Access to lighting wiring under loft floor

[Dave Plowman (News)]

While pics are useful, they don't replace drawing out a simple wiring diagram. And of course marking the cables so you know which is which after removing the fitting.

[Mike Barnes]

"Dave Plowman (News)" :

Agreed, I didn't mean to suggest not doing any of those things. Apart from anything else they promote understanding, and taking a picture doesn't. Pictures are most useful when disassembling something mechanical.

[Adam Funk]

>>> This is but one example, but there are lots out there - all with

I noticed that while browsing the catalogue recently & this seems like a good place to mention what I was wondering about.

I guess it's called "Maintenance Free" because it can be buried under the floor without worrying about future access to check that the screw terminals are still tight. Is that correct? What kind of terminals does this box use that are more secure than normal screw terminals?

[John Rumm]

Something the common availability of camera phones makes much easier these days. Less useful in the days of needing to get the roll developed.

[Roger Mills]

>>>>> This is but one example, but there are lots out there - all with

Basically, they're spring-loaded clamps. Some have levers which open the clamp, and make it easy to insert and remove wires. These are ok for solid or stranded wire. Others are just two metal strips in the form of a V, sprung together at the pointy end. Pushing a wire down the middle separates the strips - which then grip the wire. This type is only suitable for solid wire, and is more difficult to take apart - but you can usually remove a wire by twisting and pulling at the same time.

[David WE Roberts]

> That way you can just drop a single cable to each rose.

those Wago things :-) Thanks again to all who responded.

[Adam Funk]

> I noticed that while browsing the catalogue recently& this seems like

I wondered if they were sprung like that. I guess they are secure because the cables are clamped in the box itself so the individual wires can't be pulled loose (unlike a traditional junction box).

[Roger Mills]

...

Not really. Strain relief is something different. With this sort of connection, the security of the actual electrical connection is better than a junction box with screws because of the constant spring pressure. The screws in a junction box can work loose over time - possibly due to expansion and contraction - and you might then get arcing and, in extremis, a fire. That's why anything with screw connections needs to be 'accessible' - whereas these maintenance-free jobbies don't.

[Adam Funk]

> ...

Sorry, what I wrote was a bit muddled. What I meant was that without the built-in cable clamps, push-in terminals wouldn't be secure (because they are subject to pull-out).

[Dave Plowman (News)]

I've heard this before but am a bit sceptical. I've never known any terminal in house wiring properly tightened work loose. Plenty which aren't properly tightened give trouble, though.

[Bill]

In message , Nightjar writes

They are the best thing since sliced bread, in fact somewhat better!

[Roger Mills]

Well indeed! I've got some screw terminals in inaccessible places - which I installed long before I became 'enlightened' - and they still seem to be fine! I was simply following the party line in my previous post.

[John Rumm]

My feeling with screw terminals[1] is that with circuits that are not routinely loaded to close to full capacity (i.e. most circuits) it is a bit of a non issue in practice. The screws will slacken with time, but without significant thermal movement of the wires, it will not have much effect as long as they don't get so lose as to allow air into the joint to start tarnishing the copper. On fully loaded circuits then its more of a problem since there is more routine movement.

[1] Having said that, there are screw terminals and screw terminals - some get a very much better grip than others. I have also read some comments on the modern trend for cage terminals (like on modern MCBs) possibly not performing as well long term.

[Dave Plowman (News)]

All the connections between my riser through to CU (including meter) are screw terminals. The loading on those pretty well never approaches the maximum since I don't use electric heating.

So what is the 'routine maintenance' spoken of? The connections to the riser have not been touched in the 40 years or so I've been here...

[John Rumm]

Checking and tightening if required...

I have come across a few of occasions where it was worthwhile (and plenty more where it was not).

I was re cabling an immersion heater circuit back to a wylex re-wireable fuse CU once - it probably had been installed relatively recently (say within 25 years), and was surprised to find the circuit termination was surprisingly loose. Checking all the other terminations in the CU revealed a similar situation where it was easy to tighten all the connections by a significant amount. This may have just been a reflection of lack of sufficient tightening when installed. There were no obvious signs of heating in there - although all lightly loaded circuits.

Also an immersion heater FCU where terminals had worked loose. That was showing significant heat damage internally and had hardened the (high temperature) flex insulation locally. Another similar case with an electric shower pull switch (which I know had been tightened well on installation), also showing local heating damage.

[Dave Plowman (News)]

Oh indeed - I've seen plenty where the screws were never properly tightened. Just poor workmanship. Or maybe even hoping for a return visit (paid for) to sort a fault.

But then poorly tightened screws ain't the only thing that poor workmanship will show on.

[Adam Funk]

Coming back to the maintenance-free junction box, though --- I've been told in this group that foreign connection methods are inferior because they don't put enough pressure on the wires to make a gas-tight connection. How can a push-in spring-clip exert enough pressure to compare with screw terminals?

[David WE Roberts]

The problem I've seen twice recently is the outside plastic casing around the post in a junction box fracturing off. Presumably the brass post was expanded too much by tightening down on the wires and pushing them sideways in the slot. I don't know how much this weakens the post - if it relies on the plastic to stop it expanding with time - but not good anyway.

One was in a junction box I was using. The other was in a junction box I was removing.

Cheers

Dave R

[ARW]

Today I used a circular dry lining box and a conduit box lid. That was flush.

[SteveW]

Our conservatory has ceiling lights, a pair of spotlights, round-pin sockets for table lamps (although usually only used for the Christmas tree and other Christmas lights) and a three-gang lightswitch. Although the sockets are daisychained, the rest are wired back to a single point and connected in a 12-way central heating box.

SteveW