Post by thread:[OT] Cable retained energy, was Super Caps

Hi Alex At 12:28 98.03.06 -0800, you wrote: {Quote hidden}>richard skinner wrote: >> >> No, I haven't but, I ran across something very interesting, at least to me, >> but I am Ignorant to allot >> of things in this world. >> >> A SUPER CAP. I watched a guy last week charge a roll of clx wire on a >> spool, then shoot sparks >> from the ends when he shorted the wire at the end. I never much thought >> about a large spool >> of wire acting as a capacitor, but all the ingredients are there. He was >> telling me that you should >> always short the wires on a spool before working with it as it can store >> static electricity and it can get >> rather high over time, if the conditions are correct. Hum, that ought to run {Quote hidden}>> a clock for sometime? > >???? Capacitance in a coil? The basic ingredients of a capacitor are two >conductors seperated by an insulator ---||--- >A coil of wire on the other hand is just one long conductor. It may have >a lot of inductance, but I can't see it having much capacitance (or are >you talking about a two cored cable? Even then there would only be a >small amount between the cores). > >-- >------------------- Linux- the choice of a GNU generation. >-------------------- >: Alex Holden- Caver, Programmer, Land Rover nut, and Radio amateur (M1 >CJD). : >-------------- www.geocities.com/CapeCanaveral/Lab/1532/ >--------------- > When you test the insulation of a long spool of cable (one end connected to a power source and the other open), when you disconect it from the power source and leave it open the transient efect can creat a surge at one end of the cable (the one connected with the power source). As the cable is open at both ends this surge travels from one end to the other (as a reflectd wave) until all its energy is exausted by the cable losses. If you have a good quality cable this energy can stay there for quite a while. If we are talking about high voltage cables (energy transportation lines), this efect can kill pepople toutching the cable days after it has been tested. The only safe way to avoid this is to conect the cable to a correctly adapted load until all residual energy gets exausted before stocking the cable. Jorge F =============================================================== cumprimentos / best regards Jorge Ferreira //spam_OUTjorgegfTakeThisOuTmail.telepac.pt ------ Make sure brain is in gear before engaging mouth ------- ===============================================================

>When you test the insulation of a long spool of cable (one end connected to >a power source and the other open), when you disconect it from the power >source and leave it open the transient efect can creat a surge at one end >of the cable (the one connected with the power source). As the cable is >open at both ends this surge travels from one end to the other (as a >reflectd wave) until all its energy is exausted by the cable losses. If you >have a good quality cable this energy can stay there for quite a while. >If we are talking about high voltage cables (energy transportation lines), >this efect can kill pepople toutching the cable days after it has been tested. >The only safe way to avoid this is to conect the cable to a correctly >adapted load until all residual energy gets exausted before stocking the >cable. Are you saying that the resistance of the cable is so low that a signal can bounce along the unterminated transmission line for _days_ without undergoing significant attenuation? (If so, wouldn't that essentially be a superconducting tuned transmission line oscillator?) Isn't it _much_ more likely that the cable (I'm assuming we're discussing coax or two conductor cable) is acting simply as a capacitor? After all, what's two conductors seperated by an insulator? newell

At 02:20 PM 3/10/98 -0600, you wrote: {Quote hidden}>>When you test the insulation of a long spool of cable (one end connected to >>a power source and the other open), when you disconect it from the power >>source and leave it open the transient efect can creat a surge at one end >>of the cable (the one connected with the power source). As the cable is >>open at both ends this surge travels from one end to the other (as a >>reflectd wave) until all its energy is exausted by the cable losses. If you >>have a good quality cable this energy can stay there for quite a while. >>If we are talking about high voltage cables (energy transportation lines), >>this efect can kill pepople toutching the cable days after it has been >tested. >>The only safe way to avoid this is to conect the cable to a correctly >>adapted load until all residual energy gets exausted before stocking the >>cable. > >Are you saying that the resistance of the cable is so low that a signal can >bounce along the unterminated transmission line for _days_ without >undergoing significant attenuation? (If so, wouldn't that essentially be a >superconducting tuned transmission line oscillator?) > > >Isn't it _much_ more likely that the cable (I'm assuming we're discussing >coax or two conductor cable) is acting simply as a capacitor? After all, >what's two conductors seperated by an insulator? > > >newell > I find either case (the "superconductivity" or the capacitance theory) unlikely under normal circumstances. If it did happen, I would attribute it to the capacitance. First off, Scott (or Newell, sorry, still not sure which you prefer) is right, as far as I know, that no ordinary conductor can possibly support currents for more than a millisecond or so with out an external source. (even an ms is an EXTREAMLY long estimate). Secondly, lets suppose that there was enough wire in the cable to creat e a significant capacitance. The effective circuit would look like a capacitor with a resistance in parallel (we can ignore the inductance, it certainly won't make much difference beyond seconds of time). The value of the effective parallel resistance can be approximated by the resistance of the cable. Assuming the cable is copper and of a resonable diameter, lets say 26 ga. 26 ga copper wire has a linear resistivity of .0408 ohm/ft. So, even if this cable were 10 miles long, the effective resistance would only be around 2.2k. Now, suppose we had 1 farad of capacitance. The time constant for the circuit would be 2200 seconds. So, the voltage would drop to less than 1% of its original value within hours of charging, and this is for an extream example. The spool of wire holding 10 miles of wire would probably barely fit on my desk. So, I guess if you had a huge spool, you could theoretically have it hold charge for days or weeks, but it would have to be HUGE. Besides, this effect diminishes with wire diameter so anything which one could rightfully call "cable" instead of wire would probably not exhibit this effect at all. In order for a static charge to naturally build up on the cable, the average rate of energy transfer to the cable would have to exceed its discharge rate. This also seems unlikely. However, I have no experiance dealing with any really large amount of wire or cable, so I certainly could be wrong. Sean +--------------------------------+ | Sean Breheny | | Amateur Radio Callsign: KA3YXM | | Electrical Engineering Student | +--------------------------------+ Fight injustice, please look at http://homepages.enterprise.net/toolan/joanandrews/ Personal page: http://www.people.cornell.edu/pages/shb7 .....shb7KILLspam@spam@cornell.edu Phone(USA): (607) 253-0315

At 14:20 98.03.10 -0600, you wrote: {Quote hidden}>>When you test the insulation of a long spool of cable (one end connected to >>a power source and the other open), when you disconect it from the power >>source and leave it open the transient efect can creat a surge at one end >>of the cable (the one connected with the power source). As the cable is >>open at both ends this surge travels from one end to the other (as a >>reflectd wave) until all its energy is exausted by the cable losses. If you >>have a good quality cable this energy can stay there for quite a while. >>If we are talking about high voltage cables (energy transportation lines), >>this efect can kill pepople toutching the cable days after it has been >tested. >>The only safe way to avoid this is to conect the cable to a correctly >>adapted load until all residual energy gets exausted before stocking the >>cable. > >Are you saying that the resistance of the cable is so low that a signal can >bounce along the unterminated transmission line for _days_ without >undergoing significant attenuation? (If so, wouldn't that essentially be a >superconducting tuned transmission line oscillator?) > > >Isn't it _much_ more likely that the cable (I'm assuming we're discussing >coax or two conductor cable) is acting simply as a capacitor? After all, >what's two conductors seperated by an insulator? > > >newell > In normal low power aplications, all the energy is lost in fractions of a second, but in cables for energy transportation lines who work at very high voltages (several KV) and low freq the insulation testing is above the double of the nominal working voltage, so if you have 1000 meters of cable its a pretty good amount of energy we are talking about and in this case you can get killed days after the testing if that energy isnt properly drained. About beeing a capacitive efect, I think you can call it that. We shouldn't forget that one of the matematical models for a cable (or trnsmition line) is a RL series circuit with caps in paralel. R L ------/\/\/\/\----@@@@@----- | | --- --- C | R | L ------/\/\/\/\----@@@@@----- (hope you can understand this, first time, ASCII line art) Jorge F =============================================================== cumprimentos / best regards Jorge Ferreira //jorgegfKILLspammail.telepac.pt ------ Make sure brain is in gear before engaging mouth ------- ===============================================================

> Secondly, lets suppose that there was enough wire in the cable to create >a significant capacitance. The effective circuit would look like a RG-58 is about 30 pF/foot, according to my Belden catalog. >capacitor with a resistance in parallel (we can ignore the inductance, it >certainly won't make much difference beyond seconds of time). The value of >the effective parallel resistance can be approximated by the resistance of >the cable. Assuming the cable is copper and of a resonable diameter, lets Sorry, if you take a hunk of coax with both ends open, any parallel resistance _across_ the cap has to be from the insulation resistance of the dielectric. I don't have any teflon coax, but I'll bet it makes a _very_ good low-leakage cap. Look, at low frequencies, the capacitance of coax is like any other cap. It stores a charge. Put enough voltage across that cap and it can bite you. Use a high-quality dielectric and the stored charge will be there for quite some time. >for an extream example. The spool of wire holding 10 miles of wire would >probably barely fit on my desk. So, I guess if you had a huge spool, you I've got a spool that's about 26 miles long, and it isn't very big. It's not coax, and it's only 34 gauge. Too bad I don't have access to both ends--it'd be a neat inductor! newell

At 07:34 PM 3/10/98 -0600, you wrote: >> Secondly, lets suppose that there was enough wire in the cable to >create >>a significant capacitance. The effective circuit would look like a > >RG-58 is about 30 pF/foot, according to my Belden catalog. > > Ok, maybe I was getting confused, I thought we were talking about single conductor wire (loosely called cable). Of course, my whole discussion would be incorrect for coax. Jorge has mentioned that this phenomenon is observable when dealing with power transmission line. Power transmission line is not coaxial, is it? I have always been told that it is single conductor woven cable, sometimes with a hollow core with a coolent run through it. {Quote hidden}>>capacitor with a resistance in parallel (we can ignore the inductance, it >>certainly won't make much difference beyond seconds of time). The value of >>the effective parallel resistance can be approximated by the resistance of >>the cable. Assuming the cable is copper and of a resonable diameter, lets > >Sorry, if you take a hunk of coax with both ends open, any parallel >resistance _across_ the cap has to be from the insulation resistance of the >dielectric. > >I don't have any teflon coax, but I'll bet it makes a _very_ good >low-leakage cap. > >Look, at low frequencies, the capacitance of coax is like any other cap. >It stores a charge. Put enough voltage across that cap and it can bite >you. Use a high-quality dielectric and the stored charge will be there for >quite some time. > > Yes, I understand this, but as I said above, I thought that you meant single conductor. I think the original author was refering to single conductor wire, or at least was initially interpreted as such. The reason for the resistance in parallel with the cap. is that you can view a single wire as split up into elements, each one forming a plate of a capacitor with adjacent elements as the opposite plates, and each little element forming a little resistance. I then mentally integrate over the length of the cable to form an electrical picture of what is going on. >>for an extream example. The spool of wire holding 10 miles of wire would >>probably barely fit on my desk. So, I guess if you had a huge spool, you > >I've got a spool that's about 26 miles long, and it isn't very big. It's >not coax, and it's only 34 gauge. Too bad I don't have access to both >ends--it'd be a neat inductor! > Wow, I bet it would be! Even better if you stuck a core in it! > >newell > +--------------------------------+ | Sean Breheny | | Amateur Radio Callsign: KA3YXM | | Electrical Engineering Student | +--------------------------------+ Fight injustice, please look at http://homepages.enterprise.net/toolan/joanandrews/ Personal page: http://www.people.cornell.edu/pages/shb7 .....shb7KILLspam.....cornell.edu Phone(USA): (607) 253-0315

On Tue, 10 Mar 1998 21:38:31 -0500 Sean Breheny <EraseMEshb7spam_OUTTakeThisOuTCORNELL.EDU> writes: > Jorge has mentioned that this phenomenon is >observable when dealing with power transmission line. Power >transmission >line is not coaxial, is it? The stuff that is buried underground and used from about 2 KV up to maybe 50 KV (e.g. for distribution to transformers in neighborhoods) is. It has a copper or aluminum conductor at the core, thick polyethylene insulation, then a shield made out of metal braid and conductive plastic, and finally a black plastic outer covering. The shield is likely not intended to normally carry current. It is connected to ground at both ends for safety reasons. Maybe some single-phase circuits use it as the return conductor. In any case, the coaxial construction makes it difficult for high voltage to appear on the outside of the cable if there is a leakage, cut or hole in the insulation. Such a circumstance will cause the cable to arc and the fuse or circuit breaker to open. This line is of course routinely "hipot" tested before installation by connecting a high voltage between the center and the shield and measuring any leakage. A big spool of it charged to many KV would indeed be dangerous. The polyethylene insulation would prevent the charge from leaking off for a long time as well as maybe causing a phantom "recharge" from dielectric absorption. Of course such cable is intended for use at 60 Hz and is not designed for any particular impedance. >I have always been told that it is single >conductor woven cable, The wire strung overhead between poles is laid up of strands of aluminum on the outside, and steel on the inside. The steel is to make it stronger. Even at 60 Hz, there is enough of a "skin effect" to reduce the effectiveness of the conductors in the center, so the aluminum is outside. Except in special cases, it is bare. Please do not climb power poles and touch the wires. You will get hurt. Really high power lines have several cables in parallel. They are held apart in a triangle or square arrangment to make the apparent diameter of the conductor as large as possible. This improves the impedance and current distribution along the line. When dealing with hundreds of km of cable, AC effects such as phase shifts are very real at 60 Hz. sometimes with a hollow core with a coolent run >through it. In power "substations" the conductors are sometimes placed inside much larger outer pipes. The pipes are filled with sulfur hexafluoride gas. SF6 is a much better insulator than air, as well as being certain to be clean and dry, so the conductors can be in closer proximity than if they were strung out in the open. This is rather expensive so it is done only for extremely high voltages or where the real estate to lay out the station with larger seperations would be even more expensive. I don't think the conductors in transmission systems are hollow or actively cooled in any way. Hollow cooled wire is used to wind generators and big motors. Hydrogen (H2) gas was used as the coolant in one example I saw. It's both very "thin" and light (i.e. easy to move at high velocity through small hollow passages) and absorbs heat well. It doesn't seem that H2 gas and big electrical machines should be used near each other. This is what I remember from several years ago; current practices may be different. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

At 06:47 PM 3/10/98 -0500, Sean Breheny wrote: > Secondly, lets suppose that there was enough wire in the cable to create >a significant capacitance. The effective circuit would look like a >capacitor with a resistance in parallel (we can ignore the inductance, it >certainly won't make much difference beyond seconds of time). The value of >the effective parallel resistance can be approximated by the resistance of >the cable. Sorry, Sean. The resistance in parallel would be the resistance of the insulator between the two conductors, not the resistance of the wire, itself. This is typically *very* high. To make calculation easier, it is typically specified as a certain conductance per unit length (conductance is just the reciprocal of resistance). - Rick "micro-mhos per meter" Dickinson +---------------------------------+---------------------------+ | Enterprise ArchiTechs Company |"You can't reason someone | | Lotus Certified Notes | out of a position they | | Appl. Design & Administration | didn't reason themselves | |(818)563-1061 rtdspam_OUTnotesguy.com | into" -- Rick Adams, | | http://www.eArchiTechs.com | in alt.folklore.urban | +---------------------------------+---------------------------+

The cable he used was clx, I think. It is built almost like coax. It can have any number of pairs in it. Each individual wire inside consists of a core, insulator, Wrapped with a thin layer of foil. Some of this wire has anywhere from a single conductor to say 12 conductors in side. The very outside has a dielectric type of grease before the final sheath or insulation. Nice wire, used offshore on platforms all the time, however, it is a pain to work with. When it gets old, it is tough to peel the foil of the outside of each strand, then ofcourse, the grease sure doesn't help matters any trying to tape it or grip it. Static Electricity? I don't know, can it be created by salt water waves sloshing against the legs of the platform? Could it be parasitic charges from the generators on board? Geez, I have no idea. I know that it should definetly have a good ground since its sitting on the ocean flooring with a ton of dirt or mud holding it in place. The cable was intentionally charged and then discharged to prove to me it would hold a charge, and to prove to me it must be discharged before handling. It had to be proved as I though my leg was being pulled. I have seen formulas here saying that it is not possible, and I've seen people saying yes it was possible for these spools to hold a charge, All I know, and I have NO reason to make up short stories on spools of wire, is he proved it to me by doing it. It did seem like an interesting debate, Richard Skinner @spam@rwskinnerKILLspamworldnet.att.net http://home.att.net/~rwskinner ---------- {Quote hidden}> From: Mike Keitz <KILLspammkeitzKILLspamJUNO.COM> > To: RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU > Subject: Re: [OT] Cable retained energy, was Super Caps > Date: Tuesday, March 10, 1998 10:18 PM > > On Tue, 10 Mar 1998 21:38:31 -0500 Sean Breheny <spamBeGoneshb7spamBeGoneCORNELL.EDU> > writes: > > Jorge has mentioned that this phenomenon is > >observable when dealing with power transmission line. Power > >transmission > >line is not coaxial, is it? > > The stuff that is buried underground and used from about 2 KV up to maybe > 50 KV (e.g. for distribution to transformers in neighborhoods) is. It > has a copper or aluminum conductor at the core, thick polyethylene > insulation, then a shield made out of metal braid and conductive plastic, > and finally a black plastic outer covering. The shield is likely not > intended to normally carry current. It is connected to ground at both > ends for safety reasons. Maybe some single-phase circuits use it as the > return conductor. In any case, the coaxial construction makes it > difficult for high voltage to appear on the outside of the cable if there > is a leakage, cut or hole in the insulation. Such a circumstance will > cause the cable to arc and the fuse or circuit breaker to open. This > line is of course routinely "hipot" tested before installation by > connecting a high voltage between the center and the shield and measuring > any leakage. A big spool of it charged to many KV would indeed be > dangerous. The polyethylene insulation would prevent the charge from > leaking off for a long time as well as maybe causing a phantom "recharge" > from dielectric absorption. > > Of course such cable is intended for use at 60 Hz and is not designed for > any particular impedance. > > >I have always been told that it is single > >conductor woven cable, > > The wire strung overhead between poles is laid up of strands of aluminum > on the outside, and steel on the inside. The steel is to make it > stronger. Even at 60 Hz, there is enough of a "skin effect" to reduce > the effectiveness of the conductors in the center, so the aluminum is > outside. Except in special cases, it is bare. Please do not climb > power poles and touch the wires. You will get hurt. Really high power > lines have several cables in parallel. They are held apart in a triangle > or square arrangment to make the apparent diameter of the conductor as > large as possible. This improves the impedance and current distribution > along the line. When dealing with hundreds of km of cable, AC effects > such as phase shifts are very real at 60 Hz. > > sometimes with a hollow core with a coolent run > >through it. > > In power "substations" the conductors are sometimes placed inside much > larger outer pipes. The pipes are filled with sulfur hexafluoride gas. > SF6 is a much better insulator than air, as well as being certain to be > clean and dry, so the conductors can be in closer proximity than if they > were strung out in the open. This is rather expensive so it is done only > for extremely high voltages or where the real estate to lay out the > station with larger seperations would be even more expensive. > > I don't think the conductors in transmission systems are hollow or > actively cooled in any way. Hollow cooled wire is used to wind > generators and big motors. Hydrogen (H2) gas was used as the coolant in > one example I saw. It's both very "thin" and light (i.e. easy to move at > high velocity through small hollow passages) and absorbs heat well. It > doesn't seem that H2 gas and big electrical machines should be used near > each other. > > This is what I remember from several years ago; current practices may be > different. > > _____________________________________________________________________ > You don't need to buy Internet access to use free Internet e-mail. > Get completely free e-mail from Juno at http://www.juno.com > Or call Juno at (800) 654-JUNO [654-5866]

On Wed, 11 Mar 1998, richard skinner wrote: > > The cable was intentionally charged and then discharged to prove to me it > would hold a charge, and to prove to > me it must be discharged before handling. It had to be proved as I though my > leg was being pulled. I'm sorry I missed some of this discussion but I was wondering how he proved t held a charge? How did he charge it (voltage level, type of instrument, lenght of time...etc)? How did he show it held a charge (voltmeter)? How did he discharge it (short, resistor leak path)? Where was the cable during the test (rolled, laid out..etc)? Did he show the cable was at close to no voltage after discharge? I have heard of antenna wires showing charges, but this was because of the natural EMF of the background. Just curious. Rob {Quote hidden}> > I have seen formulas here saying that it is not possible, and I've seen > people saying yes it was possible for these > spools to hold a charge, All I know, and I have NO reason to make up short > stories on spools of wire, is he proved > it to me by doing it. > > It did seem like an interesting debate, > > Richard Skinner > RemoveMErwskinnerTakeThisOuTworldnet.att.net > http://home.att.net/~rwskinner >

Rob said: >I'm sorry I missed some of this discussion but I was wondering how he >proved t held a charge? How did he charge it (voltage level, type of >instrument, lenght of time...etc)? How did he show it held a charge >(voltmeter)? How did he discharge it (short, resistor leak path)? >Where was the cable during the test (rolled, laid out..etc)? Did he show >the cable was at close to no voltage after discharge? > >I have heard of antenna wires showing charges, but this was because of >the natural EMF of the background. > >Just curious. > I too am curious about the the specs on this cable. As a reference, a small camera flash stores about 5 joules of energy. That's enough to make some decent sparks, and more than enough to be dangerous. The formula for capacitive energy storage is [C*V^2]/2. As an earlier poster mentioned, RG-58 is approx 30pf/ft. When you do the math, you'd have to charge about 666 ft to about 1KV (probably wouldn't handle that) or 66666 ft to 100V to get 5 joules. That's 11 miles of cable. Or maybe this cable is something really exotic... always possible, given the eclectic nature of PicLister backgrounds. Reg Neale

Okay, Okay, Next time I go out to the platform, I will get you the specs on the cable. It shouldn't be too long as I get to live there most of the time anyways. And, to answer the question how it was discharged, it was shorted (touched against) some plate steel, and it made a small arc. It was charged probably a few minutes, directly removed and shorted. I do not know the voltage, but I will ask more when I go out. It couldn't have been tooo much as The most I "think" they have on site is 480 vac 3 phase. Yes, it was still spooled on the spool. I will also get the length, I'm sure its written on the spool. The spool was approx. 3 feet in diameter, CLX Wire, and It was mutiple conductor (want me to find that out too)? It wasn't intended as a scientific experiment, but to show me and others, that sometimes things "can" get you when you least expect it. I was being a smart ass about powering a clock from it, but the main content was if anyone knew, or seen this trick before, as I never expected such. Geez, I think Ryan was right about people being very agressive on the list here. I made a mistake to begin with, I thought I posted to the stamp list, but mistakenly posted here. If I was making this crap up, I would have bailed out when I had the chance? Richard Skinner rwskinnerEraseME.....worldnet.att.net http://home.att.net/~rwskinner ---------- {Quote hidden}> From: Reginald Neale <EraseMEnealeSERVTECH.COM> > To: RemoveMEPICLISTEraseMEEraseMEMITVMA.MIT.EDU > Subject: Re: [OT] Cable retained energy, was Super Caps > Date: Wednesday, March 11, 1998 4:08 PM > > Rob said: > > >I'm sorry I missed some of this discussion but I was wondering how he > >proved t held a charge? How did he charge it (voltage level, type of > >instrument, lenght of time...etc)? How did he show it held a charge > >(voltmeter)? How did he discharge it (short, resistor leak path)? > >Where was the cable during the test (rolled, laid out..etc)? Did he show > >the cable was at close to no voltage after discharge? > > > >I have heard of antenna wires showing charges, but this was because of > >the natural EMF of the background. > > > >Just curious. > > > I too am curious about the the specs on this cable. As a reference, a small > camera flash stores about 5 joules of energy. That's enough to make some > decent sparks, and more than enough to be dangerous. The formula for > capacitive energy storage is [C*V^2]/2. As an earlier poster mentioned, > RG-58 is approx 30pf/ft. When you do the math, you'd have to charge about > 666 ft to about 1KV (probably wouldn't handle that) or 66666 ft to 100V to > get 5 joules. That's 11 miles of cable. Or maybe this cable is something > really exotic... always possible, given the eclectic nature of PicLister > backgrounds. > > Reg Neale

At 09:22 PM 3/11/98 -0600, you wrote: Hey Richard, I didn't mean to ruffle your feathers. I was just very curious to the phenomenon you saw. As an engineer I like to try to understand what goes on. I appreciate what you've told us. If you decide to not respond that's fine. Rob {Quote hidden}> >Geez, I think Ryan was right about people being very agressive on the list >here. I made a mistake to begin >with, I thought I posted to the stamp list, but mistakenly posted here. If I >was making this crap up, I would >have bailed out when I had the chance? > > >Richard Skinner >RemoveMErwskinnerspam_OUTKILLspamworldnet.att.net >http://home.att.net/~rwskinner > >---------- >> From: Reginald Neale <RemoveMEnealeTakeThisOuTspamSERVTECH.COM> >> To: EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDU >> Subject: Re: [OT] Cable retained energy, was Super Caps >> Date: Wednesday, March 11, 1998 4:08 PM >> >> Rob said: >> >> >I'm sorry I missed some of this discussion but I was wondering how he >> >proved t held a charge? How did he charge it (voltage level, type of >> >instrument, lenght of time...etc)? How did he show it held a charge >> >(voltmeter)? How did he discharge it (short, resistor leak path)? >> >Where was the cable during the test (rolled, laid out..etc)? Did he show >> >the cable was at close to no voltage after discharge? >> > >> >I have heard of antenna wires showing charges, but this was because of >> >the natural EMF of the background. >> > >> >Just curious. >> > >> I too am curious about the the specs on this cable. As a reference, a small >> camera flash stores about 5 joules of energy. That's enough to make some >> decent sparks, and more than enough to be dangerous. The formula for >> capacitive energy storage is [C*V^2]/2. As an earlier poster mentioned, >> RG-58 is approx 30pf/ft. When you do the math, you'd have to charge about >> 666 ft to about 1KV (probably wouldn't handle that) or 66666 ft to 100V to >> get 5 joules. That's 11 miles of cable. Or maybe this cable is something >> really exotic... always possible, given the eclectic nature of PicLister >> backgrounds. >> >> Reg Neale > >

If capacitive storage is the mechanism here, as I believe it is, then the energy may be seen to be high enough to be "impressive" as follows Use 30pf/ft = 158 nF/mile - say 160nF - about double what I recalled for buried telephone communications cable PER PAIR.. Imagine that there are about 6 separate wires - the description of the cable suggested the possibility of a large number of multiple cores (I choose 6 for obvious reasons - choose your oiwn figures to suit). 6 x 160 = approx 0.1uF. Charge this to 100 volts. Now, any volunteers from amongst the ranks of the electrically experienced to seize a 0.1uF cap charged to 100 volts? At higher, say 500 volts, there will be even fewer. Surprisingly, even at 500 volts we only have a small fraction of a joule here (0.5 x 0.1E-6 x 500^2) and yet practical experience tells you you are going to get a nasty shock from it. (Or, if it doesn't, grab hold and see :-)). You would have to grab the ends of all pairs at once, logistically difficult, but the danger is a real one. I am vaguely disturbed by the thought that N wires in close proximity may not produce N times the capacitance but no doubt someone will comment on this (too lazy to go and find textbook on fundamentals to refresh memory). >I too am curious about the the specs on this cable. As a reference, a small >camera flash stores about 5 joules of energy. That's enough to make some >decent sparks, and more than enough to be dangerous. The formula for >capacitive energy storage is [C*V^2]/2. As an earlier poster mentioned, >RG-58 is approx 30pf/ft. When you do the math, you'd have to charge about >666 ft to about 1KV (probably wouldn't handle that) or 66666 ft to 100V to >get 5 joules. That's 11 miles of cable. Or maybe this cable is something >really exotic... always possible, given the eclectic nature of PicLister >backgrounds. > >Reg Neale >

Sorry Rob, I was a little on edge last night to begin with, then after reading all the flames, I started to overheat a little. At any Rate, When I go out to the platform, I will get the info off the spool for everyone. The Nice thing about this wire is, it seems to last forever (a matter of speaking) through some pretty rough conditions. Richard Skinner RemoveMErwskinnerKILLspamworldnet.att.net http://home.att.net/~rwskinner ---------- {Quote hidden}> From: Rob Zitka <robzsSTOPspamspam_OUTHICOM.NET> > To: spamBeGonePICLISTSTOPspamEraseMEMITVMA.MIT.EDU > Subject: Re: [OT] Cable retained energy, was Super Caps > Date: Wednesday, March 11, 1998 10:24 PM > > At 09:22 PM 3/11/98 -0600, you wrote: > > Hey Richard, I didn't mean to ruffle your feathers. I was just very > curious to the phenomenon you saw. As an engineer I like to try to > understand what goes on. I appreciate what you've told us. If you decide > to not respond that's fine. > > Rob > > > > >Geez, I think Ryan was right about people being very agressive on the list > >here. I made a mistake to begin > >with, I thought I posted to the stamp list, but mistakenly posted here. If I {Quote hidden}> >was making this crap up, I would > >have bailed out when I had the chance? > > > > > >Richard Skinner > >KILLspamrwskinnerspamBeGoneworldnet.att.net > >http://home.att.net/~rwskinner > > > >---------- > >> From: Reginald Neale <EraseMEnealeEraseMESERVTECH.COM> > >> To: @spam@PICLIST@spam@spam_OUTMITVMA.MIT.EDU > >> Subject: Re: [OT] Cable retained energy, was Super Caps > >> Date: Wednesday, March 11, 1998 4:08 PM > >> > >> Rob said: > >> > >> >I'm sorry I missed some of this discussion but I was wondering how he > >> >proved t held a charge? How did he charge it (voltage level, type of > >> >instrument, lenght of time...etc)? How did he show it held a charge > >> >(voltmeter)? How did he discharge it (short, resistor leak path)? > >> >Where was the cable during the test (rolled, laid out..etc)? Did he show > >> >the cable was at close to no voltage after discharge? > >> > > >> >I have heard of antenna wires showing charges, but this was because of > >> >the natural EMF of the background. > >> > > >> >Just curious. > >> > > >> I too am curious about the the specs on this cable. As a reference, a small > >> camera flash stores about 5 joules of energy. That's enough to make some > >> decent sparks, and more than enough to be dangerous. The formula for > >> capacitive energy storage is [C*V^2]/2. As an earlier poster mentioned, > >> RG-58 is approx 30pf/ft. When you do the math, you'd have to charge about > >> 666 ft to about 1KV (probably wouldn't handle that) or 66666 ft to 100V to > >> get 5 joules. That's 11 miles of cable. Or maybe this cable is something > >> really exotic... always possible, given the eclectic nature of PicLister > >> backgrounds. > >> > >> Reg Neale > > > >

Here I have attempted to derive some basic numbers for the capacitance and time constant of a cable. I admit I am somewhat out of practice so someone scream if I have made any major errors. r = radius of the wire in meters b = distance of wire to ground in meters e = 8.854 * 10^-12 F/m 2 * pie * e C/m = -------------------------- b + (b^2 - r^2)^0.5 ln [ -------------------- ] r I get about 8pF / meter of capacitance between a small bare wire suspended 1 meter above ground and ground. The resistivity of qood quality plastic dielectrics are commonly 10^16 ohm cm and can reach 10^19 ohm cm for teflon. For a 0.1 mm insulator and a 1mm diameter wire I get about 0.01 cm^-1 for 1 meter of wire. Time constants of a wire. 10^14 ohms * 8pF = 800 seconds. 10^17 ohms * 8pF > 9 days I am making a lot of assumptions here but I could see where you could achieve some very high time constants. Many plastics will absorb water so these numbers can differ by orders of magnitude. --------------------------------------------------------------------- | Dr. Kevin Dale Kirmse | PhD Electrical Engineer | | King of Prussia, PA 19406 | spamBeGonekirmseKILLspamnetaxs.com ---------------------------------------------------------------------