C&g 2396 November / December 2012

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wozz

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Anyone else doing it?

Any advice for those that have passed?

I know this sounds sad but really looking forward to it!

 
Not popular then! O well I will update anyway once started. Picked up the books today.

 
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??!

 
I believe it was the 2391-20. Its the Design course rather than the test and inspect.

 
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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!

 
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??!
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)?

 
Got the project now, basically a argos catalogue store should be interesting, with 10kW pv. cant wait to get started but still doing past exams in my spare time.

 
Quick one when calculating Zs and using figures at 20 degrees to get r1+r2 and then x1.2 to account for full loading, we dont multiply the Ze up, why dont we?

Or have i got it wrong? 

 
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.  

 
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.  
Wozz, which element of impedance would you expect to be the overriding factor in the dno's cable?

 
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!  

 
Hi Wozz ill PM you the Method i use for Domestic Supply's upto 100 amp, you could also use Attenuation tables too.

 
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?

 
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?

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 :)

 
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