Power Cable Under Carpet

andrew-b

The simplistic view for back of envelope calculation..
Power = current x voltage ...so if you know the power in watts of a device (input power for items with transformers) divide by 230 volts to give you the current in amps .. sum together the current for all devices to be connected. If it's mainly electronics like tvs, dvd player it's very unlikely to be an issue though..problems arise when you start plugging kettles, toaster, storage heaters, hairdryers, vacuum cleaners etc and other high powered devices. In reality not all devices will be on at the same time though.

So for example a 60W lamp divided by 230v = roughly 0.26W ...so you could power 50 light bulbs off it - though the cable would get warm before all 50 were connected!

However something like a fastboil 3kW kettle... 3000W / 230 = 13amps and your extension cable will get very hot so obviously not suitable for connecting along with your toaster on the same cable. The fuse is probably more likely to blow before the cable melts TBH but it's best not to overload cables in this way. I've run a wallpaper steamer (a glorified kettle!) on an extension cable rated 13A which got pretty hot - though the cable reel has a thermal cut out to protect against overheating and i had it fully unwounded to allow heat to dissipate.

This all assumes that the cable is in good condition and not damaged in any way though.

As for conduits...in house wiring between plug sockets the wiring is done in 2.5mm twin and earth cable is rated at around 24amps (i.e substantially higher)....but most sockets will be in a ring main with 2 cables connected which adds even more protection.

For low power devices running the cable through conduit is ok as it's unlikely to rise in temperature to be a problem. But you can't guarantee someone won't connect high powered devices to it.

supermonkey

ok, thats very helpful.

the items running off it are - lcd tc, wii, dvd player, set top box, amp, router, lamp & i think that's it. its in our front room, so toasters & kettles are not used and if anything more high powered where used there are sockets the other side of the room. I can try to work out the total current in amps, but would you agree the extension should be able to run this? And would you expect it to get warm / hot?

i really dont want to have to retrieve the cable now, but i am rather concerned. can conduit / trunking being used under carpet (obviously provided size isn't an issue?)

andrew-b

Despite not being recommended, for what your using it for you should be ok and you wouldn't normally have wii, dvd and set top box on all the same time anyway ..if the conduit is rigid, isn't a trip hazard, and no chance of cable being damaged it should be ok and i'd think it's a little safer than directly under the carpet as if it did overheat and catch light it's less likely to set the carpet alight! Doesn't sound like you'd have anywhere to connect a kettle in it anyway! I wouldn't really recommend what your doing as a permanent solution though and would favour a dedicated power socket - doesn't have to be routed into the wall and can be put in trunking along skirting but obviously doesn't look as good. Just make sure the extension doesn't get overloaded with high-power devices and if you sell up remove it and all should be fine!

Incidentally as an aside, for the electronic equipment you've got connected i would ensure the extension cable is a surge protected one (i've had a computer motherboard fried by power surges during storms in the past!)!

Andy

supermonkey

thanks for your quick reply... again very helpful.

out of interest, how is a dedicated power socket any different? please forgive me for my ignorance! and where would this be wired in? would it be connected to the original socket? i take it your an electrician, so how much would it cost to have this added in, routed in the wall and finished off nicely? thanks

andrew-b

Not an electrician no so don't take my advice as gospel..just a diyer with electrical knowledge (electronic engineering, physics and reading up on the subject) plus some fire prevention knowledge to get duke of edingburgh award years ago!

A dedicated power socket because it's cabled with thicker heavier cable will take a much greater load and stand upto higher currents without overheating (for high powered cookers and electric showers even thicker cable is used - the longer the cable and higher the power the thicker the cable used).

Costs depends on cable route and how much channelling out is needed. Usually easiest to create a spur socket by running one cable from a socket on the ring main (i.e has 2 cables but if it already has a spur with a 3rd cable it's not suitable) either in same room or adjacent room. If there's an adjacent room you could have a socket on either side of the wall cabled together to avoid channelling out beyond the socket itself. If you channel out yourself it might save a few quid but there are recognised cabling routes so discuss with your electrician before getting the hammer and chisel out.

As always with electrics..if you don't understand it and not confident doing it get someone in

supermonkey

ok, well i'm going to have to think about this for a while... i could do without the extra work and expense and I do feel that it's such a short length to warrant extra work (and needing to chase out the wall.

muckybutt

Speaking as an electrician I would certainly NOT recommend running any cable either low voltage or mains voltage under the carpet.
If you have the need for a trailing lead ie an extension lead then run it above the carpet, do not place anything over the top of it, extension leads DO get hot and can over heat very quickly, leads are generally a smaller csa than wiring found in you wall. In todays regulations it is frowned upon to place household wiring under loft insulation as cable calcs for wires running through insulating material coule mean for instance a normal lighting circuit would be 1.5mm csa but if run under could be upgraded to 2.5mm csa, same goes for running your lead under a rug or carpet...its being insulated, doubt your insurance would cover that in the event of a fire, why dont you either clip it around the skirting or place it in some surface mounted trunking ?

supermonkey

thanks for your reply.

I think I will have for clipping or trunking then for the power cable. as an electrician, what would you expect to charge for an additional socket to be wired in? and would it cost extra to hide it and make the wall good again?

Though I must say I don't see why there would be a problem with low voltage cable....lots of people hide hdmi, optical or speakers cables.

muckybutt

It really depends how far away from a socket the new socket will be, anything upwards of £50.
Not hiding cables of any sort is good practice.

supermonkey

muckybutt wrote: »

It really depends how far away from a socket the new socket will be, anything upwards of £50.
Not hiding cables of any sort is good practice.

yes, but not practical at all!

can a spur socket be added to a fused switch? there is an existing one which is closer than the closest existing socket.