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From: Arild Jensen (no email)
Date: Sat Jun 09 2007 - 23:33:21 EDT
> -----Original Message-----
> From: Norm of Bandersnatch
> Ton
> I am looking at the data on page 16, Figure 10, of the transformers manual
> which is the most informative. It describes a transformer with a center
> tapped primary.
>
> The secondary winding is almost identical with the primary with the
> exception of the two taps X4 and X3 which deliver a slightly lower voltage
> (104/208) which apparently allows one to use 50 cycle power to operate 60
> cycle equipment.
REPLY
There is an additional undocumented featuer availabel with this model
transformer.
For those people docked in marinas fed from 3 phase power transformers, the
so called 220V in a50A 4 wire socket is often only 208V nominal and drosp
way down to 185 durin gpeak load periods.
If you take the Charles transformer and wire it in reverse so that you use
the two 15% taps on the secondary side to L1 an dL2 on the shore cord side
then the ratio change will produce an honest 220V from the 208 supply.
If the input side has the center tapped winding then this center point
becomes your neutral for 120V.
Norm commented on "grounding. If yo uhave a metallic hull, especially
aluminum the you need to be real careful in how the grounding is done.
you should be aware that the GFCI require a solid ground to provide good
poretection. If the neutral is not grounded, then your polarity checker will
give false readings and the GFCI may or may not work when you do need it.
I prefer to bring all DC and AC ground wires to one single bolt which is
welded to the metal hull. To detect AC leakage current use a current
transformer selected to read low values. If DC leakage curent is a concern
then arrange a millivolt sensing ciruit to use the singel grounding cabel
from ground bus bar to hull shell.
Between these two detectors you will get an early and immediate warning if
any leakage current exist.
This is in essence what Norm was refering to on commecial ships. It is not
had to do nor is it expensive in its basic form.
for non metallic hulls where the bonding of thru hulls and underwater metal
fittings will resul tin galnavic damage i prefer to use a square meter
grounding plate as the AC system ground. All underwaer metal can then be
kept isolated while still conforming to th eNFPA NEC and ABYC standards.
regards
Arild
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