All agreed. However, to have a safety feature which 'might well work satisfactorily' if/when it is needed 'in anger' is hardly an ideal situation, is it?Only IF, as your example, Ze is 0.8Ω. Most these days have to be considered as TN-C-S despite appearing TN-S, so who knows? I obviously have to agree that if only 0.3Ω is left for the circuits then they might not be compliant with the numbers; 45A shower circuit max.Zs- 0.78Ω; that does not mean they won't cause ADS satisfactorily in the actual circumstances. 240V, conductors not at 70°, MCB at 4 In. etc.
That's not what I'm really suggesting, and I'm not criticising or 'blaming' anyone.... You seem to think the electricians do not know what they are doing. You might be right so where does that leave us?
However, in all the years I have been talking/listening to electricians, and seeing what they advise, I don't think I've even seen/heard this issue being discussed (or even mentioned) before - and it's only in the past couple of days that I (and, very possibly, others) have even been aware of the 'lower max Zs figures' quoted by the OSG. All I've ever seen/heard, or seen being advised, is the need for a circuit to have a Zs (by implication, when measured at ambient temp) no greater than the (BS7671) 'maximum Zs' - so I can but assume that a lot of electricians (and myself) have always believed that that was adequate.
As I said when this started, it might be an exceptional case in which the OSG is actually 'less potentially misleading' than is BS7671 itself!
Kind Regards, John
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