Help with crimping

[JohnW2]

John/Bernard, Do either of you have experience (real, not made up) of a failed crimped joint in a domestic setting?

Certainly not me, but neither Bernard nor I are practising electricians, so our exposure is very limited. However, nor have I seen many of the other types of failure that I know can occur, but I nevertheless take steps to minimise the risk of their occurring, and would not want to see such risks left unaddressed in my home, or the home of anyone I cared about.

I certainly have seen automotive crimped joints fail, and that's even with stranded conductors, although I accept that the stresses are then much greater.

Kind Regards, John.

 

[bernardgreen]

Do either of you have experience (real, not made up) of a failed crimped joint in a domestic setting?

I haven't seen one in a domestic setting. I have seen several in industrial equipment, both electrical power and electronic control systems.

As an electronics design engineer I do know the difference between a crimped joint that relies on compression and a crimped joint that relies on cold welding. Those in electronics tend to be small but the princible is the same. Crimp joints with cold welded areas are many time more reliable than compression only crimped joints.

 

[JohnW2]

Certainly the allowing of such crimped joints to be inaccessible while other types of joint must remain accessible is something I don't like.

Not only don't I like it, but I find it astonishing and inexplicable.

Of course, the whole belief that BS7671 allows crimped joints to be non-accessible relies upon interpretation of "A joint made by .... appropriate compression tool" in 562.3(iv) - so it begs the question as to whether the 'squashers' people use actually quallify as an 'appropriate compression tool' in this context.

Kind Regards, John.

 

[mikhailfaradayski]

I too have never seen a failed crimped joint in a domestic setting. However, I have seen a terminal with a screwed joint fail.

I have also seen quite a number of crimps fail in various industrial/engineering situations due to external influences which would not really ever be present in a home.

 

[mikhailfaradayski]

Crimp joints with cold welded areas are many time more reliable than compression only crimped joints.

Once a joint is found to be adequate for its intended purpose, what benefit is there to having a different kind of joint which is many more times reliable than the simply 'adequate' type?

 

[JohnW2]

I too have never seen a failed crimped joint in a domestic setting. However, I have seen a terminal with a screwed joint fail.

Well, for a start, there are far far more screw terminals out there than crimped joints - so, even if failure rate was similar for both, statistically speaking one would expect to see far fewer (if any) failures of crimped joints. Given my intuitive concerns about the type of crimped joints we're talking about, I suspect that the very low rate of failures seen may be more a function of the relatively small number of such joints which exist, rather than of high reliability.

However, no-one is suggesting that screw terminal joints do not fail. You will probably agree that the most common reason for such failure is 'human error' in making the joint in the first place (not tight enough, or too tight, being the most common) - and I would suggest that at least the same scope for human error exists in relation to making a crimped joint. So do you really think it's reasonable or safe that crimped joints are allowed to be inaccessible whereas (I would say very reasonably) screwed ones are not?

Kind Regards, John.

 

[mikhailfaradayski]

I too have never seen a failed crimped joint in a domestic setting. However, I have seen a terminal with a screwed joint fail.

Well, for a start, there are far far more screw terminals out there than crimped joints - so, even if failure rate was similar for both, statistically speaking one would expect to see far fewer (if any) failures of crimped joints. Given my intuitive concerns about the type of crimped joints we're talking about, I suspect that the very low rate of failures seen may be more a function of the relatively small number of such joints which exist, rather than of high reliability.

possibly correct. But as of today, faradayski has seen zero failed crimps and 'some' failed screw terminals, so although you might possibly be correct, you could equally be incorrect. Given your admission that you are not a practicing electrician, i would be wary of relying on your personal point of view as any kind of basis for dreaming up statistics - just say what you see (or have seen)

However, no-one is suggesting that screw terminal joints do not fail.

I knew that

You will probably agree that the most common reason for such failure is 'human error' in making the joint in the first place (not tight enough, or too tight, being the most common) - and I would suggest that at least the same scope for human error exists in relation to making a crimped joint.

Hmm, not 100% convinced by that. JBs tend to be used by anyone who chooses to connect two wires together (skilled or otherwise), crimped joints tend to be the reserve of sparkies (hopefully skilled), so im not sure the human factor is even for both. Decent crimp tools are have ratchets, so they should give a correctly squished joint time after time, screw terminals can be used by ham-fisted gorillas or by dainty little ballet-dancer-types.

So do you really think it's reasonable or safe that crimped joints are allowed to be inaccessible whereas (I would say very reasonably) screwed ones are not?

I imagine that some thought went into the regs(although some might say 'not enough') and those who wrote them had some reason for their choice of what was reasonable and what wasn't.

FWIW, i don't think that screwed terminals should be placed in inaccessible positions.

Kind Regards, John.

 

[bernardgreen]

Once a joint is found to be adequate for its intended purpose,

How was this joint found to be "adequate for its intended purpose" ?

In a test laboratory where conditions were ideal and the tools were correct tools and the person conducting the test was not working under under time and cost contraints ?. Or in a difficult to reach place with a worn tool by someone under pressure.

what benefit is there to having a different kind of joint which is many more times reliable than the simply 'adequate' type?

Do you really need to be told the benefits of a type of joint that is accepted by informed people as being far more reliable and often is the minimum level of reliability acceptable in safety and life critical installations.

 

[mikhailfaradayski]

Once a joint is found to be adequate for its intended purpose,

How was this joint found to be "adequate for its intended purpose" ?

I don't know, i didn't test it, but thats not relevant anyway. It would seem that they are adequate for the intended purpose, after all, they've been around for many years now, wouldn't you agree?

In a test laboratory where conditions were ideal and the tools were correct tools and the person conducting the test was not working under under time and cost contraints ?. Or in a difficult to reach place with a worn tool by someone under pressure.

again, not sure, i didn't test it, but its not relevant anyway.

what benefit is there to having a different kind of joint which is many more times reliable than the simply 'adequate' type?

Do you really need to be told the benefits of a type of joint that is accepted by informed people as being far more reliable and often is the minimum level of reliability acceptable in safety and life critical installations.

Nope, the question was (see what was written above) Why, when something is adequate, do you need to have something that is many times more than adequate?

What benefit does it bring?

 

[JohnW2]

possibly correct. But as of today, faradayski has seen zero failed crimps and 'some' failed screw terminals, so although you might possibly be correct, you could equally be incorrect.

I agree that it's difficult when one of the figures is zero - but I presume you must accept that crimped terminals must fail sometime, so the fact that you have yet to see even one is inevitably a consequence of the limitations of the extent of exposure of any one electrician.

Given your admission that you are not a practicing electrician, i would be wary of relying on your personal point of view as any kind of basis for dreaming up statistics - just say what you see (or have seen)

Saying what I have seen would not be helpful to this discussion, since my exposure is inevitably very limited - and I'm certainly not suggesting that anyone should 'rely upon my opinion'. Indeed, I have acknowledged on many occasions (including today) that my opinion about crimped joints is 'out on a limb', but that doesn't alter the fact that it's my opinion.

Hmm, not 100% convinced by that. JBs tend to be used by anyone who chooses to connect two wires together (skilled or otherwise), crimped joints tend to be the reserve of sparkies (hopefully skilled), so im not sure the human factor is even for both.

I didn't mean to imply that it was. However, you presumably don't deny that screwed joints made by electricians have been known to fail, and sometimes even because of 'human error', and I was merely pointing out that human error is also a potential factor with crimping. You presumably also acknowledge that there are some electricians who are less skilled than one would hope - witness some of the stories one reads here, and everywhere else.

Decent crimp tools are have ratchets, so they should give a correctly squished joint time after time,

.
As I keep saying, I'm less than convinced by the design of ratchet crimpers that most people seem to use; the ratchet, per se, doesn't seem to add very much to the equation - and, as I keep saying, I personally regarded single-plane squashing of a non-slit crimp as being conceptually iffy.

I imagine that some thought went into the regs(although some might say 'not enough') and those who wrote them had some reason for their choice of what was reasonable and what wasn't.

That must be true, but it doesn't stop me being astonished at what they decided - particularly given the unknown of the level of skill of the person who made the crimped joint before they rendered it inaccessible. Many aspects of the regs are, understably, verging on the over-cautious. In relation to this issue, they seem to have gone to the other extreme, for whatever reason.

Kind Regards, John.

 

[tambourineman]

Where do these devices (WAGO connectors) sit in respect of the regs when making a join in an inaccessible location?

 

[JohnW2]

Where do these devices (WAGO connectors) sit in respect of the regs when making a join in an inaccessible location?

There's really not any scope for argument or discussion, is there? Such joints are clearly not "made by welding, soldering, brazing or appropriate compression tool" (and don't come into any of the other special categories in 526.3) and therefore presumably cannot be in inaccessible locations.

Kind Regards, John.

 

[JohnW2]

possibly correct. But as of today, faradayski has seen zero failed crimps and 'some' failed screw terminals, so although you might possibly be correct, you could equally be incorrect.

Since it's the sort of activity which is part of my life, I've been trying to get some sort of numerical handle on the statistics of this, but (as so often is the case) it does require some wild guesses. If anyone would like to improve upon my guesses, I'd be grateful...

I would imagine that the average domestic property probably has at least a couple of hundred screw terminals/joints. I haven't really much of a clue, but crimped joints are pretty rare, so I would be surprised if, on average, there is more than one such joint per every 10 properties. If those guesses are remotely correct, that would represent at least a 2000:1 ratio. In other words, if failure rates for both were the same, one would expect an electrician to see, on average, one failed crimp for every 2000 failed screwed connections that they saw. If (s)he had seen far less than 2000 failed screw connections, the most likely number of failed crimps (s)he would have seen would be zero.

With those figures, even if the rate of failure were, say, 10 times greater for crimps, one would expect to see, on average, only one failed crimp for every 200 failed screwed connections that one saw.

Kind Regards, John.

 

[bernardgreen]

Nope, the question was (see what was written above) Why, when something is adequate, do you need to have something that is many times more than adequate?

As I have said I do NOT consider the cromp joint can be ensured to be "adequate".

So therefore any installation that I am involved in will NOT have crimped joints. Not even in a box with a removable blank front plate.

 

[JohnW2]

As I have said I do NOT consider the cromp joint can be ensured to be "adequate".
So therefore any installation that I am involved in will NOT have crimped joints. Not even in a box with a removable blank front plate.

As you know, you are speaking for me as well. However, I accept that my view is based as much on lack of information as anything else - so I remain open to being convinced, if someone can show me good data which establishes that crimped joints are "adequate" both in the short and long term - and that's before I would be happy to have them in accessible locations in my house. If you wanted me to accept that it was sensible to have them in non-accessible locations, you'd also have to provide me with strong evidence that they are not just "adequate", but that they are a lot more reliable than screwed connections (and I have to say that my bones tell me that such evidence is unlikely to be forthcoming).

Kind Regards, John.