"ground" terminology from what I have seen, it a power company concept, (you know, the 50/60 hertz AC power distributed all over). They started out, and still in some rural areas, use earth as the "ground" for the return of the AC power being provided to users. I can right now today in 2019, take a short drive out to the rural regions and look at the power poles at the farm where my horses are boarded and wonder how the current loop is completed. One hot wire along the road of poles to a transformer that obviously is connected to real earth. A copper wire along the side of the pole that is wrapped around the bottom of that pole when installed into the ground. It also serves as a path for lightning. The slightly more modern road poles will have a "ground" wire routed above the insulated mounted hot wire. A close look will reveal that the non-insulated wire is also connected to another wire, usually on each pole, that goes down to the bottom of the pole for ground contact. It catches lightning, and serves as a known and controlled return for the AC power, since earth as a "return" is somewhat variable. Since all of our electrical and electronics have evolved from this origin, "ground" has become the catch all for any and all returns for power and signals going out. I like to point out that the vast majority of schematics use a variety of "ground" symbols to indicate some sort of universal return path that is not defined, and maybe it means the return path in the schematic is on the back side of the paper. Oh that is blank !! And so our EMC industry is created.
As our electronics migrated to cars, then portables, then aircraft, then space ships, cell phones, etc. The concept of "ground" got rather messy since it lost the "earth" connection. Our continued employment is dependent on those that still trying using "earth" (or ocean) as "ground" to drain away EMI and solve all the EMI problems. ps. And I love those that still chop up the return paths into all sorts of named "grounds" ! The highly imaginative tales of why it is necessary to divide the returns into various names is always entertaining. Do tell me more !! Return path impedance's are key to our trade ! Review the classic "field and waves" class in college. Also AC circuits, Kirchhoff current law in particular with respect to fields and waves. I work today designing ~15 kW inductive transmitters that also receive nano-watt return signals on the same circuit, and I do not get to use any shielding chassis, etc. It is all pcb's and plastic only.I have not done any radar, but that is what I imagine the environment is about. On Monday, July 8, 2019, 4:50:09 PM EDT, Ken Javor <ken.ja...@emccompliance.com> wrote: On US military surface ships, power is ungrounded. Green wires do connect to structure, so in the case of a fault the equipment enclosure is at ground potential, but it isn’t going to trigger a protection device that way. The whole discussion about sea water conductivity is moot. You could ask the same question about an airplane: it’s ungrounded in flight; metal structure works just fine as John Woodgate says. Where sea water is useful is transmitting hf. As Rich notes, the large surface area of the ship’s hull in contact with conductive sea water allows the surface of the sea to act as an extended counterpoise for hf masts operating against the ship as a counterpoise. At frequencies where the ship is electrically short, sea water makes these masts much more efficient than they would be if only the ship structure acted as counterpoise. Ken Javor Phone: (256) 650-5261 From: Richard Nute <ri...@ieee.org> Reply-To: <ri...@ieee.org> Date: Mon, 8 Jul 2019 12:48:24 -0700 To: <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Ground on ship Hi Peter: Sea water is a very good conductor, better than soil. Fresh water is an okay conductor. Pure water is a poor conductor. The hull of a steel ship is well grounded in the ocean, and reasonably well grounded in fresh water due to the large contact area with the water. If the hull is not steel, there usually are enough fittings that the ship is reasonably well-connected to the water. The propeller and drive shaft also provide a connection to the water. I've heard of ship-board hams who will tow a large brass plate for a good ground for their transmitter. Commercial AM transmitters try to locate their antennas near a body of salt water like San Francisco Bay or the Great Salt Lake. I would guess that a ground pin of a shipboard outlet would be connected to the hull metal. This gives the same protection from electric shock as land-based outlets. See also: http://electrotechnical-officer.com/primary-methods-of-grounding-and-bonding-on-ship/ Best regards, Rich On 7/8/2019 11:19 AM, 000006cee064502d-dmarc-requ...@ieee.org wrote: Hello group, Is there a real ground in a ship? i.e if a Class I product is used on the board of a ship, does the ground pin actually doing anything? The ship is floating in the ocean and I cannot understand if there is a real ground there or not? Can you guys educate me please? Thank you Peter - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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