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?
No Andy, it is not that you must assume the energy let through is the maximum, it cannot be unless the fault current is very high. The B32 for instance characteristics in the Regs shows a vertical line on the graph at 600A fault current, which according to the graph is between 10ms and 5 seconds. This is the instantaneous region, and the worst case is your energy let through. You are assuming the worst case can occur anywhere in the characteristic, but this is not the case. You will see the note on the graph, which says the worst case is at the high end of fault current. You do not and cannot have this, so the let-through must be less. Instantaneous operation is usually considered 10ms, not you see an unreasonably quick figure. Therefore the energy let through is I2t Watts, so the current is the important factor.
No Andy, it is not that you must assume the energy let through is the maximum, it cannot be unless the fault current is very high. The B32 for instance characteristics in the Regs shows a vertical line on the graph at 600A fault current, which according to the graph is between 10ms and 5 seconds. This is the instantaneous region, and the worst case is your energy let through. You are assuming the worst case can occur anywhere in the characteristic, but this is not the case. You will see the note on the graph, which says the worst case is at the high end of fault current. You do not and cannot have this, so the let-through must be less. Instantaneous operation is usually considered 10ms, not you see an unreasonably quick figure. Therefore the energy let through is I2t Watts, so the current is the important factor.
