Another electrical question

[craigb]

My 15 amp extension cord has a safety card on it that says "Caution: Comletely uncoil before using".

So what's the big deal? As far as I can see, the worst that can happen if I use it coiled is I'll induce a magnetic field around the coiled cable .

So what?:confused:

Is there more to it than this?

I've pondered this for a while and the time has come for the definitive answer.

So...?

[echnidna]

The electrons are much happier running in a straight line, they get dizzy if'n they have to run around in circles

[Wood Butcher]

In inducing the magnetic coil, I think that you also generate a certain amount of heat. If there is enough "coil" generating heat you could (and it is a very loosely defined could) cause the plastic to melt and the wires to short. You would need a decent size coil of lead and to have sufficient amount of continous current passing through the lead for this all to happen.

[Clinton1]

Yep, heat.

[Sturdee]

In my younger days I used a 30 metres extension cord without fully unwinding it. After a few hours the wound up part of the cord became quite warm. Now I always uncoil a cord before use.


Peter.

[outback]

I have seen the result of a really long cord left mostly wound on the hose reel on which it was stored. After a few hours of use it let out all the smoke. :eek:

[craigb]

Well I've got a 15m cord and the coils are about 450mm in diameter.
Even drawing max current all day (which I don't) is that sort of coil really going to generate a problem amount of heat?

I kind of think that Boban's explanation is the most likely.

Ie cover your asre with both hands.

[boban]

I deleted my post because even though I think its unlikely, I still, out of habit or overcaution, undo my cords completely.

Im no scientist so I'd probably better keep my trap shut.

All said with both hands on my bum

[journeyman Mick]

Years ago my brother's mate came over to my brother's place to do some welding. Used a tradesman's single phase arc welder for a good part of the day, running off an extension cord that was in a pile on the ground. My brother went to use the welder the next day and it wouldn't go. He went to uncoil the lead to see what was wrong and discovered that the lead had melted together in several places and shorted out. :eek: I don't think it's the magnetic field being induced that causes the heat, just the current draw.

Mick

[Harry72]

It makes a big inductor!

[Bodgy]

Covering one's ass against heat.

If you really ran the 15 amps to its max, probably 25amps, then, if coiled, it would overheat.

Another example of Seppo and lawyer inspired bs.

[Schtoo]

The reason they out that on the lead is because it's a plug in thingy, and as such the regs regarding it are open to interpretation.

Short version is there are no enforcable regs to speak of.

If it was fixed wiring, there are rules and regulations governing how many bits of wire are allowed to fit into a certain space in a certain place.

As 'they' can't know how or where the lead will be used, they try to minimize the worst case scenario by taking one factor out of the equation, that being several bits of wire all heating each other up.

'They' figure that taking out a big bit of the problem makes the problem (the problem being turning customers into crispy critters) unlikely to occur, even when you do lots of other bad things to the lead.

And it's only resitance.

If the cable was, say 15mm in diameter per wire, then inductance does come into it and you have to fix the cable in a proper manner to reduce the effects of inductance.

And there you go.

Schtoo, card carrying dumb ex-sparky.

[knucklehead]

Craig most 15 amp cables are over designed. Nearly all 15 amp extension leads are used by tradesmen or in industry. Therefore the cables are heaver duty (both wire and insulation). If you are getting a 15 amp cabel hot there maybe something wrong with it.
With standard 10 amp extension leads the quality of construction varies widely. Running max current through a cheap (thin) lead while it is coiled up will produce a lot of heat. The same load run through a better quality (less current loss and thicker) will have no effect.

I only by heavy duty extension leads, which are really 15 amp cables with 10 amp plugs on the end. This gives a lot more protection against physical damage but also lessens the current loss and heat build up.

[Clinton1]

For all the different views on the subject, using it when coiled has led to enough accidents to warrant the warning being used.
Do it and cause a fire or accident and it'll probably void the insurance. Doesn't take much to uncoil it and stay safe.

[Iain]

The Medical profession are major shareholders in cable companies, by uncoiling the leads gives one something to trip over thereby generating dual income (dividends and business).......honest
If the cable is wound on a metal spool it will generate more heat than on a non conductive spool......fire risk is the key word here, regardless of how slight.