ABSTRACT
Table 54.7 in BS 7671 gives the minimum size for circuit protective conductors. This is a simple table to use, however it is often useful to use a smaller c.p.c. than that required by Table 54.7. On larger cables cost is a major factor as is space. If it is required to select a size of conductor smaller than is given in the table, a calculation must be carried out to ensure the conductor temperature will not rise above its final limiting temperature under fault conditions, this is called the adiabatic equation (final limiting temperature for conductors can be found in Table 43.1).
