Junction box cable capacity

[Nemo2000]

Owing to a 'slight accident' while in the loft, I smashed a junction box on the lighting circuit feeding the floor below, so I bought a new one of a well-known brand. This was advertised specifically as a 5A 4-terminal lighting junction box.

The damaged box was rated for 5A and had 4 x 1.0mm cables: feed loop in, feed loop out, switch cable, light-fitting cable. Consequently 3 of the four terminals (L,N,E) each had 3 cable cores, the 4th terminal having just 2 cores. Seems quite normal to me.

Curiously though the new box was labelled for two x 1.5mm cores only. I tried it with 3 x 1.00mm and they did fit enough to get the grub screw to engage, but not very far. I was not happy with the result, so I have replaced it with a larger 20A box instead. Bigger terminals, got the 3 cores in easily, much better grip, so happy with the result.

But....even the 20A box was also marked as two x 1.5mm cores only. What is the point of a 4-terminal box, especially one sold specifically for lighting circuits, if the terminals are sized only for two cores? Or am I misunderstanding something here???

 

[sparkwright]

It probably differs from make to make, but I have found the so-called 5 amp junction box to be useless, and always use a 20 amp junction box for lighting.

A lot of the spiel about what can be put into a junction box is often rubbish.

That said, JBs do vary a lot depending on the make.

I once bought a cheap unbranded 30 amp junction box (3 terminals) which was usless for what I wanted as the terminals were so tiny. In the end I used it for lighting cables.

Hager junction boxes are usually the best, though some years ago they went through a bad period where the screws just broke the ends of the wires off far too easily. That seems to be resolved now.

 

[SUNRAY]

It probably differs from make to make, but I have found the so-called 5 amp junction box to be useless, and always use a 20 amp junction box for lighting.

A lot of the spiel about what can be put into a junction box is often rubbish.

That said, JBs do vary a lot depending on the make.

I once bought a cheap unbranded 30 amp junction box (3 terminals) which was usless for what I wanted as the terminals were so tiny. In the end I used it for lighting cables.

Hager junction boxes are usually the best, though some years ago they went through a bad period where the screws just broke the ends of the wires off far too easily. That seems to be resolved now.

I sympathise/empathise with all of that. The Hagar issue took a lot by surprise.

I will say that for a long time I've been thinking JB terminals are smaller than they used to be until I recently did some fault finding in a 1950's house with PVC/PVC cable where 5A JB's had been used for power circuits with 2 or 3 7/0.029" cables. Now I know JB terminals are smaller than they used to be.

Anyone remember the JB's with the SRBP insert with the brass contacts passing through 2 slots?

 

[Sureitsoff?]

MK 1131 are the only ones I use for lighting circuits as it is so easy to wire them up logically

 

[SUNRAY]

MK 1131 are the only ones I use for lighting circuits as it is so easy to wire them up logically

TBH I've always found them to be a pita having to run the wires right round the outside. But aren't they discontinued?

 

[Sureitsoff?]

TBH I've always found them to be a pita having to run the wires right round the outside. But aren't they discontinued?

no still available but they have changed colour, still makes them easier to spot in a loft

https://www.tlc-direct.co.uk/Products/MK1131W.html

 

[chivers67]

https://www.tlc-direct.co.uk/Products/ASJ804.html

I just use these now.

 

[SUNRAY]

https://www.tlc-direct.co.uk/Products/ASJ804.html

I just use these now.

My preference too. Maybe 50:50 with these

 

[SUNRAY]

no still available but they have changed colour, still makes them easier to spot in a loft

https://www.tlc-direct.co.uk/Products/MK1131W.html

Ah, OK thanks for that, A little while ago they were spec'd for a job but came up as 'no longer available'. Maybe it was just the brown version. Luckily the work we were doing threw a couple spare so the problem went away.

Still doesn't change the fact I find having to run wires round the box fiddly