Safety of phone chargers

[MeunierParticipant @meunier]

Just to add that in France, (since you mentioned colonials and foreign climes) ring mains are forbidden, MCB's are two-pole, and Twin&Earth is forbidden on the grounds that the earth wire is not double-insulated. There are both recommended and permitted numbers of outlets on each spur.
DaveD

[Phil WhitleyParticipant @philwhitley94135]

Posted by Meunier on 22/04/2019 19:15:14:

Just to add that in France, (since you mentioned colonials and foreign climes) ring mains are forbidden, MCB's are two-pole, and Twin&Earth is forbidden on the grounds that the earth wire is not double-insulated. There are both recommended and permitted numbers of outlets on each spur.
DaveD

Interesting! Can't see a reason for banning rings, and 2 pole MCB's must make for massive CU's, but I can see the point about the earth wire, but you can go back to the days when even some lead covered cables had a seperate tinned earth wire, (although most used the lead sheath as earth) and there has never been a problem, at least with rewirable fuses, but given that the MCB provides much coarser over current protection, you can see the logic. The size of the earth wire in some T/E has been increased, due to the fact that under fault conditions the earth wire may become a current carrying conductor.

When I first did my training, the reg for domestic ring installations was " Any number of sockets on the ring, and any number of sockets on a spur, so long as the number of spur sockets did not exceed the number of ring sockets, and the whole did not serve an area bigger than 100 sqm (?) That sounds like a lot, but I think that was the figure. Over the years, the ring final subcircuit has proved itself to be very safe indeed, as both incidence of electrical accidents in the home and domestic electrical fires caused by the wiring, as opposed to connected appliances has fallen steadily since the early sixties, and is now virtually flat lining! With the advent of MCB's and as witnessed by the new fire regs covering consumer units (they ARE catching fire!!) I fear this will not be the case for much longer. Really bad regulations, and really bad "solutions" . Consumer units catching fire? best find out why (we alredy know) and stop it happening? Nah mate, to diff, just stick it in a fire proof box!!

Having spent time in France, some of the wiring I have seen and experienced, especially in the older Parisien hotels, with flickering lights and crackling switches, made me cringe and one of my wifes relations has had several houses in rural France where a fault in the house could blow the fuse on the utility pole, and there would have to be a call out to fix it! Just remembered, I have a coil of white 1.5mm, blu/bro with an insulated g/y earth in it, wonder if it has made the trip across the channel!

Phil

[Mike PooleParticipant @mikepoole82104]

I spent a very pleasant week in a gite and while there were no obvious problems with the property we noticed that at certain times of day the lights were rather dim and putting the kettle on for a cuppa produced a step in lamp brightness, I think the supply for the village was definitely under cabled but it all added to the charm of a gite in the Landes Forest.

Mike

[Mike PooleParticipant @mikepoole82104]

Fuses cannot provide fire protection, a fuse only offers over current protection, it has no idea what the current being supplied is doing, if a device uses the power available to heat the load to the point of combustion without drawing excess current then you can finish up with a fire. The built in thermal fuse in many wall warts is probably more useful than an over current fuse.

Mike

[Phil WhitleyParticipant @philwhitley94135]

Absolutely right Mike!

[Bill Davies 2Participant @billdavies2]

I'm no electrician, but I think I read that the ring main was introduced, post-war, as a cheaper solution due to the lack of copper for wire. The ring main has two routes for the electricity to reach the socket, until there is a failure in one arm of the circuit, when the entire current must follow the alternate route. This will not be as large a wire gauge as a spur, so may overheat. I'm not sure is there is a straightforward test for a 'broken' ring main without examining connections. Sorry, this is off-topic.

[Phil WhitleyParticipant @philwhitley94135]

Not off topic at all Bill, for a known off topic thread thief like me! After installation, but before connection, ring continuity is one of the tests done to check that all is well, and we used to attach a sticker to the consumer unit which stated

" This installation should be periodically checked and tested, and a report on its condition obtained, as recomended in the IEE regulations for the wiring equipment of buildings"

Under normal usage, if installed correctly, there should be no possibility of a failure of continuity in the ring, however, with sloppy installation and second fix, it does happen, which is why the regulations have beefed up the testing regime. The problem you have pointed out is that the circuit continues to function even if continuity has failed on one side of the ring, whereas in a radial it would stop working, and thus demand attention. The actual hand tool work done during the second fix of an electrical installation is of vital importance to the overall function and safety of any installation, and as quoted by Ian Hewson above "Any installation is only as good as the person installing it" and "Leave it safe or leave it OFF" were drummed into us as trainees!

Phil.

[Phil WhitleyParticipant @philwhitley94135]

Of course there is another factor in all this which I have not mentioned. I served a five year apprenticeship and spent three years at technical College to gain my qualifications, you may not believe this, but today you can go to a "college" tip up about £3500 and become a certified domestic electrician IN 5 WEEKS!! Is it any wonder that standards have fallen through the floor?

[Mike PooleParticipant @mikepoole82104]

I am quite glad to see the back of rewireable fuses, a press just outside my workshop had a habit of blowing fuses, on one occasion the blast ejected the fuse carrier from its base and through the cast iron fuse board cover. I suspect it had been rewired with some over rated wire but even with the asbestos pads to protect the porcelain carriers there was much damage from the vaporised copper to the porcelain. HRC fuses are pretty good at containing the blast from damaging the carrier and base, circuit breakers are very convenient but have a limited life if called upon to clear a fault on a regular basis. The press that had an appetite for fuses was a tryout press and it was probably the operator overloading it that took out the fuses.

Mike

[Bill Davies 2Participant @billdavies2]

Thanks, Phil. I used to run an apprentice school in the 1970s, and taught mech eng apprentices more recently. The extent of down-skilling is quite scary. I had thick textbooks for each subject/unit I was taught in the late '60s, today a slim booklet covers all units. And it started before my time; the 1930s and '50s books I picked up from older colleagues were harder than mine. Plus those that worked and studied during the war has reasons and motivation to be well-educated.

And trained as a mechanical engineer, we were taught that electrics were things we didn't touch (three phase industrial voltages), although I did an HNC electrics/electronics unit, which covered quite a lot.

Bill

[Robert Atkinson 2Participant @robertatkinson2]

To add to Dave and Phil's comments on plug fuses, the plug fuse is there to protect the cable between the pulug and appliance. The fuse rating is based on the cable size. Obviously ther is releationship to th load because the cable must also be large enough for the load.
The letter rating of modern MCBs is mainly related to the time-current relationship and the higher ratings apply to the fast trip time (short term overload) of the MCB, the long term overload ratinging is the same. For examble a B or C rated MCB may be needed to stop start-up tripping with motors and VFDs.
I think the French ban ring mains because they are English
The ring main was developed during WWII and notably had a woman on the committtee. Saving copper was a goal but not the only one. TV crews hate radial circuits becuase if the turn one light off or on the voltage changes and this can affect the colour balnce of the other lights.
Leaving the earth bare in T&E is a good idea particuarly in conjuncton with a RCD. Any damage to or water leakage into the cable is likely to result in leakage to the ground conductor rather than external conductive parts so less chance of shock or fire.
I was taught electrical installation decades ago and would never have been allowed to get away with the workmanship prevelant today. Haven't done it as part of a job for a very long time but checked on what would be required to get "part P" competency last year. It mostly depends on the reporting body you join, one needed me totake a course with one of their approved training providers. The course was 3 days and mainly seemed to cover uing a Multi Function Tester and reading cable and MCB sizing tables. They did say if you have no prior experience you should tkae their 5 day initial course- nothing to part P in 8 days!

Robert G8RPI.

[HopperParticipant @hopper]

Posted by FMES on 22/04/2019 13:20:05:

Posted by Paul Lousick on 22/04/2019 10:49:56:

Electrical plugs / chargers in Australia and those countries that I have recently visited do not have inbuilt fuses. All new house instalaltions here, have earth leakage detectors which will cut the power if a short or overload should occur.

Paul.

How does that work if the chargers don't have an earth connection, as is the norm with most modern units?

They are not really an earth leakage detector per se, although they are traditionally called that. They are a Residual Current Device that measures very finely the current in both the supply and return lines to the house. Any imbalance — which means some electrickery is awol somewhere — trips the breaker switch.

[duncan webster 1Participant @duncanwebster1]

So how do you check that the ring is continuous? First thoughts are that you need to make it discontinuous at one socket and check that both ends are still live, but then you have to put it back together and so can't check this last connection

[Nick Clarke 3Participant @nickclarke3]

Posted by Phil Whitley on 22/04/2019 18:08:43:

"As you can see this means that a rewirable fuse is far safer than an MCB," should have added there, "provided it has been rewired with the correct rated fuse wire"

and theres the rub!

Phil

And when it comes to plug fuses they are still available in a choice of ratings 1,2,3,5,7,10,13A – when first introduced as far as I recall even more intermediate values were available – I remember a yellow coloured fuse, but not its value. Does this suggest that even the plug manufacturers want different values to protect the appliance not the cable?

Moving from an Edwardian house with 2,5 and 15A round pin plugs to a new one that my father had built in 1962 or 63 we were presented with a couple of boxes of 13A plugs and a load of different fuses to convert all our existing appliances. I seem to remember the colour code was even moulded into the underside of the MK plugs themselves.

Edited By Nick Clarke 3 on 23/04/2019 09:16:41

[SillyOldDufferModerator @sillyoldduffer]

Warships are a real world example where a ring-main can be undesirable. Ships are compartmentalised by waterproof doors and bulkheads making wiring, piping and ventilation a challenge!

It's good when several compartments are serviced by a ring main because the lights stay on should the ring be cut in one of them by battle damage. Not good if damage or flooding shorts out a ring in one compartment because that removes power from all the others and causes chaos.

The account I read (long ago!) concluded ring circuits were to be avoided afloat, but it also criticised radial installations, for example because they imply complicated duplication and rerouteing switchgear. Anyone know what's recommended afloat today, perhaps they mix and match?

Dave

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by duncan webster on 23/04/2019 08:42:38:

So how do you check that the ring is continuous? First thoughts are that you need to make it discontinuous at one socket and check that both ends are still live, but then you have to put it back together and so can't check this last connection

Hi Duncan, I would have thought the best way would to remove the ends of the ring from the connections in consumer unit and do a continuity test with all the sockets void of plugs. That's the way I would do it and probably do a megger check between each wire at the same time.

Regards Nick.

Edited By Nicholas Farr on 23/04/2019 09:19:20

[Phil WhitleyParticipant @philwhitley94135]

Posted by duncan webster on 23/04/2019 08:42:38:

So how do you check that the ring is continuous? First thoughts are that you need to make it discontinuous at one socket and check that both ends are still live, but then you have to put it back together and so can't check this last connection

https://www.google.com/search?client=firefox-b-d&q=testing+a+ring+main#kpvalbx=1

There you go Duncan!

[Martin 100Participant @martin100]

Posted by Phil Whitley on 22/04/2019 17:51:12:

In the interests of electrical correctness, ther are one or two things in daves post I must take issue with, because we are all here to learn, everyday is a school day, and safety matters in electrical installations.

The point you make about the plug fuses being there to protect the wiring and not the appliance is partly semantic, and electrically incorrect! The fuse or MCB which protects the ring (or radial) is the coarse protection, the fuse in the plug is the fine or selective protection, and although no fuse will protect against electrocution, it is there to isolate the appliance in the event of a fault, thus stopping the risk of a localised fire at the appliance by isolating it from the ring. Take the instance where a double insulated vacuum develops a fault and begins to draw excessive current. There will be no tripping of the RCD, because the current in live and neutral are the same, and let us assume that the fuse in the Vacuums plug is 13A, with a fusing factor of about 1.2 for a cartridge fuse. When the current rises to 15.6 amps, the plug fuse will rupture, and disconnection will occur. Now let us look at the same situation from the point of view of the ring main, it only sees a current flow of 15.6 amps, but if additional load on the ring takes the total load on the ring to more than its protection (fuse or MCB) then the whole ring will be dissconnected, before the cables in the ring even get warm. there is no situation in an otherwise correctly wired installation where the ring will overload to the point of ignition. Also note in the above example a vac should be fused between 5 and 10 amps! I do know however, and have read in publications which should know better, that "the plug fuse is not there to protect the appliance" and semantically, it is not, it is there to prevent temperature rise in the appliance getting to ignition level, it is there for safety, but it does NOT protect the ring main from overload, that is what the fuse or MCB in the consumer unit does.

You could argue that the ring main is even more suited to todays low current applications, but please note that the immersion heater should NEVER be put on a ring main!

Now to my main point, as I mentioned above, fusing factor! I am now retired from the electrical industry, but I have installed many consumer units and distribution boards that use MCB and RCD protection, all done without going too deeply in to the technical side of MCBs. Indeed I have just completed the installation of the 3 phase and single phase distribution boards in my own workshop.In the older Wylex and similar rewirable fuse consumer units the fuse has a "fusing factor" which is given as a figure used to calculate at what current the fuse will actually rupture and isolate the circuit. For rewirable fuses, it was originally set at 1.5, IE a 10A fuse would blow at 15amps, and we did experiments in the college lab to prove this was the case. Since my original training, that figure has been increased to 1.8, and even 2 in some cases, won't go into it here as I am already long winded but looking at the actuall tripping currents for MCBs, which I had assumed would be much closer to the rated current and thus provide "better" protection I find to my surprise that the following applies.

Type B 3 to 5 times rated current.

Type C 5 to 10 times rated current

Type D 10 to 20 times rated current

Type K 8 to 12 times rated current

Type Z 2 to 3 times rated current

As you can see this means that a rewirable fuse is far safer than an MCB, in that it will isolate a circuit reliably at a lower current, and when you add to this the fact that an MCB DOES NOT FAIL SAFE, you can understand that the new (new new corrected reprint) book of latest regulationd now requires all consumer units to be metal clad and installed in such a manner that an internal fire cannot escape the enclosure. I am really glad to be out of an industry where good engineering has been thrown to the wind, and regulations, which used to be made by senior engineers, are made by wet nosed uni graduates and electrical equipment manufacturers. rant over!

Apologies for the long quote but the whole context needs quoting and preserving.

'electrical correctness' is not a word I would use to describe significant parts of what is said above.

Holding the view that rewireable fuses are 'safer' is staggering, they are by nature always slower in operation, they are prone to abuse, unreliability and early failure

The 3 to 5 times rated current for a type B MCB, and similarly for the other types is for a fault clearance time of 0.1 seconds. At around 2 x their rated current they will trip in around 2 minutes

A BS1362 plug top cartridge fuse rated at 13A requires around 150A to clear a fault in 0.1 seconds

Rewireable fuses are long since deprecated. Cartridge fuses or MCB's are the norm worldwide because they are good sound reliable and dependable engineering practice.

[EmgeeParticipant @emgee]

Posted by Martin 100 on 23/04/2019 09:27:45:

Rewireable fuses are long since deprecated. Cartridge fuses or MCB's are the norm worldwide because they are good sound reliable and dependable engineering practice.

Martin, cartridge fuses are wire fuses, enclosed in sand and IMO preferable to mcb's for close protection, just not as convenient if they rupture but can be relied upon to provide consistent results, unlike mcb's after short circuit or fault current overloads.

Emgee

[duncan webster 1Participant @duncanwebster1]

Posted by Phil Whitley on 23/04/2019 09:24:41:

Posted by duncan webster on 23/04/2019 08:42:38:

So how do you check that the ring is continuous? First thoughts are that you need to make it discontinuous at one socket and check that both ends are still live, but then you have to put it back together and so can't check this last connection

https://www.google.com/search?client=firefox-b-d&q=testing+a+ring+main#kpvalbx=1

There you go Duncan!

Good stuff, I don't think I'll be buying one of those meters tho'. If I arrange a 12v battery in series with a 120 ohm resistance (to get 0.1 amps current), a 0.1 ohm resistance and the circuit under test and then measure volts from ground to top of test circuit (V1) and top of circuit to top of 0.1 ohm (V2) and then work out R = 0.1*V1/V2 will this work, or am I missing a trick. I know it's long winded, but I only intend doing it once. I don't think I have any spurs, but we'll find out. As my distribution board is not easily accessed, can I do the same test at a socket?

[Martin 100Participant @martin100]

Posted by Emgee on 23/04/2019 10:07:53:

Posted by Martin 100 on 23/04/2019 09:27:45:

Rewireable fuses are long since deprecated. Cartridge fuses or MCB's are the norm worldwide because they are good sound reliable and dependable engineering practice.

Martin, cartridge fuses are wire fuses, enclosed in sand and IMO preferable to mcb's for close protection, just not as convenient if they rupture but can be relied upon to provide consistent results, unlike mcb's after short circuit or fault current overloads.

Emgee

Yes I agree as that is what I said, and you quoted

In a home consumer unit context rewireable fuses hung on for a long while. Rewireable fuses may at some time been the norm in an industrial engineering context but it must be a very long time ago, some of our systems replaced around a decade ago had elements of the original designs dating from the early 1950's and updated many times since. It was clear from the panels, the drawings and the documentation that cartridge fuses were always used, and in some parts of the modern implementations they still are alongside MCB's that can provide perfectly adequate means of protection.

[SamsarandaParticipant @samsaranda]

I find the training and certification of those who install and service our domestic electrical installations is certainly very lacking, I am horrified that someone with no or very little experience of electrics on payment of the requisite sum of money is then set free to certify installations in accordance with Part P. A friend of ours has had a very close experience of disaster, a recently built extension of their house, containing a shower room, study and lounge area suffered a water leak in the shower/toilet room. Unfortunately the leak had damaged the stud walls and they had to be removed as part of the repairs. The water leak was due to poor soldering on a joint but the builders carrying out repairs found that the electrical supply to the macerator unit for the toilet was not properly carried out, the supply wires had just been twisted together and wrapped in insulating tape, the mind boggles. This is in an area which is legally required to have had a Part P certification carried out!!! I have worked in engineering all my life and received at various times the necessary training to enable me to undertake diagnosis and repair of electrical systems and equipment, so I do have training and experience stretching back over many years but I am not considered competent to carry out basic wiring in my own workshop I have to use some numpty who has probably no experience but does have a certificate which I do not. I for one have no confidence in the current training and certification system, when will those in charge wake up to the potential disasters waiting to happen, how many have to die.

Dave W

[John HaineParticipant @johnhaine32865]

It was a "professional" electrician of many years experience who wired our immersion heater to a lighting circuit then confidently stated that the MCB tripping was due to an earth fault, and buried a miniature PSU for an LED downlighter in the loft insulation – fortunately a diode in it went o/c and isolated it before the house caught fire.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Samsaranda on 23/04/2019 14:45:59:

I find the training and certification of those who install and service our domestic electrical installations is certainly very lacking, I am horrified that someone with no or very little experience of electrics on payment of the requisite sum of money is then set free to certify installations in accordance with Part P. A friend of ours has had a very close experience of disaster…

… not properly carried out, the supply wires had just been twisted together and wrapped in insulating tape, the mind boggles. This is in an area which is legally required to have had a Part P certification carried out!!!

…

Interesting, let's hope it's a rogue example.

What's your friend doing about it? Did he use a Registered Electrician or notify Building Control himself? Either way there's a complaints procedure.

Awkward questions may be asked if he doesn't have a certificate as a result of having a cowboy to do the work and not telling Building Control. 'By law, all homeowners and landlords must be able to prove that all electrical installation work meets Part P, or they will be committing a criminal offence.' Likewise, if your friend is a fraud victim, pretending to be a Registered Electrician could be embarrassing for the offender.

I'm not defending the current way of doing things. Shifting responsibility to the purchaser and supplier rather than having an Government Inspector on the job makes it too easy for shady types to get away with stuff. It also puts responsibilities on customers they may not be aware of, like only recruiting qualified people. Unfortunately it would require a major policy change to undo 40-odd years of deregulation and I don't think politicians of any flavour have it on the agenda, nor are they keen on funding enforcement.

We live in an imperfect world!

Dave

[Harry WilkesParticipant @harrywilkes58467]

Posted by John Haine on 23/04/2019 15:01:46:

It was a "professional" electrician of many years experience who wired our immersion heater to a lighting circuit then confidently stated that the MCB tripping was due to an earth fault, and buried a miniature PSU for an LED downlighter in the loft insulation – fortunately a diode in it went o/c and isolated it before the house caught fire.

'Professional' " engaged in a specified activity as one's main paid occupation rather than as an amateur " should imply he/she knows what they are doing but sadly not in all cases

H

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