Mystery connection

[Mr Gear]

Back again for more advice & opinions on electrical matters! Hope I get my terminology correct in what follows....

After recently sorting out the outside socket thanks to previous help on here, I'd become aware of 2 x T&E cables leaving a 32A MCB in the CU dedicated to the garage circuit. Initial thoughts were it was a ring... but one of the cables appears to be 4mm and the other a 2.5mm. Therefore, I was curious regarding the design of the garage circuit.

Bit of background info. The previous owner had partly converted the garage - fully plasterboarded, carpeted, cupboards and utility area / boiler. This obviously makes it trickier to trace cables etc.

Working safely (after isolation, checking for dead etc) I concluded that the 2.5mm cable ran only to a double socket on the nearest wall (no spurs off this socket). The 4mm cable ran to a double socket the other side of the garage, a spur off this to another double socket (in 2.5mm), and off this socket ran 2 x spurs (in 2.5mm) to 2 x FCU's - one for the boiler, one for the outside socket.
Not great, but at least I could see what had been done. [Is a 'Radial' the correct term for that configuration ??]
However... another double socket appeared to be fed from the 4mm cable as with everything but the 4mm connected, its live. As its not spurred from any socket, my conclusion is there must be a hidden junction box somewhere along the path of the 4mm cable, but just where I can't tell and if I start ripping up the walls & ceiling the wife will not be happy!

Anyway, for now I've swapped the 32A MCB for a 20A (more than adequate for current demand) which I'm hoping at least makes the situation somewhat 'safer' ? - was that a reasonable move?

Thanks in advance....
(I have another question but one thing at a time eh!)

 

[JohnW2]

Working safely (after isolation, checking for dead etc) I concluded that the 2.5mm cable ran only to a double socket on the nearest wall (no spurs off this socket). The 4mm cable ran to a double socket the other side of the garage, a spur off this to another double socket (in 2.5mm), and off this socket ran 2 x spurs (in 2.5mm) to 2 x FCU's - one for the boiler, one for the outside socket.
Not great, but at least I could see what had been done. [Is a 'Radial' the correct term for that configuration ??]

That sounds fine. It's essentially a 32A 4mm² radial with various 2.5mm² branches/spurs from it (one of those branches/spurs originating at the CU). Provided none of those 2.5mm² branches/spurs supply more than one socket (single or double) or one FCU, that's fine.

However... another double socket appeared to be fed from the 4mm cable as with everything but the 4mm connected, its live. As its not spurred from any socket, my conclusion is there must be a hidden junction box somewhere along the path of the 4mm cable, but just where I can't tell and if I start ripping up the walls & ceiling the wife will not be happy!

I don't really understand that. Can you perhaps try to explain in a manner that even I could understand?!

Anyway, for now I've swapped the 32A MCB for a 20A (more than adequate for current demand) which I'm hoping at least makes the situation somewhat 'safer' ? - was that a reasonable move?

As for what I commented on in my first paragraph above is concerned, that is not really necessary. Provided only that none of those 2.5mm² cables supply more than two things, a 32A MCB would be fin.

Kind Regards, John

 

[Mr Gear]

However... another double socket appeared to be fed from the 4mm cable as with everything but the 4mm connected, its live. As its not spurred from any socket, my conclusion is there must be a hidden junction box somewhere along the path of the 4mm cable, but just where I can't tell and if I start ripping up the walls & ceiling the wife will not be happy!

I don't really understand that. Can you perhaps try to explain in a manner that even I could understand?!

LOL, thanks John, I'll try to explain a little better...!

There is a double socket (actually thinking about it with a spur off it to yet another double socket) but I cannot find where it connects into the radial.

When everything else was disconnected from the 'socket end' of the 4mm cable, this socket was still live.

Therefore, I can only think that there is a junction box in wall / ceiling somewhere.

Does that make more sense ?

 

[plugwash]

Back again for more advice & opinions on electrical matters! Hope I get my terminology correct in what follows....

After recently sorting out the outside socket thanks to previous help on here, I'd become aware of 2 x T&E cables leaving a 32A MCB in the CU dedicated to the garage circuit. Initial thoughts were it was a ring... but one of the cables appears to be 4mm and the other a 2.5mm. Therefore, I was curious regarding the design of the garage circuit.

Seems reasonable to be curious when you see something unusual.

Working safely (after isolation, checking for dead etc) I concluded that the 2.5mm cable ran only to a double socket on the nearest wall (no spurs off this socket).

That is fine, same principle as a spur off a ring, overload of the 2.5mm cable is assumed to be unlikely if it only feeds one acessory.

The 4mm cable ran to a double socket the other side of the garage, a spur off this to another double socket (in 2.5mm), and off this socket ran 2 x spurs (in 2.5mm) to 2 x FCU's - one for the boiler, one for the outside socket.

If i'm reading this correctly you had three accessories being fed by the same 2.5mm cable. off a 32A circuit. That is indeed something that should be dealt with.

Not great, but at least I could see what had been done. [Is a 'Radial' the correct term for that configuration ??]
However... another double socket appeared to be fed from the 4mm cable as with everything but the 4mm connected, its live. As its not spurred from any socket, my conclusion is there must be a hidden junction box somewhere along the path of the 4mm cable, but just where I can't tell and if I start ripping up the walls & ceiling the wife will not be happy!

Inaccessible junctions are supposed to be done with specific types of join. Of course the problem is that if you can't find the box you can't tell if it's a type that is supposed to be used in locations that are not accessible for inspection.

Personally I wouldn't worry too much about it though, the whole "accessible for inspection" thing seems kind of silly when you think about how installations in practice are rarely inspected and how most inspections only look at a sample of points.

Anyway, for now I've swapped the 32A MCB for a 20A (more than adequate for current demand) which I'm hoping at least makes the situation somewhat 'safer' ? - was that a reasonable move?

Yes

 

[Mr Gear]

If i'm reading this correctly you had three accessories being fed by the same 2.5mm cable. off a 32A circuit. That is indeed something that should be dealt with.

Yes - thats why I reduced it to a 20A MCB as I thought/hoped that would improve the situation.

 

[JohnW2]

If i'm reading this correctly you had three accessories being fed by the same 2.5mm cable. off a 32A circuit. That is indeed something that should be dealt with.

Yes - thats why I reduced it to a 20A MCB as I thought/hoped that would improve the situation.

Indeed. Sorry, when I responded before, I read that as meaning that each of the three accessories had its own 2.5mm² cable - in which case the 32A MCB would have been OK.

Kind Regards, John

 

[plugwash]

Yes - thats why I reduced it to a 20A MCB as I thought/hoped that would improve the situation.

It did.

To be absoloutely sure things were ok you'd want to know whether there was any thermal insulation surrounding the cables but honestly i'd stop worrying at this point.

 

[JohnW2]

LOL, thanks John, I'll try to explain a little better...! ... There is a double socket (actually thinking about it with a spur off it to yet another double socket) but I cannot find where it connects into the radial. ... When everything else was disconnected from the 'socket end' of the 4mm cable, this socket was still live. ... Therefore, I can only think that there is a junction box in wall / ceiling somewhere. ... Does that make more sense ?

Yes, I think I understand now. I think I was being thrown by the fact that you said it was 'live' even though you had "isolated and tested for dead"!

If the only issue is that you don't know where the (assumed) JB is, as plugwash has said, I don't think you should be too concerned about that. If anything ever goes wrong with the circuit, you might have to find the JB but, in the meantime, it can probably join the millions of other 'JBs in unknown places' which are out there! Certainly so long as you have a 20A MCB protecting the circuit, that's not really an issue. If it were still the 32A one, then, strictly speaking, you ought to find the JB in order to make sure that it really does originate from a 4mm² cable - otherwise the spur off that socket would be a non-allowed 'spur off a spur'.

Kind Regards, John

 

[Mr Gear]

Great, thanks both.

Its been like it for many a year with no issues so with the 'improvement' my mind is at ease.

Whilst I'm here then... part 2 of 'mystery connections'...

We have a gas cooker. It does plug in for the ignition though to a standard socket behind the cooker. Ideally, the wife would like a new electric cooker, so thought I'd have a look to see what's what.

We have a dedicated 32A MCB in the CU marked up as "Cooker". It looks like a 6mm cable. All good so far?

Not when it gets to the cooker! Behind which is a socket which is connected with 2.5mm cable

The socket is situated within the tiled area. Tapping the wall above the tiles there is a hollow sound in line with the socket, so it appears there may potentially be another one of those millions of hidden JBs.....

First and foremost - I'm assuming this is 'pro time' rather than 'DIY fun & games' ?

Either way, if, and only if, she really really really wants that new cooker to be electric - and is prepared for the disruption/redecorating - what would be the options here?

If that 'hollow' opens up to reveal somewhere a cooker switch was connected and is indeed the other end of that 6mm cable, can it be safely extended down in 6mm (out of the way of the hob area) to a suitable outlet (flex?) for a cooker?

Will the 32A MCB provide the required isolation ???

 

[JohnW2]

We have a dedicated 32A MCB in the CU marked up as "Cooker". It looks like a 6mm cable. All good so far?

Yep, 6mm cable on a 32A MCB is very standard for a cooker circuit, and would be adequate for virtually any cooker.

Not when it gets to the cooker! Behind which is a socket which is connected with 2.5mm cable

Ah! As you imply, not so good!

First and foremost - I'm assuming this is 'pro time' rather than 'DIY fun & games' ? ... If that 'hollow' opens up to reveal somewhere a cooker switch was connected and is indeed the other end of that 6mm cable, can it be safely extended down in 6mm (out of the way of the hob area) to a suitable outlet (flex?) for a cooker?

Yes, although there would be considerations about the routing of the cable. As you imply, it may well be best to employ an electrician.

Will the 32A MCB provide the required isolation ???

As above ... yes.

Kind Regards, John

 

[Mr Gear]

Thanks again John.

One on the back burner (so to speak) at least for now.

It may be we keep the status quo until a more thorough 'upgrade' of the kitchen is on the cards, at which point I think the cooker might be relocated so definitely time for an electrician.

But if not at least I know it's worth further thought. I like to do what I can myself and I'm never totally sure what is within the allowed limits of DIY so it's always nice to be able to ask for advice on here first!

 

[JohnW2]

Thanks again John. ... But if not at least I know it's worth further thought. I like to do what I can myself and I'm never totally sure what is within the allowed limits of DIY so it's always nice to be able to ask for advice on here first!

There are actually no 'allowable limits'. In the UK anyone who is competent (in an everyday sense) to do it correctly and safely can do any electrical work. In England (different in Wales) just a few things require notification to the local authority ('new circuits', CU replacements and certain work in bathrooms) - and the bureaucratic systems (and charges) are such that it can often be more cost-effective to employ a 'self-certifying' electrician for such work than to DIY it and have to pay substantial LA fees.

The biggest problem with DIY electrical work is that virtually all such work should be tested, and very few DIYers will have the necessary equipment, or necessarily the expertise, to undertake proper testing. Having said that, an awful lot of electrical DIY work is done, so I leave it to you to draw conclusions from that!

Kind Regards, John