Could I have some advice please.
I need to get a twelve volt, 1/2 amp supply five
hundred metres up a hill.
I do have a fence a metre high made from wooden posts and

seven runs of Num eight (4 mil) galvanised steel
wire.
Is it feasible to use two of these wires to carry twelve
volts that distance ?
Thank you.

-----------------------
If you use # 8 copper, the voltage drop at 1/2 A will be about 1V. However
the resistivity of iron which would be approximately that of steel would be
about 5 times as much giving a 5V drop so for 12V at the sending end, and
1/2 A load, the load voltage would be about 6-7V.
Chances are highly likely that this would not be satisfactory.

--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer

4 mil wire is pretty flimsy stuff even if made from steel. With a
breaking strength of 100,000 psi,it would take only a bit more than one
pound of force to break.
Aside from the low electrical conductivity compared to pure annealed
copper, the conductivity of alloys like steel is greatly reduced. by
impurity (non-ferric atoms) scatter electrons as they flow. Dislocations
from drawing the wire also decreases conductivity. Rule of thumb: The
harder the metal alloy, the lower the conductivity.
Bill

I suspect he means number 8 steel wire, which has a diameter of about 4
millimeters (not 4 circ mills area). That gives it a cross-section of about
0.02 in^2 and if your 100,000 psi is right for his stuff, a breaking
strength of about 1900 lbf.
What good would a fence be if the wire broke with just one lbf ?

Steel wire is usually drawn 'hot' and kept flexible for obvious reasons. It
isn't all that 'hard'. But excessive working of the wire can end up 'work
hardening' it and make it harder and subject to cracking. But if he ran his
own fence, I suspect he knew not to keep bending and kinking it until it
started cracking :-)
He doesn't mention much about the application, but I wonder if he might use
a somewhat higher AC voltage and a step-down / rectifier at the far end.
Not so high a voltage that he has to worry about insulation, safety,
insulators and all, maybe just 30 VAC or so. Would reduces his losses.
daestrom

Feasible means capable of being used or dealt with successfully.
Successful surely means legal. So no, you cannot use the fence wire
as electrical conductors because it is not legal by the NEC. You
shall use approved wiring methods or be subjected to a curse from the
electrical devil who appears as the authority having jurisdiction.

"Feasible means capable of being used or dealt with successfully.
Successful surely means legal. So no, you cannot use the fence wire
as electrical conductors because it is not legal by the NEC.
Good point.
What's the highest AC voltage that can be used without getting into "code
problems?" Is it 48 VAC? No question that 24 VAC is OK.
It might make good sense to ship up 24/48 volt AC and transform it to DC at
the load.
You
shall use approved wiring methods or be subjected to a curse from the
electrical devil who appears as the authority having jurisdiction.

If he isn't using the Code, he could try jacking the voltage up and
down and use the steel wire. Maybe, the electric fence idea would
work. It sure would beat buying enough copper wire to go 3200 feet
with the price of copper being so high.
Cheap fence wire insulators and transformers can be purchased at a
food lot store, the kind farmers use. An ignition transformer might
also work.
A used oil burner ignition transformer could raise the voltage to
10,000 volts then at the other end back feed another transformer to
get 120 volts. Then feed the 120 volts into a common Class 2 50 va
bell transformer to get 12 volts. I have never seen this done, and
do not know if it would work.
At 10,000 volts:
Power at 12 volts:
P= EI =12 x 0.5 = 6 watts
At 10,000 volts:
I = P/E = 6 / 10,000 = 0.0006 amperes
VD = VD=2(95.8)(1640)(0.0006)/16512
VD = 0.01 volts
Percent voltage drop = insignificant
I would place signs around the fence warning people, and tell the
inspector that the fence is electrified to keep the wildlife out.
Electric Fences are not covered by the NEC for obvious reasons. The
NEC has a purpose that is the practical safeguarding of persons and
property from the hazards arising from the use of electricity while an
electric fence has the prupose of shocking. When I was an inspector,
the foreman at the Atigun camp for the Trans Alaska Pipeline repair
job in about 1990 asked me about this. They installed an electric
fence around the camp to keep the grizzlies out and he wanted to know
where the code rules were. There are none! Atigun Pass is in the
Brooks Range in Alaska and is a very beautiful place. It is also the
highest point on the pipeline. I flew in there from Fairbanks in a
Cessna 150 with a bush pilot. He couldn't make it over the pass
because of fog so we landed at Chandalar field and I hitch hiked over
to Atigun. Those were the days, my friend, those were the days.

If he isn't using the Code, he could try jacking the voltage up and
down and use the steel wire. Maybe, the electric fence idea would
work. It sure would beat buying enough copper wire to go 3200 feet
with the price of copper being so high.
Cheap fence wire insulators and transformers can be purchased at a
food lot store, the kind farmers use. An ignition transformer might
also work.
A used oil burner ignition transformer could raise the voltage to
10,000 volts then at the other end back feed another transformer to
get 120 volts. Then feed the 120 volts into a common Class 2 50 va
bell transformer to get 12 volts. I have never seen this done, and
do not know if it would work.
At 10,000 volts:
Power at 12 volts:
P= EI x 0.5 = 6 watts
At 10,000 volts:
I = P/E = 6 / 10,000 = 0.0006 amperes
VD = VD=2(95.8)(1640)(0.0006)/16512
VD = 0.01 volts
Percent voltage drop = insignificant
I would place signs around the fence warning people, and tell the
inspector that the fence is electrified to keep the wildlife out.
Electric Fences are not covered by the NEC for obvious reasons. The
NEC has a purpose that is the practical safeguarding of persons and
property from the hazards arising from the use of electricity while an
electric fence has the prupose of shocking. When I was an inspector,
the foreman at the Atigun camp for the Trans Alaska Pipeline repair
job in about 1990 asked me about this. They installed an electric
fence around the camp to keep the grizzlies out and he wanted to know
where the code rules were. There are none! Atigun Pass is in the
Brooks Range in Alaska and is a very beautiful place. It is also the
highest point on the pipeline. I flew in there from Fairbanks in a
Cessna 150 with a bush pilot. He couldn't make it over the pass
because of fog so we landed at Chandalar field and I hitch hiked over
to Atigun. Those were the days, my friend, those were the days.
And what are the voltage regulation and exciting current requirements of the
two (or 3) (high impedance) transformers needed as well as leakage on the
crappy little fence insulators? They might be such that the scheme still
wouldn't work. In addition, aren't most electric fences pulsed?
At least 24VAC makes sense from a safety point of view.

--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer

24 vac does not make sense because the voltage drop will be too high.
Do the math.
0.5 amperes at 12 volts equals 6 watts.
I for 24 volts is 6/24 = 0.25 amperes
VD=2(95.8)(1640)(0.25)/16512
VD = 4.75 volts
4.75/24 x 100 = 19.8 percent
If an igniton transformer is used the output is not pulsed and losses
are minimum.
I think some electric fence power supplies are electronic and would
not work.
Additonally, 24 volts is not safe in a wet environment. That is why
12 volts is used for bell transformers. Read note 2 to Table 11A and
B in Chapter 9 of the NEC quoted below.
This note is based on finding from the original work by Charles
Dalziel, who, by the way, invented the GFCI.
2. For nonsinusoidal ac, Vmax shall not be greater than 42.4 volts
peak. Where wet contact (immersion not included) is likely to occur,
Class 3 wiring methods shall be used or
Vmax shall not be greater than 15 volts for sinusoidal ac and 21.2
volts peak for nonsinusoidal ac.

Why would a square wave be allowed to run at a higher voltage than a
sinusoidal wave?
It seems to me that a true sine wave would have more energy and
potential to do damage than a sin wave.
--
Stephen B.
just a (possibly dumb) ME heading to bed

24 vac does not make sense because the voltage drop will be too high.
Do the math.
0.5 amperes at 12 volts equals 6 watts.
I for 24 volts is 6/24 = 0.25 amperes
VD=2(95.8)(1640)(0.25)/16512
VD = 4.75 volts
4.75/24 x 100 = 19.8 percent
If an igniton transformer is used the output is not pulsed and losses
are minimum.
I think some electric fence power supplies are electronic and would
not work.
Additonally, 24 volts is not safe in a wet environment. That is why
12 volts is used for bell transformers. Read note 2 to Table 11A and
B in Chapter 9 of the NEC quoted below.
This note is based on finding from the original work by Charles
Dalziel, who, by the way, invented the GFCI.
2. For nonsinusoidal ac, Vmax shall not be greater than 42.4 volts
peak. Where wet contact (immersion not included) is likely to occur,
Class 3 wiring methods shall be used or
Vmax shall not be greater than 15 volts for sinusoidal ac and 21.2
volts peak for nonsinusoidal ac.
-------------------------
Some time ago, I did the math at 12V and I'll generously take your math as
correct even though the numbers that you have used are undefined: 95.8
what? 1640 what? 16512 what? You appear to be using a cookbook expression
that I am not familiar with -without giving the units so I have no way to
check your data/calculation except that the result appears to be reasonable.
Yes the voltage drop is high but I wasn't considering DC and neither were
you. Now using a 24/12V transformer with a 19.2 V input at the receiving end
and converting to DC gives a peak voltage of 13.5V and a fat capacitor will
leave you close enough to 12VDC average. There will be some voltage drop in
the transformer impedances but this should be fairly small as the smallest
12/24 or 120/24 transformer that one can get will be rated at a fair amount
more than 6 Watts. In any case dropping from 19+VAC to 12VDC at 0.5A for DC
is not a big deal, even using a resistor, is actually cheaper than the
warning signs .
If 24V (42.4V peak) is not safe in wet environments and the "safe" limit is
21.2 peak( the peak voltage of a 15V sinusoid)_- then what about 10KV?
Sure- we both know fencing units are can be safe ( not according to the
code that you quote) but that is due to their high impedance and that
impedance along with wet condition leakage can have a considerable effect on
your scenario-which is not according to any code. There is no use in
considering code in one situation and ignoring it in another. If code is to
be ignored- then I would rather go with the 24V setup.
In particular, the 24V can be floating with respect to ground so contact
between both wires is needed for a hazard and this can be limited by some
planning as to which wires are "hot" and which are grounded "shield" wires.
It isn't damnfoolproof but neither are signs- in either case, the hope is
that there are no damnfools around .
I note that you did not consider the impedance of the transformers in your
proposal. It will be high- by design.
Actually, there are other alternatives and these are based on location,
purpose, etc. Paralleling conductors in a 3/4 grouping as suggested by
others will bring the voltage drop down to less than 6% so the problem,
after a 24/12V transformer is too high a voltage at the load.
My point is that 12V wont do the job so what is the lowest standard voltage
that will do the job. 24V appears to be OK.

--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer

K=95.8 circular mil ohms per foot. It is the resistance of a
conductor 0.001 inch in diameter one foot long at 20 degrees C in this
case.
L=1640 is one way circuit length in feet
CMA=16512 is the circular mil area of the No. 8 steel wire that is the
diameter in thousandths of an inch squared
I is amperes
VD is voltage drop
VD=2KLI/CMA is a standard formual for finding voltage drop for 60
hertz single phase or Direct Current
This is the standard formula used by electricians to find voltage drop
for the last 50 years or so..
We multiply VD by 0.866 for three phase three wire and by 0.5 for
three phase four wire
If you use 24 volts the NEC rules apply and bare conductors cannot be
used, but by using the electric fence model the NEC rules do not
apply.

K•.8 circular mil ohms per foot. It is the resistance of a
conductor 0.001 inch in diameter one foot long at 20 degrees C in this
case.
L40 is one way circuit length in feet
CMA512 is the circular mil area of the No. 8 steel wire that is the
diameter in thousandths of an inch squared
I is amperes
VD is voltage drop
VD=2KLI/CMA is a standard formual for finding voltage drop for 60
hertz single phase or Direct Current
This is the standard formula used by electricians to find voltage drop
for the last 50 years or so..
We multiply VD by 0.866 for three phase three wire and by 0.5 for
three phase four wire
If you use 24 volts the NEC rules apply and bare conductors cannot be
used, but by using the electric fence model the NEC rules do not
apply.
--------------------
Thanks for the definition of terms. I have not used the "standard formula"
and generally use metric so I simply go back to basics: Resistance
=resistivity*length/area for conductors and the rest follows. This is, as I
suspected, part of the basis for your standard formula but I wanted to be
sure as I suspect any "formula" until I see the basis for it. The
remaining part consists of assumptions of unity pf and negligable
inductance- both reasonable in commercial and domestic applications as well
as some industrial applications. They are reasonable in this case as
well-given negligable transformer impedances (and exciting currents) which
may not be the case.
However the reason for your proposal is to get around NEC rules Fair
enough. It is a situation that code doesn't cover or prohibits (whether, in
a specific case such as this, the code is an ass is another matter ).
Basically, a 24V scheme will work. Will it violate code? Yes. Will it work
better than a HV system- I think so. Will it be safer? Maybe, maybe not- but
it can be, in spite of the code.

--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer

In our local paper someone stole a 3500 foot spool of No. 4 copper
wire that was worth $8500. No wonder people want to use steel fence
wire.
On the KLI/CMA this is the method used by the Neher McGrath paper to
find DC resistance. Multipliers are used to convert to AC resistance
or impedance. The paper was written in 1957 using feet and not
meters.
K for steel at 20 degrees C is 95.8 ohms per foot. To find the
resistance at other temperatures the inferred temperature at zero
resistance is required and the point slope equation is used to find
the equation of the straight line. This is not entirely correct
because the actual measured values of resistance are slightly off the
straight line, but for most field applications it is good enough.
Th N-M paper in PDF format is at:
http://www.electriciancalculators.com/ampacity/ampacity.htm

In our local paper someone stole a 3500 foot spool of No. 4 copper
wire that was worth $8500. No wonder people want to use steel fence
wire.
On the KLI/CMA this is the method used by the Neher McGrath paper to
find DC resistance. Multipliers are used to convert to AC resistance
or impedance. The paper was written in 1957 using feet and not
meters.
K for steel at 20 degrees C is 95.8 ohms per foot. To find the
resistance at other temperatures the inferred temperature at zero
resistance is required and the point slope equation is used to find
the equation of the straight line. This is not entirely correct
because the actual measured values of resistance are slightly off the
straight line, but for most field applications it is good enough.
Th N-M paper in PDF format is at:
http://www.electriciancalculators.com/ampacity/ampacity.htm
-----
I have no problem with the calculator per se. You have clarified the terms
satisfactorily.
It is based on knowledge that dates back to at least the time of Ohm (well
before 1900). The 1957 reference apparently uses an older cookbook
expression as part of dealing with ampacities of underground
cables.-Unfortunately, I could not bring up the reference from your site but
it is an AIEE paper dealing with ampacities of underground cables- a much
more complex problem than simply finding resistance and voltage drops which
can be found in any decent introductory circuits text.
The resistance/ temperature relationship has also been around for a long
time. Actual measured data do have errors which cause wobbles in the curve
so least squares fitting is used.
The AC corrections do depend on frequency and wire size and the typical
corrections for copper wire will be incorrect for iron wire (and for
closely wound coils) because of enhanced magnetic effects leading to what is
called "skin effect" (Rudenberg tackled this messy problem about 80 years
ago (+/-)) .

--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer

| In our local paper someone stole a 3500 foot spool of No. 4 copper
| wire that was worth $8500. No wonder people want to use steel fence
| wire.
Do we see a pattern here?
http://www.local6.com/news/9841302/detail.html
http://www.nbcsandiego.com/news/15516726/detail.html
http://www.komotv.com/news/archive/4163491.html
http://www.wftv.com/news/9842266/detail.html
http://www.wyff4.com/news/9484796/detail.html
http://www.highbeam.com/doc/1G1-163833841.html
http://www.wmur.com/news/11425057/detail.html
http://www.pasadenastarnews.com/ci_8764005
http://www.herald-dispatch.com/homepage/x1657949065
http://www.msnbc.msn.com/id/19791644 /
http://www.dailymail.com/News/200803310220
http://news.sky.com/skynews/article/0,,30200-1287665,00.html

--
|WARNING: Due to extreme spam, I no longer see any articles originating from |
| Google Groups. If you want your postings to be seen by more readers |

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.