Spurs from breaking into ring main

[10monty]

Can someone tell me if there is a limit on how many times you can break into a ring main to spur to a new socket using junction boxes.
I know you can only spur off a single to a single and a double to a double but unsure when breaking into the cable.

I ask this because my sister has just bought a house and whilst taking the floor up to do other works we found quite a few of them. Old style brown junction boxes which I understand shouldn't be hidden under the floor anyway.
One also had an old rubber cable attached to it which disintegrated in my hand when I touched it exposing the live conductors

There is a sticker on the cu showing it had an eicr done in May this year. Should that have picked any of this up?

Just need to know whether to get the vendors sparks back to explain and put right or whether to get someone else in ourselves

 

[Lectrician]

You can spur to 1 single or 1 double from ANY socket or joint box, but you must not have more spurs than there are sockets on the ring.

Joint boxes with screwed connections shouldn't be inaccessible, but this has only been pushed for the last couple years, and wouldn't "fail" an inspection.

Rubber cables still in use isn't great, but if test results passed, and it couldn't be seen as under the floor, a sparky ain't going to pick it up.

 

[10monty]

That's really useful thanks.

I think in the interest of good practice we'll get the jbs took out and replace with wago or similar.

 

[ericmark]

The reason why you should not use screw terminals when the box is inaccessible is because it's inaccessible for inspection. So it is unreasonable to expect an electrician doing an EICR to find faults under floor boards.

You will need to submit your EICR which should be done on change of occupant, to show the EICR done by previous owner missed vital parts of the inspection, which should be done before you move in, so would need submitting to vendors within a few weeks of moving in, to find faults months after is not really a reasonable time limit, so it may simply not be worth the effort.

 

[DaveHerns]

Don't just change the JBs , rip out all the old rubber cable as well.

 

[10monty]

There was just one rubber cable connected to a jb under the floor which had broken into the ring along with a spur for another socket. As soon as I touched the rubber cable the outer and inner sheath crumbled leaving the wire exposed. I disconnected it from the jb and made sure it was dead after.
I suspect it used to feed the garage as the vendor had to have the garage cable replaced as part of the eicr.
I've only been able to trace it so far as it disappears into a wall. I'm hoping it would have been made safe somewhere and not left open ended. The wall it goes to is bring knocked down soon so will soon find out

 

[ban-all-sheds]

you must not have more spurs than there are sockets on the ring.

Who/what/where says that?

 

[JohnW2]

Who/what/where says that?

I have a suspicion that the OSG may say that, but, as you imply, there is certainly no regulation to that effect.

Indeed, like others have reported, I have actually seen ring final circuits which had no sockets, just lots of spurs (from JBs) - and I would say that even that is actually compliant with regs (provided the JBs are 'accessible' or MF!).

Kind Regards, John

 

[securespark]

Yes, it appears in the OSG.

Twice.

I only have the green book. It appears in section 7.2.2 and again in Appendix H2.4.

 

[ban-all-sheds]

Doesn't reference any regulation number(s), though.....

 

[10monty]

I have another question regarding this same house I'll put here rather than starting another thread.
She wants to put washing machine and tumble dryer in garage. There will also be a small water heater to give hot water for basin in utility wc.
The garage has its own mcb so all seemed fine but had a look at it yesterday and not sure whether it's right or suitable for running above appliances
It is a 16a mcb with 4mm t&e. Cable run is approx 10m thru mini trunking in utility.
It enters the garage where it goes into the supply side of an unswitched fcu. A 2.5mm then comes from the load side to a double socket.

We were hoping to just run another double socket from there but I have concerns as to the powet it will need.

Is 16a suitable for 4mm radial?
What is the purpose of the 13a fcu, would it be better to do away with this?

Thanks

 

[Taylortwocities]

I would expect the cable to be 2.5mm² if there is a 16A fcu in the consumer unit. Are you absolutely sure it is 4mm² cable? How did you measure it?

16amp will not be enough for WM + TD + instant water heater, unless you propose never to use more than one appliance at a time.

 

[10monty]

100% it is 4mm. The cable has 2 x 4 + 1.5mm printed on it.

I suspected 16a was unsuitable. There is currently a 32a mcb that fed an old shower. Could I get someone out to disconnect the shower cable and put garage cable onto the 32a?

What about the fcu?

 

[Taylortwocities]

If it is 4mm² then 32A is what is needed. IS the 32A MCB protected by an RCD? you'll need one for that circuit.

The FCU is not necessary as It will limit the total current to the sockets to 13A...

As you'll be adding more sockets, and a feed to the water heater, make sure that additional cabling is also done in 4mm².

 

[10monty]

All mcb in cu are rcd protected.

Thanks for your advice. I'll get her to get someone out to sort it. It's a brand new install done just before she moved in so not sure what the thinking behind it was