Extension lead cable size

[noddy997]

Just curiosity really, extension cables are known for causing fires due to being overloaded especially the 4 or 6 socket ones.

What's the cable size in them 1mm?

If it's down partially to cable size why aren't they made with 2.5mm cable (yes it will be pricey but safer).

 

[Harry Bloomfield]

Just curiosity really, extension cables are known for causing fires due to being overloaded especially the 4 or 6 socket ones.

What's the cable size in them 1mm?

If it's down partially to cable size why aren't they made with 2.5mm cable (yes it will be pricey but safer).

1.5mm is fine, at the fuse rating of 13amps, for the extension and the fuse, is in the plug. If the cable is smaller, then the fuse in the plug should be less than 13 amps, to match the cable.

Where it goes wrong, is cheaply made multi-socket units, with fuses perhaps not meeting spec., and extension reels, where the user has ignored the instruction to unreel them before use, and the extension is being used at maximum current. Many wrongly think the issue is a problem of induction, because the cable is still coiled. In fact, it is simply the cable coiled up, being unable to get rid of the heat. All cable do get warm, when carrying current, how hot, depends upon how much current, and how close to their maximum rating they are run.

I'm away from home, on a caravan site, at the moment. Yesterday, there was a motorhome, plugged into the EHU, using their 2.5mm orange lead. All fine, apart from the owners had simply run off the reel, the cable they needed, and left the remainder still coiled up on the reel. Weather is OK at the moment, but had they been using that EHU at maximum capacity, to provide heat, and hot water etc., the risk was of that coiled cable overheating, melting, perhaps causing a fire.

 

[RandomGrinch]

Supplementary to the above, the CSA of a properly designed cable would also depend on other factors, such as its length; the longer the cable, the larger the CSA necessary to enable a low enough earth bond resistance, to allow for the correct operation of trips, and to decrease voltage drop etc.
Cheaper brands seem to push the equations to the limits, with slimmer cables on long leads.
There is also a practical limit to the size of cables that can fit into standard UK plugs.

 

[ericmark]

Weight, my 16 amp 25 meter extension lead used with the caravan was 2.5 mm² and little chance of that catching fire, the main problem is when cable coiled up as both acting like a transformer and keeping the heat in, so modern versions

have a temperature sensitive overload

built in, larger versions become unwieldy, and if charging my car battery, the charger only uses milliamps so why use a heavy lead? the highest load I have outside is the leaf blower at 3 kW but 1.5 mm² still ample for that.

So indoors is the main place where overload likely, over the years I have amassed a collection of these

and looking at the advert yes this is a worry no where does it say what size of cable used. It just says 13 amp.

The caravan hook up cable BS 7671 says minimum of 2.5 mm² and 25 meters (±2 m) so google it and this is only 1.5 mm² and too short, but it does tell you the size, and why should we have to have such a hefty lead if not required?

 

[Harry Bloomfield]

both acting like a transformer

As I said above, no they do not - The current and waveform, in the live conductor, perfectly matches, opposes, and cancels out that in the neutral conductor - hence, there is no inductance, nor acting like a transformer.

and keeping the heat in

That is the issue, lack of cooling airflow, or other means to dissipate the heat generated within the conductors, due to their resistance..

 

[noddy997]

Interesting comments.

Has anyone created their own domestic use one bearing in mind plugs might not accept 2.5mm?

 

[Harry Bloomfield]

Interesting comments.

Has anyone created their own domestic use one bearing in mind plugs might not accept 2.5mm?

Over the years, I have made up lots of extensions. 2.5mm is difficult, but doable, with the right plug. More often, you would fix 2.5mm to a 16amp plug.

 

[crystal ball]

1.5mm is fine, at the fuse rating of 13amps, for the extension and the fuse, is in the plug. If the cable is smaller, then the fuse in the plug should be less than 13 amps, to match the cable.

Where it goes wrong, is cheaply made multi-socket units, with fuses perhaps not meeting spec., and extension reels, where the user has ignored the instruction to unreel them before use, and the extension is being used at maximum current. Many wrongly think the issue is a problem of induction, because the cable is still coiled. In fact, it is simply the cable coiled up, being unable to get rid of the heat. All cable do get warm, when carrying current, how hot, depends upon how much current, and how close to their maximum rating they are run.

I'm away from home, on a caravan site, at the moment. Yesterday, there was a motorhome, plugged into the EHU, using their 2.5mm orange lead. All fine, apart from the owners had simply run off the reel, the cable they needed, and left the remainder still coiled up on the reel. Weather is OK at the moment, but had they been using that EHU at maximum capacity, to provide heat, and hot water etc., the risk was of that coiled cable overheating, melting, perhaps causing a fire.

A common sight on site

 

[Ragnar_AT]

Some are 1.25 mm2 and I‘ve been told that’s enough for 13 A. I definitely have a 5 m single extension lead with 1.25 mm2 and a 13 A fuse, bought in Dublin some 15 years ago. Since that size isn‘t used elsewhere you’re more likely to find 1.5 though.

Domestic extension leads and power strips aren‘t likely to be overloaded unless you plug electric fires or large household appliances into them though. Most of our gadgets these days are in the double-digit Watt range. Plugging a dishwasher, oven or washing machine into one is obviously an entire different matter but even that doesn‘t necessarily cause a fire. A colleague in Austria managed to get her kitchen partly rewired by the landlord when she discovered that the 7 kW cooker, 2.4 kW dishwasher and microwave were plugged into one power strip (16 A unfused). She showed me pics and there were no traces of overheating.

 

[Risteard]

Just curiosity really, extension cables are known for causing fires due to being overloaded especially the 4 or 6 socket ones.

What's the cable size in them 1mm?

If it's down partially to cable size why aren't they made with 2.5mm cable (yes it will be pricey but safer).

Because a BS 1363 plugtop (don't care who that term annoys) isn't designed to accept cable larger than 1.5mm^2.