Another question for Sparks please? Ask questions and find answers to many subjects relating to electrics and electrical work

[Jeffmo]

Hi Sparks , i have a ? which might crop up in my exam on monday and i just can't remember or grasp what formula or where i should gleam the information from . Wonder if you could help ? ...Heres an example :-
A 230 V 30 A RADIAL CIRCUIT IS PROTECTED BY A BS3036 DEVICE.IF THE VALUE OF PHASE EARTH LOOP IMPEDENCE FOR THE CIRCUIT IS 2.3OHMS,DISCONNECTION UNDER PHASE/EARTH FAULT CONDITION WILL OCCUR IN .....Thats the question format and i think the answer is 3 sec's but its how i get there that is the problem please advise as its starting to make me worry about the exam , which in theory shouldn't be a problem , its just one little thing makes me doubt myself , thats just me i want everything to be perfect and to do that i need to know what and why .Cheers Jeff

[Jeffmo]

[quote="Jeffmo"]Hi Sparks , i have a ? which might crop up in my exam on monday and i just can't remember or grasp what formula or where i should gleam the information from . Wonder if you could help ? ...Heres an example :-
A 230 V 30 A RADIAL CIRCUIT IS PROTECTED BY A BS3036 DEVICE.IF THE VALUE OF PHASE EARTH LOOP IMPEDENCE FOR THE CIRCUIT IS 2.3OHMS,DISCONNECTION UNDER PHASE/EARTH FAULT CONDITION WILL OCCUR IN .....Thats the question format and i think the answer is 3 sec's but its how i get there that is the problem please advise as its starting to make me worry about the exam , which in theory shouldn't be a problem , its just one little thing makes me doubt myself , thats just me i want everything to be perfect and to do that i need to know what and why .Cheers Jeff[/quote]

[sparx]

hi jeffmo, very late, books in van but i think tables 41b1/2 give max values for 0.4 or 5.0 sec disconnection times, these being only options if i understand ?
BCNU
SPARX