Sharpend
"It Just Is"
And quite true that is, however you'd have to severely over tighten to cause the copper to weaken to breaking point. Easily done by the latest 'impact' electricians but old skool hand tightening?
Metallic containment
- Thread starter Martin
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I have two guys that just will not leave their impact driver in the van when doing certain things. Drives me nuts.
Sharpend
"It Just Is"
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That Would be an "impact nut driver then"
if you dont like them using impact driver for,certain jobs....
you're the boss
they are on your clock
tell them NOT to
end of
when I Used to employ I Had the same issue. I gave them the choice
Sharpend
"It Just Is"
Walk or leave?
Walk off the job
or leave the impact at home?
And now you no longer employ??
Just........................ paraphrasing
Rob_the_rich
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I have seen over-tightening of 5A connector strip terminals where the screw breaks through the bed of the block (cheap stuff probably). It is possible this happened here. Or that the screw jumped a thread.
Looking at the photographs at the end of the report, the inspectors certainly have a really difficult job. The last photo shows the two neutral bars with the link cable. It seems that the factory made terminations are made with hex grub screws. Counting the visible threads, the through terminal, on the right, has 3 threads, the suspect terminal has four. So maybe not a tight as they said. The hole of the suspect terminal seems bigger than the rest on the same block, but the hole on the through terminal seems the same size as the rest on that block. Maybe breakthrough occurred.
Looking at the photographs at the end of the report, the inspectors certainly have a really difficult job. The last photo shows the two neutral bars with the link cable. It seems that the factory made terminations are made with hex grub screws. Counting the visible threads, the through terminal, on the right, has 3 threads, the suspect terminal has four. So maybe not a tight as they said. The hole of the suspect terminal seems bigger than the rest on the same block, but the hole on the through terminal seems the same size as the rest on that block. Maybe breakthrough occurred.
So was I....... and I had to assume that the info came down from a far greater mind than I have,,, some of the courses that I went on, at the time, you felt were rather anal.... afterwards though you could understand where they were coming from...
Then again,,, people don't like it when multi million ££ fast jets fall out of the sky (onto god knows what)
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A correct interpretation !
used to have 20+ sparks on at one time......not any more!. I am too,old for the hassle. Owt for any easy life now
so you have a hot busbar, and then chuck water at it, and hey presto it corrodes solid almost immediately....fikin non-sense that report.
The only time overtightening causes problem is if you chop through a bit of 1mm, with cables that size, no chance unless someone stripped the thread.
The only time overtightening causes problem is if you chop through a bit of 1mm, with cables that size, no chance unless someone stripped the thread.
I think they ignored the hysteresis bit with thermal cycling and material creep & plastic deformation under compressive loads myself.
Back to the op, surely any standard construction brick built house is combustible, with its wooden floors, joists, stairs etc ?
Rob_the_rich
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Care to expand on this?
I looked up hysteresis and can't decide whether you refer to magnetic influences or to the investigation process itself in relation to history and their results.
Ok... I am no metallurgist, but i will try to explain!! An elastic material, is just that; elastic. But, when you compress and release it, energy is required in the process because some is "used up" within the material in the compressing and rebounding. This is why, if you drop a rubber ball, it will not bounce back to the original height. [air resistance would affect this too though]
So, if you exert a pressure on a material, [a stress] that deforms it [strain] by for example, restraining it while it tries to expand on the application of heat, the material will compress.
[If you know the youngs modulus for the material, you can calculate the force that would be generated by restraining the material as it tried to expand]
Anyway, say a material was subject to a stress of 10 tons in the static state, say by compressing it by doing up the screw holding it. If you then heated it, it would try to expand, and the pressure might go up to 20 tons with a corresponding increase in "strain" However, i THINK i am right in saying, that if you cooled it down again, you MIGHT find that the original preload of 10 tons, has now dropped, to say, for the sake of argument, 8 tons, due to the hysteresis effect of the material.
As i say, i am no metallurgist, [got a job to spell it!!] so Paul will no doubt have a better explanation!!! [cos he is a lot cleverer than me!!!!]
john..
So, if you exert a pressure on a material, [a stress] that deforms it [strain] by for example, restraining it while it tries to expand on the application of heat, the material will compress.
[If you know the youngs modulus for the material, you can calculate the force that would be generated by restraining the material as it tried to expand]
Anyway, say a material was subject to a stress of 10 tons in the static state, say by compressing it by doing up the screw holding it. If you then heated it, it would try to expand, and the pressure might go up to 20 tons with a corresponding increase in "strain" However, i THINK i am right in saying, that if you cooled it down again, you MIGHT find that the original preload of 10 tons, has now dropped, to say, for the sake of argument, 8 tons, due to the hysteresis effect of the material.
As i say, i am no metallurgist, [got a job to spell it!!] so Paul will no doubt have a better explanation!!! [cos he is a lot cleverer than me!!!!]
john..
John is not far off the money.
The copper when heated will be constrained by the terminal block & the screw, however, this is not a circumferential constraint.
Where the material is restricted it cannot expand in that plane (those planes), however, when the material then cools it is free to contract in all directions.
You can illustrate this with a piece of copper pipe, a vice & a blow torch.
Clamp a piece of pipe between the jaws of the vice tight enough so that it cannot move, but not so tight such that it would distort the tube when cold.
Heat the middle of the pipe up to cherry red and allow to cool naturally.
Report ones findings!
I won't be around much again until Tuesday probably, so please don't think I'm ignoring everyone!
The copper when heated will be constrained by the terminal block & the screw, however, this is not a circumferential constraint.
Where the material is restricted it cannot expand in that plane (those planes), however, when the material then cools it is free to contract in all directions.
You can illustrate this with a piece of copper pipe, a vice & a blow torch.
Clamp a piece of pipe between the jaws of the vice tight enough so that it cannot move, but not so tight such that it would distort the tube when cold.
Heat the middle of the pipe up to cherry red and allow to cool naturally.
Report ones findings!
I won't be around much again until Tuesday probably, so please don't think I'm ignoring everyone!
Oh, just to clarify, I mean lengthways between the jaws so that you are clamping on the cut ends as it were, i.e. trying to crush the pipe as a column axially.
Also make sure that the middle is nice and red, right around for a good portion.
Remember this is just an experiment to illustrate what happens, NOT necessarily a real scenario.
Also make sure that the middle is nice and red, right around for a good portion.
Remember this is just an experiment to illustrate what happens, NOT necessarily a real scenario.
Same principle is used when straighening shafts etc by means of heat.. Heat one side, let it cool, and it will have "come back" towards the heated side!! "Heat triangles" us 5ww welders [not being as good as blacksmiths [call it!!!!]
Told you Paul was cleverer than me!!!!
john...
Told you Paul was cleverer than me!!!!
john...
copper is also annealed by the manufacturing process used to create wire - stops is being too soft to work with. So again, if it gets hot it undoes the annealing process aming the copper soft again, which inturn will allow it to cold plastic flow easier.
What I was digging at is that in the procees of being involved in a fire then having water chucked at, the screw would corrode to the busbar almost immediately, so there would be no way of teliing if it had been overtightened in he first place. However to get a connection like that hot, it would be more likely to have been loose in my opinion
What I was digging at is that in the procees of being involved in a fire then having water chucked at, the screw would corrode to the busbar almost immediately, so there would be no way of teliing if it had been overtightened in he first place. However to get a connection like that hot, it would be more likely to have been loose in my opinion
Hi Binky,
You have got things back to front! Copper is not annealed as part of the wire drawing process, the drawing hardens it. It it gets hot, it does not "undo" the annealing, [which can only be done by "cold working" the stuff] it anneals it and makes it soft again.
There are TWO ways of annealing copper; Either heat it up red hot and let it cool naturally, OR heat it up red hot and quench it in cold water. The second method works best, as it removes the "scale" created by heating it, and it will be a nice reddish coppery colour again!!
You have got things back to front! Copper is not annealed as part of the wire drawing process, the drawing hardens it. It it gets hot, it does not "undo" the annealing, [which can only be done by "cold working" the stuff] it anneals it and makes it soft again.
There are TWO ways of annealing copper; Either heat it up red hot and let it cool naturally, OR heat it up red hot and quench it in cold water. The second method works best, as it removes the "scale" created by heating it, and it will be a nice reddish coppery colour again!!
Believe it or not I was taught at secondary school to anneal copper by quenching it in Spirits of Salts AKA hydrochloric acid. I can’t see that happening today.
I’ve had a few terminals that have badly overheated, mainly on motors where they have been over tightened and the copper has splayed. The copper anneals, the tinning burns away allowing the copper to oxidise. After that they are buggered along with a good chunk of cable and probably the terminal block.
One of my bugbears is “check tightening” of connections. I replaced 180Ft of 3”x¼” tinned copper busbar, everything correctly torqued. I called in on the plant during a shutdown and one of the lads is working his way along the bars over tightening every connection. Both RoB and I use varnish on each nut and screw thread to mark they are “as specified”, don’t interfere with them!
With the case of Clandon Park I wouldn’t be surprised if some person(s) unknown had in the past given them that extra tweak. I believe manufacturers should mark the connections they are responsible for.
I’ve had a few terminals that have badly overheated, mainly on motors where they have been over tightened and the copper has splayed. The copper anneals, the tinning burns away allowing the copper to oxidise. After that they are buggered along with a good chunk of cable and probably the terminal block.
One of my bugbears is “check tightening” of connections. I replaced 180Ft of 3”x¼” tinned copper busbar, everything correctly torqued. I called in on the plant during a shutdown and one of the lads is working his way along the bars over tightening every connection. Both RoB and I use varnish on each nut and screw thread to mark they are “as specified”, don’t interfere with them!
With the case of Clandon Park I wouldn’t be surprised if some person(s) unknown had in the past given them that extra tweak. I believe manufacturers should mark the connections they are responsible for.
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Certainly old Wylex NB boards used to have a spot of paint on all the manufacturers terminations.
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