Tim Attwood wrote:

>> 2. Is maximum load proportional to diameter or cross section area? (The 
>> latter is quadratically propertional to diameter.)
> 
> It's proportional to the surface area. Thus all the stranded and braided 
> wire. 

Interesting. I thought braided wire was just so it bends without 
fracturing...

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Orchid XP v7 nous apporta ses lumieres en ce 2007/11/10 04:11:
> Alain wrote:
> 
>> The price is irrelevent when the equipment allows you to do your job. 
>> Also, often, the highest priced options turns out to be the 
>> cheapest... in the long run.
> 
> I wish somebody could explain this to the idiots I work for...
You need to show them the operational cost the the lowest priced option compared 
to that of the highest priced option. You also need to compare the quality of 
the final product, and the amount of rejects with what those rejects cost.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you keep a blacklist of people who 
ask questions about 3DFX products.
Alex McLeod a.k.a. Giant Robot Messiah

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Orchid XP v7 nous apporta ses lumieres en ce 2007/11/10 12:52:
> Tim Attwood wrote:
> 
>>> 2. Is maximum load proportional to diameter or cross section area? 
>>> (The latter is quadratically propertional to diameter.)
>>
>> It's proportional to the surface area. Thus all the stranded and 
>> braided wire. 
> 
> Interesting. I thought braided wire was just so it bends without 
> fracturing...
A solid wire have a smaler cross section than a braided or stranded wire of the 
same caliber, but will be stiffer. In a braided wire, there are gaps between the 
strands, and those make the cable whider.
So, yes, braided wires are needed when you need a supple wire, like that from a 
socket to some device. But, a solid wire is beter in a wall, where it don't need 
to change it's path once in place.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you hate games, but you buy Riven 
just to look at the pictures.
AmaltheaJ5

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Alain wrote:
> Orchid XP v7 nous apporta ses lumieres en ce 2007/11/10 12:52:
>> Tim Attwood wrote:
>>
>>>> 2. Is maximum load proportional to diameter or cross section area? 
>>>> (The latter is quadratically propertional to diameter.)
>>>
>>> It's proportional to the surface area. Thus all the stranded and 
>>> braided wire. 
>>
>> Interesting. I thought braided wire was just so it bends without 
>> fracturing...
> A solid wire have a smaler cross section than a braided or stranded wire 
> of the same caliber, but will be stiffer. In a braided wire, there are 
> gaps between the strands, and those make the cable whider.
> So, yes, braided wires are needed when you need a supple wire, like that 
> from a socket to some device. But, a solid wire is beter in a wall, 
> where it don't need to change it's path once in place.
> 
Adding to that, a braided wire might break, but there are enough cross 
connections that under most circumstances you won't notice it. 
Exceptions may be when connected to an amplifier. When I was young (or 
at least younger) we had a, probably cheap, coax cable that connected a 
guitar to an amplifier. If you shook it, you could here the 'water 
sloshing' over the amp. Funny, but not very useful. Another occasion
was when connecting a bush of electrodes to a self made ecg amplifier, 
those wires were long and shielded. Stepping on them would cause 
something that superficially looks like a (part of) a ecg complex, about 
the right amplitude and width. Very annoying if you are looking for 
complexes with a different than standard morphology and have to press 
the record button if you see one and the machine can not be used for a 
minute after you did record that artefact.

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Tim Attwood wrote:
...
>> 2. Is maximum load proportional to diameter or cross section area? (The 
>> latter is quadratically propertional to diameter.)
> 
> It's proportional to the surface area. Thus all the stranded and braided 
> wire. 

No, this is not true for DC currents and AC currents at low frequencies.

(Maybe your are thinking about the "skin effect" that appears at high
frequencies ?)

Here's some relevant links:

http://www.ibiblio.org/obp/electricCircuits/DC/DC_12.html#xtocid183892
http://www.epanorama.net/documents/wiring/wire_resistance.html
http://www.interfacebus.com/Copper_Wire_AWG_SIze.html

-- 
Tor Olav
http://subcube.com

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Tor Olav Kristensen wrote:
> Tim Attwood wrote:
> ...
>>> 2. Is maximum load proportional to diameter or cross section area? (The 
>>> latter is quadratically propertional to diameter.)
>> It's proportional to the surface area. Thus all the stranded and braided 
>> wire. 
> 
> No, this is not true for DC currents and AC currents at low frequencies.
> 
> (Maybe your are thinking about the "skin effect" that appears at high
> frequencies ?)

Well, it seems there are two relevant phenomina here.

1. Heat production, which is proportional to current and inversely 
proportional to cross-section area.

2. Heat dissapation, which is proportional to surface area.

I'm not sure which one is dominant...

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4736c72d$1@news.povray.org...
> 2. Heat dissapation, which is proportional to surface area.
>
Heat dissipation is propotionnal to surface area only if this area is free 
of insulation.

Marc

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Tim Attwood wrote:
>> 1. A car runs on 12V electrics, not 250V. Does that make a difference?
> 
> Yes, lots. Voltage is the size of the elephant, amperage is how fast he's
> going when he runs you over. I think many cars will pull more than 100 A
> cold starting though.

No, not for the sizing of the cable. If the cable has resistance of
0,01ohms and the current is 100 A, the cable will heat up with
100^2*0,01=100 W (P=I^2*R) and hold up 100*0,01=1 volt (U=I*R) of
voltage (this 1V is called the voltage loss of the cable). Rest of the
voltage (11V or 249V) will get to the final device and it'll have matter
there.

Practically everyone/-thing (lets say house heating, 10kW) needs power
(P, measured in watts). While P=U*I, we can produce 10kW of heat eg.
with either 1A*10kV, 10A*1kV, 100A*100V, 1kA*10V or 10kA*1V. If the
transmission lines to the house adds up with 1ohm, we'll heat the
transmission lines up with anything from 1W (1A^2*1ohm) to 100 000 000 W
= 100MW (10kA^2*1ohm). This is why the main transmission lines do not
have 230-400V voltage, but ~10-400kV voltages instead - to minimize the
power loss, which only heats up the outside air.

> 100 A * 12 V = 1200 W (~1.6 hp)
> 100 A * 220 V = 22 KW (~29.5 hp)

True, at the final device.

-- 
Eero "Aero" Ahonen
   http://www.zbxt.net
      aer### [at] removethiszbxtnetinvalid

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Invisible wrote:
> I used to own an old HP line plotter. (Do they still make those?) 

Every time I see my wife writing chinese by hand, it reminds me of fond 
hours watching the HP line plotter label stuff on the output page.


-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Tor Olav Kristensen wrote:
>> 2. Is maximum load proportional to diameter or cross section area? (The
>> latter is quadratically propertional to diameter.)
> 
> Cross section area.

Also depends on AC vs DC.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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