"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
<[email protected]> 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 <[email protected]>
Reply-To: <[email protected]>
Date: Mon, 8 Jul 2019 12:48:24 -0700
To: <[email protected]>
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, [email protected] 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
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