OP
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This is the answer I came up with (back in the day) - unfortunately not correct
Respect
Discuss Back in the 2391 days in the Electricians' Talk area at ElectriciansForums.net
This is the answer I came up with (back in the day) - unfortunately not correct
With respect your teacher was a c u next Tuesday.
I have many arguments on site today about root 3, and doubling.
All current books will use root 3.
I would have went with 800, and came up with 0.29
On my 2391 we were told to double the highest SP PSSC to derive the TP PSSC
As this is a TNC-S supply the SP PFC will be the same as the PEFC (without the bonding)
But the question is not clear, the PSSC measurement issues aside (technically root 3), the PEFC would be taken with all bonding connected too.
Q20: For a TNC-S system, supplied at 230V, 50 Ha, state
a) why PSCC and PEFC are the same (1 mark)
b) the value of PFC if Ze was 0.01 (1 mark)
c) the approximate value of PFC between phases if the single-phase value
was 10 000A.
(1 mark)
A20: PSCC and PEFC
a. PSCC and PEFC are the same because the neutral and earth conductors are
combined up to the service head where the measurement is taken.
b. If Ze = 0.01, then using the formula
a
oc
s I
U
Z = where Uoc is taken as 240V for a
nominal 230V supply voltage (Uo), then PFC 24kA
0.01
= 240 =
c. If single-phase PFC is 10kA, an approximate value for PFC between phases is
found by doubling this value to 20kA.
Bloody Typical obtuse C&G trick questions, lol
Hawkmoon you tease LOL, great Thread though Fella, although I was wrong I still enjoyed it. Well done for a decent thread worth reading for once.
Well to be fair it was the early eighties when I did most of my college work, apart from going back to tech for the 16th and then the 17th editions and the odd testing course I am pretty much out of practice in the classroom.Don't feel bad, nobody in the class (around 20 guys) got it right although there was a few smart asses there lol
As I said half did not even consider the 3 phase element so it was a good learning exercise.
I actually only ever had a quick look at past papers before doing my 2391 (passed 1st time btw), as I found them more of a hindrance than a help.
They would often switch methodology by asking very similar questions on different paper and using a different method giving a different answer.
I am not sure of the date of these past papers, a lot were using 16th ed terminology which were not much use in a 17th ed based exam., some had 240V calcs in, or a hybrid like the question/answer I posted.
They were useful in so far as to see the layout, structure and format of the exam, but that was about it.
I have my Design and Verification exam tonight so an answer would be nice!
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