Spent a bit of time chasing a low IR on a lighting columns circuit recently, and while I've got serveral segments that are clearly faulty (as well as some faulty heads), I seem to have quite a few sections of SWA between columns returning figures barely into double digits, reading off my drawing Ive got 10.31, 7.60, 6.46, 12.01 on some sections, it clearly doesn't take many sections like this for the cirucit to be sub 1M. Whats bothering me is the failure mode at work, these are approx 35m sections of 16mm 2core SWA direct buried, and afaik there is no reason for there to be any joints on these sections (there are some sections further back where it is clear there must be joints). I'd expect that if there was damage to the cable that IR would be right down, otherwise we would have readings of several hundred meg. And indeed once section between two columns thats new colours tests completely clear, so 'something' is happening to the cables but PVC/XPLE doesn't just degrade into a poor insulator does it unless its damaged and then goes right down as soon as water gets near it
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