# Coiled Power Cables, How Dangerous?



## peejay (May 10, 2005)

Following on from a recent post it is generaly considered a bit dodgy to leave your electric cable coiled up whilst plugged in as it generates heat with the possibility of a fire breaking out and I understand that, especially as we are used to high amp hook ups in the UK, however anyone who has travelled abroad must have noticed that the majority over there don't seem to bother, full reels are a common sight when plugged in.

Is it because its mainly a low amp supply over there which won't generate too much heat through the cable or are they all mad foreigners with scant regard for safety?

pete


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## rickwiggans (May 10, 2006)

My ex-wife decided to have a bath one cold winter's night - old cottage - no central heating. Used a 2Kw ( so 8 amps or so) fan heater, on a 25 metre extension, with only 2 metres fed out. It melted!! 'Nuff said? Pity she didn't melt as well!!!!

Rick


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## DABurleigh (May 9, 2005)

pete,

There are the 'elf & safT purists who tut away when they see such criminally negligent behaviour, there are those pragmatists who understand the phenomenon and act accordingly, and lastly there are those blissfully ignorant ones who could start a fire.

So if I were using long cheap thin cable at sustained high amps in warm weather I'd run it all off the reel. Using quality cable in cool weather at moderate currents with a duty cycle, I wouldn't dream of taking any more off the reel than I need.

Dave


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## weldted (May 1, 2005)

*it is dangerous*

Any coil of wire with sufficient current passing through it will generate heat the easiest answer I have found is to carry two cables of six and fifteen meters the six meter one usually does most english sites with the ten some times used and with both I have found it to be enough for most continental


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## sallytrafic (Jan 17, 2006)

Its not a scare story but you have to take account of the current being drawn and the ambient temperature. The derating of cable when coiled or laid up close together is a fact as evidenced by the derating tables in the wiring regulations and on every cable reel that I have seen (one in front of me as I type is 13A fully extended 7A reeled. There are plenty of caravans out there that pull the full 16A from the UK hookup. One or two on here as well.


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## sallytrafic (Jan 17, 2006)

DABurleigh said:


> pete,
> 
> There are the 'elf & safT purists who tut away when they see such criminally negligent behaviour, there are those pragmatists who understand the phenomenon and act accordingly, and lastly there are those blissfully ignorant ones who could start a fire.
> 
> ...


Taking Dave's point and fully agreeing with him. More injuries are caused by slips trips and falls than are caused by cables on reels overheating.

I always ensured that my men and contractors when working on lighthouses could balance the various risks involved and sometimes that would mean that cable reels were *not* to be unwound.


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## peejay (May 10, 2005)

Thanks leccy techies  .....

My set up which is regularly used coiled and using 4 amps max should be ok then....










I hasten to add that it will be always be fully uncoiled when getting my compulsory 16 ampsworth from CC hookups :wink:

pete


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## NEV3 (Feb 7, 2007)

Cables whether coiled or not will generate heat. I proved this point on a rally two years ago in the snow. My cables melted the snow and encased themselves in ice overnight. They fully unwound.

NEV3


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## kijana (May 1, 2005)

I always unwind my cable because I'm a tight beggar.

Why should I pay to heat up the environment, when I can uncoil & use less electricity?

The above applies only on metred electric sites, but still think it's good practice to uwind.

Bruce


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## weldted (May 1, 2005)

*relax*

I thought the whole idea of camping was to unwind.


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## DABurleigh (May 9, 2005)

And I hope Bruce is trying to wind us up


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## sallytrafic (Jan 17, 2006)

peejay said:


> Thanks leccy techies  .....
> 
> My set up which is regularly used coiled and using 4 amps max should be ok then....
> 
> ...


Of course this set up does not comply with BS7671 and therefore is explicitly banned at CC sites.


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## WingPete (Jan 29, 2006)

*Fire Invetigation*

When I was in Fire Brigades, investigation was one of my more interesting jobs. 
I have come across the scenario of fires starting due to appliances drawing lots of amps, as in heaters, run from a coil of cable, overheating to the point of igniting the insulation, then any other combustibles nearby, like carpet or vinyl floor coverings.
It even happened to close friend who lived on a farm, with not much heating. She bought a convector heater for the hallway, and pulled out only about 2 metres of cable from a drum, and plugged it in overnight to warm the upstairs a little. She smelt the nylon carpet smouldering and managed to deal with the situation without misshap. Interesting to see the result at this early stage of what could have been a dissaster.
One point also, was that her smoke detector did not work, which is why she asked my advice. On checking that, there was no battery, as a daughter had removed for her tranny radio !
Take care out there, as misshaps do happen to the unwary.


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## geraldandannie (Jun 4, 2006)

sallytrafic said:


> Of course this set up does not comply with BS7671 and therefore is explicitly banned at CC sites.


Why, Frank?

Gerald


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## sallytrafic (Jan 17, 2006)

geraldandannie said:


> sallytrafic said:
> 
> 
> > Of course this set up does not comply with BS7671 and therefore is explicitly banned at CC sites.
> ...


Why they insist on the regulations or why the above doesn't meet it?

assuming the latter I can't post a link to the actual regulations but here is a link to a guide which quotes in part. >here<

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.


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## thegreatpan (Oct 29, 2007)

> One point also, was that her smoke detector did not work, which is why she asked my advice. On checking that, there was no battery, as a daughter had removed for her tranny radio !
> Take care out there, as misshaps do happen to the unwary.


I'm with WingPete on this one, I to have to investigate fires, well at least until August when I retire 

I have seen several fires caused by using an extension reel with a high load appliance whilst almost completely wound.

Unfortunately I also have been to a lot more,some fatal, where a smoke alarm was fitted but had the battery removed.

Remember with smoke alarms to test them! Also if you think you need an alarm in your house, most Fire and Rescue Service's fit them for free!

_Mod edit: quote put inside quote markers_


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## sallytrafic (Jan 17, 2006)

I have posted this on the other thread about coiled cables but its probably more relevant for future searches if its put here as well.

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'


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## framptoncottrell (Jan 6, 2006)

Thanks, everybody, for these excellent and potentially life-saving explanations.

There are so many times on this forum when I realise just what a good investment my £10 p.a. has been.

Dr (musical, not medical) Roy


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## 109621 (Jan 31, 2008)

peejay said:


> Following on from a recent post it is generaly considered a bit dodgy to leave your electric cable coiled up whilst plugged in as it generates heat with the possibility of a fire breaking out and I understand that, especially as we are used to high amp hook ups in the UK, however anyone who has travelled abroad must have noticed that the majority over there don't seem to bother, full reels are a common sight when plugged in.
> 
> Is it because its mainly a low amp supply over there which won't generate too much heat through the cable or are they all mad foreigners with scant regard for safety?
> 
> pete


Youve hit on the head pete, the higher the current flowing the more heat produced, the normal hook up abroad is normally max 6 amps , here there is up to 16amps available to draw, however it depends on what you call coiled, a normal hook up cable partlly coiled lying on the ground is no problem, if the cable is wound on a drum with coils touchinh an electromagnetic field is produced, the the higher the current the stronger the field with the result of heating

bolly (sparks)


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## sallytrafic (Jan 17, 2006)

bolly said:


> peejay said:
> 
> 
> > Following on from a recent post it is generaly considered a bit dodgy to leave your electric cable coiled up whilst plugged in as it generates heat with the possibility of a fire breaking out and I understand that, especially as we are used to high amp hook ups in the UK, however anyone who has travelled abroad must have noticed that the majority over there don't seem to bother, full reels are a common sight when plugged in.
> ...


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.

It is however a common misconception I have seen it repeated in safety instructions in University.


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## Boff (May 10, 2005)

bolly said:


> ...if the cable is wound on a drum with coils touchinh an electromagnetic field is produced, the the higher the current the stronger the field with the result of heating


No!

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.

Best Regards,
Gerhard


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## sallytrafic (Jan 17, 2006)

Boff said:


> bolly said:
> 
> 
> > ...if the cable is wound on a drum with coils touchinh an electromagnetic field is produced, the the higher the current the stronger the field with the result of heating
> ...


I agree the amount of heat generated is the same what matters is the amount of heat escaping as I'm sure you agree.


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## Wizzo (Dec 3, 2007)

So if I understand correctly then it is not so much to do with whether the cable is coiled or not but whether or not it has adequate ventilation? Hence the problem with leaving it coiled inside a plastic case?

JohnW


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## sallytrafic (Jan 17, 2006)

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


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