Why is telfon wire silver coated?

H

Harry Muscle

Guest
Why is teflon wire usually silver coated? Does this affect the resistance
of the wire?

I'm working on a project where I'm gonna be using a length of small gauge
telfon wire as a heater in water. I'm thinking of using either 24 or 26
gauge wire, but I noticed that most places that sell this stuff mention that
it's silver coated. Why is that? Does the silver coating affect the
resistance of the wire? I need to know this since I'm using the resistance
of the wire to determine which gauge to go with and how long of a wire to
use. Anyone know approximately how much (in %) the resistance would go up
or down? I've read somewhere that it probably decreases resistance,
especially with AC due to the skin effect (which is where the silver is),
but I don't fully understand what that means. I'm gonna be running about 8V
12.5A AC through this thing in case it matters.

So the thing the I especially need answered is how much (in %) it would
affect the resistance of the wire. Also, is all teflon wire (in 24-30
gauge) silver coated as a general rule. In other words, can I assume it's
silver coated even if a store doesn't mention anything about it.

Thanks,
Harry




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Harry Muscle wrote:
Why is teflon wire usually silver coated? Does this affect the resistance
of the wire?
Click to expand...
Yes, it makes it lower by a tiny bit. Teflon is a high temperature
capable insulation, and if you use the wire near the upper temperature
limit for the teflon, it is hot enough to rapidly oxidize the surface
of the copper. And teflon is expensive, so if you are already paying
that much for wire, you may as well go all out with the conductor.

I'm working on a project where I'm gonna be using a length of small gauge
telfon wire as a heater in water. I'm thinking of using either 24 or 26
gauge wire, but I noticed that most places that sell this stuff mention that
it's silver coated. Why is that? Does the silver coating affect the
resistance of the wire? I need to know this since I'm using the resistance
of the wire to determine which gauge to go with and how long of a wire to
use. Anyone know approximately how much (in %) the resistance would go up
or down? I've read somewhere that it probably decreases resistance,
especially with AC due to the skin effect (which is where the silver is),
but I don't fully understand what that means. I'm gonna be running about 8V
12.5A AC through this thing in case it matters.

So the thing the I especially need answered is how much (in %) it would
affect the resistance of the wire. Also, is all teflon wire (in 24-30
gauge) silver coated as a general rule. In other words, can I assume it's
silver coated even if a store doesn't mention anything about it.
Click to expand...
The effect is so small (except at high frequencies, when the current
is confined to just the surface of the wire) that you needn't worry
about it. The effect of temperature on the resistance will be bigger
than the effect of the silver plating.

--
John Popelish
 
"John Popelish" <jpopelish@rica.net> wrote in message
news:3FD0A453.1BC9E12D@rica.net...
Harry Muscle wrote:

Why is teflon wire usually silver coated? Does this affect the
resistance
of the wire?

Yes, it makes it lower by a tiny bit. Teflon is a high temperature
capable insulation, and if you use the wire near the upper temperature
limit for the teflon, it is hot enough to rapidly oxidize the surface
of the copper. And teflon is expensive, so if you are already paying
that much for wire, you may as well go all out with the conductor.

I'm working on a project where I'm gonna be using a length of small
gauge
telfon wire as a heater in water. I'm thinking of using either 24 or 26
gauge wire, but I noticed that most places that sell this stuff mention
that
it's silver coated. Why is that? Does the silver coating affect the
resistance of the wire? I need to know this since I'm using the
resistance
of the wire to determine which gauge to go with and how long of a wire
to
use. Anyone know approximately how much (in %) the resistance would go
up
or down? I've read somewhere that it probably decreases resistance,
especially with AC due to the skin effect (which is where the silver
is),
but I don't fully understand what that means. I'm gonna be running
about 8V
12.5A AC through this thing in case it matters.

So the thing the I especially need answered is how much (in %) it would
affect the resistance of the wire. Also, is all teflon wire (in 24-30
gauge) silver coated as a general rule. In other words, can I assume
it's
silver coated even if a store doesn't mention anything about it.

The effect is so small (except at high frequencies, when the current
is confined to just the surface of the wire) that you needn't worry
about it. The effect of temperature on the resistance will be bigger
than the effect of the silver plating.

--
John Popelish
Click to expand...
I didn't know that temperature affects resistance. Would you mind
elaborating on this a little. I'm not trying to heat the water up much,
actually just a little above room temp (ie: aprox 25-30C). However, I don't
know how hot the wire will actually get, especially since it will be covered
by about two inches of gravel. But I don't think it would reach higher than
50C, probably less. Would that start to make a difference on resistance?
Is there a formula I could use to get an idea of how resistance would change
with temperature? Btw, when temp goes up, does resistance go down or up?

Thanks,
Harry

P.S. I realize that if I only expect the wire o reach 50C using
teflon might be overkill, but I can get teflon wire pretty cheap, so for a
few extra bucks I'd rather play it safe.




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On Fri, 5 Dec 2003 10:44:10 -0500, "Harry Muscle" <fake@AT@e-mail.com>
wrote:

"John Popelish" <jpopelish@rica.net> wrote in message
news:3FD0A453.1BC9E12D@rica.net...
Harry Muscle wrote:

Why is teflon wire usually silver coated? Does this affect the
resistance
of the wire?

Yes, it makes it lower by a tiny bit. Teflon is a high temperature
capable insulation, and if you use the wire near the upper temperature
limit for the teflon, it is hot enough to rapidly oxidize the surface
of the copper. And teflon is expensive, so if you are already paying
that much for wire, you may as well go all out with the conductor.

I'm working on a project where I'm gonna be using a length of small
gauge
telfon wire as a heater in water. I'm thinking of using either 24 or 26
gauge wire, but I noticed that most places that sell this stuff mention
that
it's silver coated. Why is that? Does the silver coating affect the
resistance of the wire? I need to know this since I'm using the
resistance
of the wire to determine which gauge to go with and how long of a wire
to
use. Anyone know approximately how much (in %) the resistance would go
up
or down? I've read somewhere that it probably decreases resistance,
especially with AC due to the skin effect (which is where the silver
is),
but I don't fully understand what that means. I'm gonna be running
about 8V
12.5A AC through this thing in case it matters.

So the thing the I especially need answered is how much (in %) it would
affect the resistance of the wire. Also, is all teflon wire (in 24-30
gauge) silver coated as a general rule. In other words, can I assume
it's
silver coated even if a store doesn't mention anything about it.

The effect is so small (except at high frequencies, when the current
is confined to just the surface of the wire) that you needn't worry
about it. The effect of temperature on the resistance will be bigger
than the effect of the silver plating.

--
John Popelish

I didn't know that temperature affects resistance. Would you mind
elaborating on this a little. I'm not trying to heat the water up much,
actually just a little above room temp (ie: aprox 25-30C). However, I don't
know how hot the wire will actually get, especially since it will be covered
by about two inches of gravel. But I don't think it would reach higher than
50C, probably less. Would that start to make a difference on resistance?
Is there a formula I could use to get an idea of how resistance would change
with temperature? Btw, when temp goes up, does resistance go down or up?

Thanks,
Harry
Click to expand...
The wire resistance will increase about 0.4 per cent per degree C.
Since the teflon insulates the wire thermally as well as electrically,
the wire may get quite a bit hotter than the water you're heating.

You could use bare nichrome wire at this low voltage.

John
 
Harry Muscle wrote:

I didn't know that temperature affects resistance. Would you mind
elaborating on this a little. I'm not trying to heat the water up much,
actually just a little above room temp (ie: aprox 25-30C). However, I don't
know how hot the wire will actually get, especially since it will be covered
by about two inches of gravel. But I don't think it would reach higher than
50C, probably less. Would that start to make a difference on resistance?
Is there a formula I could use to get an idea of how resistance would change
with temperature? Btw, when temp goes up, does resistance go down or up?
Click to expand...
http://www.cirris.com/testing/temperature/copper.html

--
John Popelish
 
On Fri, 5 Dec 2003 09:53:24 -0500 in sci.electronics.basics, "Harry
Muscle" <fake@AT@e-mail.com> was alleged to have written:
Why is teflon wire usually silver coated?
Click to expand...
I don't actually know the answer, but I'd be surprised if it was anything
other than its behavior in making contact to the wire-wrap pin in the
original intended application.
 
Harry Muscle wrote:

Why is teflon wire usually silver coated?
Click to expand...

Google turned up the answer at this site:
<http://www.logwell.com/tech/shdwe/teflon_wire>.

Tin plating, as is used on ordinary wire, can dissolve into the copper and
become difficult to solder when exposed to high temperatures. Silver
plating is used on wires rated for high temperatures to avoid this problem.
Also, tin plating will melt at the temperatures used in extruding the
teflon insulation onto the wire, thus fusing the strands of the wire
together.


--
--
Steve
 
It is usually difficult to make resistors with Copper wire because is too
good a conductor.
It is NOT impossible but you have to work out the Gauge Length Resitance
Current and Voltage to produce the right amount of heat at the right voltage
(the voltage available 120AC?, 12V? etc.)

John Larking suggested bare nicrome, that would be fine at low voltage but
at 120V there are safety concerns, even if the wire is buried.

You do not indicate the project purpose, so is difficult to help or say
whether a solution is practical or not. Looks like you are trying to keep
some Dry Well from freezing, or is for a pond with turtle???

Wire 24-30 Gauge is pretty delicte to be buried under gravel.


MG

"Harry Muscle" <fake@AT@e-mail.com> wrote in message
news:3fd09bce$1_6@corp.newsgroups.com...
Why is teflon wire usually silver coated? Does this affect the resistance
of the wire?

I'm working on a project where I'm gonna be using a length of small gauge
telfon wire as a heater in water. I'm thinking of using either 24 or 26
gauge wire, but I noticed that most places that sell this stuff mention
that
it's silver coated. Why is that? Does the silver coating affect the
resistance of the wire? I need to know this since I'm using the
resistance
of the wire to determine which gauge to go with and how long of a wire to
use. Anyone know approximately how much (in %) the resistance would go up
or down? I've read somewhere that it probably decreases resistance,
especially with AC due to the skin effect (which is where the silver is),
but I don't fully understand what that means. I'm gonna be running about
8V
12.5A AC through this thing in case it matters.

So the thing the I especially need answered is how much (in %) it would
affect the resistance of the wire. Also, is all teflon wire (in 24-30
gauge) silver coated as a general rule. In other words, can I assume it's
silver coated even if a store doesn't mention anything about it.

Thanks,
Harry




-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----
Click to expand...
 
"Harry Muscle" <fake@AT@e-mail.com> writes:


I didn't know that temperature affects resistance. Would you mind
elaborating on this a little. I'm not trying to heat the water up much,
actually just a little above room temp (ie: aprox 25-30C). However, I don't
know how hot the wire will actually get, especially since it will be covered
by about two inches of gravel. But I don't think it would reach higher than
50C, probably less. Would that start to make a difference on resistance?
Is there a formula I could use to get an idea of how resistance would change
with temperature? Btw, when temp goes up, does resistance go down or up?
Click to expand...
Copper changes resistance by about 0.4%/C. or 0.4ohms/100ohms/C (4000ppm).


--
Steven D. Swift, novatech@eskimo.com, http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA
 
On Fri, 5 Dec 2003 09:53:24 -0500, "Harry Muscle" <fake@AT@e-mail.com>
Gave us:

So the thing the I especially need answered is how much (in %) it would
affect the resistance of the wire. Also, is all teflon wire (in 24-30
gauge) silver coated as a general rule. In other words, can I assume it's
silver coated even if a store doesn't mention anything about it.
Click to expand...

No, you cannot.
The designation for silver plating on wire is referred to as "SPC"

Silver Plated Copper

TPC is Tin Plated Copper

It most assuredly has a low OHMs per 1000 ft number.

The cladding depth will affect that though. There are about 3
cladding depths usually.

SPC is typical, but PTFE coated wire comes other ways as well.

SPC is the most common, because the wire type is typically used in
mil applications. It would be hard for you to find a teflon wire with
a UL rating. They don't rate it. A 1000 VDC mil rating is at 600V
for our illustrious cert lab.

Anyway. Tinned copper inside teflon oxidizes on a shorter shelf
life plan, and is very hard to wet with the solder once it does.
Perhaps another reason why SPC is seemingly always what is chosen, or
found in surplus.
 
On Fri, 5 Dec 2003 10:44:10 -0500, "Harry Muscle" <fake@AT@e-mail.com>
Gave us:

I didn't know that temperature affects resistance. Would you mind
elaborating on this a little.
Click to expand...

It's called temperature coefficient. It effects many things in
electronics, and the effect is referred to as temperature drift.

Capacitors drift with T as well.
 
On Sat, 06 Dec 2003 01:00:25 GMT, David Harmon <source@netcom.com>
Gave us:

On Fri, 5 Dec 2003 09:53:24 -0500 in sci.electronics.basics, "Harry
Muscle" <fake@AT@e-mail.com> was alleged to have written:
Why is teflon wire usually silver coated?

I don't actually know the answer, but I'd be surprised if it was anything
other than its behavior in making contact to the wire-wrap pin in the
original intended application.
Click to expand...

Wire wrap pin? You have dated yourself, but that is not the reason.

Wire wrap wire is typically solid. I'd be willing to bet the wire
he is referring to is stranded. As in not for wire wrap.
 
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