SECTION 14: APPENDICES, TABLES, GRAPHIC SYMBOLS

 SECTION 14

 APPENDICES, TABLES, GRAPHIC SYMBOLS

NOTES: 

1. Various appendices, tables, graphic symbols, etc. are provided in this Section. These are to be construed as a part of the Regulations and shall be complied with.
2. Where for a particular condition of installation, the appendix, tables etc. do not apply, then E.D.D's prior approval shall be obtained for the method adopted.

  APPENDIX 1

 CO-ORDINATION BETWEEN CONDUCTOR SIZE AND EXCESS CURRENT ROTECTION DEVICE EMPLOYED

General Condition:  For compliance with Clause No. 750.17 of the Regulation the following conditions are to be fulfilled

1. the excess current protection device's nominal current or current setting (In) is not less than the design current (IB) of the circuit, and
2. its nominal current or current setting does not exceed the lowest current carrying capacity (Iz) of any of the conductors of the circuit and
3. the current causing effective operation of the protective device (I2) does not exceed 1.45 times the lowest of the current carrying capacities (Iz) of any of the conductor of the circuit.

The above condition may-be stated as formulas

i B       1 N -<,     I Z

12        1.45 IZ

In order to determine the size of the cable to be used for a particular condition of installation, it may be necessary to apply one or more of the following correction factors:

1. For ambient temperature - Table 2.5 of Appendix - 2 which gives correction factor to be applied for the actual ambient temperature of the installation when it exceeds 40آ°C.
2. For grouping - Tables 2.2, 2.3 and 2.4 of Appendix - 2 which gives correction factors for various grouping of circuits.

Determination of Size of Cable to be used

Having established the designed current of the circuit under consideration and having chosen the type and nominal current or current setting of the excess current protective device it is intended to use in accordance with general condition above, the following procedure shall be adopted to determine the size of cable.
(i) DIVIDE the nominal current of the excess current device by the appropriate ambient temperature correction factor given in Table 2.5 for the type of cable to be used.

1. Then further, DIVIDE by any applicable correction factor for grouping given in Tables 2.2, 2.3 and 2.4.
2. The size of the cable to be used shall be such that its tabulated current carrying capacity for the installation method concerned is not less than the value of the nominal current of the excess current protective device adjusted as above.
     EXAMPLE:
   1. A circuit feeding a balanced three phase load of 21 KW at 0.8 P.F. 400 volts, at an ambient temperature of 50آ°C by means of single cote, PVC insulated cable in conduit along with another circuit.

       21  Design Current = -37.9 Amps
        F3 x 0.400 x 0.8

        Nominal current of excess current

        protective device 40 Amps

        Adjustment for ambient temperature 40
        from Table 2.5 - 47 Amps

        0.85
        47

        Adjustment for grouping from Table 2.2 =   -68 Amps
               0.69

        Size of cable from Table 2.6        = 25 mmآ².

   2. If the above circuit is ruse in a separate conduit,

        Adjustment for ambient temperature 40
        From Table 2.5 - = 47 Amps
                0.85

        Size of cable from Table 2.6. 16 mm,

   3. A single phase, 230 volts lighting circuit having a load of 2000 VA in an ambient temperature of 45آ°C and wired with single core PVC insulated cable run in a conduit having two more circuits (ie) three circuits together and protected by 10 amps circuit breaker.

           2000  Design Current = - = 8.7 Amps    230

      
      Nominal current of the excess current protective device = 10 Amps  Adjustment for ambient temperature  10 from Table 2.5 = -      = 1 1.0       0.91         1.1 Adjustment for grouping from Table 2.2 = -      = 16 Amps       0.69  Size of cable from Table 2.6  2.5 MM2

   4. If the above circuit is run in a separate conduit.  Adjustment for ambient temperature 1.0 from Table 2.5 - = 1 1.0 Amps      0.91  Size of cable from Table 2.6 1.5mmآ²