Could an unfused R.C.D. protected spur, from a complient ring final circuit, supplying a single outdoor socket via 1.5mm2 6242Y cable of max. length 300mm through a brick wall from an indoor socket outlet be considered compliant?
Don't worry Zoomup, it wasn't really you! The case we are considering is as you have probably noticed is really quite complicated, and therefore not in the "normal" range of installation designs. If you had used a bit of 2.5mm, no one would have said a word, but some quite important stuff would not have got an airing here. The discussion has covered two different scenarios, the TT one where the Earth fault current is limited to a low value by Re, and the TN-S one where the fault current is limited by the source impedance and the wiring resistance. You have now told us that each leg of the ring is probably about 15 metres, and so we can calculate the maximum fault current. We also know the ability of a 1mm cable to withstand this current for the time necessary to trip the MCB, and can therefore decide that the installation is satisfactory.
Don't worry Zoomup, it wasn't really you! The case we are considering is as you have probably noticed is really quite complicated, and therefore not in the "normal" range of installation designs. If you had used a bit of 2.5mm, no one would have said a word, but some quite important stuff would not have got an airing here. The discussion has covered two different scenarios, the TT one where the Earth fault current is limited to a low value by Re, and the TN-S one where the fault current is limited by the source impedance and the wiring resistance. You have now told us that each leg of the ring is probably about 15 metres, and so we can calculate the maximum fault current. We also know the ability of a 1mm cable to withstand this current for the time necessary to trip the MCB, and can therefore decide that the installation is satisfactory.
