OOhh Risteard you are very good to debate with but you do get a bit heated in your replies it seems. You did it in my last thread about the first three tests on a live TT installation. All good stuff though. We always get an answer to my questions though so thanks.
Anyway...
I conducted a recent PIR and wanted confirmation that the CPC size of 1.5 single core was inadequate or a code 4 (memories of an old electrician from my apprenticeship telling another electrician that he was a crap spark for doing it, you see
)
I see your point holmslaw and agree but I included that value was the worst case, maximum measured value at the upper limits of the corrected value in BS7671 but yeah.. I agree. Am I the "op" by the way? Opening Person? I would install a 2.5 everyday of the week.
Relating to a ring final I think there is a valid point from ban all sheds. Why would you be bothered making a pittance of a saving by installing a reduced cpc? You can only do this once you have:
1. Obtained the Zs
2. Calculated the fault current Ia
3. Obtain the d/c time from Appendix 3
4. Find the K factor
5. Jumble them all up in a mass of finger bashing and head scratching
6. Compare the value to the next available size.
7. Tell the lads to install 1.5 on that circuit, 1.0 on another circuit, 2.5 on that one, etc, etc. Yadadada
Good things come out of laziness and in this instance it is Table 54.7. BS7671 says that use either 54.7 OR the adiabatic equation but this thread is all about the ring final circuit only and although I agree you can use the adiabatic I would choose not to, but that's just me.
Regarding the outcome of the PIR observation the R1+R2 was 1.94 Ohms and the Zs was 2.18 Ohms so it failed verification anyway. Hmmmmm
8) [/u]
Anyway...
I conducted a recent PIR and wanted confirmation that the CPC size of 1.5 single core was inadequate or a code 4 (memories of an old electrician from my apprenticeship telling another electrician that he was a crap spark for doing it, you see
)I see your point holmslaw and agree but I included that value was the worst case, maximum measured value at the upper limits of the corrected value in BS7671 but yeah.. I agree. Am I the "op" by the way? Opening Person? I would install a 2.5 everyday of the week.
Relating to a ring final I think there is a valid point from ban all sheds. Why would you be bothered making a pittance of a saving by installing a reduced cpc? You can only do this once you have:
1. Obtained the Zs
2. Calculated the fault current Ia
3. Obtain the d/c time from Appendix 3
4. Find the K factor
5. Jumble them all up in a mass of finger bashing and head scratching
6. Compare the value to the next available size.
7. Tell the lads to install 1.5 on that circuit, 1.0 on another circuit, 2.5 on that one, etc, etc. Yadadada
Good things come out of laziness and in this instance it is Table 54.7. BS7671 says that use either 54.7 OR the adiabatic equation but this thread is all about the ring final circuit only and although I agree you can use the adiabatic I would choose not to, but that's just me.
Regarding the outcome of the PIR observation the R1+R2 was 1.94 Ohms and the Zs was 2.18 Ohms so it failed verification anyway. Hmmmmm
8) [/u]
