Electrical - an note of caution

[pappaecho]

At the boatyard today our power went off due to the area trip being continually triggered. Having unplugged five different leads from the fuseboard, we found the culprit. A 16 amp cable then fitted to a 10 amp extension lead via a 13 amp plug. The extension lead was the coiled type round a circular coiling unit. The unit had been used in its coiled form with only 2 metres having been unwound. The load on the unit and its coiled state caused the cable insulation to melt and fuse together. To find this we took the unit to bits with a disc cutter.
I was always taught to uncoil extension leads so that the heat build up is dissipated .
The owner was not aware of this.

 

[VicS]

The only bought one that I have is marked with a power rating coiled as well as un-coiled. 5 amps and 10 amps respectively.

It also has a built in thermal trip.

its only a cheap one from Lidl.

 

[snowleopard]

My father once plugged a fan hearer into a fully-coiled extension to heat his bedroom. He was fortunate to wake up to find the room filled with smoke. Most extensions have fully-wound and fully-unwound ratings. The former is usually around 4 amps.

 

[prv]

I don't think I've seen one for years that didn't have a thermal trip in it for exactly this reason. Of course there are a lot of old ones out there.

Pete

 

[ProDave]

I was rewiring someon's outhouse where they kept the washing machine and tumble dryer.

They were both being run together from one extension lead mostly still coiled that was running VERY hot.

I turned it off and uncoiled the lead, then told the customer never to use an extension lead while coiled.

Her reply was "is that why they keep melting and I have to buy a new one"

So some people just never learn, or never read the instructions.

 

[savageseadog]

One further tip. When using extension leads or marina power leads, never wind cable round marine metal work, especially winches, don't ask how I know.

 

[oldharry]

My other half melted the Flymo cable simply by leaving it loose coiled on the ground. She had taken it off its winder but not straightened it out.

 

[Bru]

Once kicked the arse of a young techy who I caught neatly coiling up the surplus of a too long 63A power feed and tucking the coil under the stage

Doubt he ever made that mistake again though

 

[Searush]

For the sake of those reading this & wondering WTF;

Coiling a cable or wire which is carrying a current creates something like the coil of a motor. Alternating current reverses its direction 50 times a second & can create a lot of heat.

Taking less power from the cable reduces the current flow & therefore the heating effect, so a coiled cable used for, say a drill for a few minutes at a time now & again may be OK, but the heating element of a washing machine or fire over several hours definitely is NOT!

 

[Leighb]

I made this mistake once many years ago.

I was working in the garage in depths of winter and had a small fan heater on . I had it plugged in to a coiled extension lead which, on that one occasion, I forgot to unwind. There was a hot plastic smell after quite a short time, and I immediately switched off. I then unwound the cable to find that some of the inner turns had started to melt and stick together.

I did not do that again. If it had been left unattended there might well have been a fire.

 

[DaveS]

Coiling a cable or wire which is carrying a current creates something like the coil of a motor. Alternating current reverses its direction 50 times a second & can create a lot of heat.

This is a common misconception. A coil of wire will indeed act as an inductor, but a coil of cable (containing both line and neutral wires) will not. At any instant the line and neutral currents are equal in magnitude but opposite in direction and the wires are sufficiently close together for the respective magnetic fields generated to effectively cancel each other out.

Which is not to say that it is a good idea to pass heavy current through a coiled up extension, just that the cause of the problem is purely thermal, i.e. resistive heating of the wire, not electromagnetic.

 

[guernseyman]

A cable carrying a current will heat up regardless of whether it is coiled or not. Uncoiled it can dissipate the heat by convection. Coiled, the heat can hardly escape from the inner turns of the coil, and their temperature will rise.

An important factor is that the heating effect is proportional to the square of the current.

You may hardly notice the warmth of a cable carrying 1 amp. But a cable carrying 10 amps will generate 100 times as much heat.

 

[VicMallows]

This is a common misconception. A coil of wire will indeed act as an inductor, but a coil of cable (containing both line and neutral wires) will not.

Nice to see a response from someone who knows what they are talking about.

Anyone notice the 'letter' in yesterdays Telegraph (travel I think) where someone was 'surprised' that their 2A plug adapter overheated when they used it with a hair dryer?

Vic

 

[Ubergeekian]

Coiling a cable or wire which is carrying a current creates something like the coil of a motor. Alternating current reverses its direction 50 times a second & can create a lot of heat.

It's actually nothing to do with AC or inductance - it's simple resistive heating of the cable and poor heat dissipation when it's all jammed together on the reel.

Because the current is going out along one wire and back along an adjacent one it's what we call a bifilar winding, and there are no significant electromagnetic effects. I spent a year or two of my life making bifilar wound coils for just this reason!

Edit: Damn, beaten to it. But I'll leave this in because I like the word "bifilar"