Sitting 2392 have practice question cant get the right answer help

[topcat]

Hi guys have a Question on a practice paper and cant get the answer to the same as paper what am i missing any help would be great thanks in advance.

A radial socket outlet is supplied in 2.5mm cable and is 20 m long the Ze of the istallation is 0.43ohms and the resistivity of the cable is 7.41mil ohms a meter at 20C what is the calculated Zs

a 0.9 ohms

b 0.6ohms

c 0.3 ohms correct answer?

d1.2 ohms

could you show your working so I can follow and work out other simlar problems Iam still learning all this so please help thank TC

 

[MarkieSparkie]

... c 0.3 ohms correct answer? ...

A clue for you. Zs must be >Ze [from Zs = Ze + (R1 + R2)] so answer c) cannot be the correct one.

Calculate the cable resistance (R1 + R2) of the radial final circuit and add that to the Ze for the installation to obtain the correct answer, you will need to round up/down for one decimal place.

 

[morph]

Hi guys have a Question on a practice paper and cant get the answer to the same as paper what am i missing any help would be great thanks in advance.

A radial socket outlet is supplied in 2.5mm cable and is 20 m long the Ze of the istallation is 0.43ohms and the resistivity of the cable is 7.41mil ohms a meter at 20C what is the calculated Zs

a 0.9 ohms

b 0.6ohms

c 0.3 ohms correct answer?

d1.2 ohms

could you show your working so I can follow and work out other simlar problems Iam still learning all this so please help thank TC

the answer is not on your options unles you round up then the answer is 0.6....

 

[topcat]

Hi all I had worked the answer out to 0.6 but as the answer on the paper said it was 0.3 I was having a bit of a problem as I could not see how they got that answer so thanks for getting the same as me paper is wrong then good.

 

[morph]

any more questions just ask i love all the 2392 questions

 

[alanl]

Either the question has been posted here wrongly, or the question is wrong. The answer, as given above, is R1+R2+Ze. You are only given 2 values, R1 presumably and Ze. You can make assumptions, but cannot give a correct answer without more information.This is not a C+G 'real' question, as they give all the onformation required to give the correct result.

 

[telectrix]

Either the question has been posted here wrongly, or the question is wrong. The answer, as given above, is R1+R2+Ze. You are only given 2 values, R1 presumably and Ze. You can make assumptions, but cannot give a correct answer without more information.This is not a C+G 'real' question, as they give all the onformation required to give the correct result.

no, alan, the resistivity quoted is that of R1 and R2 combined, therefore you can work out the R1+R2 .

 

[alanl]

Well, I would say this is not a good question then, as it is unclear. I would immediately think the circuit is 20 metres long, but the length is 10 metres long, with a combined R1+R2 of 20m.As I said, not a C+G question, as there is no doubt about what they are asking when wanting calculations.(and on thinking further, this query may be from a lecturer who is trying to make an easy question for his students, giving them one less thing to work out - no need to add up R1+R2, just mutliply once and add?)

 

[Richard Burns]

I would say that the question is unclear and inaccurately worded and possibly with the wrong answers!
The value given is resistance not resistivity. The 7.41 mohm/m value is the resistance of one length of a single conductor of csa 2.5mm2.
The question states that the SO is supplied in 2.5mm2 cable but does not specify if this is T&E or all conductors 2.5mm2.
One could either assume the total length to be measured (R1+R2) is 20m or the cable (circuit) length is 20m so R1+R2 is 40m long.
To get a result close to one of the answers you have to assume R1+R2 is 20m in total.
Certainly not C&G question despite their usually poor wording.

 

[ringer]

R1+R2 = 0.3 (assuming 2.5mm cable for both R1 and R2 over 20m)
So they forgot to add the Ze on when they gave the multiple choice answers to the question
No wonder you are struggling to work out the answer.
I would complain to your lecturer if I was you.