is it me

[russellsmiler]

Just a post to see if I am on my own with this.

Recently have completed the instalation of a consumer unit that as the main incommer cables 16mm, and also one circuit going out is 16mm swa,

Now I am meticulous in checking that terminals have been tightened.
I actually Say NEL out loud as i think i am done meaning "Never ever Loose"
which basically is me doing a check sequence of giving the terminals a final tweak (not over doing it either), I do Neutral first, "never" Then the earths "Ever" and then Live "loose"...for me its a good way to do a final check...However. On terminals that are holding multi strand conductor 6-10-16mm there seems to be something at work in that they seem to work loose on their own.

Last night i had a heavy load going through my consumer unit and could hear a buzzing, invetigated and seemed to be able to give every terminal carrying a muti strand conductor a full turn to tweak up tight..

Is it me!!

 

[Mursal]

No we get that too. A friend asked many years go "how tight do I put them"

Well we tighten, tighten and then tighten some more. Anyone watching would say he's going to pull the threads on that. If you go back after any length of time you will usually get another bit on then.

 

[JohnW2]

Well we tighten, tighten and then tighten some more. Anyone watching would say he's going to pull the threads on that.

That's the problem - have you never actually stripped the thread (I certainly have)? I went through a phase of using a torque screwdriver, but I have to say that the recommended torques (for MCBs, RCDs, Main switches etc.) feel very 'loose' compared with how tight I would (and do) tighten them by hand.

Kind Regards, John

 

[Adam_151]

check...However. On terminals that are holding multi strand conductor 6-10-16mm there seems to be something at work in that they seem to work loose on their own.

There is indeed.

The strands of the multistrand cable have a tendancy to rearrange themselves through the gradual force of the terminal, and also if the conductor is ever moved.

Ideally when terminting such a cable into the rising clamp terminal on a breaker, the ends should be de-formed from a round profile to a flast-ish one with pliers. and then after tighting the terminal, the conductor should be wiggled to allow the strands to settle then re-tightened and it is supprising how much more you can get on them

 

[SaladFingers]

Mechanical relaxation is a problem.

Personally, I use a bootlace ferrule on stranded cables.

 

[JohnW2]

Mechanical relaxation is a problem. Personally, I use a bootlace ferrule on stranded cables.

Does that not suffer from the same, perhaps worse, potential problem? Unless the crimping achieves a cold weld with a high proportion of the strands, then relaxation is still presumably potentially an issue, isn't it? - but, being within a ferrule, the effects of that relaxation are then potentially much more difficult to correct by attempts at additional tightening of the terminal screw.

Kind Regards, John

 

[SaladFingers]

Mechanical relaxation is a problem. Personally, I use a bootlace ferrule on stranded cables.

Does that not suffer from the same, perhaps worse, potential problem? Unless the crimping achieves a cold weld with a high proportion of the strands, then relaxation is still presumably potentially an issue, isn't it? - but, being within a ferrule, the effects of that relaxation are then potentially much more difficult to correct by attempts at additional tightening of the terminal screw.

Kind Regards, John

No, not at all. I've never had issues from them.

 

[JohnW2]

No, not at all. I've never had issues from them.

Fair enough. My concern would be that one probably would not become aware of any issue/problem until there was overheating (or worse), since the 'preventative maintenance' (or 'I&T') of checking tightness of the treminal screw might well not reveal 'relaxation' problems within the ferrule.

Kind Regards, John

 

[SaladFingers]

No, not at all. I've never had issues from them.

Fair enough. My concern would be that one probably would not become aware of any issue/problem until there was overheating (or worse), since the 'preventative maintenance' (or 'I&T') of checking tightness of the treminal screw might well not reveal 'relaxation' problems within the ferrule.

Kind Regards, John

Well, the ferrule can be compressed easily with large terminals, so it wouldn't come lose really. You could for example, crimp softly, and 'crimp' it more a you tighten the terminal, but it doesn't do the reverse easily.

 

[ericmark]

I have blamed strands getting between threads and binding them. I note when you get welding cable it comes with some brass foil to wrap strands with and when using that seems it does not come lose although screw invariably puts a hole in the foil. The ferrule would do the same.

 

[ban-all-sheds]

When you buy a CU the internal cables have ferrules crimped to them.

 

[JohnW2]

When you buy a CU the internal cables have ferrules crimped to them.

They do, but that probably doesn't alter my thoughts about the practice. I say 'probably' because it is just possible that the factory crimping is done with something more convincing than a hand crimper. However, given the issues surrounding terminating stranded cables without a ferrule, I guess it's all a matter of swings and roundabouts.

Kind Regards, John

 

[JohnD]

it does much more good to retighten after a couple of weeks, than to try to to them crushingly tight on the day of installation. The copper will always deform after you first tighten them.

 

[russellsmiler]

Ok, as i can see I have highlighted a real problem that exists, as you may see from my original post, it was the buzzing at the consumer unit that warranted me to power down and do some tweaks.
Dare i ask does putting power through the cable alter anything at the terminal (if a decent load goes through and raises the temperature (albeit still a safe temperature) does this create any maluinity in the wire)
Also what exactly causes buzzing, i can only think this could be vibration, which can only be expetential and ultimately create a loose connection, possibly dire situation.

Or am i looking at this all wrong??

Russell

 

[JohnD]

if it is loose, there is usually a high-resistance joint which will get hot under load. It will soften, expand, and contract, and get looser and looser and worse and worse. Eventually it will burn away and either lose contact or start a fire.

Once the copper has been softened and discoloured by heat, the damaged part has to be cut away and fresh bright copper used. The terminal and device are also likely to be damaged by the heat and need to be replaced.

The higher the load, the hotter it will get.