Dave,
Very good question. I’m no expert but here is my understanding and my solution. Since you do not have an RF ground, you can get by with grounding the shield wire to the battery ground. In principle, you should not use the same negative wire as used for supplying power. The reason is that the regular DC ground can pick up noise from other devices (most notably motors: fans, water pumps, autopilots, …) and/or not be at the true battery ground/negative voltage due to I*R voltage drop of the wire length to the battery. This noise can cause problems with device communications (i.e. NEMA-0183 & N2k variants ) and the operation of some electronic devices. Connecting the shield wire close to the battery makes it easier for the noise to drain to the battery and less likely to affect your device. That stated, I have all my device shields wires connected to the battery, but I have done so through a separate ground buss bar which I then have directly connected via a short thick wire to my main DC ground buss bar. All is working well. An additional advantage of using a separate buss is that in the future I can easily make it a part of bonafide isolated RF grounding system for a future SSB (i.e. with parallel capacitors joining the RF ground to the DC ground as shown in the photo linked below. http://newcontent.westmarine.com/content/wm-img/WestAdvisor/articles/Marine-Grounding-4.jpg <http://newcontent.westmarine.com/content/wm-img/WestAdvisor/articles/Marine-Grounding-4.jpg> - Paul E. 1981 C&C 38 Landfall S/V Johanna Rose Carrabelle, FL http://svjohannarose.blogspot.com/ > On Apr 13, 2017, at 7:05 AM, cnc-list-requ...@cnc-list.com wrote: > > Date: Thu, 13 Apr 2017 07:04:19 -0400 > From: David Knecht <davidakne...@gmail.com <mailto:davidakne...@gmail.com>> > To: CnC CnC discussion list <CnC-List@cnc-list.com > <mailto:CnC-List@cnc-list.com>> > Subject: Stus-List Grounding chart plotter > Message-ID: <788f7990-9eb6-45d8-b9f9-0e7bdce62...@gmail.com > <mailto:788f7990-9eb6-45d8-b9f9-0e7bdce62...@gmail.com>> > Content-Type: text/plain; charset="utf-8" > > Hi- I am installing a new Raymarine e95 chart plotter and am confused by the > instructions with respect to grounding. The cable includes both a Negative > (black) wire and a black Ground (drain) wire. Here is what the install > manual says: > Grounding ? Dedicated drain wire > > The power cable supplied with this product includes a dedicated shield > (drain) wire for connection to a vessel's RF ground point. > > It is important that an effective RF ground is connected to the system. A > single ground point should be used for all equipment. The unit can be > grounded by connecting the shield (drain) wire of the power cable to the > vessel's RF ground point. On vessels without an RF ground system the shield > (drain) wire should be connected directly to the negative battery terminal. > > The dc power system should be either: > > Negative grounded, with the negative battery terminal connected to the > vessel's ground. > Floating, with neither battery terminal connected to the vessel's ground > > > I have never heard of a RF ground point or a drain wire or a floating ground. > I can?t find anything about this in Nigel Calder?s book. Can someone clarify > what this is about and how to wire it? Thanks- Dave > > Aries > 1990 C&C 34+ > New London, CT
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