Grounding and GFI on a boat.

[Inq720]

In retrofitting a small sailboat, I will be buying my first Inverter. Probably a GoWISE that Will recommends.

I notice some brands tout GFI AC outlets. I'd have to add one to the boat external to the GoWISE. What is the safest concepts and are the ramification of doing this on a boat and in a more general question how does one ground a fiberglass boat? I've read various things about copper plates in the water and large gauge wiring to the mast, but I think this has more to do with lightning protection. And even with that, there are just as many people that say that kind of grounding is a waste of time OR even than such wiring is dangerous.

 

[Hedges]

GFCI sometimes fail. Installing it external to the inverter could make replacement easier and more economical.
I think (but am not certain) that a Square-D GFCI breaker is more reliable than a GFCI outlet.

Given issues of grounding and tying neutral to ground, perhaps an all-pole GFCI, which opens both line and neutral rather than just line, would be better. Those are commonly found as portable GFCI or in the cord of wet-location appliances, due to the risk an outlet they might be plugged into could be wired incorrectly.

 

[Hotdog]

Grounding a sailboat!
It is an interesting topic! I would like to know more. Have you found any answer to your question

 

[Inq720]

My untrained/non-EE thought was that a sailboat would be similar to an RV. An RV is isolated from Earth ground because of the tires. According to this article, I can not trust my assumptions. I also found counter points for just about every item discussed in that article. Such as:

1. It assumes a substantial motor with a permanent through hull shaft to an always in the water propeller. It also assumes a large keel with massive bolts tying a chunk of lead always sitting in the water. In my case, I use an outboard motor that baring occasional splashing is not in contact with the water and no metal keel. In fact I have no metal in constant contact with water.
2. The AC portion of the article seemed to be more concerned with galvanic corrosion and being tied to a dock's AC circuit. Again... I have nothing in the water, that is of lesser concern. The motor has the zinks and takes care of that WHEN it is in the water. I am more concerned about the safety. One recent summer in Atlanta a man electrocuted his grand-children who were swimming in the nearby lake water. The details were not explained. Again my untrained logic says if my Inverter based AC circuits have no path to the water there are no paths that can hurt a nearby swimmer. But I can't ASSUME that is not good enough... especially after reading that article.
3. That article states... DO create a path from the mast to the keel to the water for lightning strike protection. I've read in the past just as many "experts" saying that makes a lightning strike more likely. Of course electricity will take the easiest route... that big aluminum mast connected to the ground it wants to reach. They're contention is that if its isolated, it is no more desirable a path than the air around the boat. In my case having a deck stepped mast, the bottom of all "mast metal" is at least four feet above the water... well isolated.

For me... reading that article just added more conflicts with other readings. But maybe it'll help you.

 

[Inq720]

In my case, all my DC circuits will ground back to one common point and will be tied to the motor and negative ground of the battery. I just don't know what to do with the ground pin of the AC Inverter. I don't know:

1. if I should tie that to that same negative "ground plane" of the DC circuit as the paper above suggests. And will that now allow AC to get to the surrounding ocean... say if the motor is in the water... say under normal conditions OR say if a GFCI outlet is tripped.
2. Or do I keep them separate with no path to the water. Maybe this protects swimmers, but what about users inside the boat. My logic says that if a GFCI trips, it is trying to route that energy to the ground pin of the AC circuit. If it is not connected to anything it goes no where and is the same as not having a GFCI channel... person gets electrocuted.

I just don't know what the answer is and nothing I have read so far has assured me which way to go.

 

[LostDog88]

My understanding is that you have a hot and neutral for your AC system. Then you have a (usually green) ground for your AC system. You also have a DC negative with your DC system. AC Ground and DC ground should go to the same bus. There should also be a connection made to the engine/transmission, etc.
It seems that there is some confusion between bonding and grounding. This is considered grounding.
From there you can test all your points to make sure that you are grounded properly. And then you can check bonding and galvanic isolation. etc.
At least that is how I understand it.
I am watching this thread to see if someone corrects me.

 

[Dzl]

If you want to see what the ABYC (marine code body in the US) and Coast Guard have to say, go to the resource section of the forum look for the USCG boatbuilders electrical guide and the ABYC E-11. From what I recall you will find more info on grounding in the ABYC document.

 

[Dzl]

Also, West Marine, Blue Sea Systems, and PKYS have good articles on marine electrical topics

 

[mmtech]

First of all you NEVER connect any ac device to a boats dc system not even the ground. I had a customer put a inverter on a brand new boat and grounded it to the engine 12 volt ground stud. In less than a week It ate the drive away and sank the whole thing. 82000 dollar mistake. Warranty void. Insurance also said tough luck. Only connect the ground the outlet to the inverter.







i

 

[LostDog88]

First of all you NEVER connect any ac device to a boats dc system not even the ground. I had a customer put a inverter on a brand new boat and grounded it to the engine 12 volt ground stud. In less than a week It ate the drive away and sank the whole thing. 82000 dollar mistake. Warranty void. Insurance also said tough luck. Only connect the ground the outlet to the inverter.







i

Not according to this excerpt taken from West Marine's HOW TO Guide.

And everything else that I have read?

So am I and others wrong?

AC Ground​

See Practical Sailor, August 15, 1995 for a detailed treatment of the green wire. The best solution is a heavy and expensive isolation transformer. The acceptable solution (for the rest of us) is to install a light and inexpensive Galvanic Isolator in the green wire, between the shorepower cord socket on your boat, and the connection to the boat's AC panel. Then, connect the grounding conductor (green) of the AC panel directly to the engine negative terminal or its bus.

Note that this meets the ABYC recommendation. In choosing Galvanic Isolators, make sure that you select one that has a continuous current rating that is at least 135% the current rating on the circuit breaker on your dock box. Certain Galvanic Isolators (e.g. Quicksilver) include large capacitors in parallel with the isolation diodes, which in certain situations theoretically provide better galvanic protection. Unfortunately, these units cost substantially more than conventional Galvanic Isolators. If you feel like spending real money on galvanic isolation, you might as well do it right and buy an isolation transformer.

 

[Inq720]

Not according to this excerpt taken from West Marine's HOW TO Guide.

And everything else that I have read?

So am I and others wrong?

AC Ground​

See Practical Sailor, August 15, 1995 for a detailed treatment of the green wire. The best solution is a heavy and expensive isolation transformer. The acceptable solution (for the rest of us) is to install a light and inexpensive Galvanic Isolator in the green wire, between the shorepower cord socket on your boat, and the connection to the boat's AC panel. Then, connect the grounding conductor (green) of the AC panel directly to the engine negative terminal or its bus.

Note that this meets the ABYC recommendation. In choosing Galvanic Isolators, make sure that you select one that has a continuous current rating that is at least 135% the current rating on the circuit breaker on your dock box. Certain Galvanic Isolators (e.g. Quicksilver) include large capacitors in parallel with the isolation diodes, which in certain situations theoretically provide better galvanic protection. Unfortunately, these units cost substantially more than conventional Galvanic Isolators. If you feel like spending real money on galvanic isolation, you might as well do it right and buy an isolation transformer.

If you want to see what the ABYC (marine code body in the US) and Coast Guard have to say, go to the resource section of the forum look for the USCG boatbuilders electrical guide and the ABYC E-11. From what I recall you will find more info on grounding in the ABYC document.

Of course, I'm not questioning the document or the source. I've searched through both of Dzl's recommendations and read the pertinent parts. I do have a question about the conditions. Everything in those documents seems to center around connection to shore power. The galvanic Isolator is in-line with that connection between boat and shore and is not used when off shore power.

1. So... for the case, boat out on the water, not connected to shore - Does the Inverter ground (screw post) still get connected to this DC negative? I'm guessing so since, I would assume the ABYC would mention disconnecting if it was necessary.
2. And for my specific condition, where most of the time, my motor, prop and all other metal is out of the water, I have no real connection to Earth ground via the water. Will having a GFCI between the inverter and all AC appliances be as safe as I can be?
3. And re: mmtech's comment, would not my Zinks on the motor take any galvanic corrosion out as an issue? Is there something special about AC being grounded via motor, through the zinks (when in the water) be different than when just DC is connected to them?

 

[LostDog88]

My understanding on this is you are basically creating your own isolated power plant.
The green ground from shore would be connected to engine frame through a galvanic isolator to limit/reduce/stop stray DC voltage from exiting your vessel. Basically there would be no difference of potential.
The way I understand the boat side is that when you are not connected to shore power you are basically grounding to the DC negative bus as this would be again the (no) difference of potential. Stray DC voltage would be shunted to the negative of the battery. This also creates what we would call an earth ground if we were on land.
Please someone with more experience correct me if I am wrong, with an explanation if possible.

 

[mmtech]

The isolater is to stop feedback from a another boat on the dock that has a electrical problem r even the marinas system grounding through your rig. Most hi end boat builders have them installed from the factory. If you ground the gfci to the dc system you are connecting the ac and dc system together NOT GOOD. It takes only a small amount of current to set up galvanic reaction. Also it can damage your alternator or if is fuel injected the computer( they mostly work on 5 volt sensors.

 

[mmtech]

I for got that if you ground the outlet thru the inverter and it is connected to the shore powerit will ground by the way of the isolater electronicly and onely negitive. If you ground the outlet to the engine you have no protection from the positive side of the ac cycle and there where the problem starts.

 

[LostDog88]

The isolater is to stop feedback from a another boat on the dock that has a electrical problem r even the marinas system grounding through your rig. Most hi end boat builders have them installed from the factory. If you ground the gfci to the dc system you are connecting the ac and dc system together NOT GOOD. It takes only a small amount of current to set up galvanic reaction. Also it can damage your alternator or if is fuel injected the computer( they mostly work on 5 volt sensors.

Yah....... sorry. Wrong.

Read this excerpt from:

Ten Deadly Conditions to Check for in Your Boat's Electrical System - Part 1 - Blue Sea Systems

Engineering high quality marine electrical components for safety, reliability and performance

www.bluesea.com

4. No “Green Wire” or poor-quality connection between DC negative and AC safety ground

Without a good connection between DC negative and AC safety ground, stray AC current may enter the DC ground system. When this happens, AC current may enter the water around a boat and injure or kill swimmers near the boat.

The green wire is the safety ground wire that connects the DC negative ground block to the AC safety ground bus. The purpose of this wire is to provide a lowest-resistance path to ground for any stray AC current that finds its way onto the DC ground system. There have been cases of AC current entering the water around a boat through the engine shaft and killing swimmers near the boat.