Concealed joints again!

[JohnW2]

Current discussions in this forum about an underground joint in SWA cable have caused me to refresh my knowledge of what the regs 'actually say', and that ha led me to something I've never considered before.

In terms of underground joints, for fairly obvious reasons the regs exclude such joints from needing to be 'accessible for inspection and testing'.

In the more usual situation of joints in cables concealed within walls, below floorboards or above ceilings (hence not 'accessible foor inspection and testing') we generally interpret the regs (and advise people accordingly) as saying that such joints have to be either 'mechanical' (e.g. crimpled, soldered, brazed or welded) or else achieved with "MF" connectors/JBs (with 'sprung' terminals). In particular, we say that joints made using screwed terminals are not acceptable if 'inaccessible'.

However, I've just been reminded that the list of joints which do not need to be 'accessible for inspection and testing' not only includes 'underground' ones, but also includes "a compound-filled or encapsulated joint".

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").

Comments on a postcard?

 

[Harry Bloomfield]

I've never used gel, always resin compound, some quite large cable, some quite small, mains signal cables, but always crimped, or soldered.

 

[JohnW2]

I've never used gel, always resin compound, some quite large cable, some quite small, mains signal cables, but always crimped, or soldered.

I've used both in my time, probably always soldered (I'm nervous about crimped joints).

However, as you will presumably realise, I was talking about what the regs seem to allow (for 'above ground non-accessible joints) and that would appear to include any sort of joint (including screwed) if it is within gel or resin - unless you can find some other way of interpreting the reg?

 

[SUNRAY]

I have never been able to comprehend why screwed joints are permitted in inaccessible resin joints but not in a JB under a floor, which is significantly more accessible.

 

[morqthana]

I've never encountered any round JBs under floors which have come loose.

 

[JohnW2]

I've never encountered any round JBs under floors which have come loose.

Same here, and I've come across quite a lot of them in my time!

 

[JohnW2]

I have never been able to comprehend why screwed joints are permitted in inaccessible resin joints but not in a JB under a floor, which is significantly more accessible.

As I said, the reason I started this thread was because it had not previously occurred to me that the regs appear to allow screwed joints under floorboards (or anywhere else) provided they are within resin/gel!

 

[EFLImpudence]

Here's a thought: maybe the regulations are not as well thought out as they could be.

 

[JohnW2]

Here's a thought: maybe the regulations are not as well thought out as they could be.

Now that is a thought

 

[SUNRAY]

I've never encountered any round JBs under floors which have come loose.

Same here, and I've come across quite a lot of them in my time!

Despite 'liking' your posts I have to say yes I have found a few loose connexions over the years but of course I know not if they have been due to 'becoming loose' or bad installation or disturbance.

 

[Harry Bloomfield]

Despite 'liking' your posts I have to say yes I have found a few loose connexions over the years but of course I know not if they have been due to 'becoming loose' or bad installation or disturbance.

Not a section of the industry, where I customarily worked, but mostly DIY, and doing favours, I found a few. The usual cause, was generally poor workmanship, rather than becoming loose. Good workmanship, is feeling the screw bite, and giving each wire a tug, to ensure it is gripped. Many miss those final steps.

 

[JohnW2]

Despite 'liking' your posts I have to say yes I have found a few loose connexions over the years but of course I know not if they have been due to 'becoming loose' or bad installation or disturbance.

Fair enough - but as Harry has said, I also rather doubt (but obviously cannot prove) that such joints had actually 'become lose' over time

 

[JohnW2]

Not a section of the industry, where I customarily worked, but mostly DIY, and doing favours, I found a few. The usual cause, was generally poor workmanship, rather than becoming loose. Good workmanship, is feeling the screw bite, and giving each wire a tug, to ensure it is gripped. Many miss those final steps.

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 (which, itself, probably only happens significantly if the joint were not properly made), but I am inclined to agree that subsequently-found 'lose joints' were probably never made properly, and particularly given that cables going to 'inaccessible' JBs are extremely unlikely to ever be 'stressed' (even if there is no 'strain relief').

 

[SUNRAY]

Not a section of the industry, where I customarily worked, but mostly DIY, and doing favours, I found a few. The usual cause, was generally poor workmanship, rather than becoming loose. Good workmanship, is feeling the screw bite, and giving each wire a tug, to ensure it is gripped. Many miss those final steps.

I tend to agree with this but will add that with many JB's it can be hard to tell iof the multiple wires are positioned nicely in the terminal, or if the wires are different sizes

 

[JohnW2]

I tend to agree with this but will add that with many JB's it can be hard to tell iof the multiple wires are positioned nicely in the terminal, or if the wires are

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.

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.