[C38] Wiring Question

Thu May 15 20:39:41 EDT 2008

It seems to me that loop circuits are illegal in a/c circuits for several
reasons, the most important possibly being a safety issue with possible hot
circuits when the circuits were supposedly cut.

DC circuits don't exhibit inductive reactions like AC circuits do unless
they are inductively coupled with an external AC source.  A DC loop
actually has a lower "Q" making it even less able to exhibit parasitic
oscillations which could cause RFI than the standard harness.  "Q" is the
sensitivity of an antenna in regards to a specific frequency.  The higher
the Q, the more the antenna will react to a particular frequency and more
immune to inductive coupling to other frequencies.  A low Q antenna won't
perform like a high Q antenna but a low Q antenna will react to a broader
range of frequencies.  Every piece of wire will react to some frequency,
our job is to minimize that effect unless it is our antennas and not our
wiring.  We want a very low Q on anything but our actual antennas.

The stock lighting harness on a Catalina 38 is quite long between the panel
and last light over the ice box, possibly around 35'.  The natural resonate
frequency of such a long length of harness would have a tuned resonance
very low, too low to make much impact on any modern electronics.  The
branch circuits going from the harness to individual lights would have a
much greater chance to make a parasitic resonance but those circuits would
not be effected by the type of harness we employ in any case.

By making the shunt across the engine compartment, the effective resonate
frequency of the harness would be raised but the resonant "Q" of the
harness would be greatly lowered making parasitic oscillations much less
likely.  A loop antenna has a very low "Q" by nature and this closed loop
harness would actually have an even lower "Q" than a loop antenna because
unlike an antenna, our harness is composed of two conductors with one being
grounded to the boat battery making a ground for any parasitic voltages.

One thing I did do on the Renata that I failed to mention was that I
extended the wiring harness to the sail locker before returning through the
loop shunt back to the breaker panel. I attached an auxiliary ground at the
galley and ran this ground  to my house batteries which gave me even less
resistance in the circuit.  I expect this additional ground also acts as a
parasitic oscillation killer also.

I have had this low resistance DC harness modification for several years
and I have never experienced any hum or any other type of induced
radiation, either on the AM radio or SSB radio.  I would not be afraid of
this loop circuit on a DC circuit.  I totally agree about the dangers of a
loop AC circuit but I think the benefits of lower loss on the DC circuit is
a great plus.

If you do decide to make your harness into a loop as I did, turn on your
cabin lights before you attach the last loop connection and watch how much
your lights improve when the final connection is attached.  You will be
amazed at how much brighter your cabin will be.

Tom Troncalli
Renata #95
St. Pete, Fla

> [Original Message]
> From: Les <hlhowell at pacbell.net>
> To: Catalina 38 Listserve <listserve at catalina38.org>
> Date: 5/15/2008 1:28:01 PM
> Subject: Re: [C38] Wiring Question
>
> 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
>
>
>
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