Extending ring main and lighting in to new extension

[Taylortwocities]

So yes I am UK based and was saying that whilst competent in running T&E in to various sockets and keeping to the Horiz / Vert I am not fully Part P understanding and was hoping I could just run / extend off from one of those red star sockets. Want to keep final socket placement flexible as I build the room as still designing the layout as I go for wall mounted TV and light etc.

yes, but you must bear in mind that how you “run/extend” from existing socket has some gotchas. You can’t just connect a series string of new sockets if the original socket is on a ring final. You’d have to extend the ring.
That makes planning the sockets as you go more difficult as you always have to provision the return leg from the last new socket.

 

[markyd1]

Big thing.
New circuit means notification to LABC.
Extending existing is not notifiable.

In a perfect World then a radial circuit would be the ideal solution.
But most of us don’t live there.

Will still need a minor works cert for insurance purposes

 

[If in doubt...]

yes, but you must bear in mind that how you “run/extend” from existing socket has some gotchas. You can’t just connect a series string of new sockets if the original socket is on a ring final. You’d have to extend the ring.
That makes planning the sockets as you go more difficult as you always have to provision the return leg from the last new socket.

Cheers, I'll be tracing the existing ring over the weekend, those 2 red star sockets look to be adjacent on the ring so options there to split and extend but I'll know for sure once I have a proper look.

 

[JohnW2]

Will still need a minor works cert for insurance purposes

In theory, perhaps - but anyone can issue such a certificate (or an EIC, or even an EICR, come to that)

Kind Regards, John

 

[ericmark]

Theory is we need to keep within the limits to ensure the automatic disconnection of the supply and volt drop are within the limits published in BS 7671. In the days of the fuse, exceeding the loop impedance would mean it may take a little longer to disconnect, and a jump from 5 seconds to 6 seconds was not really too much of a problem.

However as we moved to the MCB this changed, the MCB is two devices in one, a thermal and a magnetic trip, the latter is basic to protect against the short circuit, and with a B rated MCB works at between 3 and 5 times the thermal device setting, and works very fast, around 0.01 of a second, where the thermal part can take many minuets to trip, so now going over the allowed loop impedance can mean a huge change in the disconnection time, so it is very important to keep within the limits.

It is allowed to use inquiry to work out the loop impedance, so in theory you can get out the original installation certificate and look at what the loop impedance was, or the R1+R2 and calculate how much cable you can add. And it does not need to be measured with a loop impedance meter, one can use a low ohm meter using at least 200 mA to measure the resistance with.

However the point is you can't simply add more cable without working out what you already have and how close to the limits you are. At least when you have some one leaning over your shoulder (LABC inspector) to see your doing it right.

The IET publish model forms step one is to down load the forms and see if you think you can fill them in, if you can then maybe the LABC inspector will accept your signature. For me it is relativity easy, I have the test gear, or can borrow it, some shared with my son, so I can complete the forms, and even if I didn't have the test gear, I have filled in enough to like with the Emma Shaw case make a good guess at what the results should be, I would not guess, as don't want there to be a court case for me.

I am trying to make this a real world answer, and in the real world the last thing we want to hear is "Do it again and do it properly" if LABC was not involved I may have said use near enough engineering and just use a socket tester with loop, or get an EICR done after the work is completed.

But we have seen the problems on other threads getting the LABC to accept work done.

 

[markyd1]

I don't mind people being told YES you can do it yourself and issue your own cert and do all the testing yourself, Because in a couple of weeks time when everything starts going bang I can charge them a good amount to put it all right and it's all down to the fact they should have got somebody who would have spent a bit of time working out if what they wanted was feesable. Pays for my holidays

 

[JohnW2]

I don't mind people being told YES you can do it yourself and issue your own cert and do all the testing yourself,

Well, that "YES" is true, certainly in terms of 'can', but also 'may' - provided that the individual is 'competent' to at least design and construct/execute (and, ideally, also test) the work.

Because in a couple of weeks time when everything starts going bang I can charge them a good amount to put it all right and it's all down to the fact they should have got somebody who would have spent a bit of time working out if what they wanted was feesable. Pays for my holidays

Fair enough. I'm not sure whether that is a general 'anti-DIY' comment, or in some way related specifically to the OP and the work under discussion.

What confuses me a little is that your comment (about the minor works cert) was seemingly in response to TTC having explained (to a 'foreigner') that in the UK (England and Wales) there is a big difference (bureaucratic & financial) between extending and existing circuit and installing them - the need for certification (minor works or EIC) is obviously the same in both cases.

Kind Regards, John

 

[If in doubt...]

Well I used to wire control panels for up to 500 kVA generators and nothing ever went bang so I'm not your average DIYer , but in the end circumstances have lead me to getting an electrician in anyway - the feed from meter to dist unit is right in the way of some ceiling vaulting work I'm doing so I'll get him to run the sockets and lights at the same time as diverting the other cabling. Thanks for the info though.

 

[FrodoOne]

And on that basis one may be excused for wondering if he is conversant with our electrical systems (seems to slag off our perfectly acceptable and standard ring final in favour of bulky, expensive and harder work radials). In which case it would not be unreasonable to wonder if he should be offering advice on here.

I have no idea of his experience/competence and therefore how valid his or my comments are.

We all have our opinions.
Ring circuits are "allowed" in only a few countries - of which the UK is one.

Here are some UK "opinions" concerning them

And then there are "Radials" - used exclusively in most countries.

 

[SUNRAY]

We all have our opinions.
Ring circuits are "allowed" in only a few countries - of which the UK is one.

Here are some UK "opinions" concerning them

So I've just wasted 1/2 hour watching that crap.
Good old Naggy... 3 minutes of lies - I used to have a book from the 20's which described ring main circuits,
followed by slagging off foreign workers.

Neither of those has given any real reason for not using rings... in my opinion.

Bad workmanship is no excuse for stopping using them and 'actual real faults' are not that common, certainly nowhere near as common as faulty accessories.

If I were to follow JW's advice, I'd be replacing one ring with 6 radials and end up with 96A worth of OCPD (or more) and loads more cable and the net result will be a larger CU, a lot more cable so wasting copper and a lot more expense for RCBO's. There will be absolutely no advantage... please explain what I'm getting wrong.because I just don't see what they are trying to impress upon me.

Oh and the ring circuit may be, and is, used in places other than socket circuits

 

[JohnW2]

If I were to follow JW's advice, I'd be replacing one ring with 6 radials ....

In view of the potential ambiguity, I would like to dissociate myself from the views expressed by my (abbreviated) namesake

I do agree that there is very often no great advantage (and never a 'need') to install ring finals, but nor do I think there's anything particularly 'bad' about them (after 70+ years experience of their use in the UK). I would therefore personally never advise anyone 'against' ring finals but, rather, would suggest that they should consider what they regard as the pros and cons of rings and radials in their particular situation.

Kind Regards, John

 

[SUNRAY]

In view of the potential ambiguity, I would like to dissociate myself from the views expressed by my (abbreviated) namesake

Indeed, My reference to JW being the YT video in previous post

I do agree that there is very often no great advantage (and never a 'need') to install ring finals, but nor do I think there's anything particularly 'bad' about them (after 70+ years experience of their use in the UK). I would therefore personally never advise anyone 'against' ring finals but, rather, would suggest that they should consider what they regard as the pros and cons of rings and radials in their particular situation.

Kind Regards, John

Like yourself I see absolutely no reason to think they are bad or should be banned etc. Sure faults occur, sure things go wrong, sure they take longer to test than a radial but not as long as 6 radials.

However faults occur on radials, things go wrong on radials - which reminds me I have a radial fault to return to but maybe more about that elsewhere.

I have a combination of rings and radials in my properties and always have. I wouldn't have installed any if I'd found a problem with them.

 

[EFLImpudence]

If the ring circuit regulation did not still cater for 30A BS3036 fuses, I suppose, when using a 32A MCB, conductors could be used which actually did have a CCC of 20A (Method C of course), i.e. 1.5mm², thus only requiring 3mm² of copper for the two wires instead of 5mm².

If the route of the sockets actually is a ring, then the slight benefit; if that is what it is; of having a 32A OPD instead of 25A (or indeed two 25A radials) might be a good reason to fit a ring circuit - but it seems to me equivalent to people who still use 6mm² for a 32A cooker circuit just because that is what they have always done.

Would anyone use a 2.5mm² ring for a 32A cooker circuit? No, of course not.

 

[JohnW2]

Indeed, My reference to JW being the YT video in previous post

Quite, and my point was that I am not that "JW"

Like yourself I see absolutely no reason to think they are bad or should be banned etc. Sure faults occur, sure things go wrong, sure they take longer to test than a radial but not as long as 6 radials. However faults occur on radials, things go wrong on radials - which reminds me I have a radial fault to return to but maybe more about that elsewhere.

Yes, agreed. I suppose the greatest 'concern' (about rings) for some is that a break in the (L and/or N) ring can go unnoticed indefinitely, but could theoretically result in some of the cable being 'overloaded'. I doubt that this would ever be a significant problem with Method C 2.5mm², but might be more of an issue if (as is allowed) the cable had a CCC of only 20A, given that a B32 might allow up to 46A or so to flow for an hour.

However, to somewhat balance that, a ring final provides 'CPC redundancy' whereas, again, loss of an effective earth on a radial could 'go unnoticed indefinitely'). There are some swings and roundabouts.

I have a combination of rings and radials in my properties and always have. I wouldn't have installed any if I'd found a problem with them.

Same here. It's probably 'just me' but, as I often say, I'm personally not totally comfortable with the concept of multi-socket 20A radials (but am very comfortable with 32A 4mm² ones). That's not really an issue in my own house, given that I have a good idea of what circuits are likely to be used for, but I would be less comfortable if I had no knowledge of, or control over, subsequent usage.

Kind Regards, John

 

[JohnW2]

If the ring circuit regulation did not still cater for 30A BS3036 fuses, I suppose, when using a 32A MCB, conductors could be used which actually did have a CCC of 20A (Method C of course), i.e. 1.5mm², thus only requiring 3mm² of copper for the two wires instead of 5mm².

Yes, I think you suppose correctly.

If the route of the sockets actually is a ring, then the slight benefit; if that is what it is; of having a 32A OPD instead of 25A (or indeed two 25A radials) might be a good reason to fit a ring circuit - but it seems to me equivalent to people who still use 6mm² for a 32A cooker circuit just because that is what they have always done.

Indeed. I feel sure you're right that the main reason why rings are still installed so often is because "that is what has always been done", rather than as a result of a decision based on thought.

Would anyone use a 2.5mm² ring for a 32A cooker circuit? No, of course not.

Probably not - although, electrically-speaking, there's no reason I can think of why they couldn't. Indeed, if the circuit were only supplying the cooker, what you're talking about is simply using two 2.5mm² cables in parallel - which I suppose might be done "because they didn't have any 4mm² cable in the van

Kind Regards, John