Confused beginner's question about testing

[Sats]

Dear all

I am struggling with understanding even the basics of testing. Any help in the right direction would be greatly appreciated, and I apologise in advance if this is as hard to read as it was for me to try and articulate...I'm afraid it reflects the disordered tangle in my own head.

I can't seem to get my head around is how testing for continuity of ring final circuit conductors works. When we are testing for a total resistance value for phase and neutral conductors combined why do we make temporary links at the CCU (P1-N2 and simultaneously N1-P2) then carry out resistance testing at each socket outlet between the P and N terminals? Why not just link P1 with N2 at the CCU and apply the test leads to N1 and P2? I must be missing something very basic here for a start...

Furthermore I am finding it hard to imagine what the significance is of the resistances are being tested each time at each socket outlet, and in what ways they are expected to differ. Surely once the temporary links have been made (P1-N2 and N1-P2) there are always two paths for the current sent from testing instrument to go - or does the instrument always register a reading for the path offering the least of the two values of resistance?

Am I even right in thinking that we're applying a meter across "exposed points" (socket terminals) in series along a temporary continuous loop isolated from a supply? Although the tutor explained it (and others understood) I am very far from understanding it, let alone how we reach the formula (R1 +R2)/4, and what it signifies.

Anyway I'll keep trying but I thought I would post this anyway. If anyone recognises this confusion from when they started out and can recommend a good link (no pun intended) I'd be most grateful.

Thank you

Sats

 

[green-hornet]

The continuity testing at each socket is more important for PIR testing than new installation as it will show higher readings for any spurs, it is important none the less for checking connections at each socket, I have found loose connections this way, and on a PIR a socket with no earth connection because it had been twisted together and come out of the socket back.

 

[ianmacd]

Dear allI am struggling with understanding even the basics of testing. Any help in the right direction would be greatly appreciated, and I apologise in advance if this is as hard to read as it was for me to try and articulate...I'm afraid it reflects the disordered tangle in my own head.

I can't seem to get my head around is how testing for continuity of ring final circuit conductors works. When we are testing for a total resistance value for phase and neutral conductors combined why do we make temporary links at the CCU (P1-N2 and simultaneously N1-P2) then carry out resistance testing at each socket outlet between the P and N terminals? Why not just link P1 with N2 at the CCU and apply the test leads to N1 and P2? I must be missing something very basic here for a start...

That would not be measuring the parallel paths in the ring then. By reversing the N1 to P2 and P1 to N2 you should end up getting a constant reading at all points as the parallel path lenghts will then be equal

Furthermore I am finding it hard to imagine what the significance is of the resistances are being tested each time at each socket outlet, and in what ways they are expected to differ. Surely once the temporary links have been made (P1-N2 and N1-P2) there are always two paths for the current sent from testing instrument to go - or does the instrument always register a reading for the path offering the least of the two values of resistance?

When testing R1+R2 on a ring, you are also testing the polarity is correct at the socket. The reading taken will be the combined resistance of all the parallel paths. If you have measured r1,r2 and rn (ring continuity) then the R1+R2 should be approx (r1+r2)/4.

Am I even right in thinking that we're applying a meter across "exposed points" (socket terminals) in series along a temporary continuous loop isolated from a supply? Although the tutor explained it (and others understood) I am very far from understanding it, let alone how we reach the formula (R1 +R2)/4, and what it signifies.

Think you are mixing your lower case and upper case r's there but yes its measured at as many points as practicle.

Anyway I'll keep trying but I thought I would post this anyway. If anyone recognises this confusion from when they started out and can recommend a good link (no pun intended) I'd be most grateful.

Thank you

Sats

Have you got a copy of the On Site Guide? The Part P Doc's book is good too.

 

[a1]

This is a great book, and I would recommend its purchase. the cheapest place you can purchase it is on our Auction site:

TEF Auctions

 

[JUD]

Although the tutor explained it (and others understood) I am very far from understanding it, let alone how we reach the formula (R1 +R2)/4, and what it signifies.

The best way to think of this is:

Imagine you have a 2.5mm

 

[bluetobits]

This is a pretty good video to help get your head around it:-

[YT]http://www.youtube.com/watch?v=9GRLM6sgDXM[/YT]

 

[sparky b]

If you're really stuck (like I was) PM me and I'll give the number of a brillant instructor....

 

[ADS]

Nice video, but a couple of things to be aware of.

Firstly, the safe-isolation procedure that he demonstrates is not really suitable for a three phase board - he should be doing a ten-point test.

Secondly, half way through testing the ring, just after testing between line and neutral at the socket, he states "...and that confirms polarity.."

Polarity isn't proven at this stage, as you could still have a line and neutral swap at any of the sockets.

Polarity is only proven after both figure-of-eight tests have been completed at each socket.

 

[Lee Sparks]

Hi Sats,

It seems your understanding of testing is about the same level of mine, i have lots of questions and not many answers.

Im so confused about the testing process and why its done in certain ways and all the rest of it, that ive built my own test rig in my garage to do the dead tests on, over and over again till it becomes second nature.

I purchesed a robin multi-meter from ebay for

 

[ianmacd]

One thing that helps me is the phrase, "Can I Please Leave".

Can: Continuity

I: Insulation Resistance

P: Polarity

L: Loop (Earth)

And then RCD's.

Its a good way to remember the order of tests.

 

[steptoe]

without being anything,

why arent questions like this in the beginners thread?

 

[initforthemoney]

GN3 is the book you should be getting, not someones interpretation of it.

Expensive, but you will need it anyway.

 

[soulman]

hi i found the niceic dvd's are very useful to understand some of the testing

 

[OzWiz]

GN3 is the way forward, and lots of practical experience...