Electrical conductivity in steel wire ?

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.
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----------------------- 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.
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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
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wrote:

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

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500m by steel? Volt Drop in Cu is still a question. Thinking setp up and step down the voltage in transmission?

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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.
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"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.
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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.
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wrote:

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.
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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.
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"Gerald Newton" wrote
<Big SNIP>

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
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The peak of a square wave is the same as the RMS, the peak of a sine wave is higher than the RMS.
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"James Sweet" wrote

Thanks, I forgot about RMS, since I tend to play with nominal 1/4" rods not electrons.
-- Stephen B.
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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.
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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.
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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.
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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
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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 (+/-)) .
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Skin depth has the same functional, dependence upon permeability as it does for frequency or conductivity.
Bill
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| 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
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