Rolling up an electrical cable.

[Surfer]

Watch this video. https://www.youtube.com/watch?v=Gx_LUIubmI0
He mentions that you can leave the cable still wound up on the drum. Is this feasible as to a layman looking at the way it is wound onto the drum, you now have two coils and to my mind they should countermand one another and there should be no build up of heat as per a single coil?
Any comments?

 

[Sproket]

May be the inventor does not read the news hmy:

"Extension leads should be used with caution - the flex of a coiled extension lead should be pulled out completely before appliances are used.

"If the lead is left coiled, the unit can easily overheat causing a fire.

 

[WoodlandsCamper]

Not sure what the bend radius of the cable is but it seems fairly tight when looped on the middle spigot, mainly in cold weather. Also, as we are talking about mains ac current I'm not sure whether winding in both directions would cancel out any heating effect. Will have to wait for a reply from the experts.

 

[emmerson]

Agreed, lets wait for the leccy's advice, but it sounds wrong to me.

 

[Damian]

As AC is oscillating at 50 cycles per second it makes no difference to the heating effect of wound cable.
With a draw of say 2000w, the cable will heat up if left wound on the drum with the possibility of it causing a fire.

The usual safety precaution of unwinding completely should be followed with excess cable loosely laid in open coils on the ground out of the way , like under the van .

 

[Craigyoung]

I never leave any on the coil no matter how much is left , just been away where I was backed up to the EHU post so only used a few metres of my cable so had about 22m or so neatly placed under the rear off the van - loosely to !!

 

[colin-yorkshire]

watched the video, to me looks like some Yank reinventing the wheel, as they do :woohoo:
any wire, hook up or otherwise should not be used while coiled up no matter what the direction. only thing this could achieve is to dissipate the effects of electromagnetism in the coil. doubt wether with AC current it would matter anyway.what it will not do is dissipate the heat which is the real problem as the cable needs air circulation to cool it.
if you dont want yards and yards of loose cable lying around carry a shorter cable. say 8 or 10 mtrs long for the times when you are close to the box, simple yes. :silly:

 

[Raywood]

Cables on a reel can overheat when used and it certainly shortens the working life of them so unwind every time you use.
My domestic extension cable is labelled safe to use at 5 amps but has to be unwound for 13 so it may be safe for running a single low power item but the cables are not clear on this or at least mine are not..

 

[GStockton]

Another 3.5 mins of my life wasted looking at this rubbish

 

[emmerson]

That's a bit fierce! Pray tell why you think its rubbish?

 

[GStockton]

Because it only shows him coiling a very lightweight Flex pos 0.5 or 0.75mm Try doing that with 25 metres of 2.5 mm Caravan hook up cable. After 40 odd years as an electrician I never put cable back onto a reel

 

[bertieboy1]

The cause of heat in a coiled cable is lack of ventilation and/or high current.In the past there has been mention of heat buildup in coiled cable due to electric fields around the cable caused by the current passing though,with a two core cable current is passing backwards and forwards through each core,the effect of this is to cancel out the electric field to the extent none will exist.

 

[gary]

I watched it twice! because I showed it my lad yesterday, he's 17th edition etc, when he stopped laughing....joke :lol:

Personally I don't even agree with drums, my cable is coiled up in arms length coils for storage and any excess in use is thrown pushed or kicked under the van out of harms way.

As for the idea, he bemoans one plug getting damaged on the old design, no mention of the other end floating around loose?. He then says making a tight loop on that boss and winding it up is a better idea but at the very least you now have two ends floating around to get damaged.

Either way though, if you were to damage an end it can easily be replaced, but that tight loop in the middle is a constant stress point in the middle of the cable so when that causes a problem you need a whole new cable! hmy:

 

[foggydave]

With this system on a long hook up it would leave the reel half way across the field.
Given the large diameter of the standard caravan hook up cable does anyone know how much amperage/wattage you would need to heat it up to anything like dangerous? Also given a camp sites restrictive hook up amperage would you reach this point before the fuse tripped?
Has anyone actually seen a hook up coil smouldering?

 

[Damian]

As soon as any power is drawn through the cable it will start to heat, the more Amps drawn, the quicker it will heat up.
Taking a normal hookup 0f 16Amps, is a lot of Amps when drawn through a tightly coiled cable, and although not seeing a reel smouldering I have seen several, around 10 to 12 , which the cable has melted into each coil after having a heavy load drawn for a prolonged period of time.

If the spare cable is laid in loose coils on the ground it will not heat up enough to cause any problems.

 

[ProfJohnL]

Foggy dave asks how much current you need to start it getting too warm.
The electrical basics are that every conductor has some electrical resistance, and when you pass a current through it it will use some current to generate heat within the conductor, and a potential difference across it its length.

The amount of resistance a cable has is indirectly proportional to the cross sectional area (csa) of the conductor, and directly proportional to the length of the conductor.

Most domestic cables use a copper based metal for the conductor, and Appendix 4 of the Guide to the Wiring Regulations to the 17th edition gives the resistance per kilometer for a range of standard copper conductors.

A useful note at the bottom tells us:-
" Values are for stranded conductors but solid conductors are nearly identical. Taken from BS 6360: 1991."

The EHU cables should be manufactured with 3 x 2.5mm2 csa conductors E, L & N. The E conductor will only carry a current in a fault condition which should trip the RCD. So for the purpose of this post it will be disregarded.

For an electrical circuit to work, the current supplied to the caravan along the L conductor must find its way back to the bollard so the same current returns along the N conductor. So the total length of conductor is 2 x25 = 50M.

The table tells us that 2.5csa has a typical resistance of 7.41Ohms/kM or 0.00741 Ohms/M. Therefore a 25M EHU will have a typical resistance of 0.18Ohms per conductor. and the combined L & N conductors a resistance of 0.36 Ohms.

Assuming the EHU is running at its rated capacity of 16A, the power lost in the cable will be Current x Current x Resistance = 16 x 16 x.36 = 92W

Broken down into the watts per meter 92/25 = 3.6W/M.

So thats how much heat is generated, and the cable in the open will be fine, but start to reduce free air movement around it and the temperatures will soon rise. The maximum safe working temperature of the PVC insulation around the EHU is 70C.

 

[GStockton]

Very well put together post there Prof.

As I am currently on a site using my caravan for work in Lincolnshire, doing the sites Periodic inspection and test of all the Infrastructure and 100 or so hook up points before the season starts. Your post forced me to go out and measure the Resistance of a couple of hook up leads I have wth a calibrated instrument dead on 0.17 ohms

 

[bertieboy1]

Prof,
I think you mean current x current x resistance (I2R) = 16 x 16 x 0.36 = 92W - correct answer but wrong figures !.I'll give you 8/10 for this !

 

[ProfJohnL]

Prof,
I think you mean current x current x resistance (I2R) = 16 x 16 x 0.36 = 92W - correct answer but wrong figures !.I'll give you 8/10 for this !

Opps
I was burning the candle at both ends preparing that post, so thanks for spotting it. It will correct it , though it makes no difference to the bottom line heating effect..

 

[Woodentop]

Cables on a reel can overheat when used and it certainly shortens the working life of them so unwind every time you use.
My domestic extension cable is labelled safe to use at 5 amps but has to be unwound for 13 so it may be safe for running a single low power item but the cables are not clear on this or at least mine are not..

That is for the simple reason that manufacturers keep costs down by using cable that is technically too thin for the load. Most of the thick orange EHU cables are 2.5sqmm which is plenty heavy enough for any such job. I wonder who uses enough power for the cable to warm up anyway? Try any CC site in the UK and they will ask you to keep consumption down so that the system is not overloaded. Following a measurement made by another 10A on a cable of 0.17R will disspate 17W and believe me that will cause very little heating to touch.

In terms of the cable in the cold, both the orange 2.5sqmm and the blue 1.5sqmm EHU cables are not known as 'arctic' for nothing. They are specifically designed to be used in low temperatures so coiling one up after use in the cold will not damage it.