Safety of phone chargers

Just beat me to it Phil, any installation is only as good as the person who installed it.

Thanks Phil, you spotted I was over-simplifying at best and disgracefully tongue-in-cheek at worst! Always good to be put right by someone who really knows what he's talking about!

Dave

Dave Thank you sir!

Right, so I have finished being Mr Bloody pedantic now, and one of the hats I wore during my varied electrical career was as MD of LN Communications, which brought internet services(and still does, under a new name) to various remote national park and other areas using wireless tech, One of the units we used to install had a wall wart PSU, and many of our customers started complaining of "a funny smell" in the area of the wifi adapter. One of my network oppos reported that he had gone to an installation to find that when he unplugged said wall wart, the live pin stayed in the socket, and the plastic just crumbled in his hand! We started fitting new ones, and sent the faulty ones back to the importer for replacement, I cant remember the exact numbers, but it was somewhere between 50 and 100 failed within the warranty period. This illustrates the problem with the direct plug in wall wart, which has no replacable fuse. These were protected electrically internally, but not thermostatically, the temperature rise was caused by poorly fitting undersized pins on the plug in part ( a very common problem) and allowed the wall wart to slowly bake itself without causing any circuit protection to actiivate, untill all the plasticiser was gone and the whole thing disintegrated. We installed these in places where they could not be covered, so the heat dissipated, but they were VERY dangerous, and it is a miracle that none caught fire. My own daughter had a habit of falling asleep with her phone on charge with an extension lead and the wall wart under the duvet with her, and there has been one local case , and one other reported(and probaly many more) where covered wall warts have set fire to bedding and the like without activating over current protection because the current was not excessive, even though the heat was! In short (when have I ever said anything "in short" the OP's fears are well founded!

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

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

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

Absolutely right Mike!

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.

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.

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?

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

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

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.

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.

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

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

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

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