The article mentioned is very inaccurate and downright misleading
lets look at some definitions
earth, ground neutrals etc get thrown around in that article
the green wire in an appliance is not a conductior in the true sense. it is more correctly called a protecive earth, it only carries current
in a fault and then is only deisgned to carry that current
for a very short time. its primary role is to provide a lower resistance path to earth ( or the generator
return) for fault currents then hopefully your body to earth.
Contary to what that articles says electronics
are not designed with internal AC feeds to "earth" to minimise RFI, earth is purely a protective connection to typically the box or metal case, why , soley to protect you the human. it plays no part in the electrical
circuit of the device.
Yes RF currents get impressed onto earth lines, as they get impressed onto all power lines , but the currents and voltages are tiny ( if you know how to use a scope
then you can measure them. Most designs contary to that articles try and minimise power line rf noise
as its a effective antenna
. The articels suggests opposite and is wrong. Major RF emitters will then to have a seprate RF ground buts thats another altogether
The article also misrepresents what an galvanic isolator
is for. Becuase modern safety
codes on boats requires that the protective earth is connected around the boat to many electrical
devices and usually DC negative, and in a marina many boats are effectvely plugged into the same earth line, there now exists a circuit ( or a possible circuit) between underwater metals on one boat and another ( this is one of the main reasons that bonding is sometimes ommitted on GRP boats). Hence DC
currents generated by galvanic action can flow between boats, using the earth wire as a return path. This is what a galvanic isolator
attempts to stop. It is not a device to stop external currents that might exist on an earth line.
So impressed RFI will never ( in normal conditions) cause an isolator to conduct.
secondly "hot earths", the article is compleatly misleading here. HOT earths are earth with high impedence somewhere, and hence the earth rises in potenial to "real earth" or teh generator
return ( usually neutral). Its normally measured with respect to neutral in neutral ground system or to local earth. All devices on the earth line are raised to that potential, both sides of the diodes in the isolator will be at the raised voltage so again they will not be conducting. ( everything connected the earth is also raised by that potenial, ie every AC connected device with an earth connection. In very bad cases this can cause a shock hazard that may not be protected by any fault trip. A full on hot earth is a very dangerous thing. note that a hot earth need a high impedance path to real earth to exist so a hot earth is not providing any protection anyway. ( this is the hot earth to neutral case I'm talking about.)
Galvanic isolators as not a cheaper version of IT;s they really do different things. IT's provide protection from impressed galvanic currents , ie from other DC sources as well as from underwater dissimilar metals. more importantly they provide complete onboard shock protection from live ( or neutral) to earth( ie real earth) faults. even if the protective ground inside the boat has failed or is disconnected the user cannot get a shock. The only way is to insert yourself into the live and neutral circuit. ( aka as a light bulb).
Finally comments about failure of the GI results in a break in the earth, while technically correct it is misleading, GI's are rated to carry full fault currents for 24 hours, Fault current
anyway can only exist for very short periods, as the whole idea of a protective earth is a device to trigger a protection device.
Finally ABYC standards in teh US though not so in europe
require a monitor
circuit to verify the correct operation and the new standards also allow "fail safe " isolators to be installed without needing a monitor
The fact is that protective earth connection to teh marina shorepower are two edged swords in the marine
enviroment. GI are an attemp to mitigate that problem, ITS are a further attempt.
PS: Midland, teh breaker are not in parallel. The circuits are.
ALso Victron and matervolt are two very reputable brands in the marine electronics