13 Amp socket tolerances

[ARWadsworth]

Or they could be like dennis and be unable to afford an electrician.

[John Rumm]

Yes it was quite noticeable how "not arguing" has only taken him 54 posts so far...

[dennis]

How do you know, you can buy them in poundstretcher, etc., do you think they stock stuff that doesn't sell?

You said they didn't that's what.

Its not a high resistance then is it!

Rubbish, a disconnected cpc is a disconnected cpc. If you mean a broken link then say so.

Of course the rcd will trip.

Yes what you said is dumb. If you switch L&N on a ring the effect is the same.

Rubbish, if someone is going to switch them then they will and probably leave one disconnected if the breaker keeps tripping.

So now you are saying its perfectly safe to have two sections of a ring disconnected. Yes you have just ruled out the fault that results in that so why bother completing the ring in the first place, it makes no difference according to you. A hint, the iet don't agree with you which is why you cant have 32A radials in 2.5 mm2 cable.

You should know, but don't appear to.

[dennis]

And on 2.5 mm2 cable the 32A breaker exceeds it by?

You mean a ring without a fault or any spurs will have 5 mm2. A ring with a fault or a spur will have 2.5 mm2 cable to some of it.

The fault currents are not an issue, the breaker will trip. Or are you saying the 32A one won't on 2.5 mm2 cable?

[Dave Plowman (News)]

But what if it shows everything ok when there is indeed a fault? Like as has been said, a loose connection - by far and away the most common. It could still light up a neon, but fail under load. Hence the need for a proper test.

To be perfectly honest careful removing of all the sockets and a visual inspection coupled with a check on the terminal tightness would be a better way than relying on a cheap plug in tester. Of course this won't show if there are problems elsewhere, but will give an indication of the standard of workmanship on an installation new to you.

[Mike Barnes]

"Dave Plowman (News)" :

That's a different case, obviously.

[dennis]

Then they are no worse off than before the test.

OK they will have the test in 9 years, 50 weeks time, you did suggest every

10 years. In the meantime they can test as frequently as they like knowing they will catch a large proportion of the faults and that the RCD will catch the earth faults.

And cause faults to occur when they put the sockets back on due to work hardening of the copper, pinched cables, over tightened screws, etc..

[John Rumm]

More, less, or no overload at all depending on the circumstance. Hence why, as we keep having to explain, as a designer you follow the required guidance and make sensible design decisions about the best type of circuit.

That means that if you are running cables using installation method 100, and you are doing so in a potentially high load environment like a kitchen, it would be a sensible design decision to use a B32 protected ring, and not use any spurs. However it would be very unwise to install a B20 protected radials if using 2.5mm T&E.

If running a power circuit for the bedrooms of a three bed house, using method C, then you could use either, and spurs on a ring would be perfectly acceptable.

If running a non RCD protected feed to sockets dedicated to freezers and a boiler supply using method 100, then a B20 or B16 protected radial would be fine.

If running a circuit to a room full of PCs in an office, under a suspended floor, and into floor box socket enclosures, then follow high integrity protective conductor procedures, and use a ring or a radial depending on factors like overall cable length, floor area covered etc. Long term overload is a non issue since you are designing for a high load factor with little diversity.

This is not a difficult concept for most of us, I am not sure why it causes you so much difficulty... you look at the circumstances, and work out what the typical loads are likely to be. You look at the practicalities of the cable installation - what de-ratings will apply etc. You look at the physical distances and layout and work out how you will get cables to and from the CU etc. You look at the class of user, and typical usage patterns. Once you have assessed all that you can make a sensible decision.

You don't start the process mumbling "radial good, ring bad" (or any other ill thought through pre-conceived notion) like a drooling imbecile, potentially ruling out what may turn out to be the best design option before you even start.

[dennis]

Still trying to avoid answering I see.

[Dave Plowman (News)]

Then leave such things to an expert.

[John Rumm]

Its amazing... I am sure a post ago you were saying that circuits never get tested, and yet now apparently every granny in the land is doing so.

(cheap socket testers are pretty much useless for diagnosing anything beyond go/no go, and a small number of critical faults)

You have very poor comprehension...

I did not say a socket tester won't identify L/N reversal (although in fact some don't). I said that Jo Public will not own or use one. So whether a tester can identify L/N reversal is not relevant to whether a L/N reversal fault on a circuit is user observable without one.

Basically a L/N reversal does not get hot, smell, stop a socket working, or emit smoke.

So are you saying a high resistance connection is not a high resistance connection?

High resistance terminations may affect not only the connection to the actual socket in question, but also the rest of the circuit.

Think it though, if the CPC in and CPC out are not being gripped by the terminal, there is a equally likely chance they are not connected to each other.

(this is actually a case where twisted wires have a slight advantage, although twisted wires are more likely to suffer a wire break)

I agree that if the CPC "through" connection remains intact, and the disconnection is only from a single socket, *and* use of multiple CPC connection terminals on the socket has not been made, then the increase in user risk is the same for both circuit types. For all other cases however the radial fairs less well since downstream sockets are now unearthed.

There are two serious issues here, and the RCD can only address one of them, if there is one fitted.

A RCD may not of course be fitted.

A RCD will not address class I appliance metalwork floating at half mains, and being potentially driven by high leakage levels.

You think? It depends on how you do it. Swap over both line connections with both neutral, then yes the effect is the same on that socket, and there is no impact elsewhere.

However reverse just one cable's wires and the remainder of the circuit is transposed with a radial, but you have a short circuit with a ring which will prevent you from being able to energise the circuit.

I am glad you are not an electrician if that is your approach to resolving installation problems.

I don't follow how you draw that conclusion.

Take the example of a break in the circuits CPC. A radial will now (probably) pose significantly more risk to the user, while a ring will not since most of the sockets will still have a CPC connection in spite of the break.

(This is not a justification for shoddy work, before you get ideas)

Not sure of your meaning.

A disconnected L/N on a radial is an example of where the radial performs *better* than the ring - in that it fails in a obvious user observable way. This is why I rated the risk on a radial as low. The risk on a ring is moderate, because the sockets keep working and there is no indication to the user of a fault. The fault protection remains intact, but there is now a risk of premature cable ageing or possibly overheating. (in reality fairly small, since high loading factors are not common on many circuits in domestic settings)

(you can of course have radials wired in 2.5mm^2 T&E, with fault protection provided by a B32 MCB, and overload protection provided elsewhere, and you can have spurs (fused and unfused) in 2.5mm^2 from both radials and rings)

[ARWadsworth]

I can usually guess the highest ELI on a circuit I have installed before testing the circuit.

My tests do not need socket removals.

[dennis]

Its amazing you can remember that far back, no, actually you can't. The testers are pretty well useless on rings so no they don't get tested even if people plug them in. I thought you knew that, but maybe I give you too much credit.

They are good enough to find most faults on a radial.

No you just say things you don't intend.

But according to you it is bad (not observable) in a radial and not bad (observable) in a ring (its not observable in a ring). Or did you intend to write something else? A socket tester can detect it.

It isn't half as important now we have RCDs than it was.

Why?

Well it will, if there is high leakage it will trip. That's what they do, trip if the current becomes imbalanced.

What a contrived circumstance. So if someone wires it up wrong on one socket, like brown to black and black to brown it will blow. What's the chances that anyone will actually do that? Its far more likely they will just put the wires in the wrong holes on the socket.

So you think electricians make fundamental mistakes, like swapping wires. I am glad I don't know any electricians as bad. BTW what happened to them testing and issuing certificates? It probably explains why some of the readers here have faulty rings though so maybe you are correct, you just can't trust an electrician to do wiring.

Try reading the regs about 2.5mm2 radials.

[Dave Plowman (News)]

I'd certainly hope not.

[John Rumm]

They will find total disconnections, and reversals. The won't find poor connections - or for that matter even very poor connections (they don't draw any appreciable current, and don't conduct any end to end continuity tests).

If you believe they will find most faults on any circuit type then you are deluding yourself. I agree there are some faults they will find on a radial they won't find on a ring, but that does not make them adequate.

They are useful things to have certainly, but they are no substitute for proper testing with proper test gear. They are totally unsuitable for testing following installation. Read the test procedures in the OSG - they can not be completed with a socket tester.

FFS dennis, please try and keep up.

Transpose L & N on one cables termination in a ring circuit and you will be connecting L on one leg of the ring to N on the other leg of the ring. Trust me on this, the MCB will notice!

No I think most people would have got it, unless terminally stupid, or deliberately ignorant. Which are you?

11 million homes in the UK do not have any form of RCD protection according to the ESC surveys. Of those that do, a sizeable minority do not have it at the CU where it will offer circuit protection against this type of fault.

See above for one reason.

By that reasoning, they would trip any time an earth is present.

The permitted leakage on a mains input noise filter is?

The minimum trip current of a 30 mA RCD is?

RCD minimise shock risk how?

(to answer the above questions, 2.5mA, 66% of 30mA, limiting shock duration).

Hence a circuit with a floating CPC and a number of loads each leaking within limits, could result in someone receiving a sustained shock of say 20mA which is below the RCDs threshold to trip and hence limit the duration, and for which the touch voltage is not kept below 50V due to the lack of an earth connection.

(most real fault protection (aka "indirect contact") shock scenarios don't have a current limiting circuit (i.e. the filters) in the shock patch to inhibit operation of the RCD)

Do you get irony? Mr three immersions on a pair of trailing leads....

Commonly done on installation of lighting circuits (for obvious reasons), less so on socket circuits.

Chances are low, but not as unlikely as some of your overload scenarios.

Agreed. However just because there is a more likely error, that does not change the odds of making a less likely error.

Yes. Competent ones will find and fix them before handing over to the customer however.

In fact, simple conductor mismatch errors are probably more common now following harmonisation of the colour codes, where both black and blue conductors could be live or neutral in a mixed environment. There always was and remains a transposition risk when working with MICC.

You probably don't know any electricians.

Yes, they do that. No using socket testers either.

Do you a have a faulty ring dennis? It would explain a lot.

Why, do you think there is something wrong in what I have said? If so let me know, and I will direct you to the relevant sections.

Have a think about why a spur from a ring is permitted at the origin in

2.5mm T&E, since it looks very much like a general purpose radial, but for one significant detail.

[dennis]

I will say it again, they are better than no test and will find faults in radials that they can't find in rings.

Trust you, not a chance. You tell me I contrive stuff to get an overload on a spur and then you go on about contrived faults like wiring live and neutral together.

See above.

Of those 11 million homes how many have modern radials? How many have faulty rings that are radials when they aren't?

If they fit radials now they are new circuits and have to be protected.

See above for a reason why you are wrong.

So it's an observable fault that develops after the circuit was installed and tested. Now how often does it happen so a real evaluation of the danger can be made.

I have stated at least one case that wasn't contrived but i guess you decided to ignore it.

The switching of L/N is easy to find and the risk is the same for rings and radials so I fail to see your point.

As they would for radials, what's your point?

That's true, i don't think i am talking to one ATM.

I bet you have.

Which is the whole point of the argument or have you forgotten already.

[ARWadsworth]

I still have not found a way to fix a fault without taking the socket front off.

The worst fault I have seen was a neutral earth short on a lighting circuit caused by the owner of the house. This was on a house with a Wylex fusebox and a PME supply. The NE short became a big problem because the neutral connection to the meter was loose and all the circuits on the fusebox then had their neutral divereted via the lighting earth causing a big melting of the cables. It did not take long to find the fault, however it took a while (and a lot of money) to fix it.

[Dave Plowman (News)]

Indeed. My comment about a visual inspection is for checking a new to me installation. One can get a good idea of the standard of workmanship by looking at how it's been done and checking terminal security. But not of course needed for testing a new installation done by yourself.

Sounds like a nice little earner.

But it reinforces my beliefs. On near all electrics and electronics, its the connections which are the first thing to check. Way before wiring or component failures. And test equipment to check a connection is as good as it can be is neither common or cheap. As it requires testing at or near the maximum load that connection is needed to handle.

[ARWadsworth]

When doing a PIR I usually aim to inspect behind 20 to 25% of sockets and switches and vary these around the house to try and take account of any obvious alterations to the circuits. There are often many obstacles in the way. These are usually plasterers that do not know how to plaster when there is a socket or switch on the wall and tilers who cannot tile behind the same. When you have removed the agreed number of face plates then you get an idea of the quality of the work. In some rare cases I would suggest that ALL faceplates are removed and the cables checked.

Only for the plasterer and the decorator:-) It was cheaper to smash the ceiling down than remove and replace the nice wooden floors.

There has to be some compromise between what you can actually inspect and test based against the actual risks involved to the owner of a property who may have a fault on their circuits.

I would say testing a ring is easy. The continuity readings between the LL and NN should be within 0.05 ohms of each other.

[John Rumm]

One of the reasons I will keep my old megger LT5 loop tester, even though its not a "non tripping" tester. It uses a test current of 25A which is quite handy for flushing out faults that only manifest under load.