Discuss Visualising Cont. of Ring Final Conductors test in the Electrical Courses and Electrical NVQ's area at ElectriciansForums.net

C

Carter

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This might come in handy when trying to understand what's happening when testing for Continuity of Ring Final Cct Conductors by cross-connecting opposing cct ends at the D/B.
This at least worked for one lad who just couldn't see it in a drawn diagram so one day I knocked this up from a few lengths of cable. this + 3mins = "Ohhhh yeeaah!"

A ring circuit stripped down to its bare essentials is nothing more than this; (for demo purposes cpc is omitted for clarity)...should be obvious what's going on. The line loop ends I've labelled in white 'Ph1' and 'Ph2' in pic.2. Neutral loop ends similarly labelled N1 and N2.

Dotted around the loops are the connections to the socket terminals L1/L2/L3 and N1/N2/N3 representing 3 skts on the ring....


Shot with DCR-SR30E at 2008-08-26

Next pic shows the cross connections as described in GN3 et al. Ph1 to N2 and then N1 to Ph2....


Shot at 2008-08-26

This is the trick to why the same readings are/should be obtained when measuring between line and neutral at each socket. If you pick up the line loop and turn it 180 degrees you end up with a continuous 'figure 8' shaped circuit.


Shot with DCR-SR30E at 2008-08-26

At this point the lad still was still not with the program but something was obviously stirring.
Untwist the line loop by another 180 degrees and it now lies flat on the table as one continuous conductor....sort of an electrical 'Moebius strip'


Shot with DCR-SR30E at 2008-08-26

Now he's onside! and sees how the cross connections have turned 2 loops into one single and continuous loop but not how the readings are derived.
I asked him to look at where the tape markers for each skt terminal now lie in relation to that loop and he spots that they are all diametrically opposite and therefore because these opposing terminals are physically in the same place (the socket) and will always end up opposite each other as the two loop lengths will be near enough identical (they're contained in the same cable sheath) then no matter where you measure across a diagonal of such a loop you will always measure the same resistance. Q.E.D.
Clang! penny drops,
 
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S

sparkyork

good idea that carter, when i first started out this also took me a while to get me head round, this and 2 way switches. i had to know why something was telling me something rather than been told it from a book.

this would aslo be good if it showed what happens when you have a cross connect in there and why it affects readings.

rich
 
C

Carter

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  • #3
this would aslo be good if it showed what happens when you have a cross connect in there and why it affects readings.

rich
With me the penny dropped when I saw a machine shop bloke doing that 'fold and twist' thing they do when coiling down a bandsaw blade.
Good idea about the effect of bridging out/multiple loops, erm! hang on I'm going to have to think this through a minute. :confused: it's gonna end up like a cat's cradle if I don't strangle m'self :D
 
B

Bane

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  • #4
Hmmm. This may come in very handy when I start my 2330.
 

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