Crossover in ring circuit

[KeenPensioner]

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.

 

[DPG]

Sorry I thought you wanted to remove a dumb rating that you had made.

 

[KEV 1 N]

About time ring circuits are banned....just a nuisance IMO in terms of testing, finding faults.
I remember reading somewhere that the ring main(as it was called then) came about after the 2nd world war when copper was in short supply, so the ring circuit was utilised, as prior to that they used radials.....and aren't we the only country to use them?

 

[kingeri]

About time ring circuits are banned....just a nuisance IMO in terms of testing, finding faults.
I remember reading somewhere that the ring main(as it was called then) came about after the 2nd world war when copper was in short supply, so the ring circuit was utilised, as prior to that they used radials.....and aren't we the only country to use them?

I couldn't disagree with you more. Ring finals are a very versatile circuit, when used in the right situation. Sure, I install more radials than I used to, but a 32A ring is often preferable to say a 32A 4mm radial, which you'd struggle to install in a compliant manner unless clipped direct through it's whole run. And we aren't the only country to use them! But even if we were, surely that's another reason to keep them. A Great British innovation.

 

[KEV 1 N]

I couldn't disagree with you more. Ring finals are a very versatile circuit, when used in the right situation. Sure, I install more radials than I used to, but a 32A ring is often preferable to say a 32A 4mm radial, which you'd struggle to install in a compliant manner unless clipped direct through it's whole run. And we aren't the only country to use them! But even if we were, surely that's another reason to keep them. A Great British innovation.

I was maybe a bit harsh in having them banned!
Yes there are situations where a ring circuit is better e.g. sockets in a long corridor or a large hall. I do a lot of EICRs in university buildings and sometimes there's dozens if not hundreds of RFCs that have maybe five or six sockets on them, usually 4mm and in dado trunking with the DB in the same room or close by, and I just think, surely they could have put in a 4mm radial. I guess I see them as more work compared to radials!

 

[elsparko]

Yes there are situations where a ring circuit is better e.g. sockets in a long corridor or a large hall. I do a lot of EICRs in university buildings and sometimes there's dozens if not hundreds of RFCs that have maybe five or six sockets on them, usually 4mm and in dado trunking with the DB in the same room or close by, and I just think, surely they could have put in a 4mm radial. I guess I see them as more work compared to radials!

nah, pull your 2 x T+E 2.5 cable to the last socket, then pull loops out at wherever you need them along the run, not much more effort than a radial

 

[KEV 1 N]

nah, pull your 2 x T+E 2.5 cable to the last socket, then pull loops out at wherever you need them along the run, not much more effort than a radial

Yeah it isn't much more work when installing, but when there's a 36way 3phase board with about 20 odd RFCs in it to test on an EICR, then after a while you get fed up of disconnecting the legs and fannying on with tyrapped cables

 

[elsparko]

Yeah it isn't much more work when installing, but when there's a 36way 3phase board with about 20 odd RFCs in it to test on an EICR, then after a while you get fed up of disconnecting the legs and fannying on with tyrapped cables

yea, especially when some dougnut has twisted the earths together all the way back then popped their sheath on, makes a 2 minute job take 5

ive never done student accom though so cant say ive ever come across that many rings on 1 board

 

[KEV 1 N]

yea, especially when some dougnut has twisted the earths together all the way back then popped their sheath on, makes a 2 minute job take 5

ive never done student accom though so cant say ive ever come across that many rings on 1 board

Ah yes two earths twisted in one sleeving.....thats the sign of an electrician who doesn't worry about the testing!
I do accommodation and academic buildings, the biggest EICR I did was the Engineering department, over 400 pages! And took about 8 weeks in total! It's a joy when they say you can't turn the sockets off.....great less for me to do and LIM in the boxes
The Chemistry department is even bigger, due next year...dreading it

 

[7029 dave]

The RFC is unique to the UK, IMO very clever system, and I hate it when guys moan about it, when testing faulting etc , you are all just lazy.

 

[KEV 1 N]

The RFC is unique to the UK, IMO very clever system, and I hate it when guys moan about it, when testing faulting etc , you are all just lazy.

Yes I am lazy! Anyway there's a night shift coming up soon to do an EICR in a large Uni office building......no RFCs.....it all radial circuits busbar trunking and floor sockets! Woohoo!

 

[elsparko]

Yes I am lazy! Anyway there's a night shift coming up soon to do an EICR in a large Uni office building......no RFCs.....it all radial circuits busbar trunking and floor sockets! Woohoo!

i thought i had it bad other day with a 25 circuit test split between 5 boards, any industrial/commercial i have done its been radials for the most part, and maybe a ring for the office area, rest is 3 phase machinery which is a doddle to test.

the effort they put into twisting the earths all the way back with pliers is probably more than it would take to individually sleeve them, at least i know when i leave a job nobody is going to be cursing my name when it comes time to replace anything lol

 

[Upton Sparks]

Ah yes two earths twisted in one sleeving.....thats the sign of an electrician who doesn't worry about the testing!

I know it infuriates me too! .

I pull a guy up on it once and he told me "it was because he didn't want to wast the Earth sleeving"....!!!!.???.!!!
It's £5 for a hundred meters!!!!!!
It's a shame he didn't have that concern with the Bloody Cable!!!!!......... I Wounder Why that is..

 

[elsparko]

I know it infuriates me too! .

I pull a guy up on it once and he told me "it was because he didn't want to wast the Earth sleeving"....!!!!.???.!!!
It's £5 for a hundred meters!!!!!!
It's a shame he didn't have that concern with the Bloody Cable!!!!!......... I Wounder Why that is..

sounds like if you asked some of these sparks to build you a square room you would end up with a sphere shaped room, cut all the corners

 

[Deleted member 26818]

Never actually bought sleeving.

 

[johnduffell]

it’s good practice [...] keeping the first 2 legs from the consumer unit short as possible

Actually not, in terms of imbalance, the reverse is true (although you still need to watch the Ze at the furthest point)
To illustrate I'll start with spinlondon's excellent example:

Ok.
If you have a ring that is 4m long with 3 sockets each 1m apart, the middle socket would have the same resistance on each leg. The other two sockets would have different resistance on each leg at a ratio of 3:1.
A 20A load connected to the middle socket would see 10A on each leg.
A 20A load connected to either of the other two sockets would see 15A on the short leg and 5A on the long.

Suppose we are worried about imbalance, so we shorten the two legs to the CU to 0.5m each.
The other two sockets would have different resistance on each leg at a ratio of 5:1.
A 20A load connected to the middle socket would see 10A on each leg.
A 20A load connected to either of the other two sockets would see 16.6A on the short leg and 3.3A on the long!

If you follow my suggestion and we make a loop of slack and extend the two legs to the CU to 2m each.
The other two sockets would have different resistance on each leg at a ratio of 3:2 i.e. 1.5:1.
A 20A load connected to the middle socket would see 10A on each leg.
A 20A load connected to either of the other two sockets would see 12A on the short leg and 8A on the long. Much better.

Hope this helps.