Terry,
Your questions are right on target. In Germany, the main breaker must be
GFI. Therefore all loads within the distribution will be GF protected. In my
experience, there are only two types in Europe a .030 Amp and a .3 Amp
breaker. They do measure that load current matches return current. If there
is an imbalance, then there must be another return path to safety earth. In
Europe you will never see those in-line AC filters whose case is screwed to
the equipment frame exactly for that reason, as they bleed to frame(safety
earth). On a boat, they are very useful and if a more sensitive was
available, I would use that.
Isolation transformers can be made very elaborately or very inexpensively,
depending on the application. Most importantly is the way you connect the
safety earth wire from the shore outlet to your boat. I will not ever
connect it, but to do that is illegal. If you must connect it, it must
connect only to the transformer frame and NOT anywhere else. Your ship
ground is from the centertap of the secondary winding. To determine how
large the transformer should be, add all the loads that could be
simultaneously connected and add 20%.
Isolation transformer problems and there are a few. One, when connecting the
boat to the shore connection and the transformer is larger than 1KW, you
will very likely pop the ckt breaker for the feed because of inrush current.
Two, efficiency can be a big issue, so electric use can be significantly
higher. You cannot use an Auto Transformer for an isolation role. They are
the typical step down transformers used to reduce 220 volt power for 110
volts loads. Another problem that I encountered is that the ones that I
found were not suitable for marine use, even the ones so labeled.
Problem solutions: In rush can be contained by using a common incandescent
light bulb in series with the primary and after start, shorting past the
lamp. Two, if idle current is higher than you wish, make the primary winding
Ferro-resonant, by adding the appropriate capacitance in parallel with the
winding. If you want to know how, contact me off-line and I will tell you. I
decided to design and build my own, because I could not find one that met
all my requirements. I am very happy to state that my transformer met all my
requirements, is easy to use and very economical.
My requirements:
Accept input voltage between 100 Volts and 260 Volts (Japan = 100 V / UK =
260 Volts).
Adjustable output voltage = (end of dock low voltage syndrome)
Single phase only, output = 115 Volt secondary end to center tap and 230
Volt secondary end to end.
Power needed = 10 KW
Ferro Resonant primary selectable for both 50 Hz and 60 Hz.
Steve
"terry" <tsanford.DeleteThis@nf.sympatico.ca> wrote in message
news:b6bbef48-9bab-4a25-ae9d-c8aa417aaddd@13g2000hsb.googlegroups.com...
On Feb 2, 6:23 am, Larry <no....DeleteThis@home.com> wrote:
> "Steve Lusardi" <stevenos....DeleteThis@lusardi.de> wrote in news:fma6k9$ijg$00$1
> @news.t-online.com:
>
> > People will not invest a dime to
> > correct a problem they do not understand. Stupidity has its just
> > rewards.
> > Steve
>
> This is absolutely true. Trying to explain it to them only makes them
> angry. Unlike usenet, I keep it shut on the docks...(c;
Just a comment/question about GFCIs.
The typical North American GFCI operates when there is an unbalance
beteen the amount of AC flowing in the live and flowing in the neutral
wire. That unbalance may be due a potentially dangerous leakage to
ground (or in this case the boat/water) but not necessarily. That
unbalance operation is the reason that GFCIs are not recommneded for
use in domestic situations for fridges and freezers. You can come home
to a fridge of bad food!
Not that we should not use them and also understand how and why they
operate to provide safety, but it's almost as if the designation
'Ground Fault Current ...... ' is a misnomer. In Europe and elswhere
understand they are called RCDs.
I liked the discussion about isolation transformers. What sort of
wattage ratings would be typical; realizing that when the boat is at
the wharf unused there may be a minimum load, due to a little bit of
battery top up, maybe a fridge and a small bilge pump (itself often on
12 or 24 volt DC boat supply) that may cut in occasionally. Perhaps
intermittently 500 watts?????
We have on hand, for example several hefty transformers (basically one
to one ratio, with a few extra volt taps) each capable of at least 250
watts or more. Have often considered using them as isolation and minor
voltage adjustment devices. Also as mentioned, properly arranged,
transformer/transformers can be used to 'match' land voltages of
around 230v OR 115v to the boat.
>> Stay informed about: ELECTROLYSIS 101 for boats that live in the water. 
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