So, missus buys a replacement for the hairdryer that expired amid huge
> clouds of toxic smoke - see earlier post a couple of days down. It's from
> Asda, badged with their name. Carries all the CE etc. It's rated at 2 kW = max
> (1.8kW min). Now if my poor addled brain is still doing maths correctly,
> that equates to somewhere between 8 and 9 amps depending on where your ma= ins
> lies between 230 v and 250 v ??
>
> That being the case, I would have expected to see a reasonably stout,
> probably round, cable on it, much like there was on the one that has died= .
> Instead, it has a very flimsy flat cable on it. It's about what you would
> find on a table lamp that had a sheathed cable. Think of the sort of size
> cable that you would normally find on say a detachable 'figure 8' lead fr= om
> a portable radio or some such.
>
> If someone had stuck such a cable in my hand, and asked me what I thought
> the current rating of it was, then based on 40 years experience in the
> business, I would have said 5 amps tops. As the item has the appropriate
> approvals, and is being sold by a multi-national chain, then I'm sure tha= t
> it must be safe, and have undergone the appropriate tests, but I still ca= n't
> help looking at it and thinking that the cable is just not man enough for
> the job. Does anyone know if there is any derating curve or whatever appl= ied
> to items that only run intermittently for relatively short periods of tim= e ?
> Setting that thought aside though, it would be perfectly possible to leav= e
> it running unattended for long periods of time. There's plenty of people
> around stupid enough to use one as a heater for their hamster's cage or
> something similar ...
>
> Arfa
The limiting factor for current carrying on any electric cable is not the size of the conductor but how much heat the insulation can stand without deteriorating. Obviously there is more power lost in a smaller cable. So in principle, you can uprate a cable if the insulation can stand more heat.
There is no derating curve for domestic cables, they could be too easily ignored. There is sizing issue for ambient temperature. ie bigger cables need to be installed in warm places. (Like roof spaces or inside/adjacent to insulation). And there isutilisation factor.
And there is the issue of uncoiling extension leads fully before use.
So,it's all about heat.
Some cables are oversized just for mechanical strength.