L
Luke123
[FONT="] [/FONT] [FONT="]Hey guys, iam looking for help on the question below!
Q) A 12mm[/FONT][FONT="]²[/FONT][FONT="] [/FONT][FONT="]cable with 90C thermosetting rubbers is to be used in conjunction with lighting, small power, data and fire alarm installations. It is protected by a 40A fuse to BS 88 part 2 in an installation where the loop impedance between lines of phase where the fuse is installed is 0.14Ω. If the supply is 415V three phase, what will the protective short circuit (PSC) be? Also determine the time for the current to raise the conductor temperature to the permissible level?
so far i have this
PSC - I = UL / Z - 415 / 0.14 = 2.96KA
so i believe the psc to be 2.96KA but iam not sure if i have to times this by 3 for the three phase supply or something along thos lines?
For [/FONT][FONT="] time for the current to raise the conductor temperature to the permissible level [/FONT]i am abit stuck on, i know it has something to do with this eqaution T = Ksq Ssq / Isq, but still finding it hard to work out :banghead:
A breakdown of this equation or any help would be would be great
many thanks
Luke
Q) A 12mm[/FONT][FONT="]²[/FONT][FONT="] [/FONT][FONT="]cable with 90C thermosetting rubbers is to be used in conjunction with lighting, small power, data and fire alarm installations. It is protected by a 40A fuse to BS 88 part 2 in an installation where the loop impedance between lines of phase where the fuse is installed is 0.14Ω. If the supply is 415V three phase, what will the protective short circuit (PSC) be? Also determine the time for the current to raise the conductor temperature to the permissible level?
so far i have this
PSC - I = UL / Z - 415 / 0.14 = 2.96KA
so i believe the psc to be 2.96KA but iam not sure if i have to times this by 3 for the three phase supply or something along thos lines?
For [/FONT][FONT="] time for the current to raise the conductor temperature to the permissible level [/FONT]i am abit stuck on, i know it has something to do with this eqaution T = Ksq Ssq / Isq, but still finding it hard to work out :banghead:
A breakdown of this equation or any help would be would be great
many thanks
Luke