Boat grounding system(s)...how to seperate from DC

[Franklin]

From all the articles I've read, it says that the boat is supposed to have 3 grounding systems (AC/DC 115 Volt, DC 12 Volt, underwater bonded metals) and that none of these systems are supposed to be connected. Now the AC/DC system is connected to the DC system by way of the charger but I guess the charger has the proper pieces to keep it isolated. Keeping the DC seperated from the underwater bonded system seems a bit more complicated. If the engine is connected to the tranny and the tranny connected to the prop shaft and the prop shaft is connected to all the thru hulls (either by salt water or by wire or both) and the engine is grounded, then how can you keep them seperated?

 

[Bill Roosa]

There are 5 grounds

AC, DC, bonding, lightning, and radio.AC runs to shore ground through isolation tranformer or galvonic isolatorDC runs to engine/tranny/propbonding, unbond everything and you should be OKlightning runs from mast to a keel bolt via a direct large diameter wire with as few turns as possableradio (SSB and VHF) run to keel bolt via ribbon ground strip.Now the weird partDC to AC ground busses get connected togetherDC to radio get connected via a set of capacitors. passes ac radio ground but not dc currents!AND don't forget to unconnect the VHF antenna ground from the mast. Radio shack has these DC inner-outter blocks for the antenna lines.

 

[Morrie]

Check out this article

It was originally published in Practical Sailor. This is a copy in the West Marine Advisor section of West Marine's web site. It's the most comprehensive thing I've ever found on Marine grounding systems.

 

[Hoosier Kevin]

What do you connect to - if you have an outboard?

Nice article - but what does one do when you have an outboard - what do you attach your ground wire to then?

 

[Stu Jackson]

The negative goes back to the batteries

that's all U need to do

 

[Franklin]

Bill Roosa

If the mast is grounded to the keel and the radio is grounded to the keel bolt, then they are on the same system, right?If the DC runs to the prop via the engine and the prop is connected to all other inwater metals, including the keel bolts, then that's all (DC, Radio, Lighting, and bonding) one system too (salt water connects them).Right?

 

[Don]

Franklin

Multiple grounds are not good nor are ground loops, all of which can and probably will cause different ground potentials and therefore current flow. Read Morrie's link thoroughly for the reason(s).Don

 

[Franklin]

Green wire

As far as I can tell, my green wire is not connected to anything except it's own bus bar. I know the original owner wouldn't have changed this so that must be how Hunter wired it. I don't like the idea of having the green wire connected to anything because that greatly increases the chance of electrolysis, right? Sure I could get one of those electrical devices to stop DC current coming through the green wire onto my boat from the shore power but I would not know when it's not working anymore and thus have a quiet prop killer at work.The green wire is to handle shorts. If there is a short in an appliance that I'm using, I believe it would send the voltage into the green wire and it would travel back to the shore power and be grounded at the dock (not through my metal and eating up my zincs).

 

[Franklin]

Green wire

"So the ground lead should never be directly connected to the ground bonding system we talked about earlier....You don't want it to connect all the underwater items on your boat to the underwater items on all the other boats and the dock because now your zinc is trying to protect everyone else too."Are you just trying to get me to protect your boat too "If you can't afford an isolator, then the next best choice is to DISCONNECT the TWO CIRCUITS so electrolysis currents can't flow. You will still have a solid ground connection on all the devices being operated on the AC power but this ground will not be connected to the boat underwater items or the 12 volt negative. "I don't want to be dependent on some device to be working properly like I said before. Hunter wired them separate and I believe that's the way they should be.

 

[Capn Dave]

Ahoy Bill !! The VHF

ground isn't needed if your talking about the antenna. No Ground plane is required unless you are using a SSB radio.Fair WindsCap'n Dave

 

[Gord May]

One True Ground

Ultimately all “grounds” are connected together at one, and ONLY ONE place - the final water connection.