In the UK, electricians tell me that 'it is against regulations' to plug a 4 way extension lead into an existing 4 way extension lead.

Is this a safety issue? Surely, if the first extension lead in the chain is correctly fused, there is no real hazard.

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    I'm a electronic engineer and I heard the same in the practical part of my study. Not that extension leads are a main focus there ;-) One problem is that you might draw to much current over one extension. Especially extensions without a cable can heat up if accumulated because of the current. So cheap extensions + bad fuses => fire risk you should avoid. Also longer extensions leads e.g. with 50m located in a reel must be unrolled for higher and even medium currents because the tightly packed cable would overheat otherwise (and trigger the thermo-fuse). – Martin Scharrer May 4 '11 at 9:59
  • Isn't this better over at Electronics? – Uticensis May 4 '11 at 19:49
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    Hmm it's more Electrics than Electronics but I was sceptical about it being a risk - hence starting here – Matt Wilko May 5 '11 at 8:40

Quite likely if you were to actually populate every socket on the extensions with a current consuming device, or even just a few high power devices like cookers, kettles, heaters and vacuum cleaners. As long as the total of all downstream appliances connected peak power and current usages are lower than the power/current ratings (watts and amps) of the strip and any upstream extensions leads (plus their appliances), then it would be safe.

The hazard exists if you go over the rating, which can lead to blown fuses, or overheating cabling with melting insulation or melting sockets - which then becomes a fire hazard or exposed mains voltage hazard.

As put in the UK HSE guide: "Make sure that the electrical equipment you are intending to use is suitable for the electrical supply to which you are connecting it."

References: electrical safety knowledge + experience. UK HSE Electrical Safety Guide: http://www.hse.gov.uk/electricity/electricequip.htm

  • If you are using a space heater and a vacuum cleaner, you can easily exceed the ratings without populating every circuit. The simple rule of thumb: add up the watts. The total wattage must be under the rating for the cable. – horatio May 4 '11 at 14:05
  • This is 100% correct but at risk of bring downvoted due to lack of links to references. – user5341 May 4 '11 at 14:32
  • The reference is my own experience and knowledge of electrical safety and systems. I think perhaps the "Only if" is wrong, as horatio points out - later in my answer I cover the total rating. Also worth noting that it is power, not simply current as my answer suggests. – Danny Staple May 4 '11 at 14:52
  • Welcome to Skeptics! This answer is not properly referenced. Please add citations to support your claims! :-) – Sklivvz May 4 '11 at 15:15

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