EHU leads.. a dangerous habit folk have (1 Viewer)

[buttons]

a coiled cable, ie...on a drum or tightly wound etc, is dangerous but a loosely coiled cable should be ok.

make each loop around 1 mtr and spread loosely on the ground ...still quite tidy and out of the way.

tightly coiled inner loops on a drum get no cooling air and will overheat.

This subject has been covered in depth on another forum, I thought that I would paste a couple of their posts, Have a read it could be useful.

QUOTE::welcome:

There is no appreciable external magnetic field generated by a coiled three core cable. The fields generated by the neutral current core mostly cancelling the field generated by the live current core which is why a clamp meter only works on single cores. The heating effect is solely due to bunching of the cables as I have explained earlier in the thread.

As the current flowing in one direction through the live wire is exactly the same as the current flowing in opposite direction through neutral (otherwise the RCD would trip), the magnetic fields from live and neutral cancel out each other.

The only thing that determines the "heating power" of the whole cable is the "ohmic" resistance of the wires, multiplied with the current to the power of 2. So if you go from 4 amps to 16, the current increases by a factor 4 and the heating power by a factor 16!

For the total amount of heat generated it does not matter whether the cable is coiled up or not.

I agree the amount of heat generated is the same what matters is the amount of heat escaping as I'm sure you agree.
[FONT=&quot]The key perhaps to understanding it is to think about the fact that the same current is flowing in all the cable so the same amount of heat is being produced throughout its length.

When coiled

Only the turns of the cable at the top have an air surface to give off their heat to.

Turns of the cables at the bottom and sides may have part of their surface touching a heat conductor and will fare better.

Turns in the middle are surrounded by other turns all heating up. So as heat can only flow from hot to cool there is nowhere for the heat to go and the temperature rises.

In the attached sketch shows a cross section of the coill with the middle turns heating up[/FONT]

Its a while since I have had a copy of the Regs to hand but when I inserted the amendment that brought in caravan sites I believe there was reference to the colour of the outer sheath (which may or may not have been subsequently amended).

Anyway just from the photo and the evidence I have produced it looks like more than 25m on the reel para 11 and there is no notice para 3.

Note also that this part of the regulations Special Installations is preceded by an introduction and I think this is a accurate precis

The Regulations apply to all electrical installations in buildings. There are some situations out-of-doors, as well as special indoor ones, which are the subject of special requirements due to the extra dangers they pose, and these will be considered in this chapter. These Regulations are additional to all of the other requirements, and not alternatives to them.

However my remark that you quoted was merely throwaway, PeeJay's installation looks good to me, but perhaps intended to deter DIY reel makers to meddle in stuff they don't understand.

[FONT=&quot]When a cable is rated consideration is given to:

How hot the copper core will get at a range of ambient temperatures, at a range of currents.

The heat transmission properties of the insulation

The melting properties of the insulation.

How the various wires perform when made into a (say 3 core) cable.

A max rating is arrived at for the cable in free air at say 20 degrees C. At that max rating enough heat will be given off by the outside of the cable to keep the temperature inside within specification (max about 70 degrees C for PVC/PVC insulation) Anything that stops this heat escaping will at the max rating rapidly lead to the cable melting.

They then produce a specification.

It follows from this that the effect of warm cables even fairly loosely wound on a reel will affect all the turns of the cable preventing the heat from escaping and therefore the insulation gets very quickly to its melting point.

A short between the two hot wires of a three core cable (Live and Neutral) won't trip the RCD but will trip the main MCB. If there is enough energy at the point of the short circuit a fire may start before the removal of current allows the whole thing to cool.
Derating the cable when wound on a cable to around 50-55% of it max rating is done because 8A run through a 16A cable wound up won't get any hotter than 16A when laid out.
edit added "at a range of currents'[/FONT]

 

[madbluemad]

Too much info
Jim

 

[johnp10]

This is basic schoolboy electrikkery, folks.
Lesson 1 for a sparks, PPJ?
It's dangerous.
It's also stupid.
Dont do it!

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[Bailey58]

I have a 25 metre extension cable on a drum, bought it years ago before I knew anything about this problem. The last couple of metres on the drum is flat and almost worn through the outer sheath where it has been used uncoiled. It's now been shortened to 23m with the offending section removed. oh:

 

[ROB1CHELSEA1]

I was surprised when i moved my van last weekend that Jaws had arranged my lead in the way that i always do it, a bit drunk i forgot to thank him, im always having to tell my lads how to lay out a lead and how to roll it up (like a lasoo) is the best way.

BIG THANK YOU TO JAWS:thumb:

 

[Jaws]

Anyone notice the dates on the old thread... pretty much a year to the day !

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[eddie]

Buttons is dead right 100% The cannot make an inductive coil this way, so no heat is produced in the same way as say an electric bar heater.

Also an major factor is the quality of the conductor and the insulation.

I always and will only use high quality artic flex.

I have a 25M cable and a second one cut in 10M and 15M sections so I can have pretty much any combination

When I go abroad I also take a 50M as some sites have a hopeless electrical layout.

Eddie

 

[gypsylady]

I learnt my lesson years ago, in the house.

We had one of those home extensior leads that wind into a case with the 2 sockets on the side of the casing.

I needed a lead so I could use my sewing machine and to keep it all tidy I only wound out enough lead to give the length I needed.

The inevitable happened, The lead melted in the box. I was lucky there was no fire.

Be careful out there.

June

 

[Chris]

I only knew the cable needed to be uncoiled because my stepfather told me. The dealer didn't mention it. Perhaps that should be part of the handover procedure to spread the message.

I was in St Ives a month or so ago and about 2 or 3 motorhomes had their wires coiled tightly directly under the van. I did mention it to one chap but he asked me why. I said it was because it gets too hot but that was the limit of my technical knowledge.

Anyway he ignored me. A lot of people know bestoh:

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[GJH]

When stories like this come up I'm always amazed by how many people are unaware. The danger posed by a coiled cable was one of the first things we learned in Physics at school 50 years ago.

 

[Mr Colpot]

Having seen first hand (albeit in a workplace rather than Campsite) what can happen, I have always unwound my cable fully and its a lot easier since I changed to the Arctic Blue cable which stays pliable at low temperatures.

 

[scotjimland]

When stories like this come up I'm always amazed by how many people are unaware. The danger posed by a coiled cable was one of the first things we learned in Physics at school 50 years ago.

Totally agree Graham, but sadly there are thousands of kids leaving school every year who can barely read, write or do basic arithmetic.. so little chance they have a clue about physics..

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[GJH]

Totally agree Graham, but sadly there are thousands of kids leaving school every year who can barely read, write or do basic arithmetic.. so little chance they have a clue about physics..

Yes, the failure to implement a system which provides education targeted at capabilities rather than a dumbed down one size fits none in the name of "equality" and tries to cram in advanced stuff before the basics have been given a chance.

When I was at primary school in the 1950s there was a handful of kids who struggled with the basics but the streaming at primary level meant that all learned enough reading, writing and basic arithmetic to cope in what was then secondary modern education - and enabled learning basic things like the dangers of coiled cables in a practical manner.

There were big faults with that system, not least the 11 plus for many children, which was supposed to be fixed by comprehensive schools. Too often, though, comprehensive has come to mean the same for all rather than a system which recognises individual capabilities and caters, comprehensively, for all abilities.

 

[lesleyjean]

The trouble is... most people that have decided it is fine to do something one way, will think they are right. MOST others who never thought about how they are doing something are going to say the same thing..... 'Well I have never had a problem'.
Whether you are talking about coiled up EHU leads, dodgy gas refilling adapters, A frames or the way to strap a car on a trailer.... they do not want to know.
I can be the same, backless shoes whilst driving? What the hell is wrong with that? I have been in a plane where the pilot and co pilot both had bare feet (thinking about it we did land in the sea) Jane

No offence meant,

but can you all remember recently about the guy that was warned about sharksoh:

He had been ignoring advice to stay out of the water foe a long time.

It only takes one time.

Unfortunately for him, he was bitten and I think he lost both legs

 

[JayDee]

The trouble is... most people that have decided it is fine to do something one way, will think they are right. MOST others who never thought about how they are doing something are going to say the same thing..... 'Well I have never had a problem'.
Whether you are talking about coiled up EHU leads, dodgy gas refilling adapters, A frames or the way to strap a car on a trailer.... they do not want to know.
I can be the same, backless shoes whilst driving? What the hell is wrong with that? I have been in a plane where the pilot and co pilot both had bare feet (thinking about it we did land in the sea) Jane

I nearly always drive bare footed. Contrary to what quite a few folk believe. in the UK there is no law against doing so. Personally I find it is more comfortable and I get a better 'feel' for what I'm doing with the pedals. I always slip a pair of flip-flops on when I'm refuelling - diesel isn't frightfully good for ones feet. But I spend more time bare-footed than I do in footwear anyway.


John

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