Radials V Ring mains

[Grant1987]

If you have a fault on a radial circuit when you locate the fault let’s say out of the 8 sockets on the circuit 4 of them work after finding the faulty leg. What does that mean then to get the other 4 working? Replacing the faulty leg which means no quick fix and involves replacing the damaged leg which in turn means more disruption for customer cost and time

 

[Grant1987]

If you have a fault on a radial circuit when you locate the fault let’s say out of the 8 sockets on the circuit 4 of them work after finding the faulty leg. What does that mean then to get the other 4 working? Replacing the faulty leg which means no quick fix and involves replacing the damaged leg which in turn means more disruption for customer cost and time

And that is hoping that the fault lays between 4th and 5th socket of circuit if it’s between 1st and 2nd then 7 sockets would be down so the radial would cause a far greater issue than if it was a ring 1 faulty leg doesn’t cause power to go down do you see the logic?

 

[Simon47]

vs fault in ring which never gets noticed - leaving two radials that aren't properly protected, unless you can come up with an interpretation of the regs that allows a radial in 2.5 T&E protected by a B32 or even C32. This can go on for many years, lets face it, not many people have EICRs done regularly - if ever
We know what the real reason for the introduction of the RFC was - saving copper when it was in short supply. It's stayed around because it clearly still works for a very large number of installations - and it still uses less copper than two radials for comparable load capability and volt drop.
Personally I'm ambivalent about the choice.

 

[Simon47]

And that is hoping that the fault lays between 4th and 5th socket of circuit if it’s between 1st and 2nd then 7 sockets would be down so the radial would cause a far greater issue than if it was a ring 1 faulty leg doesn’t cause power to go down do you see the logic?

So I take it then that you always wire light circuits as rings ? Surely having working lights is far more important (safety for lights vs convenience for sockets) than having working sockets.

 

[Grant1987]

vs fault in ring which never gets noticed - leaving two radials that aren't properly protected, unless you can come up with an interpretation of the regs that allows a radial in 2.5 T&E protected by a B32 or even C32. This can go on for many years, lets face it, not many people have EICRs done regularly - if ever
We know what the real reason for the introduction of the RFC was - saving copper when it was in short supply. It's stayed around because it clearly still works for a very large number of installations - and it still uses less copper than two radials for comparable load capability and volt drop.
Personally I'm ambivalent about the choice.

Sorry for late reply, what do you mean interpret regs that allows radial on 32A Mcb? Obviously when you locate the fault you leave both ends of the faulty leg disconnected at both sockets and then split the ring at the consumer unit and put each leg onto a 16A or 20A Mcb.
I also understand your point of the introduction of ring mains was to save copper but I said ONE of the main reasons to install ring mains is to then limit disruption in the event of a fault meaning once the fault is located the customer can have all sockets powered back up on 2 x radial circuits to limit disruption without having to lift carpets, laminate floorboards etc.. and save on time and money on customers side.

 

[Grant1987]

So I take it then that you always wire light circuits as rings ? Surely having working lights is far more important (safety for lights vs convenience for sockets) than having working sockets.

Also in response to this the topic isn’t lighting circuits and I’ve never seen a lighting circuit wired as a ring have you? Of course lighting is essential as is sockets but if you want to compare “safety for lights vs convenience for sockets” what if the customer loses power to downstairs sockets or kitchen sockets and then plugs appliances into an extension lead which is plugged into another extension lead and plugs in her kitchen appliances surely that’s dangerous. Where as if the customer did have a fault on lighting and few were out maybe a couple of lamps plugged into sockets could be a solution which is safer?

 

[EricMark]

Design current for circuit Ib is the big question. For a ring final we are told to consider 20 amp at centre and 12 amp even spread, so Ib = 26 amp. Do same with 20 amp radial and Ib = 20 amp.

So permitted length of 2.5 mm² with ring final is 106 meters, but with a 20A radial it's 32 meters, so it does become a little limiting.

OK limit is due to volt drop, and many seem to ignore volt drop, and we don't seem to bother measuring volt drop. Easy enough to measure loop impedance or PFC at DNO supply and centre/furthest socket allows us to enter readings in my case in a java script program and see length of cable used and volt drop.

But not so easy without software DNO line - neutral 0.35Ω and centre of ring final 0.94Ω and step one is work out corrected corrected mV/A/m which works out at 16.5197278911565. However clearly our meters don't measure that accurate, so I make it 11.4651650917593 volt drop and 106.773644469205 meters, where it gets interesting is when you start looking at errors in measuring so we may really have 0.34 to 0.36Ω and 0.93 to 0.95Ω so the volt drop is really between 11 and 11.8 volt allow for meter error then 0.02Ω each way, so 10.7 to 12.2 volt drop.

So even if I measure potential volt drop with an EICR it would be hard to say the installer got it wrong until the volt drop exceeds 15 volt. So in real terms we only measure volt drop when some thing has gone wrong.

However since ring final limit is 106 meters and a role of cable is often 100 meters easy enough to measure when installing. And unlikely to exceed in most houses, but 32 meters is another story, easy enough to exceed that.

As to splitting into circuits to "reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation." Often we don't even have a RCD per circuit, and I would say with RCBO's it is unlikley you will get unwanted tripping even with a 32A ring final.

So for those who think radials are better, the big question is do you measure the amount of cable or volt drop? If not then forget it, as you simply don't know if your radial complies anyway.

 

[Simon47]

Sorry for late reply, what do you mean interpret regs that allows radial on 32A Mcb? Obviously when you locate the fault you leave both ends of the faulty leg disconnected at both sockets and then split the ring at the consumer unit and put each leg onto a 16A or 20A Mcb.

I think you've answered your own query there. IF you carry spare MCBs for every make of CU in your van, AND every CU has a spare way, AND the wires are long enough, then you can quickly lash up two 16 or 20A radials. But the way your suggestion was written, it formed an image (for me at least) of just disconnecting the faulty cable and leaving two radials on a 30/32A fuse/breaker.

Also in response to this the topic isn’t lighting circuits and I’ve never seen a lighting circuit wired as a ring have you?

That was my point - lighting is "quite important" but I've yet to see any suggestion that we should use rings for lighting to cater for the ability to convert it to two radials in order to quickly isolate a fault.

... what if the customer ...

Ah, the "what if ..." argument. You can use "what if ..." to argue for almost anything "What if ..." is actually a pretty good argument against RFCs, "what if ... there's a break in the RFC, and near one end ?" You've now a significant chance of Zs going over limits to guarantee prompt tripping of the OPD under fault conditions, and you've now a radial wired in 2.5 and protected by a B32 or even C32 - but the user doesn't know there's anything to investigate because "stuff still works". As already pointed out, with a radial, stuff will stop working - unless it's the CPC, in which case ...
So very much, 6 of one, half a dozen of the other

 

[rolyberkin]

It's Friday evening, is nobody drinking beer?

 

[Grant1987]

I think you've answered your own query there. IF you carry spare MCBs for every make of CU in your van, AND every CU has a spare way, AND the wires are long enough, then you can quickly lash up two 16 or 20A radials. But the way your suggestion was written, it formed an image (for me at least) of just disconnecting the faulty cable and leaving two radials on a 30/32A fuse/breaker.

That was my point - lighting is "quite important" but I've yet to see any suggestion that we should use rings for lighting to cater for the ability to convert it to two radials in order to quickly isolate a fault.

Ah, the "what if ..." argument. You can use "what if ..." to argue for almost anything "What if ..." is actually a pretty good argument against RFCs, "what if ... there's a break in the RFC, and near one end ?" You've now a significant chance of Zs going over limits to guarantee prompt tripping of the OPD under fault conditions, and you've now a radial wired in 2.5 and protected by a B32 or even C32 - but the user doesn't know there's anything to investigate because "stuff still works". As already pointed out, with a radial, stuff will stop working - unless it's the CPC, in which case ...
So very much, 6 of one, half a dozen of the other

Yes I totally understand what you’re saying I’m only speaking from own personal experience with rings vs radials on domestic properties and of all the call outs to faults some late late at night I found the properties with rings meant the least disruption because I could then at least provide power to all sockets apart from some poor electrical installation properties DIYers I would obviously weigh the options up with regards to load on either radial circuits it’s a different scenario at every property and only us as qualified electricians make the best choice and right choice.

 

[Simon47]

... only us as qualified electricians make the best choice and right choice.

Would that be better phrased as "experience, skill, and a logical thought process (and the ability to comprehend BS7671)" allows people to make the best choice ?
I've seen plenty of stuff done by supposedly qualified people (in various fields, including electrical) that proves that qualifications absolutely do not guarantee doing things right. Gets all trades a bad reputation Conversely I've seen work by many a person without "qualifications" which puts many a qualified pro to shame.
Sadly, these days it more about "pieces of magic paper" than "ability to do the job"

 

[Grant1987]

Would that be better phrased as "experience, skill, and a logical thought process (and the ability to comprehend BS7671)" allows people to make the best choice ?
I've seen plenty of stuff done by supposedly qualified people (in various fields, including electrical) that proves that qualifications absolutely do not guarantee doing things right. Gets all trades a bad reputation Conversely I've seen work by many a person without "qualifications" which puts many a qualified pro to shame.
Sadly, these days it more about "pieces of magic paper" than "ability to do the job"

Yes your English vocabulary is far better than mine evidently but I’ve only stated from my own personal experience, skill, logical thought process why I believed a ring was better than a radial. Yes it’s all too easy to get “qualified” without the on site experience and aslong as you have money to pay for the course you’re pretty much sorted.

 

[Peatbog]

I haven't used a RFC for years! Separate 16 or 20 amp radials to each room for me. Several radials in a kitchen. All connected to double pole rcbos.

 

[Spoon]

I haven't used a RFC for years! Separate 16 or 20 amp radials to each room for me. Several radials in a kitchen. All connected to double pole rcbos.

Welcome to the forum mate.
So in a typical 3 bedroom house in France, how many circuits are you looking at if it's all radial?

Your location says 'Surrey' but your flag is France. That's why I put France in my post.

 

[Pete999]

I haven't used a RFC for years! Separate 16 or 20 amp radials to each room for me. Several radials in a kitchen. All connected to double pole rcbos.