Spurs off spurs

[soulman]

Hi, i have come across a situation where there are spurs off spurs from a rfc, quite a few spurs. so we have a ring with radials coming from it. I am going to connect everything up and reinstate the ring as this is all in dado trunking it shouldn't be too difficult. I have across this before and made two radials fed from a 20a breaker. however it has been suggested that i could put a 20a breaker (as long as the loading is o.k) and leave the ring with spurs as the 20a will protect the cable. Just something tells me this is not correct.

Cheers

 

[Theorysparky]

why do you think its incorrect ????

not ideal but the cable is protected and thats the concern in this instance...

 

[soulman]

It's just in the past when we have come across a broken ring, we removed the faulted cable from the circuit and split it into two radial even if it was on the upstairs circuit where loading was low. Rather than just banging in a 20a breaker and leaving it as is. i suppose the faulty section of cable has to be removed so this is what is probably confusing me.

 

[OnOff]

Could you not feed the spurs off a 13A FCU where it comes off the ring? Appendix 15 in the big red book? (Not got the green one).

 

[Steve3948]

If you've split the ring and put 20A Mcb on each radial, why would you bother with FCU.

 

[Theorysparky]

if you have the fcu then surely you are limity the loading unnecessarly

 

[OnOff]

I read the OP that it was STILL a ring and YET to be split into radials hence the suggestion to put the spurs on FCUs. Is this in T&E BTW? I would check also if the spur sections have been done in 1.5mm. Go putting them on a 20A breaker and you could be getting into current carrying capability issues.

 

[ajkend]

As long as the cable is 2.5mm and not installation method 101 or 103 (pg265 brb) then 20a mcb ok

 

[steptoe]

you may even get away with a 25A ring.......

 

[PC Electrics]

Some makes do 25A MCBs. So as long as it's method C...........

 

[soulman]

Cheers for replies, it just didn't seem correct that the ring with spurs off spurs could just be put on a 20a or 25a. I will correct the ring however as i need to add an extra six sockets into it.

 

[springcrocus]

Cheers for replies, it just didn't seem correct that the ring with spurs off spurs could just be put on a 20a or 25a. I will correct the ring however as i need to add an extra six sockets into it.

On a lightly loaded ring, it can sometimes be advantage to leave it as a ring and drop the breaker size. If one of the spurs is approaching the limits of its Zs, then the parallel earth paths created by the ring section will give a lower Zs than the single earth path created by splitting into two radials. This assumes, of course, that everything else complies e.g no 1.5 T&E as mentioned by onoff in post #7.

 

[PC Electrics]

Volt drop will remain lower too, if you keep it as a ring rather than splitting it up.

 

[SLIPSHOD & SLAPDASH]

On a lightly loaded ring, it can sometimes be advantage to leave it as a ring and drop the breaker size. If one of the spurs is approaching the limits of its Zs, then the parallel earth paths created by the ring section will give a lower Zs than the single earth path created by splitting into two radials. This assumes, of course, that everything else complies e.g no 1.5 T&E as mentioned by onoff in post #7.

Why not split the L & N and keep the earth as a ring

 

[Mark2spark]

Reading it through, I think the suggestion might have been to put a FCU at the point that the radial starts, and then you could keep it as a 32A ring?

 

[Technician]

I nearly started a new thread on this but thought better of it.

Has anyone read the article in the free magazine on Ring/

Radial Hybrid circuits and what are your views. I am still

examining it but the first thing that jumped out at me was a

possibility of someone actually doing this as a new install,

rather than doing it (as the writer states) when a pre-existing

conductor is present and could be used without installing a

ring main in full as per appx.15.

 

[PC Electrics]

I haven't read the article in detail yet. I can see the advantage in a 'retrofit' situation, ie using a redundant shower or cooker circuit to provide sockets into a loft conversion or utility room for example.

It also occurs to me that one of the advantages of a ring is its "reach". A ring can reach out quite far to provide sockets in far rooms whilst alleviating the volt drop problems of long radials. The careful use of a 6 or 10mm radial section could potentially be used to provide a ring with even more reach for rooms that are far from the CU. This is very much "thinking aloud" and I haven't looked at the engineering aspect at all yet.

I'll come back to this later as I've got to go now.

 

[roys]

Did we not call this a 'lollipop' circuit in a previous thread about a year ago? Old cooker or shower feed used to feed the start of a ring circuit, I like that descriptive word

 

[OnOff]

I haven't read the article in detail yet. I can see the advantage in a 'retrofit' situation, ie using a redundant shower or cooker circuit to provide sockets into a loft conversion or utility room for example.It also occurs to me that one of the advantages of a ring is its "reach". A ring can reach out quite far to provide sockets in far rooms whilst alleviating the volt drop problems of long radials. The careful use of a 6 or 10mm radial section could potentially be used to provide a ring with even more reach for rooms that are far from the CU. This is very much "thinking aloud" and I haven't looked at the engineering aspect at all yet.

I'll come back to this later as I've got to go now.

Not forgetting the fun you'll have getting the bigger size cables into the cr@ppy V***x, flat plate, black, double sockets the wife insisted on having "Cos, they look nice!".

 

[ProDave]

Not forgetting the fun you'll have getting the bigger size cables into the cr@ppy V***x, flat plate, black, double sockets the wife insisted on having "Cos, they look nice!".

Spent all day fitting those today.

Some of them are not sitting flat to the wall, because Mr plasterer seems to have left curves in places. I did warn the customer you need perfect plastering to get away with those.

Yes it was this forum that came up with the name Lollipop circuit when I came across one over a year ago. there was some debate if it met regs or not then. One of those situations where it doesn't explicitly say you can, but neither does it say you can't.