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

On 14/10/19 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

It's an interesting point. I wonder how Wagos would fare after 20 years?
Would they suffer from vibration-induced metal fatigue, and their spring
grip be lost? And as they aren't screwed down, would the terminal screws
have become loose if subjected to the same treatment? In other words, if
the screws had been in "flying" connector blocks, and so subject to
little - if any - vibration, would those have become loose?

Out of interest, why do the wiring regs require junction boxes to be
screwed down? They don't tend to move around with twin and earth cables
in them, anyway. Why would you expect them to move under floorboards or
in ceiling spaces?

--

Jeff

Jeff I don't know about the wiring regs, but in my case the junction box was near the CH drain off points and although I can drain off most with a hose to get the last dregs out I have to let it flow out under the floor. The amount of water at that point is minimal and soon dries out but I did not want the junction box getting wet.

Richard

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.

In my experience screwed terminals or connection blocks cause most of the
faults in wiring which has been in for some years. I think the copper
actually relaxes and hence the screw seems loose, assuming of course there
is no nasty corrosive environment around them. Only a few months ago I had
to tighten screws in a 13A socket that was getting warm.
Brian

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"Jeff Layman" wrote in message
...
On 14/10/19 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

It's an interesting point. I wonder how Wagos would fare after 20 years?
Would they suffer from vibration-induced metal fatigue, and their spring
grip be lost? And as they aren't screwed down, would the terminal screws
have become loose if subjected to the same treatment? In other words, if
the screws had been in "flying" connector blocks, and so subject to
little - if any - vibration, would those have become loose?

Out of interest, why do the wiring regs require junction boxes to be
screwed down? They don't tend to move around with twin and earth cables in
them, anyway. Why would you expect them to move under floorboards or in
ceiling spaces?

--

Jeff