# The Naked Scientists Forum

### Author Topic: How long can a power extension lead be ?  (Read 6421 times)

#### neilep

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##### How long can a power extension lead be ?
« on: 23/02/2006 03:41:37 »
What is the maximum lenghth of extension power lead I could use and still be able to send power through it when plugged into a regular household plug ?...I haven't a clue...100 meters...a mile ?...no limit ?

(note to self: What kind of stupid question is that ?)

Men are the same as women.... just inside out !!

#### another_someone

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##### Re: How long can a power extension lead be ?
« Reply #1 on: 23/02/2006 04:52:05 »
The main problem is going to be the resistance of the wire.  In part, it depends upon how good quality of cable you use – 1 mile of ½ inch thick solid gold core may well be quite ok, but ½ mm think stranded aluminium might not (don't quote me on exact numbers – I've never actually measured the resistance of mains power cables).

It also depends upon what you are going to run off the other end.  If you only need 5 watts of power running at the other end, you will be more tolerant to losses due to cable resistance than if you want to run a 3KW device on the other end.  If you have something that will auto-adjust to any voltage between 110V to 260V, then it will also be better able to adapt to loss of voltage due to a long cable, than if you have a device that must have 230/240V.

George

#### daveshorts

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##### Re: How long can a power extension lead be ?
« Reply #2 on: 24/02/2006 15:37:59 »
The other thing to be careful of is what the resistance to earth is... I am not sure what the regualtions are but I think that will be the limiting factor legally

#### neilep

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##### Re: How long can a power extension lead be ?
« Reply #3 on: 24/02/2006 16:17:34 »
Thank you George and Dave.

I am not in fact in need of a very long extension lead and I really have no idea why the thought had crossed my mind. I realise that what ever I may be powering would be fundamental to the load required and therefore affect the length of lead.

I'm certainly aware how the quality, manufacturing process and materials used all contribute. In my past life as a Specialist Hi Fi retailer the same principles were used for the construction of Intreconnects and speaker cable....10 meters was usually the cut off point when the signal would start toshow signs of deterioration if sent through a poor (budget) quality cable.

Thanks again.

Men are the same as women.... just inside out !!
« Last Edit: 24/02/2006 16:38:01 by neilep »

#### Ray hinton

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##### Re: How long can a power extension lead be ?
« Reply #4 on: 24/02/2006 16:31:31 »
neil,part of the national grid is 11,500 circuit km,but power is fed in at several points,so a couple of hundred km may be closer to the mark, thats at 44,000 volts,lower volts higher current or something,someone will have the answer.

#### another_someone

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##### Re: How long can a power extension lead be ?
« Reply #5 on: 25/02/2006 05:43:26 »
quote:
Originally posted by neilep

I'm certainly aware how the quality, manufacturing process and materials used all contribute. In my past life as a Specialist Hi Fi retailer the same principles were used for the construction of Intreconnects and speaker cable....10 meters was usually the cut off point when the signal would start toshow signs of deterioration if sent through a poor (budget) quality cable.

When your talking about signal cables, you are concerned with maintaining fidelity of the signal, and all sorts of things like phase shifting due to inductance of the cable, and all sorts of signal stuff that you really don't care that much about when you are dealing with simple power transfer.

When you feed an audio signal down a wire, you have a whole range of frequencies of signal, and if different frequencies get effected differently as they pass down the wire, it will adversely impact on the fidelity of the signal coming out the other end of the wire.

If you're sending a 50Hz continuous wave down the wire, not only will there not be multiple frequencies that may be differentially effected by the wire, but you don't really care about signal fidelity anyway, you just want to make sure there is enough power at around the right frequency.

George
« Last Edit: 25/02/2006 06:37:45 by another_someone »

#### Ray hinton

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##### Re: How long can a power extension lead be ?
« Reply #6 on: 25/02/2006 09:33:46 »
Tv cable companies changed to fibre-optics,because these carry their signal further,by keeping it "clean".
it depends on the"load" that will be applied to the cable,and if there are any joints in it,more joints,more hot spots,should the load start to excede the cables carrying capacity,as for a wires physical length,that is resticted by what we can actually pick up and carry,200m of three core,2mm copper wire is quite a lump to move.

measure twice,cut once.

#### another_someone

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##### Re: How long can a power extension lead be ?
« Reply #7 on: 25/02/2006 12:13:03 »
quote:
Originally posted by Ray hinton

Tv cable companies changed to fibre-optics,because these carry their signal further,by keeping it "clean".
it depends on the"load" that will be applied to the cable,and if there are any joints in it,more joints,more hot spots,should the load start to excede the cables carrying capacity,as for a wires physical length,that is resticted by what we can actually pick up and carry,200m of three core,2mm copper wire is quite a lump to move.

measure twice,cut once.

Actually, as I under stand it, the driving force for moving towards cable was not about increasing the distance the signal could travel, but because it allowed them to increase the bandwidth, and so carry more signals down the same piece of fibre, as well as (as you point out) being thinner and lighter than copper (thus easier to lay).

In fact, early cable was very restrictive over the distance it could comfortably carry a signal.

On the other hand, more recently, while there have been advances in improving the distances that signals can travel down fibre optics without having to be cleaned up by repeater stations, there have also been improvements in wave shaping that allow higher frequencies of signal to be succesfully carried over copper, which is how BT have been delivering ADSL at 8Mb/s to our homes without having to lay new cable.

George

#### The Naked Scientists Forum

##### Re: How long can a power extension lead be ?
« Reply #7 on: 25/02/2006 12:13:03 »