CU change - ring on end of radial

[SPECIAL LOCATION]

I would suggest provided some suitable documentation, circuit schedules, sketch or drawing is near to the fuse box so any person working on it can suss out how its wired..

then personally I reckon it cannot be much harder than figuring out a garage or shed ring circuit supplied off a single swa or similar running down the garden!

No worse than a lighting circuit where you don't know how they are all branched off?

Or a ring circuit with a whole bunch of spurs of it...

Bottom line:-

providing the Protective device will pop before the smallest cable in the circuit melts....

and that the furthest extreme of the circuit is within the max Zs for the protective device..

Then what exactly is UNSAFE???

 

[ianmacd]

I will repeat what I said in post #6.

Its NOT a ring, its a radial since it doesn't comply with the definition of Ring Final Circuit in Ch2 and also doesn't comply with 543.2.9 or 433.1.5.

It doens't comply, end of story but thats not to say its not safe.

 

[ianmacd]

Should you have a large shed you might take a feed out in 6mm and then fit a 2.5mm ring on the end. How is that any different?

That wouldn't comply either if the 6mm what part of the final circuit (i.e. has no protective device at the 6mm to 2.5mm 'loop'.

If it was treated as a 2.5 radial on the end and protected accordingly (say a 20A MCB) then that would comply as at the moment these 'lollipop' circuits do not comply with 433.1.1.

 

[Chr!s]

I will repeat what I said in post #6.

Its NOT a ring, its a radial since it doesn't comply with the definition of Ring Final Circuit in Ch2 and also doesn't comply with 543.2.9 or 433.1.5.

It doens't comply, end of story but thats not to say its not safe

Why?

it doesn't comply with the definition of Ring Final Circuit in Ch2

Ring Final Circuit.. A final circuit arranged in the form of a ring connected to a single point of supply.

In effect that's what we have?

We know its not a standard circuit, the first part is a radial the second part a ring, if you don't like the ring terminology, then perhaps you will be happier if we call it a parallel Final circuit, so radial to parallel.

Appenix 15 is informative and based on the IEE model( we are allowed to design our own circuits thats what the regs are for)

 

[spinlondon]

Is it okay to proceed with the CU change and just note this as a departure. While it's certainly unconventional, apart from not yet identifying and checking the junction box, I can't actually see anything unsafe about this.

No, you can't note this as a departure, as you did not install it.

You can however note it under comments on existing installation.

 

[binky]

It doens't comply, end of story but thats not to say its not safe.

If it's electrically safe then it complies with regs. Note findings on circuit for future reference and leave it like that. Probably find you get lower Zs readings than for a conventional ring.

Have found stuff like this several times - just makes form filling harder.

 

[ianmacd]

I will repeat what I said in post #6.Its NOT a ring, its a radial since it doesn't comply with the definition of Ring Final Circuit in Ch2 and also doesn't comply with 543.2.9 or 433.1.5.

It doens't comply, end of story but thats not to say its not safe

Why?

Why to which part?

Ring Final Circuit.. A final circuit arranged in the form of a ring connected to a single point of supply.

In effect that's what we have?

No and you contradict that with the next part anyway.

We know its not a standard circuit, the first part is a radial the second part a ring, if you don't like the ring terminology, then perhaps you will be happier if we call it a parallel Final circuit, so radial to parallel.

Call it what you want but its not a ring and therefore will not satisfy 433.1.1 using 433.1.5

It doesn't comply with 433.1.5, which part exactly?

Erm, its not a ring by your admission above.

543.2.9 Well the cpc of the second part(the ring/parallel circuit) is run as a ring, and both ends are effectively connected to the earthing terminal at the origin via that cpc of the 6mm(radial circuit).

The origin will be at the protective device not part the way along a final circuit.

Appenix 15 is informative and based on the IEE model( we are allowed to design our own circuits thats what the regs are for)

Where did I quote Apx.15?

I really wish you would learn to quote properly as it makes reading your posts harder.

 

[Chr!s]

Its NOT a ring, its a radial since it doesn't comply with the definition of Ring Final Circuit in Ch2 and also doesn't comply with 543.2.9 or 433.1.5.

Ok ill try again

We have a radial circuit which then converts to a parallel circuit AKA the Lollipop.

Call it what you want but its not a ring and therefore will not satisfy 433.1.1 using 433.1.5

Well if its not a ring why does it need to comply to 433.1.5?

therefore will not satisfy 433.1.1

Why wont it comply to 433.1.1?

 

[initforthemoney]

"A ring final circuit starts and finishes at the DB, where it is connected to a 30 or 32A protective device."

Cant get much clearer than that.

Plus, if this was an acceptable way of installing a RFC then im sure we would have seen it a lot more in many installations.

In fact, it would have been a breeze on this current rewire i am doing if this was the case.

What i am struggling to understand is why there are so many others on here that are/would be quite happy to install in this way.

Baffling.

 

[ianmacd]

Why wont it comply to 433.1.1?

433.1.5 allows a ring (which this is not) to comply with 433.1.1 (providing certain conditions are met) and without using 433.1.5 how can you justify using 2.5mm on a 32A MCB?

 

[Chr!s]

433.1.5 allows a ring (which this is not) to comply with 433.1.1 (providing certain conditions are met) and without using 433.1.5 how can you justify using 2.5mm on a 32A MCB?

But you say its not a ring so why does it need to comply with 433.1.5

 

[Chr!s]

how can you justify using 2.5mm on a 32A MCB?

Ian the cable is in parallel

We have 6mm then to 2.5mm in parallel with another 2.5mm, so the load it distributed between the two legs, using Kirchoffs law we can equate what current each leg will carry and ensure compliance with 433

 

[ianmacd]

Ian the cable is in parallelWe have 6mm then to 2.5mm in parallel with another 2.5mm, so the load it distributed between the two legs, using Kirchoffs law we can equate what current each leg will carry and ensure compliance with 433

They are not in parallel since its a lollipop.

 

[Chr!s]

They are not in parallel since its a lollipop

Ian if we have 10 amps being drawn down the 6mm cable when it gets to the junction of the ring/parallel circuit it will divide, some current will flow down both legs. how much will depend on where the load(s) are within the circuit.We use kirchoffs law to calculate the distributed loads.

 

[kme]

"A ring final circuit starts and finishes at the DB, where it is connected to a 30 or 32A protective device."Cant get much clearer than that.

Ok. But we`ve already accepted that it isn`t a "standard RFC".

Plus, if this was an acceptable way of installing a RFC then im sure we would have seen it a lot more in many installations.

I have.

In fact, it would have been a breeze on this current rewire i am doing if this was the case.

So why did you choose not to do so? Blind reliance on "the way it`s done"?

What i am struggling to understand is why there are so many others on here that are/would be quite happy to install in this way.

Simple. Because it is a compliant circuit. It is not a "standard circuit"; not a "ring circuit" - the regs do NOT preclude other circuit arrangements, if you read them.

Baffling.

Ah. We DO agree on something.

I`d like either Ian or yourself to demonstrate how this circuit fails to comply, please? Without using 433.1.5; which we`ve already negated.

KME

 

[ProDave]

I never meant to cause such argument.

I think we are all agreed the circuit is not a standard recognised circuit, so we should not be installing a "lolipop" circuit like this.

But just remember, I was only asking if it was safe to leave it like it is for a CU change.

I think most of us agree it is safe so it's fine to leave it alone and note the departure. Apart from not complying with regs, nobody has given a good reason why it is not safe. None of the conductors are going to be overloaded under any circumstances, so in my opinion it is safe (providing the junction when I locate it is adequate)

I've been at that house again today doing some more alterations, but still not located the junction from 6mm to the 2.5 ring, but then again I'm working downstairs at the moment, and expect to find the junction under the upstairs floorboards.

 

[kme]

I never meant to cause such argument.I think we are all agreed the circuit is not a standard recognised circuit, so we should not be installing a "lolipop" circuit like this.

WHY NOT??

But just remember, I was only asking if it was safe to leave it like it is for a CU change.

I think most of us agree it is safe so it's fine to leave it alone and note the departure. Apart from not complying with regs, nobody has given a good reason why it is not safe. None of the conductors are going to be overloaded under any circumstances, so in my opinion it is safe (providing the junction when I locate it is adequate)

But it IS compliant with BS7671. No-one has provided ANY reg that is doesn`t comply.

I've been at that house again today doing some more alterations, but still not located the junction from 6mm to the 2.5 ring, but then again I'm working downstairs at the moment, and expect to find the junction under the upstairs floorboards.

I wouldn`t be unduly worried, TBH. If the readings are right - what is the issue???

 

[ianmacd]

Ok. But we`ve already accepted that it isn`t a "standard RFC".I`d like either Ian or yourself to demonstrate how this circuit fails to comply, please? Without using 433.1.5; which we`ve already negated.

KME

I would challenge you to prove it passes 433.1.1 without using 433.1.5

 

[initforthemoney]

Ok. But we`ve already accepted that it isn`t a "standard RFC".

Exactly and so therefore this is not a RFC or a radial. If fact its neither.

Where in the regs does it say that this is an acceptable method of circuit design?

I have.

That i dont doubt.

So why did you choose not to do so? Blind reliance on "the way it`s done"?

I chose to install a circuit recognised in BS7671.

Simple. Because it is a compliant circuit. It is not a "standard circuit"; not a "ring circuit" - the regs do NOT preclude other circuit arrangements, if you read them.

Indeed, plus it doesnt recognise a RFRC either.

I`d like either Ian or yourself to demonstrate how this circuit fails to comply, please? Without using 433.1.5; which we`ve already negated.KME

Tell you what, lets put this another way, point out a page or reg from any book that recognises this type of circuit arrangement.

 

[Lurch]

Tell you what, lets put this another way, point out a page or reg from any book that recognises this type of circuit arrangement.

What you mean is you can;t find anything to prohibit it?

BS7671 is not a definitive reference to every exact scenario and combination of circumstances ever thought to be possible. It is a guide.