Junction Box Habit

[DIYWell]

So here's one for the proper sparkies...

You're doing a bit of work in a house and while tracing a cable you come across a junction box which you open up.

Now, do you close it up and be on your way, tighten up those screws out of habit, go crazy with your torque screwdriver and tighten them to 1.2Nm, or replace it with Wagos and an enclosure?

 

[sparkwright]

Check all is secure inside, put the cover on, and forget it.

The one in the picture is presumably accessible, since you have accessed it.

 

[ericmark]

I may look at putting some cleats on the cable as strain relief, but other wise OK. It would depend where found, in an empty loft likely not touched.

 

[chivers67]

Although clearly it's accessible I'd replace it with a maintenance free box after tidying it up a bit and introducing a little more earth sleeving.

 

[JohnW2]

Although clearly it's accessible I'd replace it with a maintenance free box ...

As a matter of interest, why? Do you perhaps not believe in non-MF JB's being left in service anywhere?

Kind Regards, John

 

[plugwash]

I wonder, are modern "MF" boxes actually safer?

On the one hand they seem to have better strain relief and have terminals that aren't subject to the vaugarities of whoever tightened the screws.

On the other hand they generally tend to be made of thermoplastics that are prone to disintegration during thermal events, whereas the oldschool JBs like most UK electrical accessories tend to be made of thermosetting materials.

 

[JohnW2]

I wonder, are modern "MF" boxes actually safer?

As I often say, so do I !

On the one hand they seem to have better strain relief ...

They do. In fact, very few traditional JBs have any strain relief at all. However, particularly in the case of 'non-accessible' JBs, I do wonder what 'strain' people think needs to be 'relieved' (rodents playing "tug of war", perhaps? ). Ironically, it's much more of a potential issue with accessible ones

and have terminals that aren't subject to the vaugarities of whoever tightened the screws.

That, coupled with the fact that, at least in theory, sprung thermals do not loosen (e.g. in response to thermal cycling) are presumably the main 'USP's of the MF ones.

On the other hand they generally tend to be made of thermoplastics that are prone to disintegration during thermal events, whereas the oldschool JBs like most UK electrical accessories tend to be made of thermosetting materials.

All true - but of course, it didn't have to be that way, since thermosetting plastics are still available (and still used for many/most domestic electrical accessories)!

The other issue which I usually mention (which obviously becomes less of a concern as time goes on) is that we have fairly limited experience of the long-term behaviour/performance of 'MF' JBs in domestic installations, whereas we have many decades of experience of 'traditional' ones. There is a limit to how much 'accelerated testing' can tell us about what an MF JB will be like after a few decades in service!

Kind Regards, John

 

[chivers67]

As a matter of interest, why? Do you perhaps not believe in non-MF JB's being left in service anywhere?

Kind Regards, John

It's all I use now John. I find them easier to terminate & better designed to clamp cables.

 

[bernardgreen]

is that we have fairly limited experience of the long-term behaviour/performance of 'MF' JBs in domestic installations,

Decades ago various types of connectors were evaluated for their performance.

One comment made about spring loaded contacts with small areas of pressure on the contact area was the possibility of springs "softening" if the contact was affected by heat generated in the areas of contact.

 

[JohnW2]

It's all I use now John.

Interesting. I suspect that is far from common practice.

I find them easier to terminate & better designed to clamp cables.

As I said, traditional JBs do not have any provision for 'cable clamping'. However, I personally find J803/804s somewhat of a pain to use (more time-consuming than conventional JBs) because it is (at least for me) very difficult to push the conductors into the connectors with the cable going through the clamp. I therefore nearly always have to completely undo and remove one of the screws on each clamp so that i can 'swing it out of the way' - and then 'put it back' again.

Am I the only person to have that 'problem'?

Kind Regards, John

 

[JohnW2]

Decades ago various types of connectors were evaluated for their performance. One comment made about spring loaded contacts with small areas of pressure on the contact area was the possibility of springs "softening" if the contact was affected by heat generated in the areas of contact.

That, of course, is my 'potential concern'. It is, of course, to some extent 'balanced' by the fact that thermal cycling can result in loosening of screwed terminals. I'm unfortunately not going to be around for long enough to find out, but I would certainly be more comfortable about 'sprung terminals' after large numbers have been in service in domestic installations for 'a few more decades!

When I raise this issue, some people usually point out to me that 'sprung' terminals have been used industrially for a long time, but I don't know how true that is, nor how such terminals have fared in the very long term.

Kind Regards, John

 

[Murdochcat]

I see lots of wagos used without any form of enclosure - that’s poor to say the least.

 

[JohnW2]

I see lots of wagos used without any form of enclosure - that’s poor to say the least.

It certainly far from being 'nice', and definitely not compliant with any regs, but provided that the conductors are stripped to the apricate length (hence no exposed bare conductors, I imagine that, in reality, it is probably actually pretty 'safe'.

 

[Murdochcat]

It certainly far from being 'nice', and definitely not compliant with any regs, but provided that the conductors are stripped to the apricate length (hence no exposed bare conductors, I imagine that, in reality, it is probably actually pretty 'safe'.

But probably don’t meet with MIs

 

[JohnW2]

But probably don’t meet with MIs

Undoubtedly - and, as I said, non-compliant with explicit regs, anyway.