Change junction boxes for "maintainence free"?

[piggoy]

I am in the process of laying laminate floor across the whole of one floor in my house. I have lifted several floorboards in order to inspect the services before laying the laminate. I have noted that much of the lighting circuit and 2.5mm ring main is jointed by screw terminal junction boxes, most of them used simply to join two cables together. I am aware that the 17th edition regs state that hidden inaccessible junction boxes are a not permitted. Whilst I am under no obligation to upgrade is it ADVISED to upgrade these connections before I re-lay the floor? If so, what is recommended? Crimp, solder, Ashley J803 etc?

Cheers,
Sam

 

[Robin0577]

My personal feeling would be yes, and I'd probably go for the Hager/Ashley boxes. Obviously it's just my opinion though, as you say, there is no obligation.

 

[EFLImpudence]

The J803s are acceptable.

So is soldering when done by an acceptable method.
The join must be mechanically and electrically sound before soldering.
https://www.cedengineering.com/upload/Wiring Techniques.pdf

Many will advise crimping because that is what they do but crimps are not designed for use on solid conductors.

 

[ekmdgrf]

I hear that the problem with traditional junction boxes is that as they expand and contract over the passage of time, the screws can work loose and cause a loose connection, hence why they need to be available for maintenance (read: fixing). I don't have any stats for MTBF I'm afraid. As you point out, you don't need to replace them but it would probably be a major irritation to lift the floor if something goes bad. Given that you've contemplated replacing them, how this will play out is that if you leave them in place, one will now go bad within a few months of laying the floor. I would replace them and the Hager boxen get my vote. Although I'd also consider if it's possible to replace the two lengths of cable with a single cable, then you can remove the joint all together. This is the ideal solution but obviously one doesn't want to go ripping out meters of cable that's plastered into the wall, etc. Assess it on a case by case basis.

Finally, as it's customary for me to also offer an off-the-wall, overengineered, resource intensive, eccentric solution, another option might be to take the existing junction boxes, drill a hole in the terminals, tap it and insert a grub screw to stop the terminals slackening off.

 

[Robin0577]

Finally, as it's customary for me to also offer an off-the-wall, overengineered, resource intensive, eccentric solution, another option might be to take the existing junction boxes, drill a hole in the terminals, tap it and insert a grub screw to stop the terminals slackening off.

Love it! Although perhaps it's a solution more suited to heavy industrial or military applications.

 

[JohnW2]

I hear that the problem with traditional junction boxes is that as they expand and contract over the passage of time, the screws can work loose and cause a loose connection, hence why they need to be available for maintenance (read: fixing). I don't have any stats for MTBF I'm afraid.

True, but I presume that, given their youth, there will be no 'true long-term (decades) MTBF' data for 'MF' junction boxes, either. There will presumably be the results of 'accelerated' tests, but they don't necessarily result in an accurate reflection of what happens in the long-term real world!

Kind Regards, John

 

[EFLImpudence]

I hear that the problem with traditional junction boxes is that as they expand and contract over the passage of time, the screws can work loose and cause a loose connection,

Isn't it more that the conductors expand, become deformed and then become loose when they contract again?

 

[JohnW2]

I hear that the problem with traditional junction boxes is that as they expand and contract over the passage of time, the screws can work loose and cause a loose connection,

Isn't it more that the conductors expand, become deformed and then become loose when they contract again?

Sounds much the same to me. Once the conductors come loose, so will the screw be lose - and, furthermore, once the screw is loose, I presume that vibrations etc. can 'loosen' it even more.

I'd be interested to hear how common this problem actually is in practice. I've lived with countless (mainly 'concealed') traditional JBs for decades (many of which I didn't even know existed until I 'stumbled across' them). Whilst I do usually try to eliminate them when I find them, I haven't yet (fingers crossed!) encountered even one of them resulting in any problems.

Kind Regards, John

 

[ekmdgrf]

I hear that the problem with traditional junction boxes is that as they expand and contract over the passage of time, the screws can work loose and cause a loose connection,

Isn't it more that the conductors expand, become deformed and then become loose when they contract again?

That's an interesting question. I'm afraid that I don't have an interesting answer.

How often do you come across loose screw terminals and do you happen to notice that it happens more often a certain points in the year, eg after exceptionally cold weather?

 

[EFLImpudence]

How would you know in which season the loosening happened unless you were to inspect them twice a year instead of once in a blue moon?

Copper is, after all, soft.

 

[piggoy]

Cheers for all your responses guys Despite the lack of long term reliability knowledge I will go for the option of replacing with Hager/Ashley MF boxes. They're not very expensive. I'd definitely kick myself if one of those old traditional boxes develops a dodgy connection after laying the laminate floor!

 

[JohnW2]

Cheers for all your responses guys Despite the lack of long term reliability knowledge I will go for the option of replacing with Hager/Ashley MF boxes. They're not very expensive. I'd definitely kick myself if one of those old traditional boxes develops a dodgy connection after laying the laminate floor!

That's probably what most people would advise/suggest - and it is, I confess, what I've generally done with traditional boxes I've found in my house, if re-cabling (to eliminate joints completely) was not 'easy'.

However, there are inevitably some gambles in both directions, given the lack of true long-term experience of MF boxes - i.e. you'd probably also kick yourself if one of the new MF boxes you install develops a dodgy connection after laying your laminate floor!

Kind Regards, John

 

[ekmdgrf]

How would you know in which season the loosening happened unless you were to inspect them twice a year instead of once in a blue moon?

Copper is, after all, soft.

There are two thermal cycles, the day/night and the seasonal variation. I would expect the constant day/night cycling to evetually start to unwind the screw and I doubt there'd by a great deal of pattern in failures.

I would expect a deformed conductor to manifest itself as a fault after a period of extreme temperature.

This is off the top of my head, of course, there could be factors that I'm not taking into consideration.

 

[JohnW2]

There are two thermal cycles, the day/night and the seasonal variation. I would expect the constant day/night cycling to evetually start to unwind the screw and I doubt there'd by a great deal of pattern in failures. ... I would expect a deformed conductor to manifest itself as a fault after a period of extreme temperature. ... This is off the top of my head, of course, there could be factors that I'm not taking into consideration.

That's all reasonable conjecture. However, I'd still be very interested to hear how common the problem actually is, in practice, no matter what thermal and other environmental factors the JBs may have been subjected to.

Kind Regards, John

 

[ekmdgrf]

There are two thermal cycles, the day/night and the seasonal variation. I would expect the constant day/night cycling to evetually start to unwind the screw and I doubt there'd by a great deal of pattern in failures. ... I would expect a deformed conductor to manifest itself as a fault after a period of extreme temperature. ... This is off the top of my head, of course, there could be factors that I'm not taking into consideration.

That's all reasonable conjecture. However, I'd still be very interested to hear how common the problem actually is, in practice, no matter what thermal and other environmental factors the JBs may have been subjected to.

I've never seen the problem but then I've never looked very hard. I was hoping EFLImpudence would share his wealth of experience with us