C&g 2396 November / December 2012
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He teaches the old 2391-01 & 02 wozz!
O i see.
Right going through a exam paper and have a question.
When doing the adiabatic in order to find I you put Uo over Zs, why use Uo when by this stage you know the actual voltage at far end due to knowing the volt drop?
Hope thats clear enough??!
Right going through a exam paper and have a question.
When doing the adiabatic in order to find I you put Uo over Zs, why use Uo when by this stage you know the actual voltage at far end due to knowing the volt drop?
Hope thats clear enough??!
Can I just clarify - the 2396 is the 'old' 2391 right? :C
Correct wozz.
the 2391-10 is now the 2395.
Oh and before we get into the 2400 was more difficult etc.
That is rubbish when the 2400 became the 2391-20 it was IDENTICAL to the 2400.
So any nonsense about the 2391 being split into the 2391-10 & 2391-20 is just that nonsense!
the 2391-10 is now the 2395.
Oh and before we get into the 2400 was more difficult etc.
That is rubbish when the 2400 became the 2391-20 it was IDENTICAL to the 2400.
So any nonsense about the 2391 being split into the 2391-10 & 2391-20 is just that nonsense!
widdler
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The volt drop is obtained with the design current (Ib) whilst the adiabatic is for protective conductor sizing and so will be for fault currents of negligible impedance - in other words the volt drop doesn't affect it, as long as the Zs (which does incorporate the length) is low enough to achieve the fault current needed for the necessary disconnection time - then all is well.
i think I have it.
You wouldnt use the voltdtop figure for the adiabatic as the adiabatic just considers faults of negligible impedance (as does all of 76791?), if you use the volt drop figure you are then incorporating resistance due to the circuit resistance. Barking up the right tree?
Just strikes me as the voltdrop figure would give a more accurate assessment of fault current at the far end of circuit thus increasing time for the fault to clear at a lower current. So this leads me to, does it matter? if the fault of negligible impedance (near) is the worst thermal wise then it doesnt matter. However if the far end fault is worse thermally should it be considered (i realise bs7671 may not ask for this)?
You wouldnt use the voltdtop figure for the adiabatic as the adiabatic just considers faults of negligible impedance (as does all of 76791?), if you use the volt drop figure you are then incorporating resistance due to the circuit resistance. Barking up the right tree?
Just strikes me as the voltdrop figure would give a more accurate assessment of fault current at the far end of circuit thus increasing time for the fault to clear at a lower current. So this leads me to, does it matter? if the fault of negligible impedance (near) is the worst thermal wise then it doesnt matter. However if the far end fault is worse thermally should it be considered (i realise bs7671 may not ask for this)?
just struck me as we wasnt accounting for the temp rise in the DNO cables, but then again we dont account for much in their cables.
doing the 2396, loving it, doing exam tomorrow, have not really started the project yet just penciled basic ideas and browsed section 729 which i havnt delved into before.
doing the 2396, loving it, doing exam tomorrow, have not really started the project yet just penciled basic ideas and browsed section 729 which i havnt delved into before.
729 is a returning regulation from a long past requirement! 
Wozz, which element of impedance would you expect to be the overriding factor in the dno's cable?
AHHHHHHHH, i see where this is going, resistance would not make up much of the impedance and therefore will not change with temperature. Would i be correct in saying its the reactance? (havnt used that term for years).
Done the exam last night, was a harder paper that the previous ones. Felt it went ok though, used every minute of the three hours just to get to the end! More up beat than when I come out of the 2391. Bit silly still sitting in a exam at 21:30!
Started the project now.
im asked to 'show on drawings the proposed routes of all wiring systems'. Ive done the trunking routes do you think I will have to show the conduit off the trunking to directly above the points?
im asked to 'show on drawings the proposed routes of all wiring systems'. Ive done the trunking routes do you think I will have to show the conduit off the trunking to directly above the points?
Hi Wozz, you will need to show the drawing's for the entire system, when your ready we can go over the Thermal Constraint's using Adiabatic Lines
