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Safety of phone chargers

fused or not ?

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Phil Whitley23/04/2019 09:24:41
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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 10023/04/2019 09:27:45
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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.

Emgee23/04/2019 10:07:53
1497 forum posts
218 photos
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 webster23/04/2019 10:25:32
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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 10023/04/2019 12:38:35
262 forum posts
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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 smiley

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.

Samsaranda23/04/2019 14:45:59
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934 forum posts
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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 Haine23/04/2019 15:01:46
3103 forum posts
162 photos

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.

SillyOldDuffer23/04/2019 15:31:52
5797 forum posts
1235 photos
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 Wilkes23/04/2019 18:03:35
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897 forum posts
61 photos
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

Samsaranda23/04/2019 19:37:34
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934 forum posts
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Dave the problems with his extension are the subject of an insurance claim, the insurers have taken over sorting everything out. So far the insurance claim adds up just over £7000 so the insurance company has a vested interest in investigating the original Part P. It was fortunate in a way that the water leak caused so much damage and the electrical bodge was revealed.

Dave W

paul rayner23/04/2019 21:47:50
157 forum posts
44 photos
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, 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

It was a politicians son or daughter that died due to shoddy electrical work carried out by a builder that brought about PART P. Which in my opinion is a good thing, but would be better if it was ENFORCED, and not just a money making scam for the powers that be, and jobs for the boys.

regards

Paul

Phil Whitley24/04/2019 20:28:54
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t was a politicians son or daughter that died due to shoddy electrical work carried out by a builder that brought about PART P. Which in my opinion is a good thing, but would be better if it was ENFORCED, and not just a money making scam for the powers that be, and jobs for the boys.

Correct Paul, it was. but the reason (she) was killed was not shoddy work, but the removal of the requirement that "all extraeneous metalwork must be earthed" from the regs. A metal framed partition had been fitted and wired for lighting, then plasterboarded, and a pb screw had damaged a cable. If the metalwork had been earthed, the rcd would have tripped immediately the circuit was powered up, but it remained on, and the partition frame became live and went unknown till the unfortunae victin was mopping the concrete floor next to the partition. I had the report of this occurence sent to me by electrical review, and wrote a piece for them commenting on the problem highlighted by this unneccasary tragedy. The part p boys claimed that it was caused by a lack of proper testing, whereas it was actually caused by lack of proper earthing! A test is only valid on the day it is done, a properly fitted and earthed installation is always safe.

Phil Whitley24/04/2019 21:38:24
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1204 forum posts
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Martin 100

"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.

Staggering eh? do you have any evidence for this, I did mention they are prone to abuse, and you certainly cant fight stupid, but the vast majority of the British housing stock that was wired or rewired between the late fifties to the eighties still has rewirable fuses, and is very unlikely to be upgraded unless extended. Since these rewires were done, the number of electrical housefires fell dramatically (Rospa figures)

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

Interesting, so why are they catching fire? Could it be because of the vast numbers of chinese made mcbs on the market?. the introduction of fully metalclad CU's and fire sealed cable entries means that already, there are serious problems. Incidentally 2x the rated current for a 2 minute trip is longer than a rewirable, even at 1.8 fusing factor!

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

It may require that to clear in 0.1 seconds, but requires much less than that to clear in 1 second. I have tested this at college many years ago under lab conditions. The IEE set the fusing factor for an HRC cartridge fuse at 1.2 times the rated current, are you saying they were wrong?

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.

Explain this "deprecation", lets hear some thoughful logical reasoning if you are going to comment at all. Is it "sound reliable and dependable engineering practice" to fit a device as sole means of overcurrent protection that has no failsafe capability and can, and does stay in the on position in the event of an internal failure, and will carry current till it literally catches fire because the next line of protection is the 100 amp service fuse, which (according to your calculations)will need 1153amps to blow in 0.1 seconds, here is the clear illustration of the reason for the introduction of the Metalclad CU. IEE regs used to state that "No mechanical device or circuit breaker shall be fitted in any final sub circuit as the SOLE means of protection" In other word, use an MCB or other circuit breaker by all means, as long as it is backed up by a similarly rated fuse, ok use a cartridge fuse if you must, but electrically they are only a little better than a rewirable, although harder to fit the wrong size. To say they are "the norm worldwide" is just silly, they may be the norm worldwide IN NEW INSTALLATIONS, but that is all. The UK has the safest and most modern system in the world, and we still have a majority of "legacy" installations. I have shown that MCB's, under certain circumstances, are much less safe than fuses, and the IET regulations upgrade to metalclad (which used to be common anyway in large domestic commercial and industrial installations) and their introduction of Potential fault current calculations shows that they are literally firefighting the problem!

I stand by what I said, which is based on 50 years of practical experience of a wide range of domestic, factory and heavy industrial installation, faultfinding and maintenance You are entitled to your opinion.

Phil

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