So wife comes into my study and says "that's dangerous", pointing at the evolving nest of trailing 4-socket extension leads mostly connected together. And Googling this question results in everyone saying that "it will overload the socket and cause a fire". Why is this?
It isn't a great idea since it is also a trip hazard. I have two 6 way daisy chained in my office but that is to make all the peripherals (and there are a lot of them) power supply contingent on the PC being on.
It depends a lot on the load. An 8 way with mostly 10W wall warts plugged into it is no problem at all.
But people are inclined to forget and plug in fan heaters and vacuum cleaners and then the load can get enough to cause trouble. Some cheap and nasty 4 way sockets cannot actually cope with a 3kW load for any extended period of time and will soften and melt the plastic housing.
I have known the church tea ladies melt a 2 way 10m cable reel by plugging two 3kW kettles into it with only about 2m unrolled. All of our VH extension leads now have thermal safety cut outs (although I wouldn't put it past them to defeat that by cunning use of duct tape)
A nominal 13A BS1362 mains fuse will sustain 20A indefinitely and 30A for several minutes. eg
Provided the plug at the wall is properly fused, there shouldn't be a problem. It could be a problem with people running things off unfused adaptors. Given the large number of low-power items with power supplies that need to plug into a 13A socket, I don't see how my computer setup could work any other way. However, even with all three computers running and everything else on, the total load is under 2KW.
Because many will take a nugget of truth and expand it into a whole thesis of nonsense :-)
Overloading would be the a result of adding too much load, not a factor of the number of sockets.
So two 3kW fan heaters on a single extension lead will cause an overload. Two dozen bits of low power IT or electronic kit on a few cascaded 4 way leads would be fine.
The only particular added risk from cascaded sockets is that the earth loop impedance can creep up as a result of all those extra plugs and sockets. That can prove dangerous under fault conditions since there might be too much resistance to allow enough fault current to blow a fuse quickly enough.
That said, refreshing to see that the wife has some sense. :)
It's the first time. I have made a note ;)
That said, the extensions in question have 8 wall-wart things, and 3 USB chargers. Total load = 42W (according to my power meter plug thing). The USB chargers are not charging, and some of the wall-wart powered devices are off.
Thanks for the other replies too guys.
Don't forget to add a footnote that she actually cares about you. :)
So nothing to worry about then (trip hazard issue aside)
In many situations like this, it is unrealistic to install enough hard wired sockets to cope with some use patterns.
A quick glance round my office shows around 42 sockets on short multiway extensions. Fan that I am of decent quality fixed wiring installations with plenty of sockets, even I think that would be taking the piss for one 12x10 room!
Even the earth loop impedance problem it usually only an issue on cascaded *long* leads... (which might also cause voltage drop problems on high loads as well)
As usual I can't compete with you. I just finished my count of a total of mere 19 items from 6 trailing sockets from one double socket. Maximum total load around 900W. No trip hazard as they are all behind a desk and shelves above it. Counting them has though made me wonder if the accumulated dust might be a health hazard :(
Its probably fine so long as you don't go and disturb it :-)
And does everyone on Google even know what a watt is? An overload occurs with an excessive load.
It's really only a problem if you're running high power devices - a few lights, chargers, laptops and accessories won't overload anything, but heaters or other high power devices may. If she's worried stick a 5 amp fuse in the plug that goes into the wall socket, that will provide better protection. You could also use a RCD adaptor if the main isn't already on one; that will only help in quite specific circumstances but it looks like you're making an effort. :-)
I have 20 IEC sockets behind the AV setup. 10 always live, 10 switched (via a relay) from the pre-amp mains switch. Everything on a single radial from the CU.
A thing I try to do is not chain extensions, but tree them. In other words you have one 4 way extension plugged into the wall. Into that plug in up to another 4x 4-way extensions, ideally with the highest load plugged in nearest to the cable on the 'root' extension.
The thinking here is that any wiring and the busbars inside a strip have resistance. By keeping the highest loads (be they single loads like heaters or strips concentrating other loads) closest to the power source, you reduce the resistive path the highest current needs to travel, and so the heat and losses.
If instead you daisy chain (in the above example using 5 extensions in a chain) the last one sees the resistance of five cables and four busbars, instead of two cables and less than one busbar that you get in a tree. (plus in each case the fraction of a busbar depending on where on the final strip it's plugged in)
Theo
Just like asbestos!
Focus at first on the plug that supplies everything else. That is the thing that will get the hottest in a passable system.
a) because it carries the highest current,and, b) because it is rarely unplugged.
Work out the total power you are likely to demand of that plug and, as Rob advises, reduce the plug fuse appropriately.
I reckon that there are very few domestic 13A plug and sockets that don't get a bit warm when loaded above 2.5kW. In such situations quite a improvement occurs when you unplug and plug and flip any socket switch a few times.
Repeat for the other plugs.
PA
I have something similar here. Although only on one side of the room.
On the other side, there is a load of equipment in a rack, and a single PDU which is mainly filled with wall warts. Everything else uses good quality IEC C13/C14 socket strips, which are small and easily tucked away. Everything is low current.
Same advice applies to immersion heaters, too.
And if you want to be really smart, do all of this with an analog radio nearby. On MW but not tuned to a station. Clean click as you do the Plug and switch routine - Good; scratchy and longer sounding click/scratch - Bad.
PA
Because a lot of the web is American, and USA plugs and extension leads are (a) unfused (b) rarely able to carry the full circuit current (c) of s**te quality generally.
Owain
It's bullshit unless you have high power devices like fan heaters or electric jugs or ovens etc plugged into them.
It's fine for the endless plug packs etc most of us have plugged into them.
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