ring testing

[soulman]

i have been practicing testing before i return to college in september, i have moved from my test rig onto my own house. i was testing the downstairs ring. the problem i have is when testing at the socket outlets line & neutral cross connected. i should have had around 0.30 at each outlet, out of 12 sockets only half were this figure some were around 0.45 and some as high as 0.76. i double checked all connections were tight, all sockets are metal. Any ideas as i was expecting roughly the same at each outlet. Also there are no spurs. cheers for any help a little confused!

 

[philip962]

From what I remember they can be different as long as they are no more than 1.87 i am no testing guru but I think this is right if not I will be shot down in flames within mins on here gn3 should be able to clear it up

 

[pevvers]

From what I remember they can be different as long as they are no more than 1.87 i am no testing guru but I think this is right if not I will be shot down in flames within mins on here gn3 should be able to clear it up

Unfortunately you are incorrect, the 1.67 value you are thinking of is to calculate what the approximate value of the end to end resistance of the CPC should be, i.e. multiply the line end to end value by 1.67.

It sounds like a dodgy ring to me, or maybe shoddy sockets not making good contact. Sometimes different sides of double sockets give different readings on the low 200mA test current applied on a continuity test.

Personally, I would do the line to CPC test and see whether this gives the same magnitude of variation across the circuit at the same points.

 

[soulman]

i will try that tommorrow. it is a new build property so i would have thought that ring would be ok

 

[keniff]

some of them may be spurs? what is your end to end resistances on r1 r2 rn? try adding your end to end resistances together RN and R1 does this give you measurments a bit closer to what you are expecting?

 

[pevvers]

i will try that tommorrow. it is a new build property so i would have thought that ring would be ok

What I learnt a long time ago in this game is to trust nobody!

New builds can be just as bad as existing installations, especially if it is domestic... You don't know what's gone on in the installation, and there could be a bodge in there somewhere. As said, the line to CPC reading will show you whether it is the same across all parts of the circuit using another conductor.

 

[RETIREDSPARKY]

The 1.67 only refers to the ratio of 2.5mm2 line/neutral and 1.5mm2 cpc ie 2.5/1.5=1.67. Therfore if your ring has a different cpc csa ie smaller than line or neutral ie 4/2.5 the the ratio would be 1.6 and so on.

 

[Plonker 3]

Are you sure you have crossed the line and neutral cables correctly, these results sound like you havent if that is the case.

What were your readings for Rn & R1 continuity?

 

[soulman]

thanks for replies definately not spurs and definately cross connected correctly. i have spoken to a spark tonight and he said pick one of the sockets with high readings and change it to a plastic one and retest. he is convinced it is the metalic sockets. i never thought to ask him could it be because im testing at a socket outlet rather than the board with the neutral connected to the neutral bar.

 

[Golden_Boy]

Are you sure you have crossed the line and neutral cables correctly, these results sound like you havent if that is the case.

What were your readings for Rn & R1 continuity?

I would suggest doing the checks from the rear of the sockets, directly on the conductors , this should remove any issues caused by switches and poor conections at the plug adaptor ( I am assuming you are nseing on of these ?)

 

[JUD]

I would also check that none of the terminal screws have been tightened down on the conductor insulation

 

[thebassman]

Hi There

I had similar problem during our annual accessment whie checking a ring the socket i picked had a reading that the inspector said must be a spur, this was a complete rewire to prove my point i removed every socket, it turned out the problem was the twin socket we picked to take reading left hand side was ok right hand side was higher changed socket over and all was well, so as suggested in another test from back of socket a bit more hassle but stops sockets causing problems

Danny

 

[Golden_Boy]

Hi There

I had similar problem during our annual accessment whie checking a ring the socket i picked had a reading that the inspector said must be a spur, this was a complete rewire to prove my point i removed every socket, it turned out the problem was the twin socket we picked to take reading left hand side was ok right hand side was higher changed socket over and all was well, so as suggested in another test from back of socket a bit more hassle but stops sockets causing problems

Danny

Is there an Echo in here?

 

[pevvers]

Is there an Echo in here?

I reckon so, I said about different readings each side of the socket yesterday...

 

[soulman]

hi just to update you performed the tests today on the upstairs ring and got crazy results. so i removed sockets as advised and got perfect results, testing the actual terminals on the rear of the sockets. the sockets were mixed upstairs plastic & metal and i still got strange readings on plastic. So i,ve ruled out socket type. could it be my tester which is new, fluke 1652b i was using the socket cable that came with the machine. so i have now ordered a r2 socket interface adapter to see if that makes any difference. is this common on socket circuits. please note i'm cross connecting at a socket rather than the cu, if that makes any difference

cheers

 

[beaver74]

I have come across this many times the quality of sockets now seem poor as relation to contacts.if high or all over the shop i find that connecting to terminals direct sorts out a proper reading but it is a pain in the but

 

[WayneL]

Hi Soulman,

I'm not sure if the 'Mains Test Lead' (if that's what you are referring to) is supposed to be used for continuity - this could be your problem.

How does it connect to your tester?

 

[pevvers]

I use my Megger to do dead testing on sockets, as all you're doing is checking continuity, whether this be with a 13A plug top or a probe set, it's all the same!

I think it's actually better that way, as you'll get the reading you would actually get from the socket...

 

[soulman]

it's the mains adaptor. connects via terminal that you put probes in. spoke to fluke direct they told me to put the neutral lead into the earth to do the r1+rn crossover test

 

[soulman]

I use my Megger to do dead testing on sockets, as all you're doing is checking continuity, whether this be with a 13A plug top or a probe set, it's all the same!

I think it's actually better that way, as you'll get the reading you would actually get from the socket...

do you still get incorrect readings from time to time or not
cheers

 

[pevvers]

Yes, but this is most probably due to loose contacts inside the socket causing the extra resistance. It's only a 200mA current that's passed through it, which is why it shows.

As I said at the start of the thread, I find that sometimes different sides of the socket will give you different readings, sometimes quite a significant amount, which I can only put down to the quality of the construction of the socket.

If you are going to use the socket and see plug top tester, then this is no different to using the mains lead and in fact you may be putting more resistance into the circuit from the contacts between the leads and the socket interface...

 

[WayneL]

it's the mains adaptor. connects via terminal that you put probes in. spoke to fluke direct they told me to put the neutral lead into the earth to do the r1+rn crossover test

That's why I was asking.

So yours has the three coloured plugs on the end and you connect whichever two you require into the 'red' and 'green' on the meter?

That's ok then - you see, Megger also do a mains lead with one three way plug on it (plugs into a special socket on the meter) - I don't think this one is meant for continuity testing.


I have two more questions for you, Soulman:

Who on earth said it was okay to cross-connect at the socket?

And why would you want to?

 

[pevvers]

That's ok then - you see, Megger also do a mains lead with one three way plug on it (plugs into a special socket on the meter) - I don't think this one is meant for continuity testing.

The 13A lead for the Megger works absolutely fine for continuity testing, if it's good enough for loop testing then why wouldn't it be for continuity?!!? It's measuring exactly the same conductors, but when measuring loop it's all the way back to the tranny.

Who on earth said it was okay to cross-connect at the socket?

I have a feeling that this is a joke from earlier on in the thread, and can't be bothered to trawl through...

But there's nothing wrong with cross connecting at a socket instead of inside the board, sometimes it's much easier especially if you have a packed out board.

 

[WayneL]

The 13A lead for the Megger works absolutely fine for continuity testing, if it's good enough for loop testing then why wouldn't it be for continuity?!!? It's measuring exactly the same conductors, but when measuring loop it's all the way back to the tranny.

The Megger lead with the three seperate, coloured plugs on the end will work fine but I don't see how the 'all-in-one' plug will work on continuity.

How does the meter distinguish between which test you are doing (R1 + Rn or R1 +R2)?

On Zs testing it knows to test between L & E, but it won't know on continuity of RFC.

But there's nothing wrong with cross connecting at a socket instead of inside the board, sometimes it's much easier especially if you have a packed out board.

Sometimes.

I've got a feeling that the OP might be cross-connecting at the socket so that he only has to isolate the RFC at the MCB, instead of the whole installation.

If this was the case and he was working on a TN-C-S system, the Neutrals and CPCs of the ring final are basically connected together.

If when testing your R1 + R2, you wouldn't know if you had a neutral/earth swap at the socket, because you'ld get a reading either way.

And lets not pretend that people never just isolate the circuit that they are working on

Then, even if you isolate the whole of the installation correctly at the main switch (both poles), you could still have the same problem (as above) if there were a N/E fault on another circuit that you didn't know about.

That's probably why cross-connecting at the socket isn't a given method in any of the books - or if it is, I haven't come across it, and I certainly wouldn't do it.

 

[pevvers]

The Megger lead with the three seperate, coloured plugs on the end will work fine but I don't see how the 'all-in-one' plug will work on continuity.

Ah yes, I was just talking about the R1+R2 readings, not the R1+Rn. Which is true, you would only be able to test the former with the 13A mains lead.

I've got a feeling that the OP might be cross-connecting at the socket so that he only has to isolate the RFC at the MCB, instead of the whole installation.

If this was the case and he was working on a TN-C-S system, the Neutrals and CPCs of the ring final are basically connected together.

If when testing your R1 + R2, you wouldn't know if you had a neutral/earth swap at the socket, because you'ld get a reading either way.

And lets not pretend that people never just isolate the circuit that they are working on

Then, even if you isolate the whole of the installation correctly at the main switch (both poles), you could still have the same problem (as above) if there were a N/E fault on another circuit that you didn't know about.

That's probably why cross-connecting at the socket isn't a given method in any of the books - or if it is, I haven't come across it, and I certainly wouldn't do it.

A very good point indeed, I was taking it as he had done a whole test on the board that would have included neutral-CPC IR tests, and also had the main switch open...

Never good to assume eh!

 

[soulman]

cheers wayneL
a working spark told me it would be o.k to practice my ring circuit testing at a socket instead of the consumer, So i could get some readings as i couldnt get any on my test rig. the earthing arrangement is tncs and i did just isolate that circuit.