On 14/10/2019 12:58, Tricky Dicky wrote:
I was connecting a cable to a junction box that I had fitted some years back and noticed the terminal screws though secure were not particularly tight which is unusual for me as my torque settings are normally one grunt + 1.

The junction box was fitted to a joist and it made me wonder if the act of walking over the floor at that point was causing enough vibration to ease the screws off? I it is the cause then it certainly makes the case for Wagos.

Richard

This does seem to happen for screwed connections whether in sockets or
junction boxes. Maybe some sort of thermal ratchetting caused by
temperature variations following current variations. Hence requirement
for "accessibility".

Life of Wagos is certainly an interesting question but I assume the guys
designing and certifying them think about this.

I had a sort of parallel interest in the lifetime of PVC and ABS
pipework a few years ago. We had a failure of some 40 year old pipe in a
nuclear power station. When it was introduced both for civil and
industrial applications the life was estimated at around 40 years (there
was an upper temperature limit). Quite a bit of the pipework had been
replaced by stainless steel as a precautionary measure. Although this
was a somewhat brittle failure (partly along the "spider lines" from the
extrusion process) the pipework did not appear to be significantly more
brittle than new, or younger, pipework. It certainly hadn't got anywhere
near to the state where it snaps with bare hands, that you see in
moulded thermoplastic storage boxes after a few years exposure to light.

Also in the "nuclear" field, trying to decide whether polymers (e.g.
rubber O rings) will last for several hundred years (for waste storage)
is quite tricky. What you can say, from archaeology, is that some
organic materials containing polymers (like pitch and leather) retain
their properties provided you can retain their moisture and natural oils
while avoiding attack from insects and things microbial.