Correction factors tab is where the user can set correction factors (will be referred as rating factors from now on) to suit the condition of the selected circuit. As many other tabs of ElectrcialOM, Correction Factors tab has also a dynamic behaviour, so,  contents will change according to various other factors within the design, for example cable installation method.



All the rating factor values are based on BS7671 unless otherwise specified and related tables are also given below in case the user needs to refer to the tables. Rating factors which are used by ElectricalOM are as follows:

  • Ca        : Ambient temperature - Tables 4B1 and 4B2
  • Cc        : Circuits buried in the ground. Cc = 0.9 for installation methods in a duct in the ground or buried direct and is equal to 1 otherwise.
  • Cd        : Depth of burial for direct buried cables and cable in buried ducts - Table 4B4. Cd = 1 for cables installed above ground.
  • Cf        : Semi-enclosed fuse to BS3036. Cf = 0.725 if a fuse to BS3036 is used and is equal to 1 otherwise.
  • Cg        : Grouping - Tables 4C1 to 4C6
  • Ch        : Higher harmonic currents in line conductors - Table 4A4
  • Ci        : Conductors embedded in thermal insulation - Table 52.2
  • Cs        : Thermal resistivity of soil - Table 4B3. Cs = 1 for cables installed above ground.
  • Ct        : Operating temperature of conductor (affects voltage drop calculations, not current carrying capacity). This option is for cases where a conductor is not running near its maximum permitted operating temperature. This generally happens when a cable size is increased due to voltage drop, so, the design current becomes significantly lower than the effective current-carrying capacity of the conductor. This is applied by ElectricalOM as per Appendix 4 of BS7671 (see Equation 6 of BS7671).

If user wants to define a manual value at any point, then, Manual option must be selected from the related drop down list. On the other hand, if the user types in any value in the related text box, then the drop down list will automatically be reset to Manual by ElectricalOM.