Nigel Caulder in the latest issue of Professional Boat Builder
Magazine has an article describing the latest high tech  solution for
wiring boats. There is a large positive lead, a large negative lead
and a data cable. The switches for turning on and off all the
equipment are hung on the 2 power leads, nearest to their equipment.
The switches are controlled by signals picked off the data cable.
These 3 cables run down the center of the boat, naturally, to
minimize the runs out to the various pieces of equipment.

The next issue will have a second article describing the problems
with the approach and there will be a 3rd article.There is some
notion in all this that somehow such a solution will result in less
cost, higher reliability and easier troubleshooting. A contrary mind
could see some other possibilities, perish the thought!

Regards,
Mike

Capt. Mike Maurice
Tualatin(Portland), Oregon

<<The switches for turning on and off all the
equipment are hung on the 2 power leads, nearest to their equipment.
The switches are controlled by signals picked off the data cable. >>

A friend recently bought a new boat with a system like this.  One failure
was handled under warranty.  Several light switches are now failing again,
and the repair estimate is over $400.  He's considering ripping out the
lights and replacing with conventional wiring and switches.  Sounds like
it's not ready for prime time yet.

Mark Richter, m/v Winnie the Pooh
in Appalachicola, waiting to cross the Gulf.

IN DEFENSE OF THE 3 WIRE SYSTEM COMNCEPT
I would like to address the various objections voiced against the 3 wire
system concept.  Most of these objections appear to be based on assumptions
rather than on actual experience. I would like to make some comments based on
my experience with it.
For every objection I hear I know of a technical solution. In addition I know
of additional  benefits not readily possible with  the conventional wiring
approach.

Someone mentioned that the idea of running one large power conductor from bow
to stern  leaves the system vulnerable to a single point failure. That is no
more true than for existing systems where a single disconnect switch could
fail and burn open. Should that happen, all power to the boat would be lost.
For that matter why should this main power bus pose a greater risk when by
design and location it would be better protected  than many other wire runs.
With heavier insulation, a protected corner duct in the strongest part of the
hull,  the only way for such a power bus to suffer a direct short is if the
actual hull is crushed.  Under such circumstances it is more lilely that  the
immediate threat to the crew is of the vessel sinking, than  any
inconvenience  caused by a loss of electrical power.

A comparison could be made with a  dock at the marina. One power fed runs down
the dock and at intervals power posts are located  by which individual boats
are fed.
Should one point of failure occur ( such as at a junction box)  all poweer
posts downstream of that point would also be left without power.
Should the overloaded transformer fail, the entire dock would be left
powerless.
No one worries about a single point of failure rendering the entire dock
without power, nor do we see this main feeder suffering frequent failures.
When such damage occurs it is usually during a hurricane.  At such times
people usually have greater worries to deal with.

The objection that one fuse feeds the whole main  feeder and thus poses an
unnecessary risk also applies to the main disconnect switch. Often  these
switches are used beyond their rated capacity.  When those switch contacts
finally burn open then you have the equivalent of a fuse blowing.  Many times
I have seen 300 amp rated disconnect switches used for applications seeing
surges to 400 amps.
How many people even give a thought to increasing the ampacity of the main
disconnect switch  when they add extra loads to their electrical system.  Most
often they assume the switch will be okay if they give it any thought at all.
No one can say at what point the switch contacts will finally overload and
burn,  wheras a fuse is designed specifically to melt at a specific over
current level.

One frequently heard  objection is that  people want one central location for
all their switches.  However, lets be realistic. Just jhow often do you ned to
switch the bunk lights on or off while being at the helm under way?

Do you really need to have the laundry washing machine  and dryer located
right next to the micro wave oven breaker?

We have already recognized the impraticality of  running 2/0 cables from the
battery to the helm station and then forward to the anchor winch.  Instead we
run the power cables direct to the winch and only run  relay control wires up
to the helm station.
The 3  wire system simply expands on that principle.
The many advantages available when you use the 3 wire system far outweigh any
imagined or real disadvantages.  3 way, 4 way and even 5 way switching of
lighting circuits is now possible with much less complexcity than  using
existing systems.

For safety sake AC and DC breakers are not to be mixed together in a single
panel.
With the 3 wire system concept you can safely locate the control switches  in
close proximity if that is required. That is because the control switches
only carry a low voltage signal not the actual higher voltage.
Since the control switch does not have to carry any large amount of current,
it can be much smaller. In fact in the Teleflex  Magic Bus system these
switches are flat membrane switches requiring almost no room at all.
This is one aspect which several boat designers and builders are hoping to
exploit for innovative new hull and console designs.

Additions and expansions to a 3 wire system tend to be less labor and time
consuming not to mention costing less.  Trouble shooting circuit failures also
promise to be easier.

I realize that one of the main objections to this system approach is that it
would be more complex and thus difficult to trouble shoot but  that is not
really the case.
The technique is different, but not  really more complex.
Look at the number of times list members have asked for assistance in
diagnosing why some light or other device failed to work. We have even seen
posts where the person says there is power to the light but it still does not
work. Hmmm???

The reality is, conventional wiring involves running so many feet of wires
that installers and builders are tempted to take shortcuts  to reduce this
amount of wiring.  This the real reason why some applications are so difficult
to troubleshoot.
Lets look at a typical  situation where a cockpit light fails. There is a
breaker in the main panel labeled Cockpit Lt  but its anybodys guess as to
how the wire are run from this main panel to the light in the cockpit
overhead.  Does it run down either side of the vessel and then up to the
light?  Or does it run in the overhead  and then down?  How many minutes or
hours will you  spend tracing this?  How many panels would you like to remove
only to find that nope! the wire isnt there so it must be elsewhere.
And if you are paying a service tech at yard rates, this can add up very
quickly.

We have all been there and done that.  Or how about when you would really like
to add some accessory in some location far from the battery box.  Something as
simple as a convenience light in a hanging locker can take many hours of
fishing wires.

With the 3 wire system. You know where the main feed is located and where the
various sub panel fuses are located. Now you know that you only have to go
back as far as the nearest sub panel.  This would typically be located in the
same cabin as the hanging locker.
Objections have been made to the effect that a central  switch panel is
preferred and more convenient than having several local sub panels of fuses.
I suspect that objection is due to the confusion  between over current
protection and switch control.  We are now so accustomed to seeing these two
functions combined into a single device in a main breaker panel that  we
forget that  other options are still available.
You can have over current protection at the point where a smaller wire taps
off the main feeder and still have a remote switch located at some other point
such as the helm station.
This is the normal approach for any high current device like bow thruster
anchor winch  dinghy crane or even a wash down pump.

But lets be realistic.  How often do you need to operate utility lights inside
cabins while driving the boat from the helm station?  On the other hand  you
do need to be able to activate all navigation lights and exterior devices.
Sometimes it would be nice to be able to turn on all the outside deck courtesy
lights from any one of three or more exit doors or access points.  In fact  it
might be a good idea to be able to turn on deck lights from your bunk side if
you hear footsteps on deck in the middle of the night.
And if you anchor out a lot,  it sure would be nice to be able to turn on the
deck lights while still approaching the boat in the dinghy.

For those of you who have gone through the exercise. How about the cost of
adding a second helm station? With a 3 wire system this would be much cheaper!
The reason why is that you would only need to run control wires from the added
helm back to the main system.

Some people object to the concept because they fear they cannot repair such a
system themselves.  Or that an electronic failure would leave them in a
precarious situation.
Its a valid concern, but not something  we do not already have to deal with
using conventional wiring practice.

I dont know how many times I have seen posts asking if anyone else could help
the poster find a source for some simple device like a switch or breaker for a
Taiwanese built boat. And lets not forget plain old hardware.  We already have
that problem so the 3 wire system is not going to create this condition from
nothing nor will it likely aggravate it greatly.  As for being able to repair
problems.  Well  some list members already fix their own mechanical or
electrical problems while others simply hire a technician to do it.
I dont see that changing  even if 3 wire systems became the norm.
Some of us will readily grasp the concept and be able to fix problems while
others will prefer to let someone else tackle it.
But the 3 wire system  does mean that trouble shooting should  be faster and
allow quicker time to identify the failure point and effect repairs or
replacement.
In its simplest form  you an build an equivalent using only relays and a multi
conductor cable for control.  The more sophisticated versions would use an
addressing chip a decoder chip and a relay or other solid state switch.
Million of cars already use this approach. Mechanical relays can have manual
over ride levers and solid state switches can have bypass jumpers.
A complete rewire job  on a 36  42 foot boat will run into many thousands of
dollars.
At least half of that money will be for labor to string new wires. More than
likely there would also be considerable cost  to construct new wire ducts to
facilitate bigger bundles of cables.  A 50% saving on a 30K electrical job is
nothing to sneeze at.

The three wire system  would consist of running  one pair of large conductor
bus cables from end to end.  At intervals you cut in a sub panel with breakers
or fuses.
A control wire or cable is run along side the power pus and an electronic
switch assembly is located adjacent to the over current protection devices in
the sub panel.

Someone asked where do you hide such a thing.  How about inside a locker, or
cabinet or under the built-in settee or inset into the side wall of the
cabin?  In most cases each sub panel only contains 4, 6 or at most 8
circuits.  Local control switches would be where they always are. On the
light fixture or device or inset into a wall switch plate next to the entry
door.

The wiring from sub panel to actual device is exactly the same as  what you
have now.
The difference being you only have short runs inside a small area.
You do not have large bundles of additional cable running through a
compartment.

Cheers

Arild