just took my 2391 test

[cjp1]

Bugger I think the 1.2 factor is right for the voltage drop - got that completely wrong then!
Be interested to see the paper again

Not sure about 1.2 factor for volt drop, are you sure your not thinking of the X 0.8 tempreture correction factor for tabulated Zs to measured Zs .

 

[jstephens251]

i calculated total resistance by the 30A of motor and it got me 11.4v, felt like more was needed though...

 

[brucelee]

Hi did the volt drop question give you a resistance at 20C or a table with the m/ohm/m values at 20c if so then needed correcting by 1.2 for the increase in temp due to load current ie say a 1.83 m/ohm/m =10mm conductor with another added in parallel ie line and neutral at 20c will need increasing by 1.2 as its a conductor bunched or a core in a multicore cable for thermoplastic (pvc) 70C max operating temp
table A.3 in GN3

m/ohm/m x 2 x MF x Ib X L/1000 = Vd
1.83 x 2 x 1.2 x Ib x L/1000
which will give same value as the mv/A/M tabulated value from the regs when using
mv/A/M x Ib X L/1000
or
R1+RN x 2 x Mf x Ib x L/1000

be good if someone could remember the question or somehow found the paper in there bag lol


this sounds like a question i had for the 2391 june 2010 and the only thing i forgot to include was the MF of 1.2 which i realised later when discussing it with forum members
good luck to you all

 

[cjp1]

Hi did the volt drop question give you a resistance at 20C or a table with the m/ohm/m values at 20c if so then needed correcting by 1.2 for the increase in temp due to load current ie say a 1.83 m/ohm/m =10mm conductor with another added in parallel ie line and neutral at 20c will need increasing by 1.2 as its a conductor bunched or a core in a multicore cable for thermoplastic (pvc) 70C max operating temp
table A.3 in GN3

m/ohm/m x 2 x MF x Ib X L/1000 = Vd
1.83 x 2 x 1.2 x Ib x L/1000
which will give same value as the mv/A/M tabulated value from the regs when using
mv/A/M x Ib X L/1000
or
R1+RN x 2 x Mf x Ib x L/1000

be good if someone could remember the question or somehow found the paper in there bag lol


this sounds like a question i had for the 2391 june 2010 and the only thing i forgot to include was the MF of 1.2 which i realised later when discussing it with forum members
good luck to you all

Hi Brucelee, From memory the question said something like: the combined resistance of the line and neutral is ?? ohms can you calculate the volt drop on these conductors,
as Jstephens said he got 11.4v I think I did too
But I am sure that I forgot to put a 1.2 correction factor into the equation,
Cheers Chris.

 

[stiggy84]

you definetly have to use the x 1.2 to allow for max operating temp of 70 degrees, i did the same exam
just passed my practical today!!!

 

[cjp1]

I wonder how many marks you loose for not putting the correction factor into the equation or if you get no marks for the whole question :confused5:

 

[brucelee]

Hi mate you should get something but how many marks not sure and as far as C&G you will never know now

would be good if you got your paper marked and sent back so you could brush up on areas that you hadnt done to well but all you get is its just pass or fail

good luck mate i felt the same after my exam wondering if i had done enough nothing you can do now except wait for the outcome

HOPE ITS GOOD NEWS for you