Crossover in ring circuit

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Crossover in ring circuit

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KeenPensioner

KeenPensioner

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HI, as my profile says I'm not a sparky and know my limitations. I'm trying to learn (for the sake of it only as I'll never do it) what tests for "Ring Final Circuits" are. I understand how the Tests 1, 2 and 3 are done but in one of the videos I watched the presenter (John Ward) mentions a "crossover" see image and says that this "could lead the current being shared in an undesirable fashion. I don't understand that.
ring_main_crossover.jpg
 
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The ring is a bit of an historic artefact, but a good one in my view. With the middle cross over it is no longer possible to perform a single test end to end. It doesn't improve the current capacity but it does make it much harder to test. My quick thought is it won't ruin the current handling capacity of the ring, but it's not the construction method shown in Appendix 14 of BS7671.
 
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It's not done strictly in accordance with the good book, but there are worse arrangements!

The major issue is that, when you do testing on a ring final, you crodd connect the conductors in a sort of figure of 8 arrangement. Then you test at each socket and check the R1+R2 resistance. In a properly installed ring final, the R1+R2 at each socket should be more or less identical.

The circuit would fail this test because of the the 'lollypop' arrangement in your post.

Learn more about this test HERE

Or, if you love John Ward
 
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TBH I cant really recall any damage to cables on any of the hundreds of incorrectly wired rings I've come across over the years. In fact in the domestic sector it's pretty rare to find a correctly wired ring unless the house is fairly recent. The one I'm rewiring at the moment has spurs off spurs off spurs in the kitchen (now ripped out), no sign of thermal damage at all.
 
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I think in reality it's highly unlikely that an incorrectly wired ring in a domestic setting would ever see high enough loading of sufficient duration to actually cause any cable damage. Seen a fair few 2.5mm^2 and even a few 1.5mm^2 radials on 30A/32A OCPDs and don't recall seeing any evidence of overload damage. Obviously, it's not good though!
 
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Taylortwocities said:
I wouldn’t worry about it. Check out the profile of who gave you the rating!...
Only one post since 2012, and two dumb ratings:rolleyes:
I’ve reset the balance for you:)
Click to expand...
It's amazing in some respects, you answer a post get, say 3 likes and a couple of agrees and 1 Dumb, that's like saying all the likes and agrees are dumb as well, yes I always check the profile, some are genuine,most are as you say TTC
 
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Its an equation at the end of the Day,

The whole idea of the ring is at any socket outlet the resistance should be the same back to the Fused board.
Therefore the current will travel both way back to the fuse board at an equal 50% each way down each leg of the ring. by adding a connection between the sockets and creating a figure 8 the resistance will now be imbalanced. therefore the current will now be unevenly splite. ie 40-60% 30 -70%, it can even get to 10- 90%, depending on the resistance of the Legs, it would be a very difficult job to access this and require a level of mathematics beyond just looking at tables.

and the reason we don't see any damage is most domestic house don't use a lot of current of their ring mains.
But should they try to use the 32 amps on offer then they will most certainly start to get issue,
 
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Upton Sparks said:
The whole idea of the ring is at any socket outlet the resistance should be the same back to the Fused board.
Therefore the current will travel both way back to the fuse board at an equal 50% each way down each leg of the ring.
Click to expand...

What???

The resistance of a section of cable between the origin of the ring and the load will be proportional to the length of that cable. So a socket near the origin will pull more current along the 'short' route than the 'long' route, in inverse proportion to the resistance.
 
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The R1 + R2 should be the same at each socket (except spurs) when testing, because the conductors are joined together into a big circle.
Current sharing in normal use, will be as Handyspark says proportional to the resistance of each leg.
The longer the leg, the greater the resistance, the lower the current.
 
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Ok Boys back to the testing books for you I'm afraid.
After doing your ring continuity, I hope you then do your Figure 8, You then test each socket to obtain your R1+ R2, your expecting the resistance reading R1 + R2 of the Ring to be the same at every point!.(Give or take 0.05)
therefore the current will flow equally back to the board regardless of where you are on the Ring,( its the same resistance either way its a ring) thats the science behind and why you do the Figure 8 testing and check every socket..
If you have high reading its normal a spur, or you've connected it up wrong, (normally only happens on Single..... unless your a really idot). Or the circuit is not a ring.
 
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Upton Sparks said:
Ok Boys back to the testing books for you I'm afraid.
After doing your ring continuity, I hope you then do your Figure 8, You then test each socket to obtain your R1+ R2, your expecting the resistance reading R1 + R2 of the Ring to be the same at every point!.(Give or take 0.05)
therefore the current will flow equally back to the board regardless of where you are on the Ring,( its the same resistance either way its a ring) thats the science behind and why you do the Figure 8 testing and check every socket..
If you have high reading its normal a spur, or you've connected it up wrong, (normally only happens on Single..... unless your a really idot). Or the circuit is not a ring.
Click to expand...
Yes when testing the resistance will be about the same at each socket (except spurs), because the conductors are connected together at the CU into a big circle.
In normal use the conductors are separated into individual circles (hopefully).
 
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Its a Ring, they are connected at the board in the MCB.
Explain. how does basic ohm law explain that? your going to need to put a bit more meat on the bones for me.

But
If the resistance is the Same at each socket( as we've tested), then the equation V =I X R, we should all be familiar.
Therefore I = V / R
V is constant at 230V, and as we've said above R is the same at Each location,
therefor I will be divided equally around the circuit.
 
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Upton Sparks said:
Its a Ring, they are connected at the board in the MCB.
Explain. how does basic ohm law explain that? your going to need to put a bit more meat on the bones for me.

But
If the resistance is the Same at each socket( as we've tested), then the equation V =I X R, we should all be familiar.
Therefore I = V / R
V is constant at 230V, and as we've said above R is the same at Each location,
therefor I will be divided equally around the circuit.
Click to expand...
Yes when cross connected for testing not when uncross connected for normal use.
 
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Upton Sparks said:
Its a Ring, they are connected at the board in the MCB.
Explain. how does basic ohm law explain that? your going to need to put a bit more meat on the bones for me.

But
If the resistance is the Same at each socket( as we've tested), then the equation V =I X R, we should all be familiar.
Therefore I = V / R
V is constant at 230V, and as we've said above R is the same at Each location,
therefor I will be divided equally around the circuit.
Click to expand...
Doesn't Mr KIRCHOFF have a say in this debate, far to far back for me to remember, but it does ring a bell.
 
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Uptonsparks, in post #16 you state "The whole idea of the ring is at any socket outlet the resistance should be the same back to the Fused board"
 
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It should be its a ring, looks like this ( O), if you cut in to the Ring and measure ring continuity( R1 for example) it would be the same at the Fuse board and if we measured it at every socket as well it should be the same, providing you close it back to a ring at the Fuse board. When the Current hits the Ring it see the same resistance in the conductors and Flows accordingly,

My understanding is that the current is divided equally around the ring, therefore allow us to use a 2.5mm cable to be used on a 32amp MCB, if it took the shortest leg back, then surely you would have over current issue on the shortest section of of the Ring?..
 
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DPG said:
Uptonsparks, in post #16 you state "The whole idea of the ring is at any socket outlet the resistance should be the same back to the Fused board"
Click to expand...

He did Peter well done for remembering his name.,,something about what flow in to a junction must flow out, I think. I cant remember that far too long ago, I'm afraid I've Kill a few brain cell since those day.....
LOL that will be the Beer.
 
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Upton Sparks said:
He did Peter well done for remembering his name.,,something about what flow in to a junction must flow out, I think. I cant remember that far too long ago, I'm afraid I've Kill a few brain cell since those day.....
LOL that will be the Beer.
Click to expand...
Wrong post maybe? Ah I see now, yes it was many moons ago, now White man speak with forked tongue, or he don't understand diddly squat, I must refer to Medican Man @Hughes Electrical Technology book, he speaks words of wisdom, or he did when I was a mere Brave in this world of magic, kemosabi.
 
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