Feels like a leading (but good) question, lol - and I’d expect the ‘grounds’ could be at different potentials and that this delta would vary based on the ground at different marinas. You’ve made me curious, will measure the ground-to-ground voltage today. Not sure of the practical negative (if any) implications of the AC ground being at a slightly different potential than the isolated -12vdc ‘ground’? I can see that a poor -12vdc ‘ground’ could impact noise suppression in cable shielding or similar but otherwise Is there an issue? I’m Not a grounding/bonding expert by any means! Dave
On Sat, May 30, 2020 at 9:56 AM Neil Andersen <neil.eric.ander...@gmail.com> wrote: > Does that set up a different ground potential when connected to shore > power (AC side and 12V side)? > > Neil Andersen > Rock Hall, MD 21661 > ------------------------------ > *From:* Dave S <syerd...@gmail.com> > *Sent:* Saturday, May 30, 2020 9:41:36 AM > *To:* Neil Andersen <neil.eric.ander...@gmail.com> > *Cc:* Brian Davis <brianwdavis...@gmail.com>; cnc-list@cnc-list.com < > cnc-list@cnc-list.com> > *Subject:* Re: Stus-List Grounding > > Interesting question. The term ‘ground’ probably should be distinguished > from the negative side of the dc circuit. > Can’t speak to more sophisticated boats but in my relatively simple 33-2 > The AC system is isolated, grounded only when connected to shore power. I > do not run any AC loads otherwise, no inverter. > The 12v system would ultimately ‘ground’ To the water via the engine, prop > and shaft. > > Dave > > On Sat, May 30, 2020 at 9:33 AM Neil Andersen < > neil.eric.ander...@gmail.com> wrote: > > Where do you actually go to “ground” off the bus?? > > Neil Andersen > 1982 C&C 32 > Rock Hall, MD > ------------------------------ > *From:* CnC-List <cnc-list-boun...@cnc-list.com> on behalf of Dave S via > CnC-List <cnc-list@cnc-list.com> > *Sent:* Saturday, May 30, 2020 9:18:24 AM > *To:* Brian Davis <brianwdavis...@gmail.com>; C&c Stus List < > cnc-list@cnc-list.com> > *Cc:* Dave S <syerd...@gmail.com> > *Subject:* Re: Stus-List Grounding > > Essentially yes, however when you are thinking of the boat's wiring, I > would think of the ground bus as the centre, with the engine connected to > it, rather than the reverse. Think of it a hub or a star - with the > ground bus at the centre. (Google "star grounding") one of those paths > has to finally cross the shunt to be measured. (those loads which are > powered by the house bank) > > That green wire is the ground for the aluminum fuel tank. The rest are > batteries (house 1,2, and start) or engine, plus the shunt. All are at > the same ground potential. On the other side of the shunt is > the smartcharger, the refrigeration unit, the house breaker panel, and > anything else I want to "see" in the BMV 700. Basically anything that > impacts the house bank, (though this does not include the alternator.) > > Dave > > > > On Sat, 30 May 2020 at 08:43, Brian Davis <brianwdavis...@gmail.com> > wrote: > > Thanks, Dave. I have the same type of shunt that came with the Blue Sea > panels I'm installing and will have the same monitoring. I see in you pic > there's a green wire (grounding?) going to the bus along with the blacks > (negative batteries). So, all of that goes to the same engine connecting > point and the grounds and negatives share that single point? Just want to > make sure I completely "get it". > > Thanks for all your guys help. > > On Sat, May 30, 2020 at 8:21 AM Dave S <syerd...@gmail.com> wrote: > > Agree with Joe's comment. the engine must be grounded but should not be > used as your primary grounding point. > there are a buncha' good reasons for this. Another thing to consider is > providing for an upgrade the battery/power monitoring, for which you may > need to install a resistive shunt between the battery and the various > grounds you wish to monitor, Here's a photo of the shunt (on the > right) and ground bus (left) in my 33-2, you can see the ground bus and > various grounds attached, this bus is connected to one side of the shunt, > the other side of which is connected to the house breaker panel and the > other accessories that are measured by my battery/power consumption > monitor. This is the shunt that victron provides with the BMV-700. > > > https://3.bp.blogspot.com/-LeNHHo5kK2k/V5V0MaFJ_cI/AAAAAAAAAkc/VI_Cm3z-Aa0m_dZ9AmlgaeVdXmXQOINkgCLcB/s1600/blog%2Bgrounding%2B2.jpg > > > > Dave > > > > > > > > -- Forwarded message ---------- > From: Brian Davis <brianwdavis...@gmail.com> > To: cnc-list@cnc-list.com > Cc: > Bcc: > Date: Sat, 30 May 2020 07:32:16 -0400 > Subject: Stus-List Grounding > Hello everyone, > > Hope you quarantine projects are going well. > > I have a question about grounding. I'm currently refitting ALL wiring from > scratch on our 1980 Landfall 38. I literally gutted every piece of wire and > bought all new Ancor tinned marine cables in every guage you can imagine. > She's coming along swimmingly, and I've mapped everything out pretty well > in a 8 page layered diagram that I'm happy to email direct to anyone who > wants it. It's in PowerPoint and about 8mg. > > My question about Grounding is if it's ok to use my engine as the > grounding point? I'm using the similar area for the Negative connection for > the 3 battery banks, but a different bolt to the engine case. Several > appliances including the breaker panels, ACR, battery charger, water > heater, fuel tank, etc require a ground and I'm using a 6 awg green wire > from the engine to a large Blue Sea busbar. Then connected the grounds to > it. > > I've also run a 2awg wire from the mast step to the keel bolt and to one > of the stanchion bases from underneath for lightning protection. However I > kept that all separated and not connected to the grounding. > > Make sense? Or am I missing something? Again, happy to send my diagram for > review. > > Regards, > Brian > South FL > > > > ---------- Forwarded message ---------- > From: Joe Della Barba <j...@dellabarba.com> > To: cnc-list@cnc-list.com > Cc: > Bcc: > Date: Sat, 30 May 2020 07:52:37 -0400 > Subject: Re: Stus-List Grounding > > Don't use the engine for ship's ground. Use one of these: > > > https://www.bluesea.com/products/2127/MaxiBus_250A_BusBar_-_Four_5_16in-18_Studs > > Your AC ground bus will connect to that ground point as well. Speaking of > AC, make sure you have a galvanic isolator. > > Run ONE ground wire to the engine. You don't want your engine block to be > a routine conductor of electricity. > > Here is your lightning ground conundrum: The old way was to connect all > metal together. Coquina came with a ground wire system that connected every > single thru-hull, the mast step, the engine and the keel. The problem with > that is if the zinc does not work perfectly, you can have electrolysis on a > large scale since you have all this metal wired together. I undid all that, > no thru-hulls are wired to anything. The mast is wired to a keel bolt with > 4 gauge wire. The ship's ground bus is wired to the engine with one ground > wire. > > > Joe Coquina > On 5/30/2020 7:32 AM, Brian Davis via CnC-List wrote: > > Hello everyone, > > Hope you quarantine projects are going well. > > I have a question about grounding. I'm currently refitting ALL wiring from > scratch on our 1980 Landfall 38. I literally gutted every piece of wire and > bought all new Ancor tinned marine cables in every guage you can imagine. > She's coming along swimmingly, and I've mapped everything out pretty well > in a 8 page layered diagram that I'm happy to email direct to anyone who > wants it. It's in PowerPoint and about 8mg. > > My question about Grounding is if it's ok to use my engine as the > grounding point? I'm using the similar area for the Negative connection for > the 3 battery banks, but a different bolt to the engine case. Several > appliances including the breaker panels, ACR, battery charger, water > heater, fuel tank, etc require a ground and I'm using a 6 awg green wire > from the engine to a large Blue Sea busbar. Then connected the grounds to > it. > > I've also run a 2awg wire from the mast step to the keel bolt and to one > of the stanchion bases from underneath for lightning protection. However I > kept that all separated and not connected to the grounding. > > Make sense? Or am I missing something? Again, happy to send my diagram for > review. > > Regards, > Brian > South FL > > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each and > every one is greatly appreciated. If you want to support the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray > > _______________________________________________ > CnC-List mailing list > CnC-List@cnc-list.com > http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com > > > > > -- > Brian Davis > 1980 C&C Landfall 38 > "Nina" > Southeast Florida > >
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