Static electricity question

Static electricity? No. If you're holding the hand primer then you and it are the same electrical potential. No electrostatic discharge (ESD) will occur because there is no electrostatic differential between you and the metal tool.

In addition, the moment you grasp a case to install into the hand primer any electrostatic differential will be discharged and the case will be the same electrical potential as both you and the hand primer.

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QUOTE: Another thing to remember is that electricity flows on the outside of a conductor. That's why a stranded wire can handle more current than a solid wire for the same voltage drop.



I disagree, or I don't understand what you're saying here.

For example let's go with 12 awg copper conductors, one stranded and one solid. Both are fused at 20 amps. Both are capable of 25 amps. Both have the exact same circular mills of copper. Both weigh the exact same per foot. As seen by electric current, they are the same.

Electricity is the movement of electrons threw a conductor or path. In a copper wire, stranded or solid, all of the electrons move, not just the ones on the outside.

I'm an Electrician by trade, and yes, I've been wrong before.


As for the original poster, I believe your problem was static electricity. Ground your press. Do not ground it to an outlet. Do not ground it to a water pipe. Use an isolated ground. A ground wire firmly attached to the metal frame of the press, straight outside to a ground rod directly driven or burried in the ground. No interuptions, no splices in the wire, one solid piece straight to ground. Then you have to wear a ground strap on your wrist, connected to the ground wire, so the potential is the same. All that, or humidify the room.
 
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He's either talking about high voltage, where the charge repels itself out to the surface, or about about alternating current skin effect, which only becomes a concern for normal wire sizes at frequencies in the tens of kilohertz and up, and for which the added conductivity is only slight in standard strands, because they increase the wire surface area. Litz wire, which has individually insulated strands does a bit better.

Ferrous metal has iron in it. Non-ferrous metal does not. Ferrous comes from the Latin for fur, because smiting your enemy with iron weapons was thought to put hair on your chest. ;)

As to the Faraday shield, most of us who've been in instrument design depend on them. They have a shortcoming, though. Many a shielded piece of electronics has been blown when its shielding chassis was struck by lightning. The electrical field in that instance is so great that the momentary difference between the voltage at one end of the shield and the other, as the electrical field propagates over the surface, can induce damaging voltages on the enclosed circuit. Devices in danger from lightning or other strong electrostatic strike often require double Faraday shielding, with the inner shield tied to just one point in the outer shield. That attenuates the damaging induced voltage considerably, though not 100%. Under some extreme conditions even a tertiary shield may be required.

Cartridges are pretty safe. They are not easily fired by static charges. It is possible for an electric discharge to fire a finished metallic cartridge by heat, if the spark is strong enough or plays on the primer long enough. It is also possible, theoretically, to hit the primer with charge so fast it drives an arc from the cup to the anvil via capacitive charging, but it takes some serious juice applied very, very rapidly, indeed. Accidental static discharge will not readily fire cartridges, or they would go off spontaneously in aircraft all the time.
 
For example let's go with 12 awg copper conductors, one stranded and one solid. Both are fused at 20 amps. Both are capable of 25 amps. Both have the exact same circular mills of copper. Both weigh the exact same per foot. As seen by electric current, they are the same.
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I was speaking from memory and I last thought about this in '79 when I was taking college physics. Something about the charge always being on the surface of the conductor. Maybe it was a frequency thing with A/C currents and skin effects. It made sense at the time and I passed the course at any rate.

Do the two cables you mention have the exact same capacity or just the exact same rating?
 
Another electrician here -

The ampacity (capacity) of a conductor depends on its end area, which can be expressed in circ-mils. For a 12AWG conductor, stranded or solid, the ampacity is the same.

As another mentioned, when you get into high voltage and/or high frequency, skin effect and other nasties pop up and the rules change. For typical low voltage (< 480v) applications, I understand solid/stranded ampacities are the same for the same gauge.

Also, ampacities are determined by things like temperature rise, so "rating" depends on which design table you are using. Obviously, a conductor with a resistance of only a few ohms is capable of carrying currents far in excess of its ampacity (rating), but it is considered a fire hazard at that point... :)
 
The entire conductor carries current with DC and low frequency AC. Your ohm-meter can not tell the difference between 1000 ft of solid 10 qauge wire and 1000 ft of 4 strands of 16 gauge wire which totals to the same cross sectional area.

The "skin effect" comes into play with high frequency AC as in radio frequency. The center of the wire has more inductance than the outside because it is surrounded by more of the magnetic field that results from current flow thus the center of the conductor has a higher impedence to the current flow. Stranded wire does not cure this, in stranded wire, the center strands still have more impedence than the outer strands.
Skin effect is why TV antennas are made of hollow tubular conductors and why wires for RF are often made of large diameter silver coated tubes.

Skin effect also comes into play with lightning not because of the high voltage but because of the suddeness of the amps, which is a form of high frequency.

The Latin word for iron is ferrum, ferrous alloys contain iron. Non-ferrous alloys don't. Just because it's a non ferrous metal, it doesn't mean it can't create a shower of sparks when it touches a grinding wheel. Depleted uranium is a sparking non ferrous metal.
 
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High frequency skin effect is not due to increased magnetic field inductance at the center of the conductor. If it were, skin depth would change with conductor diameter, but it doesn't. It is, instead, due to phase shift in induced eddy currents below the surface that neutralize current flow in that region. That is why woven strand patterns and Litz wire and the the like can be used to partly mitigate the increase in resistance due to skin effect. In both cases (neutralizing weave and Litz wire), though, proximity effect often imposes greater limitations than skin effect, so no total "cure" exists, per se.

At a glance, the Wikipedia entry on skin effect looks to be correct to me, from what I still recall from school? It's worth a look if you are interested in the topic?


Dmazur,

If you poke through the ampere capacity tables, you'll find the current limits are all about heat. Thick insulation that is a good thermal insulation as well, will wind up causing the wire within it to be rated lower since it can't lose the heat easily. Insulation that melts at a lower temperature will also lower the current rating. Multiple conductors affect the heat level, and probably the worst case of that is transformer and motor and other magnet winding are the worst, since the heat is collected in the middle of the winding mass. That is why magnet wire is rated to require more circular mils per amp than other kinds of wire.
 
Unclenick -

Thanks. I was trying to briefly describe the fact that a conductor can carry a lot more current than it may be rated for...which I believe isn't understood by most folks.

The number of conductors in a certain conduit size, if the conductor is used in a heating appliance and many, many other things affect this, as I'm sure you're aware.
 
Folks - I think we are going far too afield, and getting away from the original topic of static electricity setting off primers, and how a shell/primer/bullet combo is a Faraday cage. Current carrying capacity of conductors is a good topic ... for a different type of forum.
 
I know this is an older thread for my first post but it is what made me aware of this site via a search engine so, here is my 2 cents on what could cause a static discharge in a all metal pistol round...

If the brass is used or old and not properly cleaned and there is residue or an oxide layer insided either places where the primer pocket or bullet should be seated to the casing metal to metal but is not, in effect you have two plates of a capacitor. That is, the metal of either the casing and the bullet or casing and the primer (or both ends) are separated electrically from each other by an oxide or dirt layer that acts as a dielectric medium between them. Depending if the nearest metal to metal point between them is on the inside or outside of the metal casing would influence where the spark happens when the dielectric medium/gap exceeds the breakdown threshold of applied static charge between the two separated metal conductors.

I know that the charge to bridge such a small gap would not require nuch but if it came all of a sudden in a large spike like sliding across a polymer or other static causing surface there may be the possibility of a much higher charge being produce before the spark jumps the gap. This could explain the "sliding old range shells across the car seat "claim I read about in a previous post. Just like an old plunger stick used for dynamite, if released slowly, chances are of a dud but, plunge it quickly and boom, it isn't as much about the potential voltqge as much as how fast it can be applied maybe.

Also, as far as the brass, primer and bullet working as as Faraday cage to RF energy, that only applies if all surfaces are in electrical contact and the wavelength of the RF energy is larger in size to any gaps in the surface of the 3 exterior metal parts. This is why your microwave glass can have a mesh screen of metal and not let the energy pass as if solid, the holes must be bigger than the wavelength of the applied waveform in order to pass. In the microwaves case, the holes are smaller. The odds are, if the primer pocket and primer separated by residue, it would not be exposed to any wavelength of intense enough energy to pass and cause enough heating to set it off. It that level of energy would be sustained while near your person, you would have bigger fish to fry than a round cooking off in your pocket because the paint or siding of walls would be sliding off near you.

Anyways, that's my 2 cents of a first post on the forum. I could be very, very wrong...
 
What does everyone else do to prevent setting off primers with static electricity?
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I do nothing, I can not set off a primer with static electricity, and Dillon has tried and tried with no success. Dillon had a customer that folded a primer tube. While folding the tube of primers he injured his hand and started selling the ideal it was static electricity that got him. I did not buy the ideal those little electrons would run through the tube and jump from one primer to the next. The electrons will run through and around the tube and he could not convince me the build up of electrons was on the tube or press, if there was a build up of electrons the build up was around/on the reloader.

I called Dillon, I told them I wanted to know how to set off primers with pressure/voltage and EMF. They informed me they exhausted all efforts and could not set a primer off with static electricity. I then asked them about folding a primer tube loaded with primers with a karate chop.

F. Guffey
 
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^^^
Living in air conditioning can make for mighty low humidity.
As Mr. Franklin discovered long a ago, electricity is downright dangerous.
As anyone who has witnessed a line transformer failure can testify.
 
Rereading this old thread, I noticed something I missed the first time through. That is that the OP said the case that went off could not be distinguished from others in the ammo can. That's odd. Normally, if you fire a primer in a case without anything to contain the pressure, it backs out of the primer pocket. Indeed, even for low pressure situations like firing wax bullets in a revolver, you normally have to drill primer pockets out to about 1/8" to prevent them building up enough pressure in the primer pocket to back out and jam against the revolvers recoil shield, thereby jamming cylinder rotation.

So, given that the primer did not back out, I'll suggest it underwent a slow lighting up during seating that didn't build up to a bang until later, after some portion of the mix had already smoldered and vented its gas. The fact it didn't back out suggests weak ignition, either due to that smoldering or, perhaps, due to contamination. Contamination might explain it lighting up from seating in the first place, though you do hear of primers going off during seating from time to time, anyway. The bottom line is the OP seems to have experienced a primer hang-fire.

As to static, there are lots of videos on the web of people trying to set off powder and primers with electric sparks on purpose. It takes some effort and serious energy levels. Consider that some powders don't light well with magnum primers. Now ask yourself, was your electrical spark was as big as the sparks a magnum primer makes? That's not an accurate way to compare them, but may put the energy requirements into some perspective.

If not, there are always the military specs. The energy art which primers are not expected to ignite is about two (large rifle) or 3 (small rifle) standard deviations below the 50% ignition level. The non-ignition energy level workds out to be somewhere around 0.07 Joules. A 1,000VDC charge would need to be on a capacitance of 0.14 microfarads to store that much energy. If you could insulate the primer from the case with 0.001" of oxide the capacitance would be on the order of a hundred thousand times less than that. Even if you drop the ignition energy by a factor of 100 to allow most of it to go into deforming the primer cup (and it won't take that much) there's still no enough would be stored in the capacity between an insulated primer cup and case to set the mix off. Not at any voltage that thin insulation layer could stand (and a few hundred volts per thousandth of thickness is pretty typical of insulation break-down voltages).
 
Unless one person was holding the priming tool and another person was holding the case, it wasn't caused by static. You can't get a static spark from yourself to yourself.
 
I wonder why people working on things like MOSFETs [IIRC] are grounded during the time they are in the assembly room ?
I wonder why police are warned not to carry loose batteries in the same pocket as live rounds ?
I wonder why walking across a rug ,especially in dry times , will create a spark if they ground themselves to conducting things , even other people .
I wonder how amateur radio people have so many problems when all their equipment is connected to the same ground [equipment ground ] and that is connected ,in turn to the earth ground ?
Just askin' ?? :confused:
 
Regulations require me to wear a ground strap if I pick up a 2000 Amp diode.

Of course I ignore this BS. If my body conducted enough current to blow up that diode, not only would it not be an open casket, they would have to sweep up my dust off the walls.

I put a brass case in an R8 collet in the mill and a lathe tool holder in the mill vise. I was trimming the rim for some cartridge version when the primer went off next to my ear. Note to self, never do that again. Check the brass for primers.
 
HAMs have the habit of scraping radios that have been hit by lightning .Even if the obviously totaled components can be replaced There may be others that are damaged and burn out in a few months .:(
 
The skin effect is one reason that a substation and power generating plant switch yard has tubular aluminum buss.

In the old days, it was tubular copper.
 
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