Ring or Radial

[dingbat]

Rings are best if correctly installed and maintained.

OK in a factory 3 electricians all know each others and have a degree of trust in each others work. But domestic and you haven't a clue who the last guy was and are you going to stake your reputation on his report no way.

So in a firm with in house electricians ring final circuits [are] fine.
But in a poorly maintained domestic premises forget it. Use radials.

Maybe in rented property where it is all tested on regular basis by in house electricians employed by land lord it may work! Like for example the county council! Oh sorry I've seen them houses, forget it stick with radials?

Yeah, but, no, but...

(All of this ignores the fact that the ring final circuit, as beloved by many ancient electricians, was only ever introduced as a [poorly thought-out and never completely analysed] solution for a problem that did not exist in the first place in the design of post-war council houses. Ring final circuits - being incorrectly applied for the last 64 years!)

 

[ban-all-sheds]

Can you please show me where it states ( not implies ) that a ring final with a 20 amp MCB is non -compliant.

433.1.5 explicitly caters only for 30/32A ring final circuits serving BS 1363 accessories using cable rated at no less than 20A and where the intended use of the circuit won't result in any section being overloaded.

So your 20A ring will not meet the requirements of 433.1.5, you don't have a recognised ring final you've got a circuit with parallel conductors and you'll need to consider Group 433.4, 434.4 and 532.8.

And even then that still doesn't deal with the fact that you're negating the whole raison d'etre of ring finals.

They exist solely to allow the use of a cable rated at less than the breaker - take that away and you've made the whole thing pointless.

Please quote the words or provide a link to where it can be read.

AFAIK There are no places where the regs can be read online and I've got better things to do than type out several paragraphs of them because you can't be bothered to buy a copy.

 

[ericmark]

433.1.5 Accessories to BS 1363 may be supplied through a ring final circuit. With or without unfused spurs, protected by a 30 A or 32 A protective device complying with BS 88-2.2. BS 88-6. BS 1361. BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1 (RCBO). The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5 mm² except for two-core mineral insulated cables complying with BS EN 60702-1, for which the minimum cross-sectional area is 1.5 mm². Such circuits are deemed to meet the requirements of Regulation 433.1.1 if the current-carrying, capacity (Iz) of the cable is not less than 20 A and if. under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed for long periods the current-carrying capacity (Iz) of the cable.
433.1.1 The operating characteristics of a device protecting a conductor against overload shall satisfy the following conditions:
(i) The rated current or current setting of the protective device (In) is not less than the design Current (Ib) of the circuit. and
(ii) the rated Current or current setting of the protective device (In) does not exceed the lowest of the current-carrying capacities (Iz) of any of the conductors of the circuit, and
(iii) the current (I2) causing effective operation of the protective device does not exceed 1.45 times the lowest of the current-carrying capacities (Iz) of any of the conductors of the circuit.
where:
lb is the design current for that circuit
Iz is the current-carrying capacity of the conductor (See Section 523 for cables, Appendix 8 for busbar and powertrack systems. Regulation 433.1.3 for semi-enclosed fuses and Regulation 433.1.4 for buried cables.)
In is the rated current or current setting of the protective device
I2 is the current ensuring effective operation of the protective device in the conventional time.
For adjustable protective devices, the rated current (In) is the current setting selected.

The Current (I2) ensuring effective operation of the protective device is given in the product standard or may be provided by the manufacturer.
NOTE 1: Where overload protection is provided by BS 3036 fuses, refer to Regulation 433.1.3.
NOTE 2: Protection in accordance with this regulation may not ensure protection in all cases, for example, where sustained overcurrents less than I2 occur.

Reading the above with a ring final circuit supplied by a 20A overload device then the requirements are met without needing to apply the special conditions listed in 433.1.5 so no reason to quote 433.1.5.

433.4.2 Unequal current sharing between parallel conductors
Where the use of a single conductor is impractical and the currents in the parallel conductors are unequal, the design current and requirements for overload protection for each conductor shall be considered individually.

Point is of course a single conductor is Not impractical as it does not need two in first place.

It also says:-
(ii) For two conductors in parallel, a fault current protective device shall be provided at the supply end of each parallel conductor.

Not sure I like that idea?

Plus:- 433.4 Overload protection of conductors in parallel
Where a single protective device protects two or more conductors in parallel there shall be no branch circuits or devices for isolation or switching in the parallel conductors.

Now this is really getting complicated are you sure it is worth it all?

560.6.8 goes further into duel supplies and it does get some what involved. I really can't see the point of a 20A MCB on a final ring except where spurs on spurs have been added and one as a temporary measure wants to stop overloading.

The hoops one needs to jump through do make it hard to be certain it complies.

The running of cables through insulation which has down graded the current carrying capacity of the cables is another problem area as the design current (That's different from max current) is taken as 26A so fitting a 25A MCB if you can find one does very little to help.

The same when the volt drop is two high again 25A to 26A is nothing so does not help.

I have where the ELI was above 1.44 ohms in the past before we had RCD's on everything reduced the MCB from 32A to 25A but again here we are trying to improve a bad situation and I would hope no one by design installs ring mains with the ELI or Volt Drop too high.

Splitting a ring final circuit into 2 radials is a problem as because of volt drop the amount of cable in a ring can be much more than used in two 20A radials so really it is a temporary cure only until the real fault is found.

But there are times when had it not been a ring circuit then a potential dangerous situation could have arose.
What comes to mind is where one guy does first fix and second guy does second fix. I have tested the ring to find incomplete. And after investigation found the plaster has plastered over one of the sockets. Hammer through plaster in a few places and it was found and connected up together with a few words between plaster and electrician which can't be repeated on here.
However if it had been radials then there could have been live cables without any indication they existed hidden in the wall.

But with the problems of RCD's tripping and wanting to spread the leakage of IT devices across an number of RCBO's then today the radial has become a far better option.

OK we could use a ring final circuit using Ali-tube cables and all RCD sockets. Yes and we are really going to do that? Would be good method I agree but the cost!

So I think we will see a move to the radial. And then no longer is there a problem with spurs on spurs and many of the other DIY introduced faults.

 

[PrinceofDarkness]

I note that the O/P has taken no further part in this, his thread. This is hardly surprising when he's had to wade through such irrelevant nonsense as airport runway lights, NICEIC versus IET and forum infighting - when all along he only required a little advice on his simple domestic garage installation.

Some of those points might be relevant in another thread on another day, but it seems to me that members here have forgotten their manners in not addressing the O/P directly.

Lucia.

 

[1john]

Lucia, i think his queries were covered before the end of page 1 although things have slightly got out of hand and into far more technical debates that a DIYer would ever want to read about, it has been an interesting thread.

 

[PrinceofDarkness]

Yes, 1john, I wouldn't dispute that - but it's hardly easy-reading for the O/P, is it?

Happy New Year to you......


Lucia.

 

[1john]

Some of the posts haven't been easy reading for me!!

Happy new year to you also

John

 

[bernardgreen]

Some of the posts haven't been easy reading for me!!

It appears to me that the complexity of designing, correctly installing and then testing a ring final circuit compared to the apparent simplicity of radials is a major factor influencing installers to prefer radials.

My penultimate comment on this matter is that the apparent simplicity in the design and installation of a radial final circuit compared the to perceived complexity in designing and testing a ring final circuit has taken preference over the other differences between the two methods when they come into use after the installation has been completed and signed off.

My final comment is that it is a pity that a large area of electrical "engineering" is being dumbed down to remove the requirement to have a working knowledge of electrical theory when installing or testing electrical installations.

 

[mikhailfaradayski]

Hi Bernard,


Just before you leave this thread to die, i just wondered if you would satisfy my curiosity as to how you actually test your 20A RFC?

Do you do the three step test and give Zs as the result of Ze+(R1+R2/4)?

How do you note this on your EICs?

I would think that at the least , you would need to include this as a special note as it isn't a common arrangement to expect to find from the perspective of a new domestic install. ( a remedial solution to 'make safe' a previously bodged DIY attempt, sure )

I personally think that there is no complexity involved in designing and correctly installing a standard RFC. Anyone who cannot correctly do this should really be questioning their own ability and future as an Electrician.
However, its my belief that the reason rings were introduced is old hat and redundant. They are more prone to post-installation abuse by an unskilled DIYer, which can render them unsafe (based on a standard RFC as mentioned in the BRB)

That said, just because i find them simple to work with, it doesn't mean that i favour them as a design solution in a modern installation. (never say never, just that i do not prefer them)

 

[ericmark]

I note that the O/P has taken no further part in this, his thread. This is hardly surprising when he's had to wade through such irrelevant nonsense as airport runway lights, NICEIC versus IET and forum infighting - when all along he only required a little advice on his simple domestic garage installation.

Some of those points might be relevant in another thread on another day, but it seems to me that members here have forgotten their manners in not addressing the O/P directly.

Lucia.

In some ways I agree with you. However it does highlight one of the main problems with anyone doing electrical DIY work. A little knowledge is dangerous. All too often people and that includes both the DIY guy and time served guy (or girl), do work without being able to inspect and test the work undertaken. Either because of lack of equipment or knowledge.

The question is do we make it simpler so those without tools or knowledge can do it without causing too much risk. Or do we select the best method to do the job and ignore those who don't understand?

For a garage supply I would consider a radial as being best method so really in this case it does not matter which attitude we adopt.

However to stop using rings because some people don't understand them is like reducing the speed limit because those who break the limit crash.

DIY wise the big problem is test equipment and even electricians specially those who normally work in house on maintenance often do not have loop testers, RCD testers and the 500v ohm meters or 200ma ohm meters. And for the DIY guy even if he had them would he understand what readings to expect?

We have to do a balancing act. Enough to improve safety but not enough to encourage people to take chances.

It is these debates that show the DIY person electrics is not easy and there is no best way.

 

[mikhailfaradayski]

agree with both Lucia and Ericmark,

To Lucia,

Im sure the OP has lost interest, this thread has gone from 'please help with my garage' to the repetitive ring Vs radial arguement.
Personally, i feel that as long as ring circuits are a permitted installation method, you will see this sequence repeat itself time and time again.

To Eric mark,

The 'little knowledge is a dangerous thing' is smashing the nail right on the head!!

I wonder how many electricians reading this have not heard homeowners/budding DIYers referring to virtually any circuit as a 'ring main'?
The amount of times you can see a customer's eyes light up when they start telling the electrician about how he/she is aware about 'rings' -
plugsocket [sic] rings, lighting rings, cooker rings, shower rings
-oh gawd, give me strength!
-after all, us electricians are usually nothing more than half-witted charlatans whos sole aim in life is to baffle and confuse the average joe into parting with a lot more cash than average joe thinks the job is worth. Arn't we ??

It just highlights how something so simple to a real electrician can be utterly mystifiying to a DIYer, but the situation will un-doubtedly continue for years and years

-Just as a side note, i recently had an old timer, long since retired, tell me that the £25 RCD unit i was fitting for his 'shower ring' was too expensive as he knew that a spring cost just a few pence? FFS!. But as a works engineer back in the 50's and 60's (with certificates to prove it, he showed me - All of them, pfft.) coupled with being the customer, how could i tell him that he was talking out his poopa?

 

[bernardgreen]

Hi Bernard,
Just before you leave this thread to die, i just wondered if you would satisfy my curiosity as to how you actually test your 20A RFC?
Do you do the three step test and give Zs as the result of Ze+(R1+R2/4)?
How do you note this on your EICs?

For the three full domestic installs that I have carried out the owners and the the technical people in the insurance companies concerned were happy to accept the documents of design and test results I provided.

A fourth install was my own self build house in 1980. Again this was approved even though "standard" procedures were not followed.

My testing procedures are based on the application of my electrical knowledge and my experience of installation errors that may not be detected by "standard" test processes


That is NOT a suggestion that DIY workers should try to avoid standard procedures.

 

[mikhailfaradayski]

with the greatest of respect Bernard, thats nothing like an answer, it was more like a politician's 'lets move on to the next question' kind of deflection.

When you have filled out your EIC with the details of your non-standard RFC, how do you make note of that for the next electrician (which may not necessarily be you) so that he/she is aware of this circuit arrangement.

The reason i ask is that if there is nothing on your EIC to say 'this is a 20A RFC, please treat it/test it as such' then whats to stop the next electrician from seeing two sets on cable tails entering something other than a 32A, thinking its 2 legs of a radial stuffed into one mcb, then being a good type, considering reg314.1 and subsequently removing one of the 'radial legs' and putting it into its own 20A mcb?

From your last post, does this mean that the last time you wired a domestic property was in 1980? Again, with the greatest of respect, there have been a number of changes to the regs since then, times have changed

You are not required to follow standard circuit arrangements or testing procedures, but i believe that if you don't, you should at least be able to provide details of what you have done, so proving that your arrangements provide no less a level of safety as set out in our BRB

 

[martinxxxxxx]

thinking its 2 legs of a radial stuffed into one mcb

Sounds like an oxymoron to me

Surely he would assume it is a spur at the CU?

 

[mikhailfaradayski]

Hi Martin,
That may be true, my curiosity is really focussed on how Bernard records his installation for the benefit of others, and how he actually tests and notes a value for ELI for a non-standard RFC

Assumptions are not good and should not (in an ideal world) be necessary for an electrician. So your assumption of what another assumption may be, i would assume that this may be correct, but someone else may assume something different, i would assume

Also, if it were assumed to be a radial with a spur at the cu and the inspecting spark used a live Zs test at each socket outlet, do you think he may be a little concerned/confused to find that the Zs at each socket was substantially the same, as opposed to varying along its length as you would expect to find on a standard radial?