groundhistorysymbol [~]
I Googled for hours, asked every EE professor in my college, then checked every electrical engineering book in my university's library (hours), and have found nothing about the history of the ground symbol. Please point me if you can.
Who coined it? What does the picture represent? I have many probable theories and almost no interest in theories.
Thank you
There was a little-known predecessor to the MSP430 series in the early 1990s, which was the TSS400 "uPower Programmable High-Precision Sensor Signal Processor". It had only an 8-bit processor, and the ROM contained an interpreter for a language called SMPL, so it was not intended that it be customer-programmed in machine language (or C, or any other "normal" programming language).
While the TSS400 showed promise, ultimately customers wanted a more powerful processor, and the MSP430 was the result.
Can static shocks occur from grounded and ungrounded metals?
Yes. A large ungrounded object still has capacitance. If there is a higher density of electrons on you than on the object, the electrons on you will feel repulsion from the other electrons on you and want to jump to the object where they will have more room to spread out. (Same goes in reverse if there are more electrons on the object.)
Eventually if people keep transferring electrons to the large object, then the electrons will build up on the object until they push back as much as the electrons on you, and there will be no spark. The bigger the object, the more electrons it takes to "fill" it up to having the same density of electrons as there are on you. Grounding an object connects it to the earth, which is the biggest object around and so represents a practically infinite sized holder of electrons. You can keep charging yourself up and then discharging to the earth and never make a practical dent in its charge density.
How do you prevent getting zapped when everything around you is metal and glass floors?
You can either...
Prevent yourself from accumulating a different density of charge relative to the metal building.
a. Wear a pair of diamond soled shoes. Because this material much closer to glass on the Triboelectric Series, you will accumulate less charge while walking compared to the rubber soled shoes you are likely using now. Alternately, you can cover the soles of your existing shoes with a rich red acrylic coat.
b. Keep yourself electrically connected to the metal at all times, possibly using a wrist strap that is tied into an overhead Pantograph system on the ceiling.
c. Increase the humidity in the air inside the building, possibly by installing a large fountain or waterfall in the center of the atrium area. The humidity will help excess charge bleed off your body and therefore prevent you from accumulating enough to cause a spark between you and the metal.
Prevent any charge you have already accumulated from making a spark and "zapping" you.
a. Buy a conductive arc flash protective suit and wear it whenever you are in the building. The zap between your body and the metal is just a smaller version of the arcs that linemen and electricians deal with everyday, and this suit will keep the arc between the metal and the suit rather than your skin, so you should not feel it. Be sure to get the suit inspected and certified frequently.
b. Get a hot stick. Anytime you approach a metal shelving unit, use the hot stick to equalize the charge between your body and the metal before touching it. There is still charge flowing between your body and the metal, but the high resistance slows that flow by reducing the current to levels that should not hurt.
c. Evacuate the air inside the building. With no air, there would be no gas to ionize and therefore no arc to zap you. This would require hermetically sealing the building envelope and using a large pump to remove the air and maintain the vacuum. This might also require structural modifications as the forces generated by the external air pressure on the building surfaces can be quite large.
What is the worst case scenario if I unbound the metal structure from mains earth? (Not contacts, nor lighting rods, just make sure to leave the metal book shelves ungrounded), will the user still get shocked?
People would still get shocked until the metal was charged up. Once the metal was charged, it would still zap people who had not yet been charged themselves by walking on the floor yet. It would probably make sense to divide the building into a dozen or more zones of increasing charge, each completely electrically isolated from the others. The zone near the entrance would have the least amount of charge to accommodate people first entering the building who have not accumulated any charge yet from walking on the glass floors. The zone farthest from the entrance would be at full charge and would hold the physics textbooks.
Best Answer
IEC No. 5017, better known as Earth Ground, is the result of many over a 100 years of organic evolution, convention, and most recently, rigorous international standardization.
The earth ground symbol owes its origin to the same origin that many other symbols do (notably the inductor, capacitor, and American resistor symbol): the patent drawings of Nikola Tesla.
What is arguably one of his greatest contributions is one without any patent and has no material form: the abstraction of bulk properties (inductance, resistance, capacitance) into components that possess one of these properties but very little of the other two. I don't know to what degree this attribution is fair, as Edison was also beginning to this at the same time, and considering Tesla at one point worked for Edison, and they doubtlessly were aware of each other's patents (they weren't the mortal enemies/mega rivals of modern mythos, closer to peers in an emerging field), but at the very least, that abstraction arose from Tesla, Edison, Marconi, and the great inventors the era all building off of each other.
The specific imagery, however, are obviously from Tesla, simply because his are the ones that look like our present day symbols.
Originally, these drawings represented real structures for the sake of patent submissions, but certain structures were reused over and over, and drawn over and over, and at least based on his drawings, evolved into pictograms over time and organically.
A pictogram is formally defined as a symbol that conveys meaning by approximating the physical appearance of the object it represents. In the case of the ground symbol, it's origin is from a drawing of a grounding plate buried beneath the ground. The vertical line is the wire, the top most horizontal line is the surface of the actual rock-and-dirt ground, and the lower two lines are the top and bottom of a grounding plate.
Here is such a representation, from one of Tesla's patents, dated 1900:
And shortly after, this makes it even more apparent and it is easy to see how the modern ground symbol originated from these drawings:
In that era, patents were a lot like open source is today, in a way. You were given exclusive rights to commercialize the subject of a patent, but this protection was given only in exchange for making how your invention worked available to anyone. Patents were, and still remain, completely public. Considering Nikola Tesla drew the first schematics, has a patent on several fundamental circuit components (like capacitors, or condensers as they used to be called) and, as a consequence, his drawings were made available to and were built upon by his peers of the time. Marconi adopted the ground plate semi-symbol, as did others. Given how closely knit and small the world of electrical technology was then, it makes perfect sense that the depictions used in patents would turn into shorthand for recognized concepts, and ultimately, pictrographic icons we know and love today.
Which is why, if you look at one of Tesla's early patent drawings, you can immediately recognize what everything is, because it is those very drawings that ultimately evolved into the symbols used throughout circuit diagrams today.