BotoXbz said:
Chassis is earthed (which is mandatory for a metal enclosure)
- is not connected to earth
That is confusing.
Here are my notes from googling some more
precisely worded corrections / clarifications would be **really** appreciated
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Earth vs Return vs Common / Reference
These are not the same https://youtu.be/eGeFVIJ2u0w
see Negative PSU
A. Earth / Ground - dashed down - arrow symbol
aka true EARTH
10' copper-clad steel rod, into ground water
Cars, airplanes, satellite, none are grounded
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B. Chassis Common - symbol like a 4-tined rake
aka COM
On a car, airplane, maybe? boat, use the term:
Vehicle Common
metal case, mounting points
just an arbitrary reference point for traditionally making voltage (difference potential) readings, the voltage that appears **between** a terminal and the Circuit Common
see Floating Ground
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C. Circuit Common, or Power Supply Return - down-pointing hollow triangle symbol
aka current return path, return conductor
For circuit / IC semiconductor diagrams
aka Common Reference
Reference Plane
NOT really a "ground plane"
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usually on the low-voltage side, negative supply terminal, aka Negative Return, negative terminal on the battery
but with high-side return, energized conductor is the Circuit Common reference point
negative voltages, the positive supply / battery terminal is the Power Supply Return, "positive ground", no, call that Positive Return
This also may or may not connect to Chassis / Vehicle Common
________
Floating ground, isolated system, floating output, live chassis
some potential other than earth / ground
ensure that all surfaces a person can touch are at the same voltage potential
example "low voltage" transformer, output side has no connection to mains
input side has two-prong plug, only connects to live and neutral, no ground loop is possible, helps reduce noise
can and do drift in potential and if the transformer is capable of supplying much power, they can be dangerous.
chassis can be at a very different potential from that of any people touching it, who then get an electric shock.
chance of this is increased if the floated system is near high voltage power lines.
To reduce the danger of electric shocks, the chassis of the instruments are usually connected separately to Earth Ground. This is not possible in a mobile context.
All battery powered systems are floating?
A is floating with respect to B
isolated outputs = floating, means neither positive nor negative output terminals are connected to chassis common (thus also not to Earth ground)
“Output Terminal Isolation”, aka spec'd maximum float voltage
Ground-fault monitoring devices
designed for ungrounded AC+DC systems, incl EV battery charging