TECHNICAL
Table 1 – List of current-carrying capacity tables in BS 7671 Appendix 4 for operation of thermosetting insulated cables at a conductor temperature not exceeding 70 °C BS number 90 °C currentDescription Current-carrying carrying capacity capacity table table for conductor (for reference only) temperature not exceeding 70 °C 1 2 3 4 Single-core non-armoured for voltages not exceeding BS 7211 450/750 V, for power, lighting and internal wiring, having 4E1A 4D1A low emission of smoke and corrosive gases. BS 7889 Single-core non-armoured for a voltage of 600/1000 V. BS 7211 Multicore non-armoured for voltages not exceeding 4E2A 450/750 V, for power, lighting and internal wiring, having 4D2A low emission of smoke and corrosive gases. BS 5467 Single-core armoured (non-magnetic armour) for voltages of 600/1000 V. BS 6724 Single-core armoured (non-magnetic armour) for voltages of 600/1000 V, having low emission of smoke and corrosive 4E3A 4D3A gases. BS 7846 Single-core armoured (non-magnetic armour) fire-resistant for voltages of 600/1000 V, having low emission of smoke and corrosive gases. BS 5467 Multcore armoured for a voltage of 600/1000 V.
BS 6724 4E4A BS 7846
BS 7919
Multcore armoured for a voltage of 600/1000 V, having low emission of smoke and corrosive gases.
4D4A
Multcore armoured fire-resistant cables for a voltage of 600/1000 V, having low emission of smoke and corrosive gases. 4F2A
Flexible cables with sheath (non-armoured).
4F1A*
* 60 °C conductor temperature.
4E2A, the smallest size of twocore cable giving a tabulated current-carrying capacity of not less than 30 A when clipped direct is 2.5 mm2 (tabulated currentcarrying capacity 33 A). The minimum required conductor size such that the conductor operating temperature will not exceed 90 °C is therefore 2.5 mm2. (Answer)
which is 36 A for answer (1) above and 33 A for answer (2). If the protective device is a semi-enclosed fuse to BS 3036,
then, in order to protect the cable against overload current, its rated current (In) must not exceed 0.725 times the actual current carrying capacity of the cable, as required by Regulation 433.1.3.
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Important To protect the cable against overload current, the requirements of Regulation 433.1.1 must be complied with. For example, if the circuit protective device is a circuit-breaker or fuse of a type listed in Regulation 433.1.2, its rated current or setting (In) must not exceed the actual currentcarrying capacity of the cable, given by the formula
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