# Grounding a Battery?



## ImASonOfaSailor (Jun 26, 2007)

I have a Catamaran of course its all Fiberglass but i am installing a marine battery for a Stereo and some switches to turn things off! Where would i ground this battery at can anyone give me any ideas?


thanks


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## Silvio (Nov 10, 2010)

Take what I say with a grain of salt and hopefully Mainesail or one of the other frequent contributors with more knowledge will chime in, but I assume you are talking strictly DC? If that is the case then my understanding is that a DC system on a boat should only be grounded back to the negative terminal on the battery. NOT to any portion of the boat itself. Connecting electrical equipment to the boat hull will turn your boat into an anode, if I remember Chem 1 class correctly (plus yours is all glass and wouldn't work anyway). I believe you install a DC bus and the bus gets connected to the negative terminal on the battery. Think it is referred to as a "free floating" system.


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## denverd0n (Jun 20, 2008)

It's not like a car, where you connect the battery to the body/frame and then use that as the common ground for everything else. You run a positive and a negative wire in parallel to each powered device. You can use a busbar as a common distribution point to avoid a mass of wires going back and forth, if you want, but in the end you will still be able to trace both a positive and a negative wire from each device all the way back to the battery.


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## LakeSuperiorGeezer (Oct 8, 2010)

If you have an engine with alternator for battery charging, you will have to run a ground wire to the engine. At the flange connected to the transmission, you could put in an isolation coupling that does not conduct electricity so that no stray currents can reach the prop and cause electrolysis (severe corrosion). There are through hulls that are bronze that may also be an issue. There is some controversy on whether to ground everything together or isolate. The latest I know of is to isolate. There are also separate grounds for lightening and radio transmitter installation. Do not run the lightening ground to the engine as a strike can weld components like ball bearings in the transmission. If you use shore power to charge the battery and also to float the battery to prevent it from slowly discharging and sulfating where you need a new battery many years before the guarantee runs out, you will need a marine battery charger. An automotive type charger will not isolate the ground in the boat from the ground to the rest of the marina and this can cause electrical currents that severely corrode metals completely destroying a stern drive for instance in a year, or maybe your own propeller if not isolated at the transmission. Instead of a battery charger, it might be best to use solar panels for each battery with intelligent voltage regulators to not overcharge the batteries.


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## johnnyquest37 (Feb 16, 2012)

ABCY E-11 section 11.16:

DC Grounding - If a DC grounding system is installed, the DC grounding conductor shall be
used to connect metallic non-current-carrying parts of those direct current devices identified in 11.15.2.1 to
the engine negative terminal or its bus for the purpose of minimizing stray current corrosion and ensuring a
fault current path in the event of a short circuit.


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## PaulinVictoria (Aug 23, 2009)

You have to trail a really long wire behind you that plugs into a grounded outlet at the dockside


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## hellosailor (Apr 11, 2006)

For the purpose of a "car" stereo you don't need any ground. Just run the stereo to the positive and negative battery leads, and if the stereo has a "ground" connection that goes to the negative as well.

Do use a suitable fuse, installed as close to the battery positive terminal as practical.


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## LakeSuperiorGeezer (Oct 8, 2010)

hellosailor said:


> ...Do use a suitable fuse...


You will need an electrical panel with fuses. If you want jerry rigged setup you will still need fuses to prevent an electrical fire with possible loss of boat


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## Maine Sail (Jan 6, 2003)

ImASonOfaSailor said:


> I have a Catamaran of course its all Fiberglass but i am installing a marine battery for a Stereo and some switches to turn things off! Where would i ground this battery at can anyone give me any ideas?
> 
> thanks


On a 21 footer with no in-board engine an isolated ground is fine. This means the battery - post is your ship ground...



LakeSuperiorGeezer said:


> If you have an engine with alternator for battery charging, you will have to run a ground wire to the engine.


Most likely and outboard on a 21 footer and the battery can still suffice as ship ground when the motor is lifted..



LakeSuperiorGeezer said:


> At the flange connected to the transmission, you could put in an isolation coupling that does not conduct electricity so that no stray currents can reach the prop and cause electrolysis (severe corrosion).


This is strongly advised against if you have an inboard engine. The ABYC uses the term "MUST" when referring to alternate means of grounding the shaft to the vessel if using an isolating coupling. Isolating the shaft does not solve anything as the motor is still has an electrolyte inside it and also has MANY dissimilar metals. On the vast majority of inboard boats the engine is the ships main Earth/grounding point. It only means your engine will have less protection when you isolate the shaft..



ABYC P-6 said:


> 6.5.5.2 If a non-conductive flexible coupling is used, an alternative means of grounding the shaft *must* be provided.





LakeSuperiorGeezer said:


> There are through hulls that are bronze that may also be an issue. There is some controversy on whether to ground everything together or isolate. The latest I know of is to isolate.


The only way to know for sure is to have a corrosion survey inspection by a COMPETENT ABYC trained corrosion specialist. Without this you are basically throwing craps like in Vegas..



LakeSuperiorGeezer said:


> There are also separate grounds for lightening and radio transmitter installation. Do not run the lightening ground to the engine as a strike can weld components like ball bearings in the transmission.


See below...



ABYC said:


> A lightning grounding terminal for a boat should consist of a metal surface (copper, copper alloys, stainless steel, aluminum or lead) which is in contact with the water, having a thickness of at least 3/16 inch (5 mm), and an area of at least 1 square foot (0.1m²). It should be located as nearly as possible directly below the lightning protective mast in order to minimize any horizontal runs in the primary (main) conductor.
> 
> *In order to avoid routing grounding conductors horizontally through the boat, boats that use a lightning ground plate or strip located forward should ground backstays, or other metallic objects aft, to the engine negative terminal, a metallic rudder, or other external ground at the aft end of the boat.* These grounds should also be interconnected with
> the ground plate or strip located forward.
> ...


The above has been the industry accepted method for lightning grounding for many years. Even boats from the late 60's & 70's were using this and they still use it today. In a lightning strike it is darn near impossible to isolate the engine as it is connected to the electrical system anyway.


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## LakeSuperiorGeezer (Oct 8, 2010)

One can use an electrical conducting brush on the propeller shaft and have the engine isolated. Here is some research on lightening protection with a lot of various links on the subject: http://www.kp44.org/LightningProtection.php and http://www.kastenmarine.com/Lightning.htm and http://www.sailmail.com/grounds.htm


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## Maine Sail (Jan 6, 2003)

LakeSuperiorGeezer said:


> *One can use an electrical conducting brush on the propeller shaft and have the engine isolated.* Here is some research on lightening protection with a lot of various links on the subject: Lightning Protection on Sailboats and Lightning Attenuation Onboard and Grounding


Please explain that one.. The shaft brush is connected to the batteries, earth, bonding and lightning systems and the engine is connected to all this too with large wire for starting loads... No isolation with a shaft brush..

The engine is also in an electrolyte, has it inside it, with all sorts of dissimilar metals. The idea behind an isolating bushing actually isolating the engine from "corrosion" just does not work unless you have a closed non-conductive ball valve and you remove the electrolyte from your engine each time you shut it down..


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## LakeSuperiorGeezer (Oct 8, 2010)

I would ground the propeller and shaft to the lighting protection system, not the DC electrical ground nor tie it into a ground that ties all metals on the hull to anodes. Here's a link on it: BoatUS: Seaworthy Note the part about the galvanic series. For submerged metal parts, and parts in an anaerobic environment such as chain plates and keel bolts where stainless corrodes like mild steel because without oxygen, the protective oxide coating is not produced, I prefer silicon bronze.

Concerning internal parts of an engine made of dissimilar metals; most engines have a zinc sacrificial anode that will protect the dissimilar metals in an engine. Metals have to be close to the zinc for protection and an engine has a lot of twists and turns with all those cooling passages in head and block so there will still be corrosion if directly cooled by salt water. Corrosion is a real problem even with a zinc in the engine because salt water is a very good electrolyte and the chloride ion also promotes corrosion. If the engine has a heat exchanger, then the engine will have a water antifreeze mixture that does a very good job of protecting the internal parts from corrosion if the antifreeze is more than 50% of the mixture and the rust inhibitors are not worn out. Modern inhibitors in antifreeze are good for about 5 years if my memory is correct.


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## Maine Sail (Jan 6, 2003)

LakeSuperiorGeezer said:


> I would ground the propeller and shaft to the lighting protection system, not the DC electrical ground nor tie it into a ground that ties all metals on the hull to anodes.


This goes against ALL CURRENT ACCEPTED SAFETY STANDARDS IN THE US..... But, your boat your choice. On the other hand perhaps poor public advice on a forum read by many who may not know any better.

A 100% isolated lightning ground to the shaft is not what the ABYC means when they say:



> [Originally Posted by ABYC P-6
> 6.5.5.2 *If a non-conductive flexible coupling is used, an alternative means of grounding the shaft must be provided.*





LakeSuperiorGeezer said:


> Here's a link on it: BoatUS: Seaworthy


Your link is in agreement with everything I have been saying as were the ones form the other day that referenced the ABYC nearly every other sentence... Thanks....



LakeSuperiorGeezer said:


> Note the part about the galvanic series. For submerged metal parts, and parts in an anaerobic environment such as chain plates and keel bolts where stainless corrodes like mild steel because without oxygen, the protective oxide coating is not produced, I prefer silicon bronze.


Yes bronze is more resistant to corrosion such as crevice and pitting corrosion but all metals can be subject to galvanic corrosion and no boat uses 100% the same metals below or above water. There are still metals on a boat that are more noble than silicon bronze including most stainless, nitronic or aqualoy shafts, rudder shafts etc. and most NiBrAl props.. This creates electrical potential differences and silicon bronze can still be the less noble or sacrificial metal.

All metals have an electrical signature/voltage. Props are either NiBrAl or high zinc Manganese bronze. Prop shafts can be tobin bronze, a high zinc alloy, or any one of the stainless family from 304 to the Aqualoy or the Nitronic family and each has it's own voltage. Bronze struts often hive high zinc content, though some are NiBrAl, as do many stuffing boxes. "Proper seacocks" are often made of 85-5-5-5 bronze yet European seacocks are made of DZR-1 a high zinc alloy with some tin added for corrosion resistance. Add in a lead keel or a sintered bronze plate or copper grounding plate and you have a real galvanic soup. Owners then add things like graphite packing etc. etc. etc. and can make the soup even more electrically challenging. Finding the right amount of "protection" for your boat is, and can be, challenging especially if you don't have the tools to know of you are over or under protected.

There is no one fits all answer to individual boat corrosion though some have tried to apply "one fit" before. The only answer is that each boat needs a corrosion survey by a COMPETENT corrosion specialist to determine the amount of protection needed and whether you need to bond or are safe to un-bond. Over zincing can be as bad as under zincing but like anything people assume "bigger is better" or more is better when that may not be the case at all.



LakeSuperiorGeezer said:


> Concerning internal parts of an engine made of dissimilar metals; most engines have a zinc sacrificial anode that will protect the dissimilar metals in an engine. Metals have to be close to the zinc for protection and an engine has a lot of twists and turns with all those cooling passages in head and block so there will still be corrosion if directly cooled by salt water. Corrosion is a real problem even with a zinc in the engine because salt water is a very good electrolyte and the chloride ion also promotes corrosion. If the engine has a heat exchanger, then the engine will have a water antifreeze mixture that does a very good job of protecting the internal parts from corrosion if the antifreeze is more than 50% of the mixture and the rust inhibitors are not worn out. Modern inhibitors in antifreeze are good for about 5 years if my memory is correct.


The zincs in engines are barely suitable to protect the engine this is where the shaft zincs help and help protect other underwater metals. Owners also rarely change these zincs and some don't even know they are there or they just don't change them often enough. Heck some engine manufacturers never installed them. Some heat exchangers alone have more than FIVE metals in them and the teeny tiny pencil zinc barely even protects that let alone the rest of the boat but that teeny tiny pencil zinc is what you'd be relying on by decoupling the engine.

I won't even go into the AC/DC safety aspects of decoupling the Earthing system on the boat from the Earth as that opens another whole area of safety matters...

For some back ground on where I come from regarding these issues I am ABYC trained in marine corrosion, too many courses, seminars and webinars to count, and am ABYC certified electrical systems specialist. I do own a silver/silver half cell and know how to use it. I feel I can speak with some level of understanding because I do this stuff every day on more than just an n=1 basis.... No one has to listen to it, but I can't just let potentially dangerous suggestions about a boats electrical system go without comment.... 55% of boat fires are electrical in nature so clearly lots of folks don't do things safely...

The one common denominator I see when doing corrosion inspections is the ones who think they know the most sometimes know the least and often do the most damage to their boats or other boats.

One can read articles on corrosion but I find when they do they tend to take the points they agree with from one article, and the points they agree with from another article, and make an entirely different can of electrical soup.

The safest thing you can do electrically is to wire your boat to the accepted industry safety standards, which in this country, and many others for that matter, are the American Yacht & Boat Council standards. These standards are used as the primary evidential standards in many court cases involving boats and are actually based in federal law across many areas, they line up identically with the CFR (Code of Federal Regulations) on lots of safety measures.

Suggesting to isolate the ships ground from the rest of the vessel, and use the shaft as a lighting ground, is a recipe for problems and goes against current accepted safety standards. I tend to see it as little different than advising someone, on-line, to go lick the 240V studs on their incoming AC panel to the house to see if they have power....

No "competent" surveyor would sign off on that type of installation, nor should they, but I am sure you can find at least one "unqualified" surveyor who would.

Our boat has been direct hit by lightning and the engine is fine BTW. The vessel is wired to ABYC standards and uses the engine as the ships main Earth point. Even if the engine did get fried, COOL!!!!!! Ours has 3300 hours and I was actually kind of pissed it was not cooked. Who doesn't want a new engine especially when lightning strikes don't generally raise your premium.......

That said I know of no instances where lightning ruined an inboard diesel engine in a vessel wired to current industry standards of secondary/primary Earthing.. Of course with lightning anything is possible.

P.S. Lighting pretty much does what it wants. The items below were not plugged into anything and were all TOASTED... Because they were not plugged in I'd call these devices "electrically isolated"....

*Fried Without Being Connected To The Vessel*

3 Hand Held GPS devices, one Magellan, two Garmin. The Magellan was wrapped in tin foil and in a waterproof plastic Pelican ditch box the Garmins were in the chart table. All three still cooked though were not plugged in to the boat..

1 EPIRB (on bulkhead above nav station)

1 iPod (in v-berth on shelf)

1 Laptop Computer (on nav desk)

1 Wireless Ram Mic (on galley counter)


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## hellosailor (Apr 11, 2006)

"This goes against ALL CURRENT ACCEPTED SAFETY STANDARDS IN THE US..... "
Forgetting about safety, who would really want to _encourage _some capricious demon like lightning to come visit the engine, shaft, bearings, and all the associated electrical wiring?

Here'e the mast, here's the keelbolt, straight in one ear and out the other, no waiting, no detours.

Narwhals, giant kraken, these you can always sell to the Japanese for sushi. Lightning? Scares the * out of me, because Zeus really doesn't care what offerings you have made, he just wants to wreak havoc with it.


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## peterchech (Sep 2, 2011)

Thanks Mainesail, I think you cleared up an issue that many of us face, using commonly accepted standards.

Haha one more argument for a tiller though, since that grounded metal rudder will zap right up to a metal steering wheel and electrocute you in case of a lightning strike


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