: > : > :>
: > :> Oh, so taking out just a room rather than a floor (as is : > usual : > :> with a ring circuit) is worse?! : > : : > : Oh so taking out a room, rather than just the plug fuse for the : > : appliance in question is better? : > : : >
: > No, but we were talking about faults that DO trip the D-board : > protection, that said it is FAR better just to take out one room : > than a whole floor/all power in the dwelling. : : Indeed, the whole principle of discrimination is to isolate power as : close as possible to the fault location - and affect the fewest possible : other circuits. The plug fuse is the best currently used example of this : - for the vast majority of faults in an appliance or its flex it will : limit the isolation to just that one device.
In the perfect world, in the real world it's a gross over simplification, especially in these days of RCD protected circuits!
: : > :> introduced, now the ring has just become the day-facto : > standard : > :> and is often installed without (prior) thought. : > : : > : Given it has proved its versatility and safety, then that is : > probably a : > : good thing. : >
: > But radials were also common in the 1950s, they were (and where : > they still exist, are) safe, most will have had modern sockets : > fitted and as such have the one advantage (local/final protection : > of the appliance) of the BS1363 plug but without the possibility : > of gross abuse that is possible when used on ring circuits. : : Radials were common in the 50s, but most were wired with rubber sheathed : cable that is typically getting into a poor state now.
A straw man comment if ever! How does that effect the safety or otherwise when comparing the merits of radial and ring circuits considering that, as you yourself IIRC pointed out, many radial circuits from the 1950s were converted (without any change of cable) into ring circuits in the late 60s and 1970s, thus many of those circuits will also be showing the same insulation faults.
Thye fundamental : problem is that the circuits were sized to support usually no more than : 4 or 5 single sockets. Hence they have usually been extended way beyond : a sensible level by now.
Err, how can they, unless someone replaces the original fuse, the same problem could exist on a ring circuit too, try using four or five 3Kw fires on a standard ring without up-rating the whole circuit! Again John you are indulging in straw man arguments.
: : > :> But the use of ring circuits HAS resulted in a reduction in : > the : > :> number of ways in the average domestic D-board. : > : : > : Compared to what? : > : : > : 40 years ago a domestic house probably had a four or five way : > board if : > : you were lucky. These days 8 - 12 is more common. : >
: > Yes, and that is for ring circuits! : >
: > Lets look at what could be a typical radial circuit instillation, : > take the average modern 4 bed (CH installed) two floor family : > house with a living, dinning, study. Dealing with just the power : > circuits most dwellings will have no more than two ring circuits : > (perhaps three if it's thought that diversification will be : > insufficient in the kitchen/utility room), plus a circuit each : > for emersion heater, cooker feed, shower - that equates to SIX : > power circuit protection devices at the D-board. Now lets take : > the same dwelling that has been fitted with radial circuits : > through out, we will need at least one protection device [1] : > (@15A) for each bedroom, the living room, dinning room, study, : > hall + landing - that is NINE circuit breakers (allowing for two : > double sockets in each room) without even considering the kitchen : > or other currently installed radial circuits, one could easily : > get close to needing a 15 to 20 way D-board JUST for the power : > circuits. This is the only advantage of ring circuits, but only : > then at installation, and of course architects and builders would : > have to think were to site such a D-board - no more just bunging : > it behind the swing of the front door in the entrance hall... : : I have already explained the number of ways in which rings handle most : common fault conditions better than radials.
So you are suggesting that each room should have a ring circuit of their own, so that a fault (that would trip the CB) in one room will not trip-out any other room?!
Also keep in mind that if : there is a particular reason that you want dedicated circuits to serve a : bedroom, there is nothing stopping you doing it here. However experience : suggests that for most properties, having one circuit feeding all the : sockets in all the bedrooms for example, poses no real problem. Typical : loadings will be a fraction of the circuit capacity,
No, experience has shown that most people will accept the cheapest (or what ever they are given) rather than the best, hence builders still get away with fitting one ring circuit for the whole house bar possibly the kitchen.
: and trips due to : overload will be almost unheard of.
Taking that rational, considering that the tripping of lighting circuits are very rare, would it be sensible to put all lighting (including stair-wells) on the one CB?...
: : Also keep in mind that one is using decent quality circuit breakers with : dual acting trip mechanisms (magnetic and thermal), while these are : fairly cheap these days there is little to be gained from speccing an : extra £100s worth just to have a extra dozen circuits.
Come back to my point about best vs. cheapest, aka cost, the point made way up in the thread regarding why the UK opted for ring circuits in the 1950s.
: : > : What has changed massively is modern usage. : > : : > : A few years ago I rewired a neighbours house. It had its : > original wiring : > : as installed in the early '50s (plus a bit of bodging from the : > owner!). : > : It was instructive to see what constituted a typical electrical : > : installation. : > : : > : There were four circuits in total - two lighting, two power : > (the power : > : circuits were radials wired in rubber sheathed cable with a : > separate : > : bare earth wire). Each power circuit fed approx 4 sockets - : > giving a : > : total of 9 for the whole house (and these were all single : > sockets). : > : : > : When we designed what was needed for their actual usage, we : > ended up : > : with something like 34 double sockets. That was three rings : > (upstairs, : > : downstairs, and kitchen), two lighting circuits (one per : > floor), and : > : high integrity radial with its own dedicated higher threshold : > RCD for : > : the freezers, CH boiler, and fish tank, plus a sub main feed : > for the : > : outbuildings. : > : : > : One could have slapped in a a few extra radials for each floors : > sockets, : > : but it would have added little of any great value. Its unlikely : > the : > : circuit breaker for any power circuit will ever trip. If the CH : > fails, : > : and they want to plug in a couple of 3kW heaters, then they can : > do that : > : pretty much anywhere, without fear or tripping something. : >
: > Hmm, with a separate radial circuit to each bedroom it would be : > possible (within the limit of the company fuse...) to have a
3Kw : > fire in each bedroom, one will start having problems trying to do : > that with the typically wired ring circuits found in the average : > modern house. : : Not really - at least not in a three bed house! Fan heaters are : thermostatically controlled. Three to a circuit ought not cause a major : problem.
But we were not talking about a three bed house but four, never mind the fact that other rooms that will need to be heated electrically could be on the same ring, it would be very easy for the average to large family in the depth of winter to get close or beyond the ring circuits capacity. Yes, the capacity of a radial circuit can be exceeded but a tripped-out CB will only affect the one or possibly two rooms and not the whole floor or house.
: : >
: > Meanwhile : > : should a wire work loose somewhere, there is a reduce chance of : > : overheating of loss of earthing due to the redundancy of the : > ring circuit. : >
: > Bollocks, with respect, the same loading could be applied to the : > faulty circuit, that could well mean that the one 2.5T&E will be : > taking the full 30A load (your ideal failure would *have* to be : : Given one 2.5mm^2 T&E is good for 27A continous operation with common : installation methods, an extra 3A is not going to cause a significant : reduction in service life.
So why the need for ring circuits then if there would be no problem in using a faulty ring that has become nothing more that a radial circuit feeding how ever many sockets have been installed on the ring, and why bother checking for a broken ring when the instilation is inspected?!
Also for that to be the case the break in the : circuit would need to be at one end of the circuit. Anywhere else and : the situation would be less severe.
Yes, but again, if it's acceptable to have a broken ring circuit and thus two radial circuits with an unlimitted number of sockets on each then why not an intentionally installed radial circuit?
Note also that susstaining a 30A : load using normal appliances for any period of time is highly unlikely. : (if it were likely, then the designer would spec a dedicated circuit for : the load).
Who knows what appliances house owner #1 will want to use, never mind owner #10 in twenty years time, as you (in a less direct way) has already pointed out when commenting about diversification?
: : However this misses the point - a high resistance connection (the most : common circuit fault) usually affects a radial more severely than a ring : - all circuits downstream of the fault will be supplied via said poor : connection. Especially when the fault is in the earth - which is the : most common place to have it due to the wire being less robust and also : uninsulated.
But the fault will be *more* noticable, unlike a ring were it might well be hidden untill a specific test in carried out.
: : > exactly half way around the ring, so not to unbalance the : > circuit)... If the same wire came loose within a radial circuit : : You actually have to try quite hard to unbalance a ring enough to be a : problem. Basic physics also comes to your rescue a bit - if you load one : leg significantly hotter than the other, then that one exhibits a higher : resistance which helps redistribute the imbalance.
Which also applied to a radial, surely, considering that a broken wire fault in a ring creates two seprate radials?...
: : > it would either fail completely or the serious fault would be : > very evident to all by the terminally and literally mentally : > clueless. : : How would you know that your radial has a 10 ohm resistance half way : along it in the earth conductor?
How would you know that your ring has a broken wire halfway along, and remeber that "my" radial will be subjected to a lower total load that your ring circuit?
: : > :> Sorry but that sounds somewhat like a straw-man argument, how : > :> many domestic kitchens would draw that sort of (non : > "diverse") : > : : > : Domestic kitchens with an appliance load of 9 - 12kw are common : > here. : > : Most will have dish washer, washing machine, and drier, and : > each of : > : those will often pull 2 - 3kW. On top of that many single ovens : > up to a : > : couple of kW are designed to "plug in". A kw of microwave, and : > on top of : > : that you will usually have a few "small" appliances like a
3kW : > kettle, : > : and 2kW toaster etc (you can ignore those from loading calcs : > since they : > : are such short term loads). There will often be dedicated
32A : > or 40A : > : radials for cooker supplies where electric cookers and hobs are : > installed. : >
: > But as you say, most if nor all have more than one circuit : > supplying the kitchen, thus one is having to build diversity into : > the instillation anyway... : : Most will have a general purpose socket circuit for the kitchen, plus : additional ones for cookers etc.
Your point being what exactly, considering that on that one socket the loading could be close to 6Kw, whilch leaves little for the rest of the ring, which probably means the rest of that floor in the dwelling.
: : : > :> ring circuit tripping out. : > : : > : Again we keep coming back to "rings tripping out". As a general : > rule not : > : something that happens with great regularity. : >
: > In the perfect world it will never trip out, or would any radial, : > the problems start *when* it does. : : Well so far I have never experienced a circuit trip due to general : overload. Its just not something that happens on domestic circuits here : in most peoples experience since you need to conjure up something like : 10kW or sustained load to do it. : : Again this is nothing to do with circuit topology, and just the pros and : cons of having additional fusing per appliance so as to allow higher : power circuits. I have experienced a trip on a fault current (when I : drilled through a cable in a mates house a few weeks back for example!) : I have also experienced trips due to RCD detected faults.
Not sure what your point is, other than to make a very good argument for radial circuits. :~)
: : > : The most common "trip" problem we tend to get here is with RCD : > trips : > : caused by faulty appliances (or damaged wiring). Neither of : > which are : > : going to benefit from being ignored from prolonged periods. : >
: > Indeed, but if the appliance is being feed via a radial it can : > *often* be ignored - in so much as the circuit being left : > isolated until such time (when ever that is), with a ring one has : > to deal with fault by either correcting the fault or by removing : > the appliance for the circuit unless one is prepared to have : > everything feed from that ring circuit isolated also. : : One would usually unplug it rather than turn off the whole circuit!
Assuming that it's that simple, access wise etc, also one has to find the faulty load first.
: : > :> [1] and as has been pointed out elsewhere, if 7.2KW of non : > :> diverse load does need to be supplied then 2/3rds of the : > cabling : > :> needed for three radial circuits would be needed in a : > dedicated : > :> ring circuit anyway. : > : : > : yes, and? : >
: > I was merely pointing out that the only saving between three : > separate radials and one ring circuit was a length of wire and a : > couple of CBs in the above scenario, in other words we're back to : > arguing instillation costs. : : I would rather have a system where I can generally plug what I like in : where I like, know it will remain safe and adequately protected, and not : need to worry about will it cause a trip etc. I am not really fussed : about the cost.
Which is exactly what you can do with radial circuits, far more so than with ring circuits, remember that I'm not suggesting the use of crap specs found in N.America, or even those found in much of Europe but a modern UK spec for radial circuits.
: : > :> : You have a circuit that behaves better under most of the : > common : > :> failure : > :> : modes in circuit wiring (i.e. high resistance or broken : > :> conductors), and : > :> : retains higher levels of protection under most of these : > failure : > :> modes. : > :>
: > :> In other words, what you seem to be saying is, the ring : > circuit : > :> is good at masking (possibly) fatal faults, such as a : > :> disconnected conductor, thus the circuit has the same load on : > a : > :> single 2.5mm T&E rather than sharing the load between two : > sets of : > :> such conductors... : > : : > : The most common fault is a high resistance connection (loose : > screw : > : terminal etc). You will tend to get less serious overheating on : > a ring, : > : and usually no increase in fault disconnection times. : > : : > : The next most common fault is a broken earth conductor (its : > thinner and : > : uninsulated), again a ring carries on safely while a radial : > will have a : > : proportion of its sockets without any earth. : >
: > Not sure if we are getting close to a strew man argument here, : > surely the most common point of such failure is at the mechanical : > joint(s) and as such both conductors could - if not would - fail : > at that point, thus in both a ring and radial circuit if it is a : : By "both conductors" I presume you mean live in and live out or earth in : and out etc?
Yes, such as a fault caused by the over/under tightening of a terminal screw, the chances are that both conductors will fail at that point.
: : > positive or neutral conductor fault then that socket is likely to : > stop working (or worse still, become intermittent under load) but : : High resistance connections won't necessarily stop it working, but they : will certainly get hot!
Which is true of any circuit, so is not specific to either the radial or ring circuits under discussion.
: : > on a ring every other socket will carry on regardless, on a : : Indeed the fault current flowing through the high resistance it limited : to that which is plugged into the socket with the fault. All the others : have their own low resistance feed. On the radial the fault current : flowing in the high resistance connection is potentially that of a : proportion of the whole circuit.
Whilst the load being applied down-stream of the high resistance will, highly likely, cause the fault to show up, OTOH you are making a very good argument for not only the banning of radial circuits but also the use of spurs on ring circuits...
: : > radial anything down-stream of the fault will also fail. In the : > above earth conductor fault occur then that socket will have lost : > it's earth with either ring or radial circuits. I can accept that : > there is an added (theoretical) risk on radial circuits should : > the earth conductor fault occur, not only would the socket in : > question have a earth fault but any socket down-stream would too. : : Hence why high integrity earthing is specified in certain circumstances : for radial circuits.
I have already conceaded that, but (as pointed out above) surely the same issues arise were spurs are taken off a ring circuit?
: : > : The next most common is a broken live or neutral conductor. : > Here a ring : > : *can* mask the condition where it should be apparent on a : > radial. : > : However on most real world ring circuits you would still : > probably get : > : away with a fault like this without anything serious happening. : >
: > Well yes, but in most modern real world faults, what with the : > typical double insulated, low consumption, devices in used today, : > many faults can go undetected for years, but is that really the : > point, if it is then what's with all the regs... : >
: > : : > : Needless to say you can't always have the best of all worlds, : > so it seem : > : preferable to me that you use what performs best with the most : > likely : > : faults and that is the ring circuit. : >
: > So you advise the masking of *possibly* dangerous faults, that is : > what you seem to be saying?Cough! :~) : : Both topologies can mask potentially serious faults. So (to my mind at : least) one chooses based on which deal best with the most common ones, : unless there are special circumstances to suggest otherwise.
But the typical maximum load on a radial will be a lot less than that on the typical ring circuit, and as there would be natural circuit redundancy [1] (per floor/room) built into a dwelling using radial circuits for power there will be less risk of the continual use of a circuit that is/has caused in service problems.
[1] and due to that redundancy it might be feasible to protect each circuit far more closely than is advisable on a ring circuit currently (no pun intended).
: : : > :> : Ring circuits typically have lower earth fault loop : > impedances : > :> as well, : > :> : result in quicker clearing of faults. : > :> : : > :>
: > :> Why should that be, and what would need to be changed in a : > radial : > :> circuit spec to mirror the results found in ring circuits? : > : : > : A radial will typically be wired in 2.5 or 4mm T&E, both of : > which have a : > : 1.5mm CPC (earth), a ring in effect has two of them in : > parallel. Hence : > : the fault loop impedance tends to be lower on the ring due to : > the area : > : of copper involved. : > : : > : Radials can be wired with what is called high integrity : > earthing - here : > : the CPC is returned to the origin as if it were a ring, and : > also the two : > : earth connections to each socket are made to independent : > terminals on : > : the socket. This system is usually specified for when it is : > known there : > : will be high earth leakage currents - typical with lots of IT : > or other : > : electronic kit where there are lots of mains input filters : > sticking : > : capacitors between line and earth. : >
: > Cheers for that. : >
: > : : > : With regards dealing with the effects of loose connections, : > there is not : > : much you can do with a radial intrinsicly to improve it, other : > than : > : specify more frequent inspection and test, and to ensure a good : > standard : > : of workmanship is maintained during construction. : > : : >
: > Surely all it would just require is the installation of a return : > earth, either via a new spec of 4 core cable (T&E[x2]) or a : > separate earth wire run along side, either method would add : > little to the work or cost of instillation of each radial : > circuit - yes it will cost more, radials circuits do cost more, : > I've already conceded that point. :~) : : By the time you have found a double insulated earth cable, and returned : it, you may have well used normal T&E and got the return benefit on the : L and N as well! ;-)
The same could have been said about T&E cable when first introduced, the tooling for 4 core cable already exists, the production of a double insulated earth cable would thus not be a major issue if that is what a future 18th edition called for, as wound't the use of already existant single core earth. :~))
: : (stick a 20A MCB on it and call it a dual redundant radial if you like). :
Back to your suggest of having a ring circuit for every room...