Indeed, the answer from me is no different from when I answered the question a few days ago. However, as I pointed out then, this proves nothing - and, indeed, as I attempted to demonstrate with some guesstimated figures, the fact that a busy electrician with decades of experience hadn't seen a failed crimp wouldn't prove much, either.
I don't doubt that's true - but if the joints are inaccessible, none of them will get inspected.
Is that really true? I'd be very interested to hear other views on that, particularly from practising electricians who do PIRs. If one adopted that interpretation, then I would think that a high proportion of 'concealed JBs' out there would actually be compliant.
Needless to say, I don't know enough about their rules and standards to answer that. Some of the environments will obvioulsy be extreme, but the NASA prohibition (which is the only one I've seen) sounds like a pretty 'blanket' one, which very probably applies to any environment.
Was that also assuming that no floor coverings were present?
Thanks. I don't have access to them either but, in any event, I suspect that some of those here wuld (rightly) say that the environment of an aircraft (and the consequences of failure) are not comparable with domestic electrical installations!
Thanks again. That's very interesting, and certainly the closest to 'data' that I've yet seen. I think we're probably all agreed that if cold welding does occur, then it's likely to be a pretty reliable joint, and the doubts relate primarily whether or not that occurs. Did your research give any insight into how commonly one does get a true cold weld?
That's obviously part of it, but I think there's an 'inspection' element as well as a 'maintenance' one - i.e. looking for any evidence of overheating - and that would be relevant in terms of crimped as well as screwed joints. I suppose my view is that all joints in cable should be accessible for inspection, with the possible exception of welded/brazed ones (which I imagine are very rare in domestic installations).
Maybe - but, as you've probably seen, I've questioned this in relation to crimped joints produced by a single-plane hand 'squashing' tool - which I can't help feeling might leave opportunity for sideways creep in at least some cases. The real problem with a crimped joint is that without destructively testing it (sectioning for microscopical examination), one can't be sure what has exactly happened inside an individual crimp.
Every time once you've got the hang of it.
I see your point, but a properly made crimped joint will not overheat, whereas a screw terminal is very likely to loosen over time, as shown by many of the posts on this forum.
This is a difficult discussion without finding pictures and I don't have BAS' skills at searching for images, but if you mean the sort of tool that Halfords sell, that squashes a circular tube to an oval or diamond shape, then I agree. The good crimping tools squash to something like a hexagon shape and surround the terminal while doing so, such that the airspace is squeezed out of the terminal and replaced by copper. The old AMP ones we used in the college consisted of two semi-circular dies, with a single point protruding into one of them. That made the cold weld. There was also another die set, to be used further along the cable (i.e. where the tail of the terminal approaches the insulation) that had one semicircular die and one shaped like a rounded letter W, which rolled the seam of the tube into the conductor and the insulation.
Many thanks. I'll be interested to hear what it has to say. Hopefully it will also reference some data.
Interesting, and surprising to me. I certainly don't think I managed to achieve a cold weld in many of the crimps I've tried to make - but see below about tools.
That's obviously dependent on 'answers' which I don't feel I have. If I had been convinced that "properly made crimped joints don't overheat", then I would be on the way to agreeing with you - but I think I'd still have fears about the "properly made" bit. Let's face it, you don't have to look any further than this form to hear about some of the diabolically incompetent things that some electricians have been known to do - so the idea that they are also allowed to 'hide' some of their handywork is always going to be a concern to me. ... I would imagine that we can all agree that a badly made crimped joint can overheat or otherwise fail.
That's how it should be, and I imagine that such tools are probably pretty good at producing cold welds. However, I own three different makes of ratchet crimpers (acquired over time), similar to the ones that BAS advocates, and have examined many others in shops, and none of them correspond remotely to what you describe. None of those I have, or have seen, are much more than a glorified pair of pliers; the dies are slighly concave on one side and U-shaped on the other, with the gap between dies (when closed) a bit smaller on one side than the other. There is no way that such tools could producing anything like a hex crimp.
That's certainly one concern but, as above, my other is that I don't believe that even the best design possible (certainly along the lines of the ones I've seen) would be foolproof enough to ensure that some of the jokers who are undoubtedly out there would always produce reasonable joints.
It is directly relevant to the question I asked.
How can you say that your experience with crimping has shown that a joint has a significant chance of failing if you have never seen a crimp fail ? How odd
Oh, please forgive me, but it sounds like you are against crimping as you believe they have a 'significant' risk of failure.
I have seen failed welds on structural steelwork (on machinery) due to stress and vibration. So surely if a crimp needs to be accessed, so should a weld?
I would say that a safety-critical weld has to be inspectable, and has to be inspected periodically, even if that involves some dismantling.
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