense and trouble of pipe replacement, and the comprehensive usage cost is low. All raw materials use grades 304, 304L, 316, and 316L, all meeting JIS4305 requirements. The above grades have the features of stable performance, high strength, and low thermal expansion coefficient, as shown in Fig. 8-56.

Fig. 8-56 Stainless steel water pipe

VII. Drainage Pipes

1. PVC Drainage Pipes

In laboratory construction, the drainage of the great majority of projects uses PVC pipe. PVC is the abbreviation of Polyvinylchlorid; its main component is polyvinyl chloride, a material to which other components are added to enhance its heat resistance, toughness, and ductility. The top layer of this surface film is lacquer, the main component in the middle is polyvinyl chloride, and the bottom layer is a back-coated adhesive. The production of pipes and fittings is completed through processes such as cooling, curing, shaping, inspection, and packaging.

It is a synthetic material that is deeply loved, quite popular, and widely used in the world today. Its global consumption ranks second among various synthetic materials.

Fig. 8-57 PVC drainage pipe

The conventional specifications of commonly used PVC drainage pipes are as follows: the nominal outside diameters are respectively 32 mm, 40 mm, 50 mm, 75 mm, 90 mm, 110 mm, 125 mm, 160 mm, 180 mm, 200 mm, 250 mm, 315 mm, 400 mm, 500 mm, 630 mm, etc. The length of PVC-U pipes is generally 4 m or 6 m, with other lengths determined by negotiation between supplier and buyer, as shown in Fig. 8-57.

2. Ductile Iron Pipes

During laboratory construction, occasionally the construction party specifically requests the agent-construction party to use ductile iron pipes for the drainage pipes. Ductile iron pipe has the essence of iron and the performance of steel, hence its name. In ductile iron pipe the graphite exists in spherical form, and the graphite size is generally grades 6–7. In terms of quality, the nodularization grade of the cast iron pipe is required to be controlled at grades 1–3, with a nodularity of ≥80%; consequently, the mechanical properties of the material itself are well improved, giving it the essence of iron and the performance of steel. After annealing, the metallographic structure of ductile iron pipe is ferrite plus a small amount of pearlite, with good mechanical properties, so it is also called cast-iron steel pipe. Ductile iron pipe is a type of cast iron pipe. It has excellent anti-corrosion performance, good ductility, good sealing effect, and simple installation, and is mainly used for municipal water supply, gas transmission, oil transmission, and so on in industrial and mining enterprises.

A certain quantity of spherical graphite is distributed on a ferrite and pearlite matrix; depending on the nominal diameter and the different requirements for elongation, the proportions of ferrite and pearlite in the matrix structure differ—the pearlite proportion for small diameters is generally no more than 20%, while for large diameters it is generally controlled at about 25%, as shown in Fig. 8-58.

Fig. 8-58 Ductile iron pipe