Alternatives to grounding on the engine block?

Questions & Answers
1

I’m getting ready to install some electronics which assume grounding to a true ground, vs. routing back to a battery’s negative post.

It dawned on me that, because I’ve got an electric engine, I don’t really have an engine block any more that I can use as a ground.

I’ve seen installations of equipment where this injunction was ignored (i.e., ground and negative both back to the battery). The equipment seemed to work just fine. But I don’t know whether that’s just getting away with something, or if it’s an acceptable practice.

Is it ok to route ground wires back to the battery? If not, what’s a viable alternative?

Advice, please?

Thanks,

– Bob

2

I’m not a fan of a bunch of connections on the battery. It’s messy and just a bad practice. Go for a bus bar and have all your negative connections there. If you have multiple batteries, they all go to the bus bar. All the negative connections for everything on the boat go there. You end up with a really well grounded system. Most issues with 12v are bad grounding. The bus bar solves that.

Not sure about the electric motor though. Is it DC?

RonB.

1 Like
3

Ron,

Thanks – I should’ve been clearer that the negative wiring does go to a bus bar rather than the battery. There’s a single wire from that bus bar to the negative post.

My batteries for electricals and electronics are a pair of 100A 12v LifePo4 batteries. With electric and thus no alternator, they charge only from shorepower, and there’s no need for separate house and starting batteries. Thus, they’re ganged to operate as a 12V 200A unit. The negative bus bar’s currently connected to the negative battery post of one of the two batteries.

Let me know if that’s wrong set-up. But my primary concern isn’t bus bars vs. direct connections. It’s understanding the distinction between connecting to negative vs. connecting to ground.

Specifically, my question is about electrical devices with instructions that differentiate between connecting to a ground vs. to a negative. Some are DC with three wires, others are two-wire DC with wiring diagrams that show the second wire going to ground rather than to a negative bus.

As I continue to refurbish the boat, I’m now putting in devices like that but have discovered the grounding cable to the diesel engine block got removed along with that engine.

It hasn’t seemed to matter for the simple equipment currently on the boat. I’ve had no electrical problems with them crop up in the nearly three years since that ground connection disappeared. But as I’m starting to upgrade to newer and better devices, I want to make sure I do it right.

My replacement electric motor is 48V DC connected to a completely separate set of dedicated batteries. It’s got a lot of aluminum components held by stainless screws and bolts. There’s enough dielectric insulation on the fasteners for that to be ok (I think, although not entirely happy about it).

I’m really reluctant under these circumstances to introduce a current flow by reinstalling a ground connection there.

So before I put in these new devices, I need to understand what’s my best alternative to an engine block for grounding things. That’s where I need advice.

Should I wait until my next haul-out and install a grounding plate?

Is that a right or wrong solution? And, regardless of right or wrong, is there a smarter solution I should use instead?

Thanks,

– Bob

4

Hi Bob, as a possible reference, Nigel Calder’s “Boatowner’s Mechanical and Electrical Manual” provides a good explanation of grounding intricacies. He distinguishes between grounded circuits that carry DC current and grounding circuits that are not normally current carrying (for example circuits for lightning protection or bonding underwater metals), and how these circuits are interconnected.

Mike

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The electric motor puts this issue beyond any experience I have. Please let us know what you find out!

RonB.

6

Bob, The best answer depends upon the wiring conventions that have been used already on Me Gusta. Lots of options will “work” but the best options will extend the existing patterns that have (hopefully) been followed by you and POs. Following wiring conventions makes it easier and safer for you AND the next wiring tech to work on the system.

On Soave, I found an existing bonding circuit with properly color coded wire green/green-yellow. Some “prior improvements” did not follow the same conventions and I’m slowly trying to return to conventions that follow patterns that are common for boats similar to Soave.

ABYC is generally considered the authority for stuff like this, but to access their documentation you need to be a member. I’m not. I usually use sites like ( THIS ONE ) to answer specific questions.

If I were to guess, I’d say your new fangled electronics is looking for a clean reference ground. SSB radios used to motivate owners to install grounding plates to provide a reference ground for the radio. The next best ground ( if you don’t have a grounding plate ) is the engine which is electrically connected to your prop shaft which is protected by anodes from corrosion.

Soave’s SSB radio was already retired when I bought her. Last winter I removed Soave’s grounding plate and connected the bonding circuit to a preexisting hull anode… which was already connected to the engine. Modern communications are not a dependent on super clean reference ground. I also removed a badly corroded a waste tank that was NOT connected to the bonding system. My fresh water tanks are connected and show no signs of corrosion.

When you say “true ground” ( I think ) you mean reference ground. I would would avoid running multiple reference ground wires to your negative DC bus. I’d combine multiple reference ground wires and if I felt I needed to ground the bonding circuit I’d run a single wire to my best ground point which on your boat may be your negative power bus. On Soave this is my engine block.

I offer my thoughts and observations not as expert advice but as a novice trying to wade through the plethora of options to find the approach that is best for Soave.

Hopefully others with more knowledge and experience will chime in.

Maybe bonding is a topic folks would like to talk about at the Rendezvous? If there is interest maybe we can invite an expert to participate ? My feeling is that bonding and corrosion are not popular topics… until something breaks.

Rob…

1 Like
7

Perhaps an overview of “grounds” would be helpful. (I realize you probably already know most of all of this, but it might help to put it all together.)

There are three “ground” systems in your boat. (Well, four if you use an SSB.) Electricity needs a complete circuit in order to flow and it is important that all portions of that circuit are correctly connected, including “grounds”. I put “ground” in quotes because it is a common term which really has no application on boats, but gives us a semantic starting point. If your new device is designed for boats, then it really does not require a “true ground” because there is none. Unless you are installing an SSB, it may be that they are just using the term “ground” to mean “DC negative”.

1. DC negative. This is the return path to the negative post on the battery. On cars it is generally run through the chassis and any connected metal, so you don’t usually have a separate negative wire to run. In boats there is always a negative wire run back to a DC negative bus bar. It is poor practice and is not ABYC compliant to actually tie every negative wire to the battery post, so bus bar(s) are used, but there can be exceptions. It is important to always ensure that the wires leading from bus bars back to the battery are sufficiently sized for the total of all current which will be run through them! For example, If you run a bunch of negative wires from 15 amp devices into a bus bar using 14 gauge wire, and then run a 14 gauge wire back to the battery, it will work fine if you only operate one device at a time. But you are going to start a fire when you turn on two or three of those devices at the same time.

2. AC safety ground. This one is there to keep you alive. Just like the AC wiring in your house, the dock wiring has a connection to actual earth ground - somewhere up on shore. And like your house wiring, a ground wire is run to each outlet along with the black and conductors. The AC safety ground wire on boats is green.

3. The Bonding System. Large metal components of your boat should be “bonded” together - connected by wires - in order to keep them all at the same electrical potential. This is for safety and to prevent stray current corrosion. At the least there is the main engine block - which you no longer have. This connects the engine to the water, which is roughly close to earth ground potential, through the propeller shaft. Your mast, keel, fuel tank (oh, you don’t have one of those, either. I am so envious), etc., might all be bonded together. I do not know if your electric motor installation retained the integrity of the bonding system, but if it did not, you should definitely correct that. If you installed a motor designed for small boat propulsion, then proper bonding should be included in the manual.

Each of these three systems should be connected together at one, and only one, point. This provides a common point of reference for every electrical (including static electrical) item on your boat. This is important for safety reasons. It will prevent stray currents and keep all exposed metal surfaces at the same voltage so you don’t get shocked. It will ensure that circuit breakers and GFCI outlets trip when they should.

4. RF ground. If you have an SSB radio on your boat, it will require an RF ground. This is a completely separate electrical path to the seawater and is usually protected from DC current by capacitors. This ground should not be connected to the other three.
Edit: I just saw Rob’s posting. The ground plate (ground plane in RF parlance) that he mentioned is where this RF ground would be attached.

If you are reworking your electrical system you should consider installing an isolation transformer, or at least a galvanic isolator. The isolation transformer breaks the direct metallic connection to shore. This eliminates galvanic paths via the green wire. And you essentially create a “new shore” on board with your own neutral–ground bond acting similarly to the “earth ground”. This will protect your zincs from being eaten up because of stray currents from a neighboring boat. I am actually in the process of installing one on my boat for that very reason: a bit over a year ago my zincs suddenly began disappearing rapidly. Zincs are cheap (except for the one on the Gori prop) but are expensive when a diver replaces them - and even more expensive if you ignore them! So in my situation, the rather expensive isolation transformer will pay for itself in a year or so.
A galvanic isolator is a cheaper alternative, but once they pop you need to replace them. And most of them don’t tell you when they pop, leaving you unprotected. ABYC compliant ones do retain the AC safety ground when they pop.

I hope this is helpful. I am not an ABYC accredited tech, so it’s worth what you paid for it.

8

Thanks very much, Brian!

This gives me what I needed to know:

The device instructions that triggered my original question were actually for a bilge pump float switch, which I feel safe in assuming was designed for boats.

Strongly concur!! To the extent of adding an extra exclamation point.

Don’t have one, but you just convinced me to add it to the to-do list.

I may come back and start a separate thread on this at a later point. I’m kind of a special case. My mast is carbon fiber and I have no fuel tank. I recently learned that carbon fiber is susceptible to current corrosion. When my aluminum mast track partially pulled off, I was told by Composite Engineering to work some fine fiberglass cloth between the track and the mast when epoxying them back together. They told me this was because of the risk of current corrosion between aluminum and carbon fiber. I have to figure out what that means for bonding.

Currently (sorry about the pun), anode replacement isn’t required very often, though.

– Bob

9

If it takes its power from a battery, it will only work if the negative lead has a solid path back to that battery. So yes, your bilge pump’s “ground” lead must return to your 12VDC negative bus bar.

10

The mast manufacturer knows what to do. If you do start that other thread, be sure and post what they tell you. Danny, at Klacko Spars, has told me that they will not be making any new Nonsuch masts, so future mast replacements will probably be CF.

11

Ted van Dusen of Composite Engineering will still answer questions and was very helpful to me with my mast track problem. However, he’s pulled out of mast production and seems to be focused on building racing shells and retiring.

He’s transferred his mast production work to Moore Brothers Company, https://www.moorebro.co/ (note that they’re .co rather than .com). I have not as of yet had any dealings with them, but it’s a good reminder that I should look into this and report back.

Thanks again, Brian.

– Bob

12

Brian,
Thanks for your usual clear explanation of a complex ( to me ) topic.

I’d second your suggestion to take steps to isolate the shore safety ground. I installed a galvanic isolator last winter and this fall I was pleased to see that the rate of anode depletion is MUCH slower during our sailing season.

For folks that don’t spring for the isolation transformer there is a procedure for testing a galvanic isolator, so it’s a good idea to mount it someplace easy to get to and periodically test it.