Zs C&G 2391 question

[CHRIS103F]

Hello everyone I'm Chris. I am taking the 2391 in February. This question is from the c&g main site under 2391 sample questions. Continuity of a ring final circuit has been tested as part of an initial verification of a new primary school. All the socket-outlets are connected directly to the ring. The circuit loop length is 58 m long, wired in 4 mm2 live and 1.5 mm2 cpc flat profile cable. The circuit is protected by a 32 A BS EN 60898 Type B circuit breaker. The installation has a measured Ze of 0.29 Ω. What is the expected value of Zs for this circuit? a) 0.24 Ω b) 0.28 Ω c) 0.53 Ω d) 0.58 Ω The answer is C.
I don't get that answer just wondered if anyone would like to help me as to what i am doing wrong. Many Thanks Chris.

 

[stevethesparks]

approx
58 mts 4mm = 0.25375 ohms
58 mts 1.5mm = 0.67666 ohms
0.25375 + 0.67666 / 4 = 0.232604 then add ZE 0.29 = 0.522 taking 0.53 as the closest

edit just to add the max zs allowed - allowing for 80% and c-diff would calc to 1.09 - approx

 

[CHRIS103F]

approx
58 mts 4mm = 0.25375 ohms
58 mts 1.5mm = 0.67666 ohms
0.25375 + 0.67666 / 4 = 0.232604 then add ZE 0.29 = 0.522 taking 0.53 as the closest

edit just to add the max zs allowed - allowing for 80% and c-diff would calc to 1.09 - approx

Thank you Steve, feel like a total bell now. I was using the 4mm and 1.5mm combined value. 16.71 Makes total sense now. Thank you again.

 

[Funky Gibbons]

Zs = Ze + R1 + R2
0.53 = 0.29 + 0.24
Steves the man ??

 

[jdawson98]

approx
58 mts 4mm = 0.25375 ohms
58 mts 1.5mm = 0.67666 ohms
0.25375 + 0.67666 / 4 = 0.232604 then add ZE 0.29 = 0.522 taking 0.53 as the closest

edit just to add the max zs allowed - allowing for 80% and c-diff would calc to 1.09 - approx

im stuck on this same question how are you working out the ohms for the meterage etc. First time using the regs book and GN3 and completely lost of where to do this calc

 

[jdawson98]

Zs = Ze + R1 + R2
0.53 = 0.29 + 0.24
Steves the man ??

where are you getting the 0.24 from?

 

[Flanders]

where are you getting the 0.24 from?

It's worked out by the resistance of the live and cpc added together then divided by 4 as it is ring shown in Steve the sparks post that you quoted