[C38] Wiring Question

[Les]

There is another issue that is not well understood (nor is it easy to
explain, probably why it is not well understood).

	If you redraw your loop and attachments, you will see that it forms a
ladder like structure around the loop, something like two hoops of wire
connected by loads from one to another.  This is not bad, IF all the
loads are almost  equal.  However this structure is also known as a
Bridge structure.  The current that balances the ladder legs is the
bridge current.  It becomes a complex sum of all the currents leading to
that particular segment of the bridge.  When this is in operation, one
of the effects of a bridge is to allow a small current at one point to
prevent current flow.  That is the current through legs on one side of a
segment are unbalanced to exactly the point that the legs on the other
side are, to the same degree and polarity.  This has the strange effect
that no current flow occurs through that segment.  Worse, the lack of
that path will unbalance the other legs in bizarre ways, leading to some
circuits getting lower voltages, others higher voltages, and the balance
points across the reaches of the ladder (your ground bus in this case)
can end up with say 3v across a length of wire.  Calculate that current
and you begin to see the problem.  

	It sounds weird, but it is true.  Circular wiring produces higher
probability of fires because of this problem.  That is why it is not an
approved means of wiring.

	And yet another problem can occur that under changing loads a segment
of the circle can end up with 0 current flow.  For example say one
segment has 1A flowing, and produces a differential from the battery
of .025v.  On another leg, some number of links away a similar load
produces the same condition.  That means the wire between those two
points has zero voltage differential.  No voltage, no current.  The
other points between those two might not even work at all.  You could
chase opens and shorts forever, but never isolate the problem because of
the effects of a bridge.

	To combat these effects the Wiring Codes specify a "star connection".
That is from the source to a distribution point, and from that
distribution point to the various circuits, just like you have in your
home.

	The reason boats (and metal framed aircraft) don't have this problem is
that they use a star distribution and the shell of the vehicle for the
return path (except I think all aluminum skinned planes are prohibited
from this due to electrolysis issues) which has so little resistance and
so many paths that the bridge effects are too weak due to multipath
effects.  That means the return circuit has lots of ways to get back,
all of very low resistance, reducing the issue of heating or balance
canceling.

Regards,
Les H
On Thu, 2008-05-15 at 08:51 -0400, Duff, Russ (R.W.) wrote:
> The only problem with your loop is that it will be more susceptible to
> electronic noise; both transmitting and receiving. The loop will act like a
> large antenna and pick up (and transmit) all kinds of noise that could
> effect any sensitive electronics (VHF, radar, autopilot....). I know it is
> only the lighting circuit (you hope), but that circuit does connect back to
> your main power bus with no filtering. You may want to re-consider.
> 
> Sincerely, 
> Russ Duff 
> RDUFF at VISTEON.COM 
> -----Original Message-----
> [mailto:listserve-bounces at catalina38.org] On Behalf Of Tom T.
> Sent: Wednesday, May 14, 2008 9:51 PM
> To: hlhowell at pacbell.net,Catalina 38 Listserve
> Subject: Re: [C38] Wiring Question
> 
> The original lighting harness on the Catalina 38 was with either crimped
> connected 16 ga or 18 ga. wires that started at the fuse panel and circled
> counter-clockwise around the hull at the chine. The lighting harness
> dropped under the quarter berth and continued around the top of the hull to
> the galley area.
>  
> That is a lot of length for 16 or 18 ga wire. I rewired my boat with marine
> grade 12 ga wire and soldered joints. I also ran a jumper wire from the
> fuse panel through the engine compartment to connect to the terminus of the
> lighting harness at the galley to make a closed loop harness. This gives
> less resistance to the entire circuit, especially the lights on the port
> side. By making a loop harness, all lights get about the same voltage.
> 
> A loop circuit harness is against wiring codes for a/c circuits but I don't
> know if it's illegal for DC circuits.  By making the circuit a loop, you
> reduce the wiring resistance greatly.  Use your own judgement, I just know
> it works great.  You could always remove  the jumper if you ever sell the
> boat or have an electrician work on it.
>  
> Another energy saving idea is to use a bungee cord to create a neutral helm
> when using an autohelm. If you neutralize the helm, it will take very
> little current to steer the boat because the autohelm won't have to
> overcome the efforts of weather helm allowing  the servo motor to have a
> minimal load on it.
>  
> Previously, on a windy day, you could have burned yourself on my autohelm
> servo motor but with a neutralized helm using bungee cords, the motor now
> stays cool to the touch and the battery stays hot much longer.
>  
> Tom Troncalli
> The Renata, hull #95
> St. Pete, Fla
>  
> 
> 
> > [Original Message]
> > From: Les <hlhowell at pacbell.net>
> > To: Catalina 38 Listserve <listserve at catalina38.org>
> > Date: 5/14/2008 8:56:09 AM
> > Subject: Re: [C38] Wiring Question
> >
> > Hi, Steve, 
> > 	The master switch on the power panel routes the starting current to
> the
> > engine.  Peak this is about 300A.  
> > 	I think I used #2 for that run from the batteries to the switch and
> > from the switch back to the engine.  If you have the 12V Bible, they
> > have some nice calculations in there for that.
> >
> > 	The rest of your calculations seem OK.  I am running 12ga for the
> > lighting when I redo mine, and should be quite sufficient for the runs
> > which average about 18' one way.  I would also caution you to use only
> > marine grade wire, because standard copper will fail in short order with
> > corrosion eating it away at each connection.  Avoid those riveted 3x
> > terminal thingies like the plague.  They invariably corrode and cause
> > poor connections.
> >
> > 	The reefer might like a 1% drop, because each bit of drop to a
> > motorized device will cause current to go up approximately 2% to sustain
> > the load.  This is rule of thumb, but you can look it up in some of the
> > books on electrical wiring if you want precise numbers.
> >
> > 	Also use the terminals that heatshrink with heat glue to seal the
> > connections.  It will save you beaucoup problems later.
> >
> > Regards,
> > Les H
> > On Wed, 2008-05-14 at 00:07 -0700, Steve Smolinske wrote:
> > > I am getting ready to replace some of my wiring and my electrical
> > > panels.  I have been drawing up my schematics and would love some
> > > input on my calculations and assumptions.  I have based my assumptions
> > > on an all night sailing scenario with continous use of systems that
> > > would quickly draw down my batteries but conservation is another topic
> > > at this time Im more interested in determining proper wire size for
> > > peak usage.   Ive assumed that I would be using:  3 cabin lights (4.5
> > > amps), Running Lights (2.5 amps) VHF (2 amps), Depth and Knot (2
> > > amps), Wind (2 amps), Auto Pilot (1 Amp) Radar (8 amps) GPS (3 amps)
> > > Heater (8 amps) and Refrigeration (5 amps) for a total of 38 Amps
> > > multiplied by postive and negative wire run length of 15 feet (Battery
> > > Cable to the batt switch then from there AWG 6-8 to the pos. bus and
> > > from the neg. bus back to the battery) which equals 570 Famps.  Based
> > > on the wire charts for a 3% drop this puts me in the 6-8 AWG wire size
> > > to and from the batteries.   Any comments on any of these numbers is
> > > greatly appreciated.   Refrigeration, Heater and lights are  variables
> > > calculated on the high side just to be safe.   
> > >  
> > > Thanks all, 
> > >  
> > > Steve
> > > Peregrine #312