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Chapter 4
BRINGING AC ELECTRICAL ON BOARD-EARLIER & LATER SYSTEMS
EARLIER SYSTEM
To this point we have covered the process of bringing
AC electricity from the marina dock power center to the
yacht shore power inlet or to the optional cord reel.
From the above point of entry earlier yachts use a system
to distribute AC electricity that includes a double pole
single throw inlet breaker, isolation transformer, triple
pole single throw breaker after the transformer and a
ship’s AC main control panel with shore power main and
auxiliary equipment breakers.
After the inlet or the cord reel AC elec-
tricity travels to a 2 pole single throw
breaker located above the swim plat-
form in the starboard stairway locker.
At this point it travels to the primary
side of the isolation transformer.
The isolation transformer is located in
the engine room (bilge). See the illus-
tration. The isolation trans-
former is used to isolate
the AC shore power from
the yacht’s AC power. AC
electrical power is trans-
ferred by the use of mag-
netic coupling. Basically,
there is no direct electrical
connection between the
shore side, earth grounded
AC power and the yacht’s
AC power system.
The shore grounding is
connected to a shield between the primary (shore) and
secondary (yacht) transformer windings. This shield iso-
lates and therefore reduces galvanic corrosion.
ISOLATION
TRANSFORMER
By grounding one leg of the
transformer on the secondary
side the “creation” of a neu-
tral exists. The “neutral” wire
(blue) along with the 2 conduc-
tor (red & brown) wires travel
to a triple pole breaker located
at the output side of the transformer and eventually to
the main AC control panel. The green earth (bonding)
ground is connected as another continuing leg of the AC
grounding side of the circuit.
See the drawing on the next page for more AC circuit
information.
TRIPLE POLE BKR.
DOUBLE
POLE BKR.
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