BS - De-rating Factor Calculation

Total de-rating can be calculated once each of following de-ratings are selected:

a. De-rating factor of Ambient Temperature ((Cat)

b. De-rating factor for Cable Grouping (Ccg)

c. De-rating factor for Number of Circuits (Cnc)

d. De-rating factor for Number of Trays (Cnt)

e. De-rating factor for depth of buried cable (Cdb)

Total De-rating factor = (a * b * c * d * e)

If De-rating is not used the factor is set to 1.

The user can select a de-rating factor which will be used instead of the calculated value.

To select a de-rating factor, click the De-rating Factors button. The Derating Factors window is then displayed:

Select the required factor from the list. The list includes the de-rating factors that are part of the standard and user-defined project specific de-rating factor set up using the Cable Sizing Configuration window.

If a value is 1 then the rating will have no effect on the calculation.

Click Save. The selected factor is then displayed in the Chosen De-rating Factor field.

The Chosen De-rating Factor field value can only be set by the user to be equal to or less than the Calculated De-rating Factor field value.

If this field is blank when the Size Cable button is clicked, it will be automatically populated with the calculated value.

Reference BS standard tables used for de-rating factors is

Table 4B1 and Table 4B2 covers De-rating factor of Ambient Temperature ((Cat)

Table 4C1 covers De-rating factor for Cable Grouping (Ccg)

Table 4C2 and Table 4C3 covers De-rating factor for Number of Circuits (Cnc)

Table 4C4 and Table 4C5 covers De-rating factor for Number of Trays (Cnt)

Table 4B3 covers De-rating factor for depth of buried cable (Cdb)

Note:
Depending on installation arrangement, methods and external situation, the factors may differ.

De-rating factors not currently covered include:

De-rating for cables enclosed in infloor concrete troughs (Reference Method E, F)

De-rating for depth of buried cable is presently not included (Assumed to be 0.7m)

De-rating for cable groups in conduit systems, cable trunking systems or cable ducting systems is presently not included