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R1+r2 reading and r1,r2 and rn on ring final

Discuss R1+r2 reading and r1,r2 and rn on ring final in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

A

Abu

Hi there
Been stuck on this for a while. What is the maximum r1+r2 reading possible on a lighting circuit in a domestic property. With a type b 6amp breaker.
Also if you guys could tell me about r1+r2 and rn Maximum readings for ring final.
Thanks
 
Zs = Ze + (R1 +R2) - so you know the Ze, then then you can calculate the R1 + R2 value, then look up the rest in the books

As for a ring - what do you understand about the configuration of a ring and how you would test it?

What are you trying to achieve?
 
Abu said:
Hi there
Been stuck on this for a while. What is the maximum r1+r2 reading possible on a lighting circuit in a domestic property. With a type b 6amp breaker.
Also if you guys could tell me about r1+r2 and rn Maximum readings for ring final.
Thanks
Click to expand...
It's R1+R2 r1, r2 and rn are the end to end resistances of the L, N and CPC R1+R2 is the reading obtained by the figure of 8 test
 
Pete999 said:
It's R1+R2 r1, r2 and rn are the end to end resistances of the L, N and CPC R1+R2 is the reading obtained by the figure of 8 test
Click to expand...
Yes i understand and know how to measure it ut was wondering what is the maximum value allowed for the test
 
For electrical certification you can only calculate Zs ,Ze and R1 + R2 are measured using test equipment. If you have a Ze then you can have a designed R1 + R2 based upon the chosen installed cable. Therefore designed Zs from that you can choose a protective device from the tables in BS7671.
 
If you have the On Site guide then in table 7.1 in chapter 7 this lists the maximum length of cable permitted for standard circuits in various installation methods and with different protective devices.
Then you can compare the circuit lengths with the resistance values given in appendix I to give you maximum values for resistance.

For instance a 2.5/1.5 ring final circuit on a 32A MCB with 30mA RCD protection has a maximum length of 106m. (this is limited by voltage drop)
Therefore on 106m your r1 and rn would be 0.00741*106 =0.785Ω
your r2 would be 0.0121*106=1.28Ω

Similarly for a 1.0/1.0 6A lighting circuit the max length is 59m and so R1+R2 would be 0.0362*59=2.14Ω.
 
Measure the ring final circuit readings i got a ze of o.14 at db on tns system i got a reading of 0.55 for r1 +r2 i would like to know what is the maximum reading allowed .
 
Richard Burns said:
If you have the On Site guide then in table 7.1 in chapter 7 this lists the maximum length of cable permitted for standard circuits in various installation methods and with different protective devices.
Then you can compare the circuit lengths with the resistance values given in appendix I to give you maximum values for resistance.

For instance a 2.5/1.5 ring final circuit on a 32A MCB with 30mA RCD protection has a maximum length of 106m. (this is limited by voltage drop)
Therefore on 106m your r1 and rn would be 0.00741*106 =0.785Ω
your r2 would be 0.0121*106=1.28Ω

Similarly for a 1.0/1.0 6A lighting circuit the max length is 59m and so R1+R2 would be 0.0362*59=2.14Ω.
Click to expand...
Thank u very much this is exactly what i wanted to know.
 
Abu said:
Measure the ring final circuit readings i got a ze of o.14 at db on tns system i got a reading of 0.55 for r1 +r2 i would like to know what is the maximum reading allowed .
Click to expand...
you mean R1 +R2. note capitals. add |R1+R2 +Ze. that will give you the Zs for the circuit. Zs must be < the max. value in (tables) for the In of the OPCD.
 
telectrix said:
you mean R1 +R2. note capitals. add |R1+R2 +Ze. that will give you the Zs for the circuit. Zs must be < the max. value in (tables) for the In of the OPCD.
Click to expand...
I have seen videos where they directly measure the zs through a megger meter. I that reliable or is it better to do the calculatio.
 

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