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FWIW, it's a popular misconception that a BS1363 plug and socket are rated at 13 A. It isn't, really, as 13 A is the maximum short duration rating. The maximum continuous current rating is 10 A, which is the reason that approved UK granny leads are all set to 10 A, and not 13 A.

The big problem we have is that there are a very large number of older (and some new) domestic electrical installations that are in poor condition. Sometimes it's just the age of the installation, and the normal wear and tear on outlets and switches, plus the less stringent requirements in years gone by, but most of the problems seem to come from poor workmanship. Top of the list has to be poor wire terminations anywhere in the installation. Sometimes this is down to them never being properly made and torqued up initially, sometimes it's down to outlets having been pulled away from the wall for decorating, loosening the terminations.

Certainly there is a lot of pretty grim DIY work around, but my experience is that this is often pretty obvious from a visual inspection. The more serious problem is the work done by incompetent people calling themselves electricians, as often this won't be that easy to spot from a quick visual inspection. Although I never worked as an electrician, I did used to teach electrical engineering science (as an evening second job) to apprentices at tech college years ago, I held a ticket for years, really just for hobby reasons, and only don't have one now because the Part P cartels won't allow retired people into their clubs.

For years I've been doing free EICRs for people I know, more recently checking prior to charge point installations and fixing some of the pretty poor work one or two "professionals" have done. I can guarantee that 99% of installations will have some issues that need to be rectified, and that a significant number will have serious faults that need urgent rectification. It seems that no one, other than landlords in the rented sector, bothers to read the sticker on their CU saying that the installation needs to be inspected not more than every ten years. Even landlords are only really doing them because they can be prosecuted if they don't. It also seems that virtually no one does the required six monthly test of RCDs/RCBOs. They can, and do, stick and fail to trip, meaning that the installation may have little in the way of effective protection from electric shock risk.

An EICR usually takes less than half a day, and in normal times should cost around £200 or so. If done properly (and not by one of the cheap cowboy outfits that seem to do them without visiting the premises) then they can be really useful. One problem with them is that there seems to be an issue with a few people using EICRs as an income generation mechanism. I've been to a few installations where the owner has been scared by the scale of work needed to make the installation safe, and in every case, without exception, there was no good reason to do most of the expensive work recommended.

The problem seems to be with some of the younger people in the trade, that assume that anything that doesn't comply with the 18th Ed needs to be replaced. The reality is that this just isn't true, and there has never, ever been a requirement to bring old installations up to the current requirements. The golden rule has always been that all that's needed is for the installation to comply with the requirements in force when it was installed. That's not to say that bringing an installation up to date isn't a good thing, it is, but for people of limited means, in particular, it's unacceptable to use scare tactics to get them to shell out thousands on a complete rewire unless it is actually needed.
 

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ok so this is a debate about granny chargers... but here is the point, its not about the granny charger its about the state of your household electrics.

Technically a ring main has 2.5mm cables burried and the circuit is rated at 32A and the socket is rated at 13A, there should be no problems with running a granny cable on that circuit.

BUT life is never that simple!!!

I was working on a house a few years ago, and the diy person had moved a socet and not put in correctly. Firstly they used 1.0mm cable and secondly they didnt connect one side of the ring properly... they had capped it off because it didnt reach!
OK so for those who dont know... sockets are wired in a ring... so you have power coming from both directions of the loop. If you cut off one side every socket in the loop is getting power from only one side. This is in effect reducing the capacity of the cable.
More current in a cable means more heat... this means likely to have catastophic cable failure and then fire.

This video shows what happens if a cable is overloaded...

Next... more recently there is a better understanding of the impact of under and over tightening screws holding cables. There are now specifications for the torque required on the screws so they are correcly connecting to the cable to avoid arcing. If cables are not fixed correctly in the fitting (socket in this case) then you can get arcing, which causes heat. Which leads to fire!

If you want to see what happens when you dont get a propper connection... read this...

The key point is an up to date; correctly installed property will have no problems with a granny cable.
An older installation might (or might not)... so it is your call on the risk.

Personally... If your installation isnt up to at least 17th edition or hasnt had an inspection for more than 10 years (or probably never been inspected!) then I would consider having a separate circuit for the socket for a granny charger, in which case you might as well get a propper charge point installed... or a 32A commando socket with its own RCBO and PEN fault detection.

But it is your choice and your risk to assess.
Everyone has a story where it is fine... but its about that 1 in a xxxxx chance its not. Is that the lottery you want to win?
A lot of over simplifications in this post which are fine until you are the one with the tale to tell.

A principle of a good design ( for a given purpose) is one of fault tolerance. So an adequate charging plug/socket design like say CEE doesn't rely on every screw being absolutely tightened to spec, every contactor being absolutely clean with no tarnish and the wind blowing in the right direction.
 

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A lot of over simplifications in this post which are fine until you are the one with the tale to tell.

A principle of a good design ( for a given purpose) is one of fault tolerance. So an adequate charging plug/socket design like say CEE doesn't rely on every screw being absolutely tightened to spec, every contactor being absolutely clean with no tarnish and the wind blowing in the right direction.
Yes there is purposely oversimplification. as Jeremy says the biggest issue is electricians who shouldn’t be let near an installation!

actually fault tolerance has nothing to do with domestic electrical installation… the fault tolerance on components does; , there are basic rules about how things are installed to ensure electrical safety And it is these principles which are critical. If someone uses the wrong cable… doesnt cap cables properly so someone puts a nail through it… doesn’t put in fitting correctl… that is installation and no amount of design or fault tolerance will fix that. Bad workmanship is bad workmanship.

the post was asking if granny chargers are safe… I’m pointing out it’s not the granny chargers you should worry about, it’s the electrical installation in general, and as most people on this site are not electricians this is why the question is asked this way.

Most people don’t know what causes electric fires, so those who do know, should help educate and explain the causes and the problems. Actually there are a number of house fires are cause by cables not secure in the fitting. So you might say it’s not important but actually it is. AgIn not a design problem, not a fault tolerance problem, but a workmanship issue.

My point when I replied was to say, people can argue about it all they want about granny chargers, but most chargers have great design with fault tolerance, so that makes no difference in the outcome… It’s really about the installation; and they don’t actually know if their installation is unsafe till it is too late.

again as Jeremy said… (and I alluded to), who gets their electrics checked every 10 years? It’s the electrical safety which is an issue here not the granny charger.

people should be asking how do I know if my installation is safe for using a granny charger?
And what’s the safest way to use a granny changer?
 

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Yes there is purposely oversimplification. as Jeremy says the biggest issue is electricians who shouldn’t be let near an installation!

actually fault tolerance has nothing to do with domestic electrical installation… the fault tolerance on components does; , there are basic rules about how things are installed to ensure electrical safety And it is these principles which are critical. If someone uses the wrong cable… doesnt cap cables properly so someone puts a nail through it… doesn’t put in fitting correctl… that is installation and no amount of design or fault tolerance will fix that. Bad workmanship is bad workmanship.

the post was asking if granny chargers are safe… I’m pointing out it’s not the granny chargers you should worry about, it’s the electrical installation in general, and as most people on this site are not electricians this is why the question is asked this way.

Most people don’t know what causes electric fires, so those who do know, should help educate and explain the causes and the problems. Actually there are a number of house fires are cause by cables not secure in the fitting. So you might say it’s not important but actually it is. AgIn not a design problem, not a fault tolerance problem, but a workmanship issue.

My point when I replied was to say, people can argue about it all they want about granny chargers, but most chargers have great design with fault tolerance, so that makes no difference in the outcome… It’s really about the installation; and they don’t actually know if their installation is unsafe till it is too late.

again as Jeremy said… (and I alluded to), who gets their electrics checked every 10 years? It’s the electrical safety which is an issue here not the granny charger.

people should be asking how do I know if my installation is safe for using a granny charger?
And what’s the safest way to use a granny changer?
So much exaggeration in this post. Granny Plugs don't overheat because of the wrong gauge of cable, you are talking rubbish.
 

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Wow you are so missing the point and not read the posts properly… I’ve never said granny cables have a problems or get hot, I keep saying the house wires and fittings are the source of the concern. As Jeremy said the fault may not be at the location of the granny cable but elsewhere in the circuit. If you knew anything about how houses are wired, or the number of houses badly wired, you would understand what I’m saying.

A granny cable puts a large load on the circuit for a long duration... this can cause weaknesses in the house electrics to show up and can cause a fire.

Now because you dont understand what I've been saying, here is a real story from someone else...


The conclusion was simple...
We concluded a loose, corroded, or damaged terminal at the mains incoming supply, which could have been that way for years. The extra power drawn from the charger over a long duration would have been the 'straw that broke the camels back'.
Note other recommendations...
...regulations specify that new consumer units now have to be made of metal for this exact reason, and the incoming tails from the meter have to be enclosed in metal conduit with the terminals torqued down to a specific setting.
So i guess you know more than me, and yes you're are right its a total exageration.

Its all your choice and your risk and personally I really dont care... Im just trying to explain that asking if a granny cable is safe, that it isnt about the granny cable itself but about how the house is wired.
For most people its perfectly safe... but for some it might not be.
 

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FWIW, it's a popular misconception that a BS1363 plug and socket are rated at 13 A. It isn't, really, as 13 A is the maximum short duration rating. The maximum continuous current rating is 10 A, which is the reason that approved UK granny leads are all set to 10 A, and not 13 A.

The big problem we have is that there are a very large number of older (and some new) domestic electrical installations that are in poor condition. Sometimes it's just the age of the installation, and the normal wear and tear on outlets and switches, plus the less stringent requirements in years gone by, but most of the problems seem to come from poor workmanship. Top of the list has to be poor wire terminations anywhere in the installation. Sometimes this is down to them never being properly made and torqued up initially, sometimes it's down to outlets having been pulled away from the wall for decorating, loosening the terminations.

Certainly there is a lot of pretty grim DIY work around, but my experience is that this is often pretty obvious from a visual inspection. The more serious problem is the work done by incompetent people calling themselves electricians, as often this won't be that easy to spot from a quick visual inspection. Although I never worked as an electrician, I did used to teach electrical engineering science (as an evening second job) to apprentices at tech college years ago, I held a ticket for years, really just for hobby reasons, and only don't have one now because the Part P cartels won't allow retired people into their clubs.

For years I've been doing free EICRs for people I know, more recently checking prior to charge point installations and fixing some of the pretty poor work one or two "professionals" have done. I can guarantee that 99% of installations will have some issues that need to be rectified, and that a significant number will have serious faults that need urgent rectification. It seems that no one, other than landlords in the rented sector, bothers to read the sticker on their CU saying that the installation needs to be inspected not more than every ten years. Even landlords are only really doing them because they can be prosecuted if they don't. It also seems that virtually no one does the required six monthly test of RCDs/RCBOs. They can, and do, stick and fail to trip, meaning that the installation may have little in the way of effective protection from electric shock risk.

An EICR usually takes less than half a day, and in normal times should cost around £200 or so. If done properly (and not by one of the cheap cowboy outfits that seem to do them without visiting the premises) then they can be really useful. One problem with them is that there seems to be an issue with a few people using EICRs as an income generation mechanism. I've been to a few installations where the owner has been scared by the scale of work needed to make the installation safe, and in every case, without exception, there was no good reason to do most of the expensive work recommended.

The problem seems to be with some of the younger people in the trade, that assume that anything that doesn't comply with the 18th Ed needs to be replaced. The reality is that this just isn't true, and there has never, ever been a requirement to bring old installations up to the current requirements. The golden rule has always been that all that's needed is for the installation to comply with the requirements in force when it was installed. That's not to say that bringing an installation up to date isn't a good thing, it is, but for people of limited means, in particular, it's unacceptable to use scare tactics to get them to shell out thousands on a complete rewire unless it is actually needed.
yeh Jerry, sorry about the 13A you are right, but it was more for the simplicity of the explination. (didnt want to explain why a 13amp socket isnt a 13amp socket!)

Like you I was qualified... i did get it when I was doing property renovations, but let it slip for 17th edition. my Dad is/was an electrician but just retiered after 50 years on the job. (so I was house bashing as a teenager before getting my degree in electrical and electronic engineering)
my borther in law runs his own firm and is very good, but he and I had the very debate about your last point... he was saying I need to replace the EV charge point and install an earth rod or pen fault detection, because of 18th edition requirements... I was arguing that just need to comply to the regs as per the install date. Why should he force a person into spending the best part of £1000 to update them when it isnt needed? (not that I would have need to pay that much, I just needed materials)

But the horror stories ive seen and been told of...Im sure you hundreds too.
And I rememeber when I was doing my ticket at night school, a young lad bragging about his mate doing EICRs and if the person wasnt in, he would do the neighbours for free and pop the report into the other property as though it was their own report!!! Why bother... you might as well make up the report!

My dad also says about the part P cartel... he is letting his ticket expire, and just sold all his test equipment because its too expensive to maintain with the regular calibration and then the NICEIC fees on top. So I can relate to that!
 

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Wow you are so missing the point and not read the posts properly… I’ve never said granny cables have a problems or get hot, I keep saying the house wires and fittings are the source of the concern. As Jeremy said the fault may not be at the location of the granny cable but elsewhere in the circuit. If you knew anything about how houses are wired, or the number of houses badly wired, you would understand what I’m saying.

A granny cable puts a large load on the circuit for a long duration... this can cause weaknesses in the house electrics to show up and can cause a fire.

Now because you dont understand what I've been saying, here is a real story from someone else...


The conclusion was simple...


Note other recommendations...


So i guess you know more than me, and yes you're are right its a total exageration.

Its all your choice and your risk and personally I really dont care... Im just trying to explain that asking if a granny cable is safe, that it isnt about the granny cable itself but about how the house is wired.
For most people its perfectly safe... but for some it might not be.
You are consistently missing the main point which is that the UK 3 pin plug is a pile of pop or BS take your pick and is entirely unsuited to sustained high current applications, for BEV charging or anything else. The fact that sometimes it works just confirms it's a marginal design, entirely unreliable and unsafe statistically.
 

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I don’t disagree a socket/plug is a point of failure.
im saying it’s more complicated than a single item being the point of failure.

the failures you refer to (but then never referenced the 3 pin plug again and just said I was exaggerating) are similar exaggerations to mine… they are caused by exactly the same issues, ie High currents for long durations, poor contacts between conductors. The difference, as I said, is you are stating the issue is nly about a single point of failure, and I’m saying it’s a wider than that.

you can’t change the plug/socket design of a plug… arguably the best design in the world! Seriously the US design is a joke! but it is able to carry the current, but cheap manufacturers use inferior quality products and designs which make it more marginal.

I said earlier, a separate circuit with a commando socket Is a better solution because it reducing points of failure, including the socket. But this arrangement is of no practical benefit, you might as well install a dedicated charge point.
 

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I was thinking about a different way to explain the point I was making and why it isnt about the granny cable, but the consequence of the grabby cable; and how to explain every situation is different. So I thought it might be best to describe a couple of scenarios…

Scenario 1
You live in an old property probably circa 1960 or earlier (maybe even Victorian). The property was renovated in the late 70s early 80s and had a rewire. (so 14th edition regs, maybe 15th edition not that you would know what that means)
The Consumer unit as a mix of fuses and MCBs but no RCBO.
The downstairs is on a single ring main (circuit) which has been changed from a fuse to a MCB because in the 90s the fuse blew a few times and someone had it replaced.
Since you moved in (and you’ve now been living there 10 years), the MCB did trip a few times but now doesn’t.
The kitchen has a load of downlights, and again this circuit used to trip regularly but since you swapped the downlights to LEDs you’ve not had a problem.
The rooms downstairs each have 2 or 3 twin sockets, so you have a few mutiblock sockets and short extension leads to give you extra sockets.

Would you run a granny cable in this situation?
Or would you consider having an electrician do an inspection of the electrics before you ran the granny cable?

Scenario 2
You live on a modern estate, your property was build around 2005. (a few years before we changed to 17th edition regs)
You got a new kettle which was super quick at heating the water, but shortly after you noticed occasionally when you had the tumble dryer running and you made a cup of tea, the MCB would trip, but you assumed it was the kettle with a fault, so you took it back and used the old one which worked fine.
The rest of the downstairs sockets, including the garage where there are two twin sockets in metal boxes, are on a single circuit (ring main). Protected by both an RCBO and an MCB on the circuit.

Would you run a granny cable in this situation?
Or would you consider having an electrician do an inspection of the electrics before you ran the granny cable?

Scenario 3
You live on an estate, where the property was built with in the last 2 years (this means 18th edition)
There is a separate circuit for the garage, all circuits are protected with MCBOs

Would you run a granny cable in this situation?
Or would you consider having an electrician do an inspection of the electrics before you ran the granny cable?

The point is each of these scenarios relate to real configurations of houses, and each carries a different level of risk.
Its nothing to do the granny cable per se, it is to do with the consequence of increasing the load and pulling 8-10 amps continuously for a long time, on a frequent basis.

Oh and my answers...
A... get it checked. there is no protection and the fact you are already using extensions leads, and it did have a history of tripping with overloaded circuits, prior to you owning more modern energy efficient appliances, implies that you might easily overload the circuit.

B... the little side story about the kitchen is because the developers in this situation skimped on the electrics (this sometimes happens with develops who want to reduce costs so want as few a circuits as possible.) The new kettle was a larger kW element, and the kitchen was overloaded because of an extra kW from kettle, caused the MCB to trip occasionally with all the appliances on. So it is conseavable you could overload the ring main for the rest of downstairs.... I would get it checked just to be sure. BUT Im only saying for this scenario because there is a history of the circuit overloading, not a generalisation for all houses built in this era. (its about the suble clues here!)

C... Modern house, upto date electrics, you will use the granny cable in the garage which is on a separate protected circuit. Why would there be a problem?

Bonus question....

You have to run an extension lead from the garage, out to the drive and you only have a 30m lead but you need 10m.

The specs are...
  • 4 sockets with 30m extension cable.
  • 10 amps - .
  • Safety thermal cut out.
  • Child-resistant sockets.
  • Suitable for indoor use.
  • Suitable for outdoor use.
  • Manufacturer's 1 year guarantee.
  • EAN: 5015056516875.
you pull the lead out to the car, leaving 2/3s of the cable on the reel. Then you plug the granny cable in and start charging.

Is this OK to do???

Quick answer... if it doesnt trip either the thermal cut out or the MCB/RCBO within 2 minutes, go grab a fire extringisher for an electrical fire... which of course you dont have! So turn of the power in the garage!!!

The typical specifiction for a coilded cable is under 1kW and you will have just gone many times over that rating... this is a recipe for a fire!
Even if you uncoiled it all... you really are pushing this cable and it will get warm. On a cold day fine, but on a summer day in a heat wave... you may not be so lucky.
Always check the rating of your extension lead (they dont always publish the wound rating on the real itself!)

145453



So the whole point of this final post from me on the topic, is that granny cables are perfectly safe if used wisely in the right situation, which is probilbly 99% of the time. BUT there are situations where it is not a great idea to use them without checking the electrics first. Its not really about design of sockets, or workman ship of the installation; these are just part of the mix that add to the complication and whether it is safe when you draw 8-10amps for a long period of time, repeatedly.

Every situation is unique and different, so a one size answer does not fit all. Just look at your own situation and ask yourself... does it seem safe, or are there clues which mean I should have an expert check to confirm it is safe? (and dont let cowboys rip you off!)

Keep safe is all it is about.
 

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I was thinking about a different way to explain the point I was making and why it isnt about the granny cable, but the consequence of the grabby cable; and how to explain every situation is different. So I thought it might be best to describe a couple of scenarios…

Scenario 1
You live in an old property probably circa 1960 or earlier (maybe even Victorian). The property was renovated in the late 70s early 80s and had a rewire. (so 14th edition regs, maybe 15th edition not that you would know what that means)
The Consumer unit as a mix of fuses and MCBs but no RCBO.
The downstairs is on a single ring main (circuit) which has been changed from a fuse to a MCB because in the 90s the fuse blew a few times and someone had it replaced.
Since you moved in (and you’ve now been living there 10 years), the MCB did trip a few times but now doesn’t.
The kitchen has a load of downlights, and again this circuit used to trip regularly but since you swapped the downlights to LEDs you’ve not had a problem.
The rooms downstairs each have 2 or 3 twin sockets, so you have a few mutiblock sockets and short extension leads to give you extra sockets.

Would you run a granny cable in this situation?
Or would you consider having an electrician do an inspection of the electrics before you ran the granny cable?

Scenario 2
You live on a modern estate, your property was build around 2005. (a few years before we changed to 17th edition regs)
You got a new kettle which was super quick at heating the water, but shortly after you noticed occasionally when you had the tumble dryer running and you made a cup of tea, the MCB would trip, but you assumed it was the kettle with a fault, so you took it back and used the old one which worked fine.
The rest of the downstairs sockets, including the garage where there are two twin sockets in metal boxes, are on a single circuit (ring main). Protected by both an RCBO and an MCB on the circuit.

Would you run a granny cable in this situation?
Or would you consider having an electrician do an inspection of the electrics before you ran the granny cable?

Scenario 3
You live on an estate, where the property was built with in the last 2 years (this means 18th edition)
There is a separate circuit for the garage, all circuits are protected with MCBOs

Would you run a granny cable in this situation?
Or would you consider having an electrician do an inspection of the electrics before you ran the granny cable?

The point is each of these scenarios relate to real configurations of houses, and each carries a different level of risk.
Its nothing to do the granny cable per se, it is to do with the consequence of increasing the load and pulling 8-10 amps continuously for a long time, on a frequent basis.

Oh and my answers...
A... get it checked. there is no protection and the fact you are already using extensions leads, and it did have a history of tripping with overloaded circuits, prior to you owning more modern energy efficient appliances, implies that you might easily overload the circuit.

B... the little side story about the kitchen is because the developers in this situation skimped on the electrics (this sometimes happens with develops who want to reduce costs so want as few a circuits as possible.) The new kettle was a larger kW element, and the kitchen was overloaded because of an extra kW from kettle, caused the MCB to trip occasionally with all the appliances on. So it is conseavable you could overload the ring main for the rest of downstairs.... I would get it checked just to be sure. BUT Im only saying for this scenario because there is a history of the circuit overloading, not a generalisation for all houses built in this era. (its about the suble clues here!)

C... Modern house, upto date electrics, you will use the granny cable in the garage which is on a separate protected circuit. Why would there be a problem?

Bonus question....
You have to run an extension lead from the garage, out to the drive and you only have a 30m lead but you need 10m.

The specs are...
  • 4 sockets with 30m extension cable.
  • 10 amps - .
  • Safety thermal cut out.
  • Child-resistant sockets.
  • Suitable for indoor use.
  • Suitable for outdoor use.
  • Manufacturer's 1 year guarantee.
  • EAN: 5015056516875.
you pull the lead out to the car, leaving 2/3s of the cable on the reel. Then you plug the granny cable in and start charging.

Is this OK to do???

Quick answer... if it doesnt trip either the thermal cut out or the MCB/RCBO within 2 minutes, go grab a fire extringisher for an electrical fire... which of course you dont have! So turn of the power in the garage!!!

The typical specifiction for a coilded cable is under 1kW and you will have just gone many times over that rating... this is a recipe for a fire!
Even if you uncoiled it all... you really are pushing this cable and it will get warm. On a cold day fine, but on a summer day in a heat wave... you may not be so lucky.
Always check the rating of your extension lead (they dont always publish the wound rating on the real itself!)

View attachment 145453


So the whole point of this final post from me on the topic, is that granny cables are perfectly safe if used wisely in the right situation, which is probilbly 99% of the time. BUT there are situations where it is not a great idea to use them without checking the electrics first. Its not really about design of sockets, or workman ship of the installation; these are just part of the mix that add to the complication and whether it is safe when you draw 8-10amps for a long period of time, repeatedly.

Every situation is unique and different, so a one size answer does not fit all. Just look at your own situation and ask yourself... does it seem safe, or are there clues which mean I should have an expert check to confirm it is safe? (and dont let cowboys rip you off!)

Keep safe is all it is about.
More cloud cuckoo land stuff
IET have been reporting on BS1363 failures on heaviiy loaded plugs, in commercial kitchens with Bain Maries (another high amperage long duration load) leading to plug/socket failures, tripping protection/melting plugs etc since the 1980s. These are on kitchens where decent electricians ON THE RECORD have installed the ciircuit, installed the socket, wired the plug. They know it is down to the inherent design nonsense of the BS1363 plug, ie a thermal insulator between the L and the flex, which prevents heat being reliably conducted away. No amount of inspection or paperwork will statistically change that design weakness. Note I said statistical.
 

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Actually, the fuse is a heat generator, rather than an insulator. All fuses heat up under load and the design of some 13 A plugs exacerbates this by not having an easy way for that heat to escape. I believe we are also seeing the law of unintended consequences kicking in to make this worse, as modern sheathed pin plugs have a very much poorer heat path away from the fuse than the older ones with the full thickness of the brass pin extending right up to the fuse clip. The conductor in the centre of a sheathed pin plug is now just a round section about 2mm in diameter, surrounded by plastic, so it cannot conduct heat away very well.

Not really an issue as long as the plug can get rid of the fuse heat via a mix of conduction down the flex and convection/radiation from the fuse to the plug body and hence to the surrounding air. The problem is when that heat loss path becomes less effective, perhaps because the sun is shining on it making it warmer, or because stuff has been piled up around the plug. Unfortunately, some people do daft things because they don't realise the risk. One example was a house where I was doing an EICR a couple of years ago. I needed to pull a TV cabinet away from a corner to get at a double gang outlet, and when I did I found there was a melted coil of extension lead welded into the carpet. The owners were using it to run a fan heater, but it was too long, so being tidy people they tucked the coil of left over cable under the TV unit, where it just got so hot that it melted the insulation. How they had never smelt the burning plastic I don't know.
 

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Actually, the fuse is a heat generator, rather than an insulator. All fuses heat up under load and the design of some 13 A plugs exacerbates this by not having an easy way for that heat to escape. I believe we are also seeing the law of unintended consequences kicking in to make this worse, as modern sheathed pin plugs have a very much poorer heat path away from the fuse than the older ones with the full thickness of the brass pin extending right up to the fuse clip. The conductor in the centre of a sheathed pin plug is now just a round section about 2mm in diameter, surrounded by plastic, so it cannot conduct heat away very well.

Not really an issue as long as the plug can get rid of the fuse heat via a mix of conduction down the flex and convection/radiation from the fuse to the plug body and hence to the surrounding air. The problem is when that heat loss path becomes less effective, perhaps because the sun is shining on it making it warmer, or because stuff has been piled up around the plug. Unfortunately, some people do daft things because they don't realise the risk. One example was a house where I was doing an EICR a couple of years ago. I needed to pull a TV cabinet away from a corner to get at a double gang outlet, and when I did I found there was a melted coil of extension lead welded into the carpet. The owners were using it to run a fan heater, but it was too long, so being tidy people they tucked the coil of left over cable under the TV unit, where it just got so hot that it melted the insulation. How they had never smelt the burning plastic I don't know.
Agreed, the fuse is a heat generator. But it is also an insulator. It can prevent heat being conducted away that originates elsewhere, eg plug contacts. It's a problem almost unique to the BS1363 design. Made worse we agree by a thermoplastic moulded plug, some of which have poor welded connections. None of this an issue in 1946 when plugs were large, with a lot of internal air volume, made from stiff heat resistant thermosets. Electric things in my house that are high load and could be on for hours have these kind of retrofitted plugs.
 

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Fortunately, the BS1363 plug on the granny charger has a temperature sensor in it and the cable will shut down if the plug gets too hot. That means you're left only with the risk from the household electrics to deal with .. in theory ..
 

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Fortunately, the BS1363 plug on the granny charger has a temperature sensor in it and the cable will shut down if the plug gets too hot. That means you're left only with the risk from the household electrics to deal with .. in theory ..
They don't all have this.....
 

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A quick question on this topic.

I understand that the electrics of the house and subsequent socket are more important than the granny lead, however, I just want to ask whether using something like this is a safe idea?

Tough Leads EV granny charger 13A weatherproof extension lead

That extension lead is rated 13A, but from this post and others, I understand that it is much better to draw 10A or less for continuous long use in a domestic socket. I am also aware that it is best to leave it uncoiled and not be tempted to roll up any excess.

I would be using the granny cable that came with my car (MG ZS EV) that is rated 10A anyway, so I am to assume that 10A is the max that would be put through the cable + extension, is that correct?

Probably answered my own question, but I am still new to this so I appreciate the help!

Thanks
 

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I made my own extension using a Schneider 13a RCD socket, and 10m of 2.5mm orange cable in a watertight box. I'm not keen on the inline RCD as in the type shown.
 

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A quick question on this topic.

I understand that the electrics of the house and subsequent socket are more important than the granny lead, however, I just want to ask whether using something like this is a safe idea?

Tough Leads EV granny charger 13A weatherproof extension lead

That extension lead is rated 13A, but from this post and others, I understand that it is much better to draw 10A or less for continuous long use in a domestic socket. I am also aware that it is best to leave it uncoiled and not be tempted to roll up any excess.

I would be using the granny cable that came with my car (MG ZS EV) that is rated 10A anyway, so I am to assume that 10A is the max that would be put through the cable + extension, is that correct?

Probably answered my own question, but I am still new to this so I appreciate the help!

Thanks

The Toughleads cables are fine, and the maximum current that a granny lead will take is 10 A, not 13 A (unless it's one of the slightly dodgy Chinese ones that can be set to too high a current for the UK). All granny leads that come with UK EVs are set to 10 A maximum so are fine for an outlet that's in good condition.
 
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