(a) Mounting Major System Components. Each instru­ment and piece of equipment in the instrument-rack structure should be mounted, wired, or piped, where possible, so it can be removed without interruption of service to adjacent instruments and equipment. The instru­ments and equipment should be located and mounted so all wiring terminals and piping connections are readily accessi­ble (see Fig. 10.4).

(b) Mounting Electrical Equipment and Hardware. The

electrical equipment and hardware, as well as the installa­tion of these items, should conform to some standard, such as the National Electrical Code. The ambient conditions at

the location where the system is to operate and the type of system will determine which sections of the electrical code are applicable.

Terminal Blocks. Terminal blocks are arranged so that one side of each block is reserved for field connections (see Fig. 10.5). Spare terminals (10% minimum) should be provided for future use and should be distributed through­out the terminal blocks. Where a field cable may fill all the spaces on a terminal block, the spares requirement should be overruled to prevent the need for splitting the cable between two terminal blocks. Terminal blocks should be located in the panels and cabinets to facilitate maintenance and testing without impairing access to other equipment mounted in the structure. Terminal blocks and terminal points should be identified and labeled.

Wiring Installation in Panels and Cabinets. The wire used for power distribution in the instrument cabinets should be adequate to carry the current used by the circuit. Design and installation engineers must adhere to the National Electrical Code in sizing wire for power-distribu­tion circuits. No wire smaller than No. 14 American Wire Gauge (AWG) should be used in power-distribution circuits. Control circuits with less than 5 amp of maximum operating current may use No. 16 AWG copper wire. Wire sizes smaller than No. 16 AWG could handle the current requirement of most control circuits; however, mechanical strength becomes an overriding consideration, and these wires are not recommended for installation in panels and cabinets.

Architect—engineers and reactor designers have speci­fied both stranded and solid wires for instrumentation and

control applications in nuclear plants. For power and control circuits, stranded wire is preferred and is much more widely used than solid wire. The flexibility of stranded wire facilitates installation and maintenance. Either stranded or solid wire can be used without affecting the electrical characteristics or performance of the circuit.

All wiring should have a minimum of 600-volt insula­tion and should be resistant to heat, oil, moisture, flame, and corrosive vapors. Insulation materials have been devel­oped which meet the requirements for switchboard and control-panel wiring without requiring braid or fibrous coverings. This results in a smaller overall diameter with fewer stripping and terminating problems.

All wiring connections in the instrument panels and cabinets should be made with preinsulated compression — type terminals unless a solder connection is required. For solder connections, insulated sleeves should be used to snugly cover the finished solder joint.

Wires entering or leaving the instrument cabinet should be terminated in terminal boxes to facilitate maintenance. However, some wires, such as coaxial, triaxial, and thermo­couple lead wires, should be terminated through appropri­ate connectors directly to the instruments or thermocouple junction boxes.

Multiconductor or twisted-pair shielded cable should be used for analog signals (low-level, millivolt or milliampere) in instrumentation circuits. Wire no smaller than No. 18 AWG is recommended to minimize wire breakage during installation. Each conductor and the outer jacket or sheath
of the shielded cable should have a flame-resistant insula­tion. The shield is carried as a separate conductor at all cable junction points.

The signal wires are run in wireways separate from the control and power wiring to minimize noise pickup in signal wiring. Separate terminal boxes are recommended for the signal and the power wiring. Lacing of low-level signal cables into bundles with power or control wiring should be avoided. Wiring in the instrument racks should not be spliced; each wire should run unbroken from terminal to terminal.

Wiring between panel-mounted instruments and termi­nal boxes should be grouped in a neat and orderly manner and run in enclosed metal wireways. Exposed wiring should be laced or bundled together with lacing, tie straps, or similar means.

Each wire should be properly identified. There are several coding or identification methods, such as noncon­ductive markers, color-coding the wires, and providing label identifications on the terminal blocks. Proper identification facilitates testing and maintenance. Wiring identification should correspond to that shown on the elementary and connection diagrams.

Terminations. The termination of conductors, whether they carry low-current signals or high-current power, is an important part of installation. Whether the termination is made by a simple “crimp-on” lug or a complex triaxial connector, good workmanship is of the utmost importance. Careful adherence to the manufacturer’s mounting instruc­
tions, including the use of proper tools, can save many hours of troubleshooting and wire tracing

Instructions and procedures for installing lugs and connectors on wire and signal cables are shown in Figs 10 6 to 10.9 The most widely used hardware for terminating

wiring and cabling is shown in these drawings Recommen­dations are included on how to avoid common problem areas in the installation of connectors

Crimp-on lugs Figure 10 6 shows the proper proce­dure for installing crimp-on lugs. To avoid installation problems, it is essential that

1 1 he proper type of lug (insulated or nomnsulated, ring or spade, etc ) be used.

2. The proper si/e lug for the wire and terminal be used

3. The insulation be stripped to the proper length (refer to “a” in Fig 10.6). The conductor should be inserted completely through the lug with the insulation butted up against the shoulder and the conductor cut so that it protrudes just past the crimped portion of the lug

4. The lug be properh crimped, using the proper crimping tool, with the wire conductor and insulator, where applicable, completely compressed to the lug It is recom­mended that a fixed-release crimping tool be used. This tool assures proper crimping of the lug evert time by not allowing release of the lug until the full amount of crimping pressure has been applied

Standard Coaxial (BNC) Connector I igure 10.7 show’s the proper procedure for installing standard coaxial (BNC) connectors. ‘I о avoid installation problems, it is essential that

1 All strands of the shield be free of the center conductor

2. All strands of the shield make a good contact with the connector shell.

3 All dimensions on the assemble drawing be followed precisely so that the connector will fit together properh.

4. A good solder connection be made between the contact tip and the center conductor

5. The connector and cable be cleaned properly with an appropriate cleaning agent

Crimp-On Coaxial (BNC) Connector Figure 10.8 shows the proper procedure for installing crimp-on coaxial (BNC) connectors To avoid installation problems, it is essential that

1. All strands of the shield make good contact with the connector shell

2 All assembly instructions and dimensions be followed precisely.

3. The connector and cable be cleaned properly with an appropriate cleaning agent

1 riaxial Connector. Figure 10.9 shews the proper procedure for installing triaxial connectors To avoid installation problems, it is essential that

1 All strands of the two shields make good contact with their conductor Strands left out of the conductor have been a source of noise problems, particularly with pulse circuits having fast rise times in the microsecond and nanosecond range

2. None of the shield strands from either shield touch each other or the center conductor

3 All assembly instructions and dimensions be followed precisely.

4. The connector and cable be cleaned properly with an appropriate cleaning agent.

(c) Mounting Pneumatic Equipment and Hard­ware. The pneumatic instrumentation system uses com­pressed air for the operation of the measuring devices, indicators and controllers, and final control elements

Relatively trouble-free operation can be realized. In systems requiring 100% availability, a backup or dual system as shown in Figs. 10.4 and 10.12 should be used. The installation of an instrument air sy’stem should con­form to a standard of the industry, such as the American Standard Association Code for Pressure Piping, ASA B31.1.*

Instrument Air Supply. In a pneumatic system the air is supplied by7 a compressor to a storage tank, and the system is supplied from the tank. The compressor and storage tank are sized so that the air usage of the system does not require continuous operation of the compressor. These items are generally located in a service equipment area 1 he air is then piped to the instrumentation-rack structure.

Condensation in a compressed-air piping system must be limited because moisture can damage instruments and make the system inoperative Several air-dry ing techniques are available to remove the moisture from compressed air.

Desiccant dryer A desiccant dryer is located in the piping between the compressor storage tank and the filter—regulator station. The dryer consists of two identical units, each unit has a desiccant chamber, check valve with a reduced-area bypass, and a solenoid valve, connected as shown in Fig. 10.10. Part of the dried air from the chamber

•See Vol 2, Chap. 14, for a discussion of standards and the addresses of standards organizations.

Fray shield and strip inner dielectric ^32 in. Tin center conductor.

Taper braid and slide nut, washer, gasket, and clamp over braid. Clamp is inserted so that its inner shoulder fits squarely against end of cable jacket.

With clamp in place, comb out braid, fold back smooth as shown, and trim З/32 in. from end.

Slip contact in place, butt against dielectric, and solder. Remove excess solder from outside of contact. Be sure cable dielectric is not heated excessively and swollen so as to prevent dielectric from entering into connector body.

Fig. 10.7—Assembly of standard coaxial connector.

in service is used to regenerate the other chamber; this

amounts to about one-third of the dried air produced.

Because additional air is required for regeneration of the system, the compressors must be sized to supply the

regeneration air in addition to the air required by the

instrument system. As the chamber drying the air becomes saturated, the chamber on the regeneration cycle is dried out. An electric timer controls the solenoid valves and periodically switches them, reversing the operating cycle of the system.

After-condensers, After-condenser air dryers are also located in the air line between the compressor-storage tank and the filter—regulator station. The after-condenser con­sists of a heat exchanger that uses water as a cooling agent. Figure 10.11 is a simplified diagram of a water-cooled moisture condenser. The use of chilled water for cooling increases the capacity of the condenser.

Filter—Regulator Station. A filter is located upstream of the pressure regulator and is used to remove foreign matter or contaminants from the air stream. The pressure regulator reduces the air pressure to the level required by the instrument system.

Where instrument air must be available to the system 100% of the time, a dual filter—regulator station is used. A typical dual station is shown in Fig. 10.12 in schematic form, and an actual installation, in Fig. 10,4. Each of the parallel filter—regulator stations is sized to handle the total requirements of the system. Isolation valves in each of the parallel piping arrangements allow either of the filter — regulator stations to be isolated from the system for repair and maintenance without shutting down the entire system. Each instrument using air is connected to the instrument air header through an isolation valve. Each instrument air header should have spare air takeoff points (10% mini-

Strip cable jacket, braid, and dielectirc to dimensions shown in table All cuts are to be sharp and square Important Do not nick braid, dielectric, and center conductor Tinning of center conductor is not necessary if contact is to be crimped For solder method, tin center conductor avoiding excessive heat Slide outer ferrule onto cable as shown

Stripping dimensions (+ ^/04) MIL-Crimps Quick-Crimps a b c a b c Plugs and lacks 114 13/64 1/8 1/4 7/32 11/64 Right-angle plugs 1 /4 13/64 1/8 1/4 3/l6 11 /64 Bulkhead lacks 1/4 13/64 1/8 v4 1/4 11/64

CONTACT MUST BUTT AGAINST CABLE DIELECTRIC

Flare end of cable braid slightly as shown to facilitate insertion onto inner ferrule Important Do not comb out braid Place contact on cable center conductor so that it butts against cable dielectric Center conductor should be visible through inspection hole in contact Crimp or solder the contact in place as follows

l——— a —

Crimp method Crimp center contact using either of the following two tools Tool No 227-912-1000—To crimp the male contact (pin), insert the end of the nest bushing marked "P" into the tool To crimp the female contact (socket) insert the end of the nest bushing marked "S" into the tool Tool No 227-917 (MS-3191-A)—To crimp the male contact (pin), insert the positioner marked 227-918 into the tool To crimp the female contact (socket), insert the positioner marked 227 919 into the tool

CABLE DIELECTRIC MUST

Solder method Soft solder contact to cable center conductor Do not get any solder on outside surfaces of contact Avoid excessive heat to prevent swelling of dielectric

CABLE DIELECTRIC MUST

Install cable assembly into body assembly so that inner ferrule portion slides under braid Push cable assembly forward until contact snaps into place in insulator Slide outer ferrule over braid and up against connector body Crimp outer ferrule with tool specified in table

Fig. 10.8—Assembly of crimp on coaxial connector

mum) The spare takeoff points should be equipped with isolation valves to allow the addition of new instruments to the system without requiring system shutdown. The header is sloped to the output, and so any condensation collects at the dram cock (see Fig 10.4)

Pneumatic Signal Lines The air supply and signal lines downstream of the instrument air header are plastic or copper tubing Runs of this tubing should be straight, parallel, accessible, and logical with vertical runs plumb and horizontal runs dropping away slightly from the instru­ments Tubing runs must be rigidly supported and fastened to the instrument structure or supporting braces These installation requirements ensure that the tubing installation
will not only have a pleasing appearance but also will be easily maintained.

bach instrument signal input line should be equipped with an isolation valve and a test tee with a shutoff valve This arrangement allows maintenance or testing without shutting down the whole system.

Pneumatic Input-Output Terminal Panel The fact that instrumentation systems are generallv assembled and tested at the vendor’s plant and not at the location where the system will be used requires that provisions be made for terminating the pneumatic input—output lines One method of providing a terminal for both instrument structure lines and field-installed lines is to use a bulkhead tubing

Slide nut, washer, and gasket over cable. Cut off outside jacket (using razor blade or wire strippers) to dimension a. Make a clean cut, being very careful not to nick braid. Cut first braid to dimension b.

Slide first braid clamp over braid up to jacket of cable. Fold first braid back over clamp, making sure braid is evenly distributed over the sur­face of the clamp. Trim second jacket to dimension c, again being very careful not to nick braid.

Trim second braid to dimension d. Slide on outer ground washer. Insulator, and second braid clamp. Fold second braid back over braid clamp, again making sure that braid is evenly distributed over surface of clamp.

Plug only: Place front insulator and outer contact assembly into back of connector body and push into proper place. Insert cable contact assembly into body. Screw nut into body with wrench until moderately tight.

Tin the inside hole of the contact. Tin wire and insert into contact and solder. Remove any excess solder. Be sure cable dielectric is not heated excessively and swollen so as to prevent dielectric from entering body of fitting.

NOTE: "a" thru "f" dimension depends on cable and connector type

Fig. 10.9—Assembly of triaxial connector.

connector (see Fig. 10.13). The bulkhead connectors are mounted on the enclosure surface or on a mounting plate in a panel. The connectors are located in an area accessible to the field lines.

After the pneumatic systems have been installed, each system must be pressure-tested to be certain that leakage in the system does not affect the operation of the system. The Instrument Society of America (ISA) Pneu-

Fig 10 10 —Air dryer desiccant type

matic Control Circuit Pressure Test, ISA RP7 1, is one test procedure for verifying the leakage in pneumatic systems and establishing the criteria for acceptance of the work