Anyone can make a mistake. But how many is too many?

[ToughButterCup]

Electric circuits - loads of them 👍

Sockets - loads of them 👍

 

Are they in the right place? 👎

 

"Oh but, I want that [...]  there now, not where we planned it ..... soz .."   Weak smile. 

"Needs an extension then dunnit. Grrrrr."

 

Rinse repeat.

I'm not prepared to admit how often I've smiled disingenuously , swearing under my breath, gone out to the workshop, got another extension out and fitted it. (6)

Whassa point of asking what electrics she wants where at the design stage?  None. None AtBloodyAll

 

Wimmin change their minds all the foggin' time.

 

Another self-build dream down the plug'ole innit. Phhhhhhhhhhhhh.

 

Is it me   - it is innit ....?

[Andehh]

Going through this right now. We both (expletive deleted)ed it up due to an emergency change in direction on the project mid way through planning the electrics... And we never went back to it till electrician was on site. 

 

 

It's bloody expensive now.... 

[ProDave]

I repeat it retrospectively in this case.

 

Socket circuits, you only have to put ONE socket on each wall, then route the ring final cable horizontally around the room at socket height in the safe zone created, leaving a little slack in the cable at least at the ends.

 

Then when you know where you actually want the sockets, cut the hole in the plasterboard, fish out the cable and connect the correct number of sockets in the right place.

 

Experience says putting them in too early just means at least half of them are behind furniture, even worse half the socket is behind a unit........

[Radian]

20 minutes ago, ProDave said:

Socket circuits, you only have to put ONE socket on each wall, then route the ring final cable horizontally around the room at socket height in the safe zone created, leaving a little slack in the cable at least at the ends.

 

It wouldn't make any difference if was a ring or radial. I don't know why anyone would opt for a ring final. A work of the devil IMHO. 👿

[ToughButterCup]

2 hours ago, Radian said:

 

... I don't know why anyone would opt for a ring final. A work of the devil IMHO. 👿

 

May I play Devil's advocate then please @Radian ?

 

What's wrong with a (my) ring then?

[Radian]

1 hour ago, ToughButterCup said:

What's wrong with a (my) ring then?

 

To begin with you have to wonder why ring finals are peculiar to the UK. Their origins go back to their introduction circa 1942–1947 and the materials shortages of the time. It was a crafty trick to effectively get more current through less copper wire. It makes it possible to supply twice the safe current carrying capacity of the cable  to any given set of loads on the circuit due to current being shared across two cables: Topologically, every socket is being fed by two paralleled cables. Except when it isn't.

 

If a screw works loose somewhere in the circuit, the ring can be broken - yet you might not know it as there may still be an intact connection to every socket from one direction. Now the ring becomes two radials but sod's law states that the tumble dryer, kettle and toaster all huddle together at one end of the break. And then the burning smell isn't necessarily the toast.

 

A radial will have an MCB rated for the safe current carrying capacity of the cable it feeds and at no time can the cable be stressed beyond that limit. A ring final may become inadequately protected due to a (relatively common) defect.

 

 

[ToughButterCup]

Right. Thank you very much for that post. You've set me off on yet another steep learning curve.

It might be useful for me to pull together a couple of images, one of a ring circuit and the other a radial circuit and post them here so that others can have a look at what you are talking about.

 

There is so much in your post above which I just don't understand, by that I mean fundamentally don't understand.

 

 

[billt]

Radials might be better in theory, but you need a MCB/RCBO for each circuit. Already have 20 RCBOs in the consumer unit here. There are 38 sockets, so another 23 breakers needed, so an enormous CU and lots of extra expense. (We don't actually have enough sockets.) And that's just in the house, the outbuildings would also need extra circuits.

 

The danger of a broken ring are somewhat overblown. the ring is only likely to get broken after it has been disturbed and the continuity should be tested after a disturbance. These days it is quite rare to have many high consumption devices on a ring so overloading the ring is unlikely. The multiplicity of sockets is used for the many very low consumption devices that get accumulated.

[Radian]

34 minutes ago, ToughButterCup said:

There is so much in your post above which I just don't understand, by that I mean fundamentally don't understand.

 

I wish I was better at explaining. Perhaps this article on the TLC-Direct website might do a better job. This picture from there should help:

 

 

They arbitrarily chose to show a break just after the first socket to the right of the 30A breaker but of course it could be anywhere. But you should be able to see how up to twice the expected current might end up in the cable if a fault develops. The big fail is that users may be blissfully unaware of the problem. In practice one socket (the one with a loose terminal) is very likely not to work but it doesn't necessarily even have anything plugged in to it.

[Radian]

10 minutes ago, billt said:

Radials might be better in theory, but you need a MCB/RCBO for each circuit. Already have 20 RCBOs in the consumer unit here. There are 38 sockets, so another 23 breakers needed, so an enormous CU and lots of extra expense. (We don't actually have enough sockets.) And that's just in the house, the outbuildings would also need extra circuits.

 

 And then you go on to say

 

10 minutes ago, billt said:

These days it is quite rare to have many high consumption devices on a ring so overloading the ring is unlikely. The multiplicity of sockets is used for the many very low consumption devices that get accumulated.

 

Because you can protect a radial cable with a MCB of the appropriate current rating you can have as many socket as you like, as long as it's in an area not exceeding 50 square metres (IIRC). This should allow you to meet the requirement of lots of low consumption devices.

[ProDave]

In defence of the ring final.  In most instances the Current Carrying capacity of 2.5mm t&e is 27 amps, and rarely less than 20 Amps, so it would not be overloaded in most cases if there was a break.  (certainly not overloaded to twice it's rating)

 

And testing the end to end loop integrity of a ring final is a very easy test that can be performed at the consumer unit or any socket on the ring.

 

 

[ToughButterCup]

10 minutes ago, ProDave said:

.....

And testing the end to end loop integrity of a ring final is a very easy test that can be performed at the consumer unit or any socket on the ring.

 

Go on, show me. I dare ya. 

 

26 minutes ago, billt said:

Radials might be better in theory, but you need a [...] RCBO for each circuit. Already have 20 RCBOs in the consumer unit here. There are 38 sockets, so another 23 breakers needed, so an enormous CU and lots of extra expense. ...

 

Found that out the very hard way.

2 CUs, 20 circuits in each. 28 used so a fair few spare.  Every one on an RCBO. 

 

Winced a bit when the bill arrived. But,  DeleteTheExpletivePlease(expletive deleted) [thanks very much] It, overall its not worth worrying about.

Edited January 27, 2023 by ToughButterCup

[TerryE]

17 hours ago, ToughButterCup said:

Wimmin change their minds all the foggin' time.

 

Mine didn't 🤣

[ProDave]

48 minutes ago, ToughButterCup said:

Go on, show me. I dare ya. 

Turn the power off and test that it is really off.

 

Remove a convenient socket and take the wires out.  you will have 2 live, 2 neutral and 2 earth.

 

Measure the resistance between each L, each N and each E cable.  Ideally using a proper continuity meter but an ordinary multimeter on ohms will do for a quick test.  You should get the same reading for L-L and N-N and E-E will typically be about 1.4 times greater as the earth core is smaller.

[Radian]

5 minutes ago, ProDave said:

In defence of the ring final.  In most instances the Current Carrying capacity of 2.5mm t&e is 27 amps, and rarely less than 20 Amps, so it would not be overloaded in most cases if there was a break.  (certainly not overloaded to twice it's rating)

 

Last year I got called out to our rental property about a funny electrical smell first thing in the morning. Tumble dryer (10A), kettle (12A), and toaster (8A) had all been on at the same time. They'd also used the microwave (5A) but couldn't remember if it overlapped use of the kettle. It's simply all too easy to innocently rack up well over 30A on a ring final.

 

There's a good reason we do impedance checks, the theoretical current carrying capacity of 2.5mm² cable can be diminished in numerous ways  once installed and in service (although it never, ever, goes up). In a radial it would be protected at 16A and nothing's realistically going to come to harm with that. OTOH as part of a ring final, any snags with less than perfect junctions or wire condition (trapped or stretched) can suddenly rear their ugly heads as a consequence of a less severe problem cropping up.

 

The test to establish a broken ring is easy once you've been alerted to the failure but actually locating the offending socket isn't anywhere near so trivial. Unhooking both ends of the ring and continuity testing out to each socket is easy in theory, but in practice you need to know the layout and where every socket is located. Naturally this one, underneath a dresser in an upstairs bedroom, didn't have anything plugged in but a terminal screw was loose.

 

[ProDave]

My favourite tip for finding the break point in a ring is power up one end of the ring only then go round with a socket tester.  It helps narrow it down a bit but won't obviously say "this one"

 

The fun and games start when there is more than one fault (loose L in one socket, loose N in a different one)

[ToughButterCup]

1 hour ago, TerryE said:

 

Mine didn't 🤣

 

I'm in love....

[ToughButterCup]

41 minutes ago, Radian said:

...

underneath a dresser in an upstairs bedroom, didn't have anything plugged in but a terminal screw was loose.

 

 

I remember a post by @TerryE advising us to - after 6 months or so - going round to check the tightness of terminal screws. And I thought - well I winced - 'tain't gonna ' appen pal. An' anyway the man's retired innee...

 

Hmmmm. 

[Radian]

23 minutes ago, ToughButterCup said:

 

I remember a post by @TerryE advising us to - after 6 months or so - going round to check the tightness of terminal screws. And I thought - well I winced - 'tain't gonna ' appen pal. An' anyway the man's retired innee...

 

Hmmmm. 

 

It's why we have the "maintenance free connector". Screw terminals are not in this class. 

 

Another related gotcha is tinning stranded wire. Some people think it's a good idea to apply solder to the stripped ends of the strands in order to tame them before tightening the screw holding the wire in a terminal block. It certainly looks neater but invariably the wire will eventually work loose. This is because the softer alloy solder gives under the pressure of the screw and is so malleable it can readily loose that contact pressure over time. But copper is only a bit less ductile so the same also applies only over longer time-scales. There is also a very subtle electromagnetic effect from the constant alternation of current that can result in minute mechanical forces acting on the conductors so, in addition to thermal stresses, even fixed installation wiring be less fixed than you might think it would be.