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Default Any way to "measure" wire gauge in power cord?

To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks
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Default Any way to "measure" wire gauge in power cord?

blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

....
So is there any simple way of determining whether cord is 12 gauge or
not?


12 AWG -- ~0.081"
14 AWG -- ~0.064"

So, 12 is a little over 1/16", 14 is about 1/16" diameter. Enough
difference if the connection at either end is visible to tell easily.

That said, what horsepower is the motor rated/current draw on the motor
plate? If the cord is the OEM-supplied one, it's unlikely it's so
undersized as to be discernible difference in changing it out...

Assuming it's a dual-voltage motor, you could always go to the 240V
connections and cut current draw in half...

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Default Any way to "measure" wire gauge in power cord?

On Sep 2, 2:21*pm, blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks


I assume that you don't trust Sears to have installed to proper size
cord for the unit in the first place, right?

If you can disconnect the cord at the saw end (unplug it first!),
possibly in a junction box near the switch, you should be able to
determine the size by using any device that is marked with wire gauge
sizes, such as a wire stripper with pre-set holes/markings.

On the other hand, if you are going to disconnect it to check it, you
might just as easily replace it with a known 12 gauge cord.

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Default Any way to "measure" wire gauge in power cord?

DerbyDad03 writes:

On Sep 2, 2:21*pm, blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks


I assume that you don't trust Sears to have installed to proper size
cord for the unit in the first place, right?


Well, it is a 15A motor, so "technically" 14 gauge would be OK, but
I'm getting some bogging down so I thought maybe I could get a few
ounces more of power by upgrading to 12 gauge if it is not already. On
the other hand if it is already 12 gauge, seems like it would be a
waste to replace it.


If you can disconnect the cord at the saw end (unplug it first!),
possibly in a junction box near the switch, you should be able to
determine the size by using any device that is marked with wire gauge
sizes, such as a wire stripper with pre-set holes/markings.

On the other hand, if you are going to disconnect it to check it, you
might just as easily replace it with a known 12 gauge cord.

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Default Any way to "measure" wire gauge in power cord?

dpb writes:

blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

...
So is there any simple way of determining whether cord is 12 gauge or
not?


12 AWG -- ~0.081"
14 AWG -- ~0.064"

So, 12 is a little over 1/16", 14 is about 1/16" diameter. Enough
difference if the connection at either end is visible to tell easily.


Do these numbers apply to stranded too? (I believe the power cord is stranded)


That said, what horsepower is the motor rated/current draw on the
motor plate? If the cord is the OEM-supplied one, it's unlikely it's
so undersized as to be discernible difference in changing it out...


My concern was just that at startup (or when bogging down) it will
draw more than the rated 13A/1.5HP so that maybe moving to 12 gauge
would help me out given that the total cord length is about 15 feet.

Assuming it's a dual-voltage motor, you could always go to the 240V
connections and cut current draw in half...


I would like to do that but the manual says "It is wired for
operation on 120 volts, 60 Hz alternating curent. IT MUST NOT BE
CONVERTED TO OPERATE ON 230 VOLTS". Now someone mentioned in another
thread that this may just be due to the fact that the switch only
switches one leg and that everything would be ok if I swapped in a
DPDT switch to switch both phases.

But I don't have any manual for the motor itself and don't know what
needs to be rewired.



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Default Any way to "measure" wire gauge in power cord?

blueman wrote:
....
Well, it is a 15A motor, so "technically" 14 gauge would be OK, but
I'm getting some bogging down so I thought maybe I could get a few
ounces more of power by upgrading to 12 gauge if it is not already. On
the other hand if it is already 12 gauge, seems like it would be a
waste to replace it.

....

The drop in as short a cord as the typical cord is likely so little as
to be significant even if it is 14ga.

As noted in earlier response, if it were a dual-voltage motor moving it
to the 240V will cut the draw (but not make any real difference otherwise).

15A would be 3/4-1 hp which is (as is typical for contractor saws) on
the underpowered side for a 10" saw.

Probably you'll get more satisfaction by improving the quality of the
sawblade and possibly going to a thinner kerf blade and ensuring blades
are quite sharp and the saw is well aligned than in the minimal benefits
of the cord gauge.

That said, if must stay on 110V and if it were by chance only a 14ga
cord, I'd certainly not recommend against changing it out but I would
still doubt it will help the problem significantly.

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Default Any way to "measure" wire gauge in power cord?

blueman wrote:
....

Do these numbers apply to stranded too? (I believe the power cord is stranded)


Yes, gauge is gauge...

....

My concern was just that at startup (or when bogging down) it will
draw more than the rated 13A/1.5HP so that maybe moving to 12 gauge
would help me out given that the total cord length is about 15 feet.


Not really as somebody else already said, in 15-ft the difference in
voltage drop between the two is going to be in the mV range.

See other response for more likely things that could actually make some
difference.

....

But I don't have any manual for the motor itself and don't know what
needs to be rewired.


Any dual-voltage motor will have lead diagram with it on the motor or in
the connection box or similar. If it doesn't it's not likely it is.
Even if it were, it wouldn't provide more power, only cut the current draw.

If there were anywhere in the circuit that was a limiting factor, it
would be the overall circuit being 15A and 14ga therefore. If you're
running it on a 20A/12ga supply circuit, again the short length of power
cord just isn't going to be enough to make any discernible/practical
difference.

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Default Any way to "measure" wire gauge in power cord?

In article ,
blueman wrote:

To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks


Uh, you want to avoid voltage drop, so you want to measure the wire
gauge to see whether you might be theoretically exposing your saw to
voltage drop? Sounds a little back asswards to me. Why not put a
voltmeter on the saw (while running and under load) and see whether
you're getting significant voltage drop or not?
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Default Any way to "measure" wire gauge in power cord?


"blueman" wrote in message
...
DerbyDad03 writes:

On Sep 2, 2:21 pm, blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks


I assume that you don't trust Sears to have installed to proper size
cord for the unit in the first place, right?


Well, it is a 15A motor, so "technically" 14 gauge would be OK, but
I'm getting some bogging down so I thought maybe I could get a few
ounces more of power by upgrading to 12 gauge if it is not already. On
the other hand if it is already 12 gauge, seems like it would be a
waste to replace it.


For only 15 feet of wire, it would not make any noticiable differance if
you went from 14 to 12 gauge wire. YOu could go to #6 wire and not notice
any differance in your saw.

..


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Default Any way to "measure" wire gauge in power cord?


"blueman" wrote in message
...
DerbyDad03 writes:

On Sep 2, 2:21 pm, blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).


One other thought, how far is the saw from the main breaker box ? It could
be the drop in the wiring going to the receptical.
..




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Default Any way to "measure" wire gauge in power cord?

On Tue, 02 Sep 2008 14:06:28 -0500, dpb wrote:

blueman wrote:
...

Do these numbers apply to stranded too? (I believe the power cord is stranded)


Yes, gauge is gauge...


Then with stranded there's less copper to make up for the extra air.
Air will be present because of the (space-filling) inefficiency of
ROUND things.

[snip]
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http://notstupid.laughingsquid.com

"The government of the United States is not, in
any sense, founded on the Christian religion."

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Default Any way to "measure" wire gauge in power cord?

Mark Lloyd wrote:
On Tue, 02 Sep 2008 14:06:28 -0500, dpb wrote:

....

Then with stranded there's less copper to make up for the extra air.
Air will be present because of the (space-filling) inefficiency of
ROUND things.


Well, actually, there is a very small difference that does account for
it, but it's not of much importance for any practical purpose...typical
specs for stranded vis a vis solid--except for the last column which I
backed out of the previous three columns of data, these are from the
American Insulated Wire catalog.

(AWG NUMBER PVC NYLON APPROX. APPROX.
OR OF INSUL. JACKET OUTSIDE Conductor
KCMIL) STRANDS THICK. THICK. DIAMETER DIAMETER
(INCHES) (INCHES) (INCHES) (INCHES)
14 Solid .015 .004 .104 .066
12 Solid .015 .004 .121 .083
....
14 19 .015 .004 .112 .074
12 19 .015 .004 .131 .093
....

--
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Default Any way to "measure" wire gauge in power cord?

On Sep 2, 1:49*pm, blueman wrote:

snip


Well, it is a 15A motor, so "technically" 14 gauge would be OK, but
I'm getting some bogging down so I thought maybe I could get a few
ounces more of power by upgrading to 12 gauge if it is not already.


snip


A saw that bogs down needs a sharp blade. Or the right blade. Look
over your stock, take the dull ones to a good sharpening shop and you
won't have to fuss over power cords. HTH

Joe
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Default Any way to "measure" wire gauge in power cord?

blueman writes:
dpb writes:


blueman wrote:


12 AWG -- ~0.081"
14 AWG -- ~0.064"


So, 12 is a little over 1/16", 14 is about 1/16" diameter. Enough
difference if the connection at either end is visible to tell easily.


Do these numbers apply to stranded too? (I believe the power cord is stranded)


Close, but not exactly. Stranded wire of a particular gauge will have
the same amount of wire cross-section area to carry current as solid
wire of the same gauge. Because there's some air spaces between
strands when they are packed as tightly as possible, the overall
diameter of the bundle will be slightly larger for the stranded wire,
but only by about 10%.

You can calculate the size increase yourself fairly easily:

Perhaps the simplest stranded wire that's still well-packed has 7
strands, one in the centre and 6 around it. This gives hexagonal
packing, with the centre strand touching all 6 outer strands, and each
outer strand touching two neighbours as well as the centre strand. If
the diameter of one strand is 1 unit, the diameter of the whole bundle
(measured in the direction that gives the largest measurement) is 3.
With 7 strands, the wire has 7 times the cross-sectional area of one
strand, and will carry 7 times the current. A *solid* wire with the
same current capacity and resistance would be sqrt(7) = 2.645 units in
diameter, while the 7-strand wire is 3 units in diameter - about 13%
larger.

(On the other hand, if you measure across the "flats" of the stranded
wire, with the caliper jaws touching two wires each, the measured
diameter is only 2.732 units, or only 3% larger than a solid wire of the
same metal cross section. So it matters how you measure).

In a wire with many more strands (e.g. welding cable), the outside
becomes rounder, so the diameter measurement doesn't vary significantly.
And the "extra" diameter for stranded approaches the ratio of the area
of a hexagon to a circle inscribed in it, which is sqrt(12)/PI, or about
1.103. In other words, the many-strand cable is 10% larger than the
equivalent solid wire.

Dave
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Default Any way to "measure" wire gauge in power cord?

Is that data for solid or stranded? He did mention "cord" which implies
stranded conductors.

If a train stops between stations, and the man with the hat gets off. He's
out there in the middle of no where hollering "all aboard". Now, that's a
stranded conductor.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"dpb" wrote in message ...
blueman wrote:

12 AWG -- ~0.081"
14 AWG -- ~0.064"

So, 12 is a little over 1/16", 14 is about 1/16" diameter. Enough
difference if the connection at either end is visible to tell easily.

That said, what horsepower is the motor rated/current draw on the motor
plate? If the cord is the OEM-supplied one, it's unlikely it's so
undersized as to be discernible difference in changing it out...

Assuming it's a dual-voltage motor, you could always go to the 240V
connections and cut current draw in half...

--




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If the saw is stationary, please consider hard wiring it with Romex. Skip
the plug and socket. I suspect that a plug and socket are only good for some
number of amps before they start being inefficient.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"blueman" wrote


Well, it is a 15A motor, so "technically" 14 gauge would be OK, but
I'm getting some bogging down so I thought maybe I could get a few
ounces more of power by upgrading to 12 gauge if it is not already. On
the other hand if it is already 12 gauge, seems like it would be a
waste to replace it.



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Default Any way to "measure" wire gauge in power cord?

On Sep 3, 9:05*am, "Stormin Mormon"
wrote:
If the saw is stationary, please consider hard wiring it with Romex. Skip
the plug and socket. I suspect that a plug and socket are only good for some
number of amps before they start being inefficient.

--
Christopher A. Young
Learn more about Jesus
*www.lds.org
.

"blueman" wrote

Well, it is a 15A motor, so "technically" 14 gauge would be OK, but
I'm getting some bogging down so I thought maybe I could get a few
ounces more of power by upgrading to 12 gauge if it is not already. On
the other hand if it is already 12 gauge, seems like it would be a
waste to replace it.


You ought to be able to determine the wire gage with an accurate
postal scale One that reads to 0.01 gram would be right. Maybe 0.1
gram if you want to waste some wire. Cut equal lengths of known and
unknown wires. Strip insulation and weigh. If the weights are the
same, the gage is the same. HTH

Joe
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Default Any way to "measure" wire gauge in power cord?

On Sep 3, 10:04*am, "Stormin Mormon"
wrote:
Is that data for solid or stranded? He did mention "cord" which implies
stranded conductors.

If a train stops between stations, and the man with the hat gets off. He's
out there in the middle of no where hollering "all aboard". Now, that's a
stranded conductor.

--
Christopher A. Young
Learn more about Jesus
*www.lds.org
.

"dpb" wrote in ...
blueman wrote:

12 AWG -- ~0.081"
14 AWG -- ~0.064"

So, 12 is a little over 1/16", 14 is about 1/16" diameter. *Enough
difference if the connection at either end is visible to tell easily.

That said, what horsepower is the motor rated/current draw on the motor
plate? *If the cord is the OEM-supplied one, it's unlikely it's so
undersized as to be discernible difference in changing it out...

Assuming it's a dual-voltage motor, you could always go to the 240V
connections and cut current draw in half...

--


If a train stops between stations, and the man with the hat gets off.
He's out there in the middle of no where hollering "all aboard". Now,
that's a stranded conductor.

How can you call him stranded if there's train right next to him?
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Stormin Mormon wrote:
Is that data for solid or stranded? He did mention "cord" which implies
stranded conductors.


Jeesh...don't you read the rest of the thread????

The gauge is based on total of conducting material, stranded or solid.
Yes, there's a slight diameter increase of stranded over solid to
account for the geometry but it's essentially immaterial in the actual
dimensions as far as determining whether one is talking of 12 vs 14 ga.

Is that good enough?????

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Sigh. One in every group. You're right, of course.

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Learn more about Jesus
www.lds.org
..


"DerbyDad03" wrote in message
...

If a train stops between stations, and the man with the hat gets off.
He's out there in the middle of no where hollering "all aboard". Now,
that's a stranded conductor.

How can you call him stranded if there's train right next to him?




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Buy a new cord and you'll know for sure, if it's 15 years old it just
may be weathered and brittle. Do as you may see fit .
Jerry




http://community.webtv.net/awoodbutc...oodWorkingPage

http://community.webtv.net/awoodbutcher/CARWRECK

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Default Any way to "measure" wire gauge in power cord?

(Dave Martindale) writes:

blueman writes:
dpb writes:


blueman wrote:


12 AWG -- ~0.081"
14 AWG -- ~0.064"


So, 12 is a little over 1/16", 14 is about 1/16" diameter. Enough
difference if the connection at either end is visible to tell easily.


Do these numbers apply to stranded too? (I believe the power cord is stranded)


Close, but not exactly. Stranded wire of a particular gauge will have
the same amount of wire cross-section area to carry current as solid
wire of the same gauge. Because there's some air spaces between
strands when they are packed as tightly as possible, the overall
diameter of the bundle will be slightly larger for the stranded wire,
but only by about 10%.

You can calculate the size increase yourself fairly easily:

Perhaps the simplest stranded wire that's still well-packed has 7
strands, one in the centre and 6 around it. This gives hexagonal
packing, with the centre strand touching all 6 outer strands, and each
outer strand touching two neighbours as well as the centre strand. If
the diameter of one strand is 1 unit, the diameter of the whole bundle
(measured in the direction that gives the largest measurement) is 3.
With 7 strands, the wire has 7 times the cross-sectional area of one
strand, and will carry 7 times the current. A *solid* wire with the
same current capacity and resistance would be sqrt(7) = 2.645 units in
diameter, while the 7-strand wire is 3 units in diameter - about 13%
larger.

(On the other hand, if you measure across the "flats" of the stranded
wire, with the caliper jaws touching two wires each, the measured
diameter is only 2.732 units, or only 3% larger than a solid wire of the
same metal cross section. So it matters how you measure).

In a wire with many more strands (e.g. welding cable), the outside
becomes rounder, so the diameter measurement doesn't vary significantly.
And the "extra" diameter for stranded approaches the ratio of the area
of a hexagon to a circle inscribed in it, which is sqrt(12)/PI, or about
1.103. In other words, the many-strand cable is 10% larger than the
equivalent solid wire.

Dave


Cool! Thanks for the detailed explanation.
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Default Any way to "measure" wire gauge in power cord? Blueman is a troll!

blueman posted for all of us...

To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks

Bite the cord blueman
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Tekkie - I approve this advertisement/statement/utterance.
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Default Any way to "measure" wire gauge in power cord?

blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks

Measure the resistance. 14 gauge is 60% higher than #12 so it should be
easy to do.
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Default Any way to "measure" wire gauge in power cord?


"Boden" wrote in message
...
blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks

Measure the resistance. 14 gauge is 60% higher than #12 so it should be
easy to do.


Almost no home owner will have a meter that can measuer the differance in
the resistance of 10 feet of # 12 and # 14 wire. It would be the differance
of about .0159 and .0252 ohms for 10 feet.

Good thought , but impractical for almost every one.
It would almost take lab grade equipment to do that.







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Default Any way to "measure" wire gauge in power cord?

On Thu, 04 Sep 2008 22:43:56 -0400, Boden wrote:
blueman wrote:
To avoid voltage drop (and power loss) at startup, I want to make sure
that the power cord to my 15 year old Craftsman table saw is 12 gauge
(or upgrade it if it is not).

There are no markings on the cord and no reference in the manual. The
saw is long discontinued so Sears is no help.

So is there any simple way of determining whether cord is 12 gauge or
not?

Thanks

Measure the resistance. 14 gauge is 60% higher than #12 so it should be
easy to do.


Measuring resistance of wire is difficult with a common multimeter. The
resistance of one's probes tends to be greater than the resistance of the wire
and most 3 1/2 digit meters are very inaccurate for milliohm readings.

You either need to measure at least 100' of it, or use a 4 wire
probe.

Why wouldn't the table saw already have an appropriate line cord?
s
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Default Any way to "measure" wire gauge in power cord?

"Ralph Mowery" writes:

"Boden" wrote in message


Measure the resistance. 14 gauge is 60% higher than #12 so it should be
easy to do.


Almost no home owner will have a meter that can measuer the differance in
the resistance of 10 feet of # 12 and # 14 wire. It would be the differance
of about .0159 and .0252 ohms for 10 feet.


Good thought , but impractical for almost every one.
It would almost take lab grade equipment to do that.


Few people have a single meter with a sufficiently low-range ohms scale
at home, but you can still do it with a bit of ingenuity. If you pass
a constant current through the wire, you get a voltage across the ends
that is proportional to the wire resistance, and many DMMs (even some
of the cheapest ones) have a 200 mV scale. For example, with a 1 A
current source, the two 10-foot pieces of wire in the example above
would have a voltage drop of 16 and 25 mV, enough to be told
apart by a DMM on even a 2 V range.

The most convenient current source for this would be a lab supply with a
few amps of output and a constant-current mode. But a 6 V or 12 V
battery (or power supply) plus the appropriate resistor to give an amp
or two of current will also work. Just measure the actual current and
the voltage across the wire and divide to get resistance. The resistor
needed will be a few ohms, so inserting a meter set to its 10 A range
will have negligible effect on the current.

I once had a problem figuring out how a particular circuit was wired in
a previous home. I opened the breaker, then connected a lab supply set
to 1 A constant current mode to one outlet that I thought was probably
near one end of the string. I shorted hot to neutral at another outlet
that I though was near the other end. Then I measured the voltage at
all of the other outlets on that circuit. There was an easily
measurable voltage drop (tens of mV) between boxes along the circuit,
so I could tell what sequence they were wired in, and where an outlet
was fed from a "tee" along the main path. (It turned out that some
previous owner had routed the circuit through a junction box that was
completely buried inside a wall, with no access from any side).

Note that this method only works when power is completely disconnected
from the house panel. If you try it on an energized circuit, you'll
probably destroy your power supply!

Dave
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Default Any way to "measure" wire gauge in power cord?

On Fri, 5 Sep 2008 20:27:38 +0000 (UTC), Dave Martindale wrote:
"Ralph Mowery" writes:


"Boden" wrote in message


Measure the resistance. 14 gauge is 60% higher than #12 so it should be
easy to do.


Almost no home owner will have a meter that can measuer the differance in
the resistance of 10 feet of # 12 and # 14 wire. It would be the differance
of about .0159 and .0252 ohms for 10 feet.


Good thought , but impractical for almost every one.
It would almost take lab grade equipment to do that.


Few people have a single meter with a sufficiently low-range ohms scale
at home, but you can still do it with a bit of ingenuity. If you pass
a constant current through the wire, you get a voltage across the ends
that is proportional to the wire resistance, and many DMMs (even some
of the cheapest ones) have a 200 mV scale. For example, with a 1 A
current source, the two 10-foot pieces of wire in the example above
would have a voltage drop of 16 and 25 mV, enough to be told
apart by a DMM on even a 2 V range.


That is the basic gist of a 4 wire probe. With one pair of leads, put some
current through the resistance under test. a 10V supply and a 100ohm resister
will put 100ma through and be fairly immune to the resistance of the first
set of probes. Measure the current going through the first pair of leads
(or it has to be regulated). With the second set of probes, measure the
voltage drop across the resistance under test. R=E/I.
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Default Any way to "measure" wire gauge in power cord?

AZ Nomad writes:

Few people have a single meter with a sufficiently low-range ohms scale
at home, but you can still do it with a bit of ingenuity. If you pass
a constant current through the wire, you get a voltage across the ends
that is proportional to the wire resistance, and many DMMs (even some
of the cheapest ones) have a 200 mV scale. For example, with a 1 A
current source, the two 10-foot pieces of wire in the example above
would have a voltage drop of 16 and 25 mV, enough to be told
apart by a DMM on even a 2 V range.


That is the basic gist of a 4 wire probe. With one pair of leads, put some
current through the resistance under test. a 10V supply and a 100ohm resister
will put 100ma through and be fairly immune to the resistance of the first
set of probes. Measure the current going through the first pair of leads
(or it has to be regulated). With the second set of probes, measure the
voltage drop across the resistance under test. R=E/I.


That's more or less where I got the idea. The difference is that the
pair of measuring probes could move along the "resistor" and observe
the voltage drop. The amount of voltage drop between two outlets is
reasonably correlated with the length of wire between them.

Dave
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Default Any way to "measure" wire gauge in power cord?

On Sun, 7 Sep 2008 07:33:25 +0000 (UTC), Dave Martindale wrote:
AZ Nomad writes:


Few people have a single meter with a sufficiently low-range ohms scale
at home, but you can still do it with a bit of ingenuity. If you pass
a constant current through the wire, you get a voltage across the ends
that is proportional to the wire resistance, and many DMMs (even some
of the cheapest ones) have a 200 mV scale. For example, with a 1 A
current source, the two 10-foot pieces of wire in the example above
would have a voltage drop of 16 and 25 mV, enough to be told
apart by a DMM on even a 2 V range.


That is the basic gist of a 4 wire probe. With one pair of leads, put some
current through the resistance under test. a 10V supply and a 100ohm resister
will put 100ma through and be fairly immune to the resistance of the first
set of probes. Measure the current going through the first pair of leads
(or it has to be regulated). With the second set of probes, measure the
voltage drop across the resistance under test. R=E/I.


That's more or less where I got the idea. The difference is that the
pair of measuring probes could move along the "resistor" and observe
the voltage drop. The amount of voltage drop between two outlets is
reasonably correlated with the length of wire between them.


If you're measuring resistance between outlets, you could plug in a small
resistive load like a 25W bulb and slap on a clamp on amp meter to
know the current through the circuit. Then you could measure the
voltage drop between outlets and know the resistance. To get from
there to the wire gauge, you'd have to know the length of the wiring
between the outlets.
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