fused or not ?
|Anthony Knights||22/04/2019 09:38:23|
|462 forum posts|
I have been retired for 10 years and am not up to date with present electrical regulations. I have a number of mobile phone chargers, some of which are the same size as a normal 13 amp plug. There is no access to a fuse as on a normal plug and I was wondering if they are internally fused with one of a suitable rating. If not, a catastrophic failure could result in a large current flowing until the ring main fuse or breaker operated. Surely this represents a fire risk.
My chargers are no longer plugged directly into wall sockets. Instead I use a short extension lead to a 4 way block with switched sockets. The plug for this has a 3 amp fuse. Hopefully my fears are unfounded, but perhaps someone with more knowledge than me, will put my mind at rest.
|not done it yet||22/04/2019 10:21:46|
|5391 forum posts|
Cheap ‘wall warts’ were a notorious fire risk. Likely far better now. Better ones are switch mode type which are better from safety and efficiency. Alternatively charge from a USB socket on the computer?
Edited By not done it yet on 22/04/2019 10:22:25
6688 forum posts
I hate generalising because there are always exceptions, in this case if someone has picked up a cheap nasty example!
However, the few phone chargers I've opened up have all been fused internally without a conventional mains fuse in the 'plug'. With one exception, the fuses were soldered in and it wasn't immediately obvious which sub-miniature component it was. The sub-miniature fuses used may be more sensitive than usual mains types, the only one I was able to identify was rated 160mA, which makes a 3A fuse look like a monster.
Another generalisation is the design of these small power-supplies makes them unlikely to fail in a way capable of drawing a heavy fault current. Most of the components are delicate and fuse-like in themselves. Overstressed they either go open circuit or burn-out in a flash. An older transformer based wall-wart might be more hazardous, but the examples I've disembowelled have all had wired in fuses and sometimes a thermal cut-out as well.
These units aren't intended to be repaired when the fuse blows.
Little cause for concern if the charger came with a new phone, or is a genuine replacement. All bets are off if the charger was bought new for a quid from Flash Harry at a car-boot sale...
|Robert Atkinson 2||22/04/2019 10:37:25|
883 forum posts
A charger that meets the safety requirements will have internal over current protection but it may not be a "fuse" in the traditional sense. Often they use a fusible resistor is used. This resembles a normal resistor but is designed to go open circuit before it goes up in smoke. The problem is the cheap chargers and clones, often from the far east. The cut costs and compromise safety. Running from a 3A fused extension is a good precaution and chargers should always be switched off or unplugged when not in use.
|Paul Lousick||22/04/2019 10:49:56|
|1649 forum posts|
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.
|Neil Wyatt||22/04/2019 11:05:13|
18414 forum posts
I heard that a £1M visitor centre burnt down because someone left a phone charger under a pile of paper overnight; it would have been a transformer one in those days, almost certainly.
|Robert Atkinson 2||22/04/2019 11:27:34|
883 forum posts
The chargers should have fuses, but not the replacable type. The earth leakage and overcurrent breakers protect from leakage or shorts to ground and overloads, but the overload protection is for the cables only. It won't stop a device like a charger overheating as the circuit has to cope with wvething from a 10W charger to a 3000W heater. The current generation of overcurrent breakers can't detect arcing between live and neutral where hundreds of watts coulld be setting a fire. The latest designs can detec arcing and add extra protection but cost more. The earth leakage breaker protects against shocks and shorts or arcing to ground.
1019 forum posts
I think what we gain from the above is cheap chargers from dubious sources should definitely be avoided, I have a policy in our house that no chargers are left connected and switched on if no one is present, that way safety can be assured. I have seen a charger burst into flames although it was many years ago so hopefully modern technology is now much safer.
|Guy Lamb||22/04/2019 12:40:25|
|104 forum posts|
Once global warming really starts to demonstrates the catastrophic consequences predicted by many and the total break down of civil society that is bound to follow in the wake of such cataclysmic change, I wonder if we will look back on this time of abundant and ubiquitous electric power with teary eyed nostalgia or condemn our cumulative profligacy at its misuse. So, think on next we charge our mobile devices or motor 1/4 of a mile to get a daily paper. Dystopia beckons!
|not done it yet||22/04/2019 13:08:31|
|5391 forum posts|
We have the technology to produce electric power from non-climate-warming sources. All we need to do is to get on with it, instead of the usual government ‘head in the sand’ mode of operation - mainly caused by fear of losing their elected positions or from the lobbyists (and some well heeled people/companies who want to prolong their lucrative profit making activities, come hell or high water).
|Frances IoM||22/04/2019 13:19:41|
|947 forum posts|
|the high water - several metres above current level tho not quite Hell like temps are promised within 20yrs or so - the flames of hell will however be missing as many areas esp in USA will be dust bowls|
|606 forum posts|
How does that work if the chargers don't have an earth connection, as is the norm with most modern units?
|Russell Eberhardt||22/04/2019 14:08:08|
2609 forum posts
While you are absolutely right about unnecessary car use, leaving modern phone chargers permanently connected is no problem. My recent Samsung charger consumes less than 1 mA when not charging and close to zero power (below the limit on my power meter) having a small power factor and is certainly less than 0.1 W. The power consumed rises to 5.3 W maximum while charging and goes back to near zero when the phone is full.
|Robert Atkinson 2||22/04/2019 14:33:51|
883 forum posts
If the insulation in the charger breaks down making the output "live" then any current to ground over a few milliamps, includng through a person, will trip the earth leakage device. The earth leakage device does not even have an earth connection to it's circuits. It works by sensing any difference in current between live and neutral so will even protect against shocks between phases e.g. if you ran an extension lead from next door who are on a different phase.
|Robert Atkinson 2||22/04/2019 14:43:10|
883 forum posts
Even if we assume 0.1W (1mA is around 0.2W) and 3 chargers per home thats 7.2Wh per day times 27 million households is nearly 200 Megawatts hour per day! Many people have more than 3 chargers and then there are business users. It all adds up.
Edited By Robert Atkinson 2 on 22/04/2019 14:44:50
|Jeff Dayman||22/04/2019 15:13:44|
|1974 forum posts|
If you think phones are a charging capacity issue - just wait until electric cars come down in price and up in battery capacity to become really popular. No way gen capacity in cities will be able to catch up with the demand.
6688 forum posts
Two basic ways of wiring a house for electricity. You can either connect each socket individually back to the consumer unit where it is fused (star or radial) or you can connect several sockets in a loop connected at both ends back to the fuse box (a ring main).
There are advantages and disadvantages to both systems, but being a true-blue Englishman I shall claim the British ring main is for real men while radial systems are for girly girls and nervous colonials.
Not only is UK mains full throttle 240VAC but our domestic ring mains are typically good for at least 32A each. Pumping 32A or more into an electrical fault is a bit scary. The UK designers knew there might be a lot of heat if something went wrong and to minimise the fire risk they decided to fuse all the plugs in the system 13A, 5A, 3A or 1A depending on the appliance. The fuses aren't there to stop people being electrocuted or to protect the appliance, they are installed to stop the wiring catching fire and burning the building down.
Not all countries are happy with ring mains. A safety advantage of radial wiring is the lower current available at the socket (which is often fused) makes overloading of the wiring less likely, in consequence such systems don't require plugs to be fused. Not inferior or better, just a different approach.
Wherever you live appliances are mostly fused internally to protect themselves; these typically blow well before any fuse that might be in a plug. These appliances are suitable for both Ring and Radial systems.
A criticism of the ring-main approach might be it was designed at a time when people owned small numbers of power hungry domestic appliances: irons, kettles, immersion heaters, electric fires, and vacuum cleaners etc. In contrast most modern homes actually contain large numbers of small consumers - radios, TVs, computers, hifi, phones, clocks, printers, wifi, and rechargeable toothbrushes.
Which system best suits today's homes could be debated endlessly, I reckon its six of one and half a dozen of the other.
|Michael Gilligan||22/04/2019 17:05:49|
17047 forum posts
Although E.ON's handling of the recall was exemplary ... This was perhaps one of the more unfortunate examples in recent years: **LINK**
|Phil Whitley||22/04/2019 17:51:12|
1291 forum posts
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.
Radial circuits were the way power for connected appliances was distributed before the ring main came into being. By the late 60s, when I was serving my apprenticeship, we were rewiring all the old TRS and VIR wired installations, removing radial circuits and replacing then with ring mains. It is also wrong to say that in a radial, each socket is wired seperately back to the consumer unit, each radial is a string of sockets, and uses larger cable than a ring, otherwise you would need a consumer unit with enough ways in it to have a seperate one for each socket, but the radial has one major disadvantage, and that is that in a ring circuit, current is equal in all parts of the ring. In a radial, the first piece of wire between the CU and the first socket carries most current when all sockets on the circuit are in use. This is a major reason why radial circuits were scrapped and replaced with ring circuits, and whilst I know they have been reintroduced, there is no good electrical reason to do this (if you know of one, please let me know!)
I know of no disadvantages of the ring system, and it is generally accepted that the UK wiring system is (or at least, used to be, more later) the safest in the world bar none. Most of the world still does not use shuttered sockets, which were introduced in the UK in 1947.
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!
|Phil Whitley||22/04/2019 18:08:43|
1291 forum posts
"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!
also note that a rewirable fuse ALWAYS fails safe!!
Edited By Phil Whitley on 22/04/2019 18:24:23
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.