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Everybody Should Know this... Calculate R1+R2, Zs and Find the Length of a Circuit for Fault Finding
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- Опубліковано 6 сер 2024
- Design a circuit for R1+R2, calculate Zs - plus an explanation of Zs and Ze. Ready for the 2391 or a design module. Find the length of a cable knowing the resistance and how it could be used during fault finding.
Please note: The Max values are from the 17th edition of BS7671, the Max Zs should read 1.09Ohms.
Hi Sir, I watched all your videos and they are all brilliant thank you very much.
You are most welcome
At 10:55 you said your cable was not incorporated in a cable however you chose the figure from the incorporated table?
Hi this information is based on previous videos - ua-cam.com/video/p4Bxog90TXA/v-deo.html - Easy Guide to Cable calculations.
thanks for this
You're welcome, Please Like, Share & Subscribe.
Hi thanks for the videos . I have used the formula in this video for a ring main circuit and my assessor has told me it’s incorrect. To calculate Zs should it not be divide by 4000 ?
Hi not sure where you are getting 4000 from? A ring final is a more complex circuit to calculate as the cables are in parallel. So I am unsure what you are trying to do and what your assessor is asking. With more information I will be able to help.
Hi thanks for reply .
Ze = 0.22 ohm
R1+R2 = 19.51 Mili ohm per metre
Length = 30 metre
Correction factor = 1.2
Ring final circuit
19.51x30x1.2 = 702
then divide by 1000 = 0.70
Add to ze = 0.22+0.70 = 0.90 ohm
Was told this is incorrect
Cable is twin and earth 2.5mm/1.5mm
Hi, So assuming ring length is 30m, a Ring final is a parallel circuit therefore 0.702/4=0.1755ohms
Zs=0.22+0.1755 = 0.396Ohms @70degrees
you could check by working out r1 and r2 using OSG:
r1=30m x 7.41m/Ohms = 0.223ohms
r2=30m x 12.1m/Ohms = 0.363ohm
R1+R2 = (r1+r2)/4 = (0.223+0.63)/4 =0.146ohms @20degrees
R1+R2@70 = 0.146x1.2 =0.1755ohms
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Many thanks . Please make small correction
0.702/4=0.1755 not 0.702/2
Once again many thanks
What if the circuit breaker has to be type b at 50A I🔼n?
If it is a 50A then the corresponding maximum Zs or the type of circuit breaker ie (B,C or D). Do you mean it is an RCBO if so the corresponding Zs will apply for the milli amp Zs rating from BS7671 - but if this is the case you should not forget about the short circuit faults and their disconnection.
I think you mean using it for a garage or small extension I would assume, are you using the RCD in the main as well as in the garage lets say? Do you use tt system and what size swa would you run? Are you planning to install EV charger?These are the questions to be asked.
Hi ,i have done this questions .its A3 radial circuit 2.5mm pvc/flat cable 1.5 cpc,40m lenth and it's F 30 degrees ,with 0.35 Ze value ?
Hi, Not sure what the question is, but 'F' is a factor to raise the resistance of the cable to the desired working temperature to compare with BS7671.
Yes f is correction factor ,just need to determine the actual Zs ?
Can you please show me the calculations if different from the vídeo!?
pg 62 BS7671 table 41.3 for type B BS EN 60898 rating 40 amp i have Zs as 1.09. where do you get 1.15 from? thank you
Thank you, What an idiot I am, accept my sincere apologies, you are quite correct - the values I have put in for Max Zs are from the 17th Edition Wiring Regulations
I noticed this too. The 17th edition doesn’t contain (Cmin 0.95)
Enjoyable video all the same.
@@sparkyhelp3997 I take it this Cmin 0.95 was added in the 18th addition. Good video though.
Hi, what does it mean by bunched? In table i3
Grouped with other conductors i.e., Conduit or Trunking - Please Like, Share & Subscribe.
@@sparkyhelp3997 so if you had 3 single cores in conduit for one circuit that would count as bunched
@@willatkin1957 Hi long time since communicating, this would count as one circuit (assuming the three conductors are as described), if by themselves, then no grouping (not bunched - as it it by itself) would be applied.
Hope that helps,
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@@sparkyhelp3997 so just to clarify for 3 single cores in conduit on their own as one circuit , the not incorporated and not bunched factor would apply when working out the (R1+R2 )
@@willatkin1957 Hi this is one circuit (L,N,CPC!)
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