Concealed joints again!

[Harry Bloomfield]

I'm inclined to agree. I know there are theoretical arguments about 'creep' of copper in conductors, particularly when terminals are subject to appreciable thermal cycling

I've heard of and suffered, tinned flex end's suffering solder creep, under the pressure of terminal screws, but never bare copper.

 

[JohnW2]

I've heard of and suffered, tinned flex end's suffering solder creep, under the pressure of terminal screws, but never bare copper.

Fair enough. I've heard of it with both solder and bare copper, but, for what it's worth, can't say tat I've experienced any significant cases with either.

 

[SUNRAY]

True, but at least in the case of your illustration of the latter, the 'tug test' ought to have revealed the problem at the time of initial installation.

It feels like I should agree wholeheartedly but I have known the issue and on my work, I can only think the limited space in 5A JB's and the shape of the bends made it not so and later disturbance, maybe at the time other work is being performed, found it - possibly no fault actually existed

I would add that, in practice, the copper conductors are usually so soft that a problem such as you illustrate probably doesn't often arise, since if one does up the screw 'pretty tightly', it will often/usually squash the larger conductor enough for both to be reasonably 'gripped'. Also, of course, by far the most common situation is for all conductors in a terminal to be the same size.

 

[SUNRAY]

Fair enough. I've heard of it with both solder and bare copper, but, for what it's worth, can't say tat I've experienced any significant cases with either.

Tinned flex is a massive no no in loudspeaker cabinets screwed or sprung clips where the added vibration will turn those 'perfect' connexions to mush PDQ. Very different to untreated Cu

 

[JohnW2]

Tinned flex is a massive no no in loudspeaker cabinets screwed or sprung clips where the added vibration will turn those 'perfect' connexions to mush PDQ. Very different to untreated Cu

Interesting. I can certainly understand that with screwed connections, but shouldn't #sprung' ones avoid that problem?

 

[Harry Bloomfield]

Interesting. I can certainly understand that with screwed connections, but shouldn't #sprung' ones avoid that problem?

I would imagine, the lead oxidises, under the spring, and perhaps causes some rectification.

 

[JohnW2]

I would imagine, the lead oxidises, under the spring, and perhaps causes some rectification.

Ah, yes, that is a possibility - I was only thinking about mechanical, rather than chemical or electrochemical, considerations.

Mind you, copper also oxidises.

 

[morqthana]

Good workmanship, is feeling the screw bite

And hearing it with those old round JBs.

 

[morqthana]

Taken as written, that would seem to mean that, per regs, one could have an 'inaccessible' joint made with screwed terminals if those terminals were enclosed in something (maybe a 'traditional' JB?) filled with 'a compound' (such as 'magic gel").

Or silicone sealant? Decorator's caulk? Silly Putty? Plasticine?

Are there any standards to which the "compound" must conform?

 

[JohnW2]

Or silicone sealant? Decorator's caulk? Silly Putty? Plasticine?

Quite so.

Are there any standards to which the "compound" must conform?

Certainly none stated ... and, of course, if it meant "chemical compound", that would not exclude very much at all (only chemical elements)

I must say that I'm very surprised that I (and seemingly everyone else here) has never 'noticed' this aspect of the regs before!

 

[morqthana]

Quite so.

Certainly none stated ... and, of course, if it meant "chemical compound", that would not exclude very much at all (only chemical elements)

Almost anything would be cheaper than Magic Gel