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'[EE] Resistance wire in parallel'
2010\01\08@170158 by ivp

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Reality check ...........

If two lengths of resistance wire are in parallel but not in intimate
contact, they will be as paralleled resistors. But what if they are in
contact, eg twisted together ? That make a large number of
paralleled segments in series wouldn't it ?

Making some low-value sense resistors with Cuprothal wire, which
is 6 ohms/metre. If I parallel 4 strands (=> 1.5R/m) then that's 40mm
to make a 60mR resistor, rather than 10mm of the single strand. I'd
rather work with 40mm than 10mm

wbr

2010\01\08@172909 by Marcel Duchamp

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Yes, that would make a large number of paralleled segments in series.
And the total resistance will be the same as if the two wires did not
touch anywhere but the ends.  So you are good to go.

On 1/8/2010 2:00 PM, ivp wrote:
{Quote hidden}

2010\01\08@174556 by Dave Tweed

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Marcel Duchamp wrote:
> On 1/8/2010 2:00 PM, ivp wrote:
> > If two lengths of resistance wire are in parallel but not in intimate
> > contact, they will be as paralleled resistors. But what if they are in
> > contact, eg twisted together ? That make a large number of
> > paralleled segments in series wouldn't it ?
> >
> > Making some low-value sense resistors with Cuprothal wire, which
> > is 6 ohms/metre. If I parallel 4 strands (=>  1.5R/m) then that's 40mm
> > to make a 60mR resistor, rather than 10mm of the single strand. I'd
> > rather work with 40mm than 10mm
>
> Yes, that would make a large number of paralleled segments in series.
> And the total resistance will be the same as if the two wires did not
> touch anywhere but the ends.  So you are good to go.

Another way to think about it: If the wire is uniform, the voltage
distribution along each of the strands will be identical, so even if
they're in contact at one or more points, no current will flow between
them.

-- Dave Tweed

2010\01\08@175933 by ivp

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Thanks

2010\01\08@181407 by David Sincock

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Practically, if you took 2 x 1m lengths of the wire and put them in
parallel, you would get 3R.
If you then joined them together at 1/3 and 2/3 of a meter, you would have 3
segments of 1R giving 3R total.
Taking it one step further and joining them together at every 1/6 you'd get
6 segements of 0R5 giving 3R again.
Taking to the extreme of contact all the way along, I would venture that the
resistance would still be 3R.

Theorectically, assuming a uniform resistance over the length of each
strand, then at any particular distance along each strand, the voltage
potential would be the same, so connecting the strands together at any
particular distance would make no difference to the current flow
distribution, and hence no change to the total resistance.

I would have thought that any change in resistance would be due to any
deformation of the wire caused by the twisting together.

regards,
david

{Original Message removed}

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