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Reactance and impedance of 300 mm2 Aluminium 4-core cable
Former Community Member
I am doing 6.3.4 example in the IET Electrical installation design guide: calculations for electricians and designers. in part 2: three-phase to earth fault current at C, it says a 100m of 300 mm2 cable aluminium SWA thermosetting (Table F7A). but the table does not have x value, only r value. where and how to find these values to help in calculating the prospective fault current ?
Note: The table being referenced here is F.7A in the Design Guide it is based on BS 6346.
I have an ealier version of the Design Guide which has basically the same question with some minor changes. Table F.7A in my book gives 0.08 ohms / km @ 20ºC for x as shown in the question solution. This is the conductor reactance (i.e. not the armour reactance). I assume you are aware that for a three phase fault to earth the armour will not carry any fault current as the the three phase currents sum to zero.
Note: The table being referenced here is F.7A in the Design Guide it is based on BS 6346.
I have an ealier version of the Design Guide which has basically the same question with some minor changes. Table F.7A in my book gives 0.08 ohms / km @ 20ºC for x as shown in the question solution. This is the conductor reactance (i.e. not the armour reactance). I assume you are aware that for a three phase fault to earth the armour will not carry any fault current as the the three phase currents sum to zero.
