I'm sure glad UK plugs have fuses - Page 1
Forum section: electronics / general

author: tom66
author_rank: Super Contributor
timestamp: January 11, 2015, 12:17:19 pm
content: So, my landlord obviously doesn't understand that overloading extension leads is a bad idea. He has a washing machine and tumble dryer connected to the same extension lead. When the washing machine heater turns on, and the tumble dryer runs, the maximum power of the system is exceeded.Came down this morning to find the power to the dryer/washer was off, they'd stopped mid cycle. Checked the plug, look what I found. Fuse was blown. It did its job. The plastic of the plug was somewhat melted, but the mains was not exposed at any point. And the plug was absolutely roasting when I pulled it out.What could have happened if the fuse was not part of the design?

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2015, 12:38:16 pm
content: Here breakers are 20A, so it would have tripped. As well all SABS ( South African Bureau of Standards) approved ( though there are a lot of fakes that NRCS destroys on a regular basis that are not compliant) multiplugs and such have to include a resettable overcurrent device, typically a thermal breaker.From your photos it looks like the fuse was in a holder with poor clamping, as evidenced by the burning on the live side only, the fuse was likely only being contacted in 2 small spots on each side, and this high contact resistance led to local heating of the fuse holder and thus the live pin, the internal connection and the live wire end. Fairly typical of high current operation, and the fuse likely was running hot due to the current through it. IIRC ceramic fuses can run at over 130C before melting from the temperature inside.

author: Bloch
author_rank: Unknown
timestamp: January 11, 2015, 01:06:32 pm
content: Wow that a bad designed plug. I am glad that did not start a fire at you place.I am 100 % that i cant be the meaning that you need to change the hole plug instead of the fuse

author: Bloch
author_rank: Unknown
timestamp: January 11, 2015, 01:12:06 pm
content: If it is a 5x20mm fuse ? Then the maximum dissipation 4 Watthttp://www.littelfuse.com/~/media/electronics/datasheets/fuses/littelfuse_fuse_217_datasheet.pdf.pdf

author: mc
author_rank: Regular Contributor
timestamp: January 11, 2015, 01:47:31 pm
content: UK plugs use 1" x 1/4" fuses.Looks like a low quality plug with poor fuse clamping/contact. Doesn't take much resistance when pulling 13A for things to start heating up. Plus I'd guess the combined load probably wasn't that much above the fuse rating, so it took a while to heat up and blow.

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2015, 01:56:57 pm
content: Quote from: SeanB on January 11, 2015, 12:38:16 pmUnlikely as the maximum allowed plug fuse is 13A.QuoteHere in the UK some extension leads have a built-in circuit breaker, especially the type which can be coiled.

author: Yago
author_rank: Frequent Contributor
timestamp: January 11, 2015, 02:01:59 pm
content: Quote from: Hero999 on January 11, 2015, 01:56:57 pmThought UK ring mains were fused at 20A?The plug contacts could have suffered corrosion/tarnishing, especially if it "lives" in a high humidity laundry room.

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2015, 02:11:01 pm
content: UK ring mains are 32A, while spurs are given a 16A breaker. There might still be old houses with fuses, but I think those likely are using the good old fashioned penny fuse or the 5p nail fuse in any case. I know the ones here with fuse boxes with rewireable fuses in them also tend to be houses where the owner has been living in it since he was a wee lad, and is now a pensioner. The electrical repairs will be expensive on sale, as it will require a total rewire.

author: Yago
author_rank: Frequent Contributor
timestamp: January 11, 2015, 02:46:43 pm
content: Cheers Sean, but I'm not quite a pensioner yet!

author: mc
author_rank: Regular Contributor
timestamp: January 11, 2015, 02:53:19 pm
content: Quote from: SeanB on January 11, 2015, 02:11:01 pmWhy would it require a total rewire?Provided the installation is fine, then there is no requirement to change anything. If you wanted, you could simply change the consumer unit without rewiring anything else.

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2015, 03:02:13 pm
content: So it still has those "quality" fuses...............As to the total rewire it will be likely that, along with the fuse box being a relic from ancient times, the wiring will be equally ancient, and made from copper wire, lovingly tinned, and with a coat that originally was a flexible gutta percha rubber overmould and with a cotton woven sleeve to keep it intact. That will now have become a blackened wire with insulation so brittle it will disintegrate on the merest touch. As well the insulation resistance will be so low that it will not pass any insulation test.

author: mc
author_rank: Regular Contributor
timestamp: January 11, 2015, 03:11:13 pm
content: So you're assuming that all houses that don't have circuit breakers, don't have modern twin and earth wiring?As I was taught as an apprentice, never assume anything, as it's makes an Ass out of U and Me.Besides, the only practical difference between using a fuse and a circuit breaker, is one is alot easier to reset.

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2015, 03:37:26 pm
content: It is a safe assumption, as fuses have been not allowed as either replacement or new here since the 1960's, and the old fuse boxes are only still allowed to be used until there is any upgrade made, which then requires the new wiring or socket outlet ( original socket outlets would be a 5A socket, the plugs for which are still common, but which are typically now only used for suspended lighting in a ceiling void or for hanging lights under 500W, and the standard now is a 15A outlet) to pass the modern standard, which calls for a circuit breaker and a residual current device. The PVC wiring was made mandatory in the 1960's, so any install with a fuse box would likely have cotton covered wire.In any case the standard now calls for the earth to be provided by a dedicated wire, not like in the old scheme where the steel conduit was used for earth. thus in any case you will be doing a rewire with 3 cores of cable, though likely you will be replacing the old 4mm cables with 2.5mm cables, so you can fit them still in the steel conduit. Most DCC wire here at the coast will fail insulation test in any case, just from it absorbing water from the humid air. 77% RH and 28.5C at the present here in sunny Durban in the evening.

author: mc
author_rank: Regular Contributor
timestamp: January 11, 2015, 03:49:16 pm
content: Quote from: SeanB on January 11, 2015, 03:37:26 pmSo, yes, you are making assumptions based on where you stay, not about where this thread is about.My parents house (that's here in the UK, not SA) was last rewired by the government in the 70s, and it has a fuse box along with PVC wiring, so in the UK, it's perfectly OK to have that combination, along with no requirement to rewire or replace anything.

author: G7PSK
author_rank: Super Contributor
timestamp: January 11, 2015, 05:00:47 pm
content: I recently had a plug (UK 13 amp) melt while running at 7 amps for 50 minuets due to poor construction and design, it carried the BS number etc and stated made in UK but was obviously not up to standard, it was fitted with a 13 amp fuse which did not blow. It came fitted to equipment I have since changed it to the last of my genuine MK branded plugs and will now have to try and source some more of the same.

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2015, 05:12:54 pm
content: Funny enough here in South Africa you find a large number of places that use the UK pattern socket outlet for IT equipment, as then they can comply with the SANS specification that all outlets that can accept a SA standard socket outlet must be protected with a RCD, and with large numbers of computers you will need multiple RCD devices as the currents that flow in the input filters quickly add up to tripping point. Newer places use a socket that has a machined key, but they often get a standard plugtop forced into them by cleaners and such, defeating the keyway by brute force and breaking the outlet partially in the process.

author: Towger
author_rank: Super Contributor
timestamp: January 11, 2015, 05:17:35 pm
content: Quote from: mc on January 11, 2015, 02:53:19 pmThe wiring might be so old the house still has 15 amp round pin sockets and rubber cloth covered wires. Do you remember 15 amp plugs.... They are will used in South African houses :-)

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2015, 05:24:11 pm
content: Don't forget that other great bastion of UK world domination, India.

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2015, 06:29:23 pm
content: Quote from: Towger on January 11, 2015, 05:17:35 pmWhen I was at university the rooms in the halls of residence were fitted with 5 amp round pin sockets to take plugs like these:http://www.amazon.co.uk/Amp-Round-Pin-Plug-White/dp/B003T1TSF0I can only guess when designing the building they were too cheap to wire up all the student rooms with 13 amp circuits. The incompatibility with normal 13 amp plugs was, of course, annoying. So you had the incongruous situation of a 13 amp socket strip to plug your stuff into, fitted with a 5 amp plug to match the wall socket.

author: Fraser
author_rank: Super Contributor
timestamp: January 11, 2015, 06:54:10 pm
content: Over the years I have used many makes of UK plug........ they ALL hurt like crazy when you stand on their upturned pins without shoesBut on a serious note, I will only use the high quality MK brand plugs on equipment that is not pre-fitted with a moulded plug. I have gained great respect for the classic MK design, having studied it as part of a project.The cable outer insulation is firmly gripped in a 'one way' clamp making it extremely difficult to pull out of the plug, even if someone trips over the cable. The conductors are secured to the pins and fuse holder using excellent clamping nuts that have an integral free floating clamping washer. The nuts sit in recesses to contain stray wires etc. The fuse holder is of high quality with good clamping pressure on the fuse caps. The shell of the classic MK plug is made from a thermo-set bakelite like material that will not burn or melt under normal conditions (i.e. not in a blast furnace !) It is also non hydroscopic. the shell cap contains moulded recesses to aid isolation of the wires and retaining nuts. Sleeved pins are now law for new mains plugs in the UK. MK use a thermoplastic with a high melting point for the sleeves of their plugs.A top class design and one that I recommend without hesitation.In plugs that I have inspected, and found overheating, I have discovered the following:1. Overloading of the fuse causes localised heating of the fuse holder and plug shell around it2. Overheating plug pins due to poor internal contacts also cause damage to the socket in which they are inserted. The pin shrouds can also melt at low temperatures on cheap plugs.3. A socket with a poor connection on the live or neutral can cause overheating in the socket and any plug that is inserted into it. It is the reverse situation of that detailed in 2.4. Any overheating of a fuse can cause the tension of the fuse holder clips to reduce, leading to poor contact and further overheating and arcing.5. Fused that are of sub standard quality may either fail prematurely due to oxidisation of the conductor, overheat, damaging the plug or fail to blow in an overload situation. Cheap fuses can be a risk.6. Moisture ingress into the plug shell can cause tripping of ELCB's in extreme cases. Plugs used in damp conditions are particularly vulnerable. The correct type of water / moisture resistant plug should be used instead.7. Never assume that a 'user fitted' mains plug is correctly wired unless you have looked inside. I have witnessed reverse L and N negating equipment 'live line' fusing and switching (if single pole). In an extreme case I found neutral and earth wires transposed..... the lamp worked ! It was a very old house with simple wire fuse DP and no ELCB or RCD !I have attached some pictures of the classic MK plug that were on the internet, including an X-Ray !The plug will always only be as safe as the installer but MK certainly provide excellent basic safety as part of its plug design.Aurora

author: Fraser
author_rank: Super Contributor
timestamp: January 11, 2015, 07:08:44 pm
content: IanB,The use of 5A plugs and sockets was common in halls of residence as students were usually banned from using high current products like kettles. The round pin sockets discouraged the use of such products that tended to come with moulded 13A plugs. A student could not claim ignorance either.Aurora

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2015, 07:33:39 pm
content: Quote from: Aurora on January 11, 2015, 06:54:10 pmI wonder, has anyone ever done an analysis of the quality of pre-fitted plugs, like tear-downs, X-rays, etc? So many things these days contain safety hazards when you take them apart, and when mains plugs are moulded closed and cannot be disassembled for checking, who knows what horrors might lie within?

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2015, 07:39:38 pm
content: Quote from: Aurora on January 11, 2015, 06:54:10 pmAnother useful feature is to accommodate equal cut lengths for the L, N and E conductors. There is nothing more annoying than having to make L really short, N medium length and E very long in order to have all the wires sitting neatly in their channels.

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2015, 07:58:03 pm
content: Perhaps we could persuade Mike to pop some in his postal Xray unit and show the internals. I have taken a few apart and there is a lot of poor workmanship under the plastic overmoulding. Poor crimps. poor wire preparation ( nicked cores and loose strands outside the crimp) and often cable that is at best optimistically rated.

author: Fraser
author_rank: Super Contributor
timestamp: January 11, 2015, 08:19:35 pm
content: And to think moulded plugs were made law in the UK in order to improve safetyI used to run a course teaching people how to wire a UK plug. The students liked the fact that they could actually put their on own plugs on rather than needing an electrician. A little knowledge can be dangerous however so I included examples of what can go wrong and the consequences.Sadly with regards to the Chinese supplied moulded IEC leads, some are less than acceptable quality. I have been send so real weird versions of the UK plug. A really small body only just bigger than the pins footprint, no fuse, no insulation sleeves on L & N and suspiciously flexible cable. Very little copper in the conductors. Total rubbish fit only for the bin.Aurora

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2015, 08:22:22 pm
content: Quote from: SeanB on January 11, 2015, 07:58:03 pmI just tried to disassemble one with a hacksaw. However, it appears they are not meant to come apart. The whole thing is layer upon layer of solid plastic. There is an outer layer of soft rubbery plastic, an inner shell of brittle plastic, and inside that the whole thing is filled with what looks like injected hard setting plastic. I can't even get to the wires and terminals.

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2015, 08:52:22 pm
content: Quote from: Aurora on January 11, 2015, 08:19:35 pmWhat law is that?Moulded plugs may be very common but there's no legal requirement for them.

author: Towger
author_rank: Super Contributor
timestamp: January 11, 2015, 09:01:05 pm
content: Unfortunately MK of today is not the same quality brand of yesteryear. For example new model redesigned the MK (Duraplug) 4 way trailing socket is not a patch on the old version. The MBA playbook rules are used to run the company now.Edit: Removed strange text at top of reply.

author: wreeve
author_rank: Unknown
timestamp: January 11, 2015, 09:02:38 pm
content: My uni (Warwick) was the same Ian! And that was the late 90's! 5 amp round plugs!

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2015, 09:22:28 pm
content: Quote from: Hero999 on January 11, 2015, 08:52:22 pmThe law requires appliances to be supplied with pre-fitted plugs. And no way is a person going to be sitting on an assembly line fitting plugs by hand. So plugs are fitted by machine on an automated production line. Which means moulded plugs.

author: Howardlong
author_rank: Super Contributor
timestamp: January 11, 2015, 09:30:35 pm
content: EU Low Voltage Directive innit. Yes, 240VAC is low voltage as far as this directive is concerned.Good idea, problem is now nobody knows how to wire a plug any more, they have to get an electrician in.

author: G7PSK
author_rank: Super Contributor
timestamp: January 11, 2015, 09:45:09 pm
content: 5 amp round pin plugs are used for lighting in places such as theatres a lot. I have seen a 13 amp socket used in airports where the pins are 90 deg rotated so that a standard plug will not fit, the idea is to stop the public plugin in their phones etc. and stealing electricity. The UK. 13 amp plug is used in Zimbabwe at least where plugs are used and bare wires are not just twisted together that is.

author: SteveyG
author_rank: Unknown
timestamp: January 12, 2015, 08:18:49 am
content: Quote from: SeanB on January 11, 2015, 02:11:01 pmNot strictly true. What are you basing this information on?

author: Red Squirrel
author_rank: Super Contributor
timestamp: January 12, 2015, 09:49:10 am
content: Wow considering the beefy design of those plugs I imagine there was quite a lot of current going through to actually melt it, like 40a or more? Those plugs seem somewhat similar to dryer plugs here in Canada which are rated for 30 amps at 240v. Oven ones are rated at 40a. Mind you the wiring in the oven and dryer plugs is probably way thicker. #8 for ovens and #10 for dryers IIRC.

author: bookaboo
author_rank: Frequent Contributor
timestamp: January 12, 2015, 09:53:00 am
content: Quote from: mojo-chan on January 12, 2015, 09:00:08 amI once had the Managing Director of a previous firm bring me a "faulty" piece of equipment that he had wired the plug on wrong. Live and earth mixed no less.

author: SteveyG
author_rank: Unknown
timestamp: January 12, 2015, 02:52:33 pm
content: Quote from: Red Squirrel on January 12, 2015, 09:49:10 amThe current was probably in the region of 20A with the fault being an inferior quality fuse holder which caused excessive heating from I²R losses.

author: Howardlong
author_rank: Super Contributor
timestamp: January 13, 2015, 01:38:10 am
content: Quote from: mojo-chan on January 12, 2015, 09:00:08 amBlimey, no fun in your house, that's for sure!

author: IanB
author_rank: Super Contributor
timestamp: January 13, 2015, 02:31:06 am
content: Quote from: Howardlong on January 13, 2015, 01:38:10 amIt was generally more fun to use a screwdriver to push the earth cover open and then push Meccano rods into the live and neutral sockets before shorting them with said screwdriver. Unfortunately the satisfying bang that resulted also resulted in significant parental displeasure at having to replace the main fuse, meaning that such excitement was only available once without risk of severe sanction

author: Chris Jones
author_rank: Regular Contributor
timestamp: January 13, 2015, 12:12:37 pm
content: Quote from: IanB on January 11, 2015, 09:22:28 pmSomeone in China hand-wired the plug on my Asda extension lead - or at least they got most of the way through it, but didn't bother to do up the earth screw so the wire subsequently lost contact with the pin.I will generously assume that it was tested and that the wire fell out after it passed the earth resistance test.

author: G7PSK
author_rank: Super Contributor
timestamp: January 13, 2015, 02:27:13 pm
content: Quote from: Red Squirrel on January 12, 2015, 09:49:10 amThe usual problem with the plugs is at the point where the fuse clip is riveted to the live pin, on all the plugs that I have had that melted or just got hot for that matter, the problem was loose riveting causing a high resistance point.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 13, 2015, 03:06:13 pm
content: Quote from: mc on January 11, 2015, 03:49:16 pmIn Australia,there was a mandatory shift to PVC wiring & a bit later,plugs in the mid to late 1950s,so that anything wired after that time will have basically similar wiring.The DCC stuff was pretty well non-existent by then,anyway.Fuse holders were made so that anything other than 10A (lights) or 16A (power) fusewire could not be used.They are still legal,but modern installations use circuit breakers.