Ring main.

[JKMRK1]

Question I have is, is it ok to have x2 ring main circuits on one 32amp type B MCB??

If so does this meet the current regs.

TIA.

 

[DPG]

My dad had his tv and video recorder into same plug. I think it would be safer than one of those cube adaptors hanging out the wall.

I've done the same in the past I must admit. In my own home. Not ideal, but as long as it is 2 small flexes and the cord grip secures them properly then not too bad.

 

[ebee]

If each one is safe if on 2 devices, what makes them become unsafe when put on 1?


There aren't.


It isn't


But why, other than testing aggro?



By exactly the same logic we should not have any ring finals, because if the ring is broken then the circuit becomes 2 radials.


A figure-of-8 actually decreases the chances of a break leading to an overload potential.

Afigure of 8 (meaning a bridge somewhere in the ring) means we can not be sure to which extent the current will flow in every scenario of current draw at any particular times .
The other meaning for figure of 8 is the test we deliberately do on an unknown circuit to see if such bridges exist.

If a ring is designed properly then the loading during is its lifetime is meant to approximate that current draw will not be unduly imbalanced therefore both legs of the ring might be expected to draw very very approximately similar loads.
That is achieved by placing outlets around the ring and not bunched by load x time or by concentrating heaviest loads in the middle one third portion.

Nobody would go to great lengths to actually measure such and make calculations (except for research) but any half decent contractor would take a few mins to make a mental note and perhaps alter things slightly from first idea to make current draw more equal.

That`s the point of having a ring (along with volt drop and R1 + R2) considerations.
We try to avoid much beyond imbalance exceeding 20 to 12 amps on a 32A ring.

The point of this thread on this forum is one ring final circuit (not ring main that`s an incorrect term and applies to something else). One ring final circuit normally consiste of one ring connected at the fuseway.
My ramblings however show thay 2 rings (or more) connected as one ring final circuit are not unsafe and not non compliant but hey yes it is an unusual set up. Just because it is not shown in the OSG as a standard circuit does not make it become "wrong".

Take a spur (spur meaning a branch off the ring, not a S F C U or F C U - again wrong term).
We can spur anywhere off a ring with no more than one twin socket, at any point or at any JB or at the fuseway. That leaves us with a single bit of 2.5 T & E on a 30 or 32 amp fuse or breaker. it passes on short cct and earth fauly but not on overload, the overload protection is provided by the twin socket having a max rating of 13A and the plugtops each having a 13A fuse in making 26A possible (though unlikely) drawn.
Just a note that use of those little "Death Cubes" should be avoided as a rule of thumb ( Cheapo 13a adadaptors 2 way unfused as it means you could have a total of 4 x 13amp plugtops in a twin socket) they could be plugged in at any point on the ring or spur and are best avoided.

Actually, just to be a bit naughty - what is unsafe about a large number of radials, each one having not more than one twin socket and all connected by say one 32A MCB. Not actually unsafe proving the joints are reliable both electrically and mechanically and all volt drop and Zs are catered for.
I wouldn`t like to see it but it would not cause piles of dead bodies to litter the place.

 

[Soi disant]

If I start with this:

and add a loop like this:

or if I start with this:

and add a link across the middle to end up with the same figure of 8, which cable(s) become at risk of being overloaded that would not if I'd done this:

?


The more paths there are for current to flow to each point of loading the less flows in any given one, not more.

Ignoring the practical realities of actually wiring it, a "full mesh" topology of interconnections

would minimise the current flowing in every single cable (apart, obv, from the ones from the OPD to the "first" and "last" sockets, but those cables are never affected by any interconnection topology anyway).

And the more connections you have the harder it becomes to turn the circuit into radials, or to create multi-socket branches, by cutting connections.

 

[Mike Johnson]

Diagram 3 and 4 are the same, just one extra socket, what are you trying to prove? or diss-prove come to that?

 

[nicebutdim]

Diagram 3 and 4 are the same, just one extra socket, what are you trying to prove? or diss-prove come to that?

They should be viewed in the context of diagrams 1 and 2.

 

[Mike Johnson]

Then why are diagrams 3 & 4 there.

 

[nicebutdim]

That's explained in the text.

 

[Soi disant]

I've done the same in the past I must admit. In my own home. Not ideal, but as long as it is 2 small flexes and the cord grip secures them properly then not too bad.

Didn't Marbo (?) used to make a plug designed to take more than one flex?

 

[DPG]

Didn't Marbo (?) used to make a plug designed to take more than one flex?

That rings a vague bell, but not sure. Need to have a Google me thinks.

 

[ebee]

Soi disant,
Nice diagrams and well put.
Yes I like it.

Ok the point I was making.

With a bridge that makes a ring final become a "fig 8" it means that we tend to lose control of which leg gets more of the current x usage factor. A I said we don`t usually go to great lengths do control this however we do a quick approx to see if it looks badly slanted in favour of one leg or the other and then perhaps re-adjust our plan in order to balance it up a bit. This helps with heating issues and therefore aging of cables and helps reduce overloads of cables.

I`m not suggesting that fig 8 or indeed that lovely matrix thingy you drew for use is going to cause fires and threaten life everytime it`s used, far from it.

It is complicated enough to make predictions even with a well designed ring final and the fig 8/matrix complicates this further.
In reality, much of the time, no great problems should arise from it and if every ring final was done that way I don`t think we`d find streets littered with dead bodies.

However, of all the differing combinations of power drawn at various points around the ring then this arrangement is far more difficult to follow, calculate and therefore enjoy the most reasonable aspects of ring benefits as originally conceived for current flow considerations. It also makes it difficut to test properly too (OK that one can be said, to a degree, about the 2, 3, 4, umpteen rings on one ring final circuit too!)

 

[Soi disant]

It's testing which is the problem, I think. Without the predictability/consistency of readings from a proper, single, ring it's harder to spot problems such as multiple socket spurs.

But as for loading and balance - I won't mind if I prove myself wrong with some worked examples, (or if someone else does to save me the effort ?), but my initial feeling is that any cross-connections which make a figure of 8 or anything else just add current paths and thus lower the current flowing in them, not increase it.

I can sort of envisage a scenario where a section near the origin of the ring could become unbalanced, but I'm not sure how improbable it is. Need to do some sketches.

Anyone out there with circuit design software which could be used to analyse different scenarios?

 

[Pete999]

It's testing which is the problem, I think. Without the predictability/consistency of readings from a proper, single, ring it's harder to spot problems such as multiple socket spurs.

But as for loading and balance - I won't mind if I prove myself wrong with some worked examples, (or if someone else does to save me the effort ?), but my initial feeling is that any cross-connections which make a figure of 8 or anything else just add current paths and thus lower the current flowing in them, not increase it.

I can sort of envisage a scenario where a section near the origin of the ring could become unbalanced, but I'm not sure how improbable it is. Need to do some sketches.

Anyone out there with circuit design software which could be used to analyse different scenarios?

Not really other than it's not called a ring main a ring main is a distribution circuit it's ring final circuit if you get your terms correct you may get some better responses

 

[telectrix]

If I start with this:

View attachment 84116

and add a loop like this:

View attachment 84117

or if I start with this:

View attachment 84118

and add a link across the middle to end up with the same figure of 8, which cable(s) become at risk of being overloaded that would not if I'd done this:

View attachment 84122

?


The more paths there are for current to flow to each point of loading the less flows in any given one, not more.

Ignoring the practical realities of actually wiring it, a "full mesh" topology of interconnections

View attachment 84124

would minimise the current flowing in every single cable (apart, obv, from the ones from the OPD to the "first" and "last" sockets, but those cables are never affected by any interconnection topology anyway).

And the more connections you have the harder it becomes to turn the circuit into radials, or to create multi-socket branches, by cutting connections.

youneed to get out more. don't the pubs open soon?

 

[Dustydazzler]

Ringadingadong

 

[Pete999]

youneed to get out more. don't the pubs open soon?

If you are referring to me Tel, then nothing gets up my snout more than Wannbee's quoting something they know little or nothing about post ban waiting, still no one likes the truth these days do they?