Sismicidad en el Perú

(1) General

(2) Factors to be considered in sizing of cable conductors (3) Method of sizing cable conductors

(4) Typical sizes of cable conductor used in general installations 13B Protection Against Direct Contact of Live Conductors

(1) Protection by electrical insulation (2) Protection by other means 13C Joints and Connections 13D Other Requirements of Cables

(1) Voltage grading of cables for low voltage application (2) Identification of cable cores

Code 13

CONDUCTORS, JOINTS AND CONNECTIONS

(1) General

A conductor should have a current carrying capacity not less than the maximum current demand it normally carries, be capable of withstanding the prospective fault current, and suitable for operation in the environment and at the design voltage of the installation.

(2) Factors to be considered in sizing of cable conductors

In general, sizing of cable conductors should take into account the following factors:

(a) the conductor material; (b) the insulating material;

(c) the ambient temperature in which the cable is installed; (d ) the method of installation;

(e) whether or not the cable is affected by thermal insulating material; ( f ) the use and type of protective device;

(g) the voltage drop from the origin of the circuit to the load; and (h) for Category 1 circuits, live conductors should have a cross-sectional

area:

(i) not less than 1.5 mm2 _{for surface wiring using PVC insulated}

PVC sheath copper cables;

(ii) not less than 1.0 mm2 _{for single core PVC insulated copper}

cables installed in conduit, duct, ducting or trunking; (iii) not less than 16 mm2_{for aluminium conductors;}

(iv) not less than 0.5 mm2_{for flexible cables and flexible cords.}

(3) Method of sizing cable conductors

(a) In determining the size of cable conductors to be used, the steps employed, in general, are as follows:

(i) Determine the design current of the circuit under consideration. (ii) Choose a suitable overcurrent protective device (refer to Code 9). (iii) Determine the current carrying capacity of the conductors required by applying suitable correction factors to the nominal setting or current rating of the overcurrent protective device as divisors.

Typical correction factors for ambient temperature, grouping, thermal insulation and type of protective device are given in Appendix 5.

(iv) Choose suitable size of the conductors according to the current carrying capacity required. Appendix 6 gives the current carrying capacities for various copper conductor sizes of PVC/XLPE insulated cables according to their installation methods. For other types of cables, reference should be made to BS 7671 or IEC 60364.

(v) The resulting voltage drop in the circuit should be checked so that under normal service conditions the voltage at the terminals of any fixed current using equipment should be greater than the lower limit corresponding to recognised standards relevant to the equipment.

Where the fixed current using equipment concerned is not the subject of a recognised standard, the voltage at the terminals should be such as not to impair the safe function of that equipment.

The above requirements are deemed to be satisfied if the voltage drop between the origin of the installation (usually the supply terminals) and the fixed current using equipment does not exceed 4% of the nominal voltage of the supply.

A greater voltage drop may be accepted for a motor during starting periods and for other equipment with high inrush current provided that voltage variations are within the limits specified in the relevant recognised standards for the equipment or, in the absence of a recognised standard, in accordance with the manufacturer’s recommendations.

Table in Appendix 6 also gives the values of voltage drop caused by one ampere for a metre run of PVC/XLPE insulated cables with copper conductors.

If the voltage drop so determined is unsatisfactory, a conductor of larger size should be chosen accordingly.

(b) To illustrate the steps used in sizing cable conductors, an example is given in Appendix 9.

(4) Typical sizes of cable conductor used in general installations

For general installations under the conditions listed below, the sizes of copper conductor in compliance with Table 13(1) are generally acceptable:

(a) the ambient temperature does not exceed 35°C,

(b) no more than one circuit of single core cables or one multicore cable are to be grouped together,

(c) for cables clipped direct on surface, the spacing between groups of single core cables or multicore cables is not less than twice the diameter of the largest cable in the adjacent group of cables,

(d ) the protective device is not a semi-enclosed fuse, and (e) the cables are not in contact with any thermal insulation. 13B Protection Against Direct Contact of Live Conductors

(1) Protection by electrical insulation

(a) Live conductors should be completely covered with insulation which: (i) is durably withstanding the mechanical, electrical, thermal and

chemical stresses to which it may be subjected in service; and (ii) can only be removed by destruction.

(b) Where insulation is applied during the erection of the installation, the quality of the insulation should be verified by tests equivalent to those specified in recognised standards for similar type-tested equipment.

(c) Non-impregnated paper, asbestos, fabric, wood or press-hemp should not be used for insulating purposes.

(d ) Where insulating tapes are permitted to be used in low voltage installations, they should have a minimum thickness of 0.21 mm. (2) Protection by other means

Other means of protective measures against direct contact as stipulated in IEC 60364 or BS7671 are acceptable.

13C Joints and Connections

(a) Every connection at a cable termination or joint should: (i) be mechanically and electrically sound;

(ii) be protected against moisture, mechanical damage and any vibration liable to occur;

(iii) not impose any appreciable mechanical strain on the fixings of the connection;

(iv) not cause any harmful damage to the cable conductor;

(v) be appropriate to the size and type of conductors with which they are to be used; and

(vi) be suitably insulated for the voltage of the circuits in which they are situated.

(b) No strand of a stranded conductor in a cable core should be cut away in making a cable joint or termination.

(c) Joints in non-flexible cables should be made by soldering, brazing, welding, or mechanical clamps, or be of the compression type. All mechanical clamps and compression type sockets should securely retain all the wires of the conductor.

(d ) Joints in flexible cable or flexible cord should be made by using appropriate cable couplers.

(e) Terminations of mineral insulated cables should be made with proper accessories and tools as recommended by the manufacturers.

( f ) Cable glands should securely retain without damaging the outer sheath or the armour of the cables.

(g) Other details relating to the workmanship of cable joint and termination are described in Code 25D.

(h) Except for the following, every connection and joint should be accessible for inspection, testing and maintenance:

(i) a compound filled or encapsulated joint;

(ii) a connection between a cold tail and a heating element (e.g. a ceiling and floor heating system, a pipe trace-heating system); and

(iii) a joint made by welding, soldering, brazing or compression tool. 13D Other Requirements of Cables

(1) Voltage grading of cables for low voltage application

(a) PVC insulated non-sheathed cables to BS6004 and BS6007 should be 450/750V grade.

(b) PVC insulated, PVC sheathed cables up to 35 mm2_{to BS6004 should}

be 300/500V grade. For cables greater than 50 mm2 _{to BS6346,}

voltage grade should be 600/1000V.

(c) PVC insulated, PVC sheathed armoured cables of any size to BS6346 should be 600/1000V grade.

(d ) XLPE insulated, non-sheathed or PVC sheathed cables to BS7211 should be 450/750V grade and to BS 5467 should be 600/1000V grade.

(e) XLPE insulated, PVC sheathed armoured cables to BS5467 and BS 6724 should be 600/1000V grade.

(2) Identification of cable cores

(a) Every cable core of a non-flexible cable or bare conductors in a fixed wiring installation should be identifiable at its terminations by appropriate labels, colours or coding. The application of tapes, sleeves or discs of the appropriate colours at terminations is acceptable. The use of colours should be in accordance with Table 13(2).

(b) Every cable core of a flexible cable or cord:

(i) for use in a single phase circuit should have its phase conductor coloured brown and its neutral conductor coloured blue throughout its length;

(ii) for use in a polyphase circuit, the phase conductors may be coded L1, L2 and L3; and N for the neutral, if any.

(c) Every cable protective conductor should be coloured exclusively in green-and-yellow.

(3) Identification of cables buried direct in ground

Where cables are buried underground, they should be identified by cable cover tiles or identification tapes for the entire underground cable route. The cable tiles or identification tapes should be marked with words ‘Danger-cables’.

Table 13(1)

Minimum Size of PVC Copper Conductors in sq. mm under the General Installation Conditions

Listed in Code 13A(4)

Table 13(2)

Colour Identification of Non-flexible Cables and Bare Conductors for Fixed Wiring

Function Colour Identification

Phase of single phase circuit Red (or yellow or white or blue) Phase R of 3-phase circuit Red

Phase Y of 3-phase circuit Yellow (or white) Phase B of 3-phase circuit Blue

Neutral of a circuit Black

Protective conductor Green-and-yellow

Current Rating (Amp)

1-Phase 2-Wire 3-Phase 4-Wire

5.0 15. 20. 30 60 80 100 5.0 15. 20. 30 60 100 150 200 300 400 1.0 2.5 2.5 04 16 25 035 1.0 2.5 2.5 06 16 035 070 120 240 400 1.5 2.5 2.5 04 10 16 025 1.5 2.5 2.5 04 10 025 050 070 150 240 Enclosed Condition

Code 14

WIRING INSTALLATION ENCLOSURE