Bonding/Grounding an AC System

Wiring your boat, How to Wire Lights/Accessories, All things electrical other than actually powering your boat by electric motors.

Moderator: Bill Edmundson

User avatar
Bill Edmundson
Posts: 10441
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Bonding/Grounding an AC System

Postby Bill Edmundson » Tue Jan 20, 2015 2:17 pm

On the Bartender, I will have both AC and DC systems. I've seen AC & DC ground run to the bonding plate. In Calder's book it shows that if two boats in a marina are connected to grounded shore power and both have bonding plates a galvanic cell can be formed and one plate may go away.

The DC side should be bonded to dissipate static from interrupting electronics. It's difficult not to do this with the engine in the water.

When I run on the generator, it will be connected to the bonding ground and is grounded to the AC board ground.

Now should the AC board be bonded or not? :?

Bill
Civil Engineers should not play with wires!
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
steveh41
Posts: 570
Joined: Mon Jun 14, 2010 7:16 pm
Location: Catheys Valley, CA
Contact:

Re: Bonding/Grounding an AC System

Postby steveh41 » Wed Jan 21, 2015 9:48 am

Bill,

Looks like you're making good progress on your build!

I have also been trying to sort out the somewhat confusing topic of bonding & stray current corrosion etc. My understanding so far is that the AC & DC bonding (non-current carrying) circuits should both go to the boat ground. Sounds like your AC board is already bonded to the boat ground through the generator.

Stray current corrosion when connected to shore power is another issue which to my understanding can only be safely avoided by either a galvanic isolator, which blocks low level stray ground currents, or an isolation transformer which isolates the shore power ground altogether. In that case, the AC neutral wire is grounded at the transformer, which becomes the power source for the boat and the shore power ground goes to the (isolated) primary shield.


Charlie Wing's book has some sample schematics... I have to refer to them before happy hour :lol:

Steve
The longest journey begins with a single step… then repeat as necessary!

User avatar
Bill Edmundson
Posts: 10441
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Bonding/Grounding an AC System

Postby Bill Edmundson » Wed Jan 21, 2015 10:13 am

Steve

Thanks for the reply. My generator is a portable that won't be in the boat very often. It also serves as standby at home and emergency for our condo at Gulf Shores. When I do take the generator on the boat, I plan to connect with the shore power cable and not directly to the AC block.

My thoughts are to let the shore power ground handle the bond when connected and then the generator bond will be there when I need it. DC will always have a bond. :?

Does any of that make sense?

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
steveh41
Posts: 570
Joined: Mon Jun 14, 2010 7:16 pm
Location: Catheys Valley, CA
Contact:

Re: Bonding/Grounding an AC System

Postby steveh41 » Wed Jan 21, 2015 11:36 am

That should work just fine. Having a portable generator is a great idea for flexibility... puts it to use where it's needed.
The longest journey begins with a single step… then repeat as necessary!

User avatar
raymacke
Posts: 732
Joined: Mon Apr 25, 2005 7:07 pm
Location: Marissa, IL
Contact:

Re: Bonding/Grounding an AC System

Postby raymacke » Mon Feb 23, 2015 10:09 pm

Bill,
This is one area I just couldn't seem to sort out. I read a bunch of stuff but the logic of much of it escaped me. Often it seemed to me to present more avenues to create problems than solve them. As it ended up I have no bonding plate on the exterior for the AC side. I assume the DC side is grounded through the O/B. I also have no through the hulls to worry about. There seems to be two thoughts and one is to bond and the other is to NOT bond.

This also leaves me with no lightning grounding protection. But reading really thorough examinations of lightning protection makes me think that a single small plate on the outside is hardly worth the effort.

See Link - http://www.marinelightning.com/science.htm#Problems

I am not saying what I have done is right. I am saying I can't figure out what IS right! I constantly keep an ear to the ground :wink: for more information and would certainly be willing to add/modify my system (or lack there of) if I find something that seems to make sense in my situation.

(BTW - I too use a portable generator and I have Charlie Wing's book)
So Many Rivers,
So Little Time....

User avatar
Bill Edmundson
Posts: 10441
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Bonding/Grounding an AC System

Postby Bill Edmundson » Tue Feb 24, 2015 5:21 pm

Ray

I've been looking at this for awhile, too. It seems the experts don't have a good grip on it either. I agree that the DC can go to ground through the engine. I'm not sure that I want the AC going that way.

Lightning? I don't think that a 12 or 10 gage wire would ever carry a strike! But, as I understand it, a strike is preceded by a static build up. In that case a static ground would prevent the build up. I don't think it is as much a risk on power boat as on sailboats.

BTW. If you want a bonding plate, I have one you can have. Don't remember how it happened. But, the bottom line is it didn't cost me anything.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
mrintense
Posts: 2516
Joined: Thu Jun 10, 2010 11:22 am
Location: Austin, Texas
Contact:

Re: Bonding/Grounding an AC System

Postby mrintense » Tue Feb 24, 2015 5:28 pm

Here's a question form someone who has absolutely no boating experience.

First off, I get it that DC can be bonded through the outboard.

Secondly, I assume most of this line of questioning has to do with bonding AC power.

So the question is this.

If one is out on the water and there is little in the way of cloud cover, is there much risk in lightning strikes? From some of the things I read it seems like you need to watch out for this every time you go out. But that seems utterly ridiculous to me. If you are out in bad weather , that is one thing, or if if you're boat has to stay outdoors, again a legitimate worry.

But f you only put your boat on the lake in good weather, is it still a concern?

Sorry of this sounds totally ignorant, but it's hard to know what the correct answer is when you have no basis for understanding the problem.
Carl
a.k.a. Clipper

Crafting a classically styled Vera Cruise named "Some Other Time"

Clipper's Vera Cruise Build

User avatar
raymacke
Posts: 732
Joined: Mon Apr 25, 2005 7:07 pm
Location: Marissa, IL
Contact:

Re: Bonding/Grounding an AC System

Postby raymacke » Tue Feb 24, 2015 6:11 pm

If one is out on the water and there is little in the way of cloud cover, is there much risk in lightning strikes?

Try Googling "blue sky lightning". It seems it is a real but somewhat rare. Usually they say if you can hear thunder you are within range of a strike as it can travel up to 25 miles from the clouds. Do I personally worry much about it when boating? No, but if you are incline to try to be 100% safety conscious I guess you might. Then again if that was the case you probably wouldn't ride in a boat to begin with - or a car, train, plane and for heavens sakes not a motorcycle. BTW I enjoy all of those things.......
So Many Rivers,
So Little Time....

User avatar
Bill Edmundson
Posts: 10441
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Bonding/Grounding an AC System

Postby Bill Edmundson » Tue Feb 24, 2015 7:24 pm

I'm with Ray. I guess I was thinking? about clean electrical for electronics.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
raymacke
Posts: 732
Joined: Mon Apr 25, 2005 7:07 pm
Location: Marissa, IL
Contact:

Re: Bonding/Grounding an AC System

Postby raymacke » Tue Feb 24, 2015 7:48 pm

Bill,
I might take you up on the bonding plate. Right now I do not believe my 120v AC system is properly connected. I wired it similar to residential wiring with the green wire connect to the same neutral block as the white wire. For marine use I believe the correct way is to keep them totally separated and connect the green to the seawater bonding plate. At least that is my understanding.

Why didn't I do this? - Two reasons. (again not sure if I am right here) First, from what I have read, the danger of my setup is always depicted when there is a fault on one of the AC appliances and its metal case or other conductive parts become energized. If you are touching it and also touch an item that IS grounded – like the engine or drive shaft – you become the conductor and electrocution can occur. I get this.

In my situation on the AC side I have a water heater, microwave, built-in battery charger and refrigerator. All of there are possible hot sources. BUT I can not see in my arrangement how I could possibly touch one of those and at the same time touch something that is actually grounded. None of the appliances are with in reach of the other (none are truly grounded anyway) and none of them are anywhere near the outboard or other truly grounded source. So is there a hazard? Doesn't seem so to me but please correct me if I am wrong.

The second reason is Galvanic Corrosion. If you separate the white and green wires and attach the green to a seawater bonding plate you have potentially created a Galvanic Cell which can lead to corrosion of underwater metals – i.e. the outboard. To avoid this I believe you then have to add a galvanic isolator or transformer to reduce the unwanted stray current. Cost for these seems to start about $200 and up for a 30 amp unit. Now considering what I have spent for the boat (don't ask) this isn't a tremendous amount of money but why spend if if there really is no gain. Is this undeeded complication?

This has been my dilemma. And I am very open to opinions and suggestions.
So Many Rivers,
So Little Time....

User avatar
Bill Edmundson
Posts: 10441
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Bonding/Grounding an AC System

Postby Bill Edmundson » Tue Feb 24, 2015 8:55 pm

Ray

Just let me know and send a PM with address. I think I once had it. But, can't find it.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
kens
Posts: 4445
Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: Bonding/Grounding an AC System

Postby kens » Wed Feb 25, 2015 2:43 pm

I been reading this with interest. As an experienced aviation avionics guy, we see similar things in the aviation world.
The really 'smart' guys (i.e. engineers) protocol some different things on different prints. It doesnt seem to be a protocol that that is cut & dried, nor standard. Different drawings deal with grounding and bonding in different ways.

For example, they always say 'never put AC & DC grounds together, however, the ultimate ground is always the airframe. it dont make sense.

There is a difference between grounding and bonding.
A ground is a electrical return path from a device such as light bulb, radio, appliance, etc. Ground is required for said device to work. A bond is not required for a device to turn on.

A bond is to connect all devices (and grounds) such that all of the total system is of the same voltage 'potential'. In avionics we deal with this in millivolts, and miliamps. We bond everything, in effort to ground out noise in all of it, shielded wires and so on.

In all cases marine or otherwise stray voltage evolves from some kind of fault. As Bill mentioned regarding 2 boats in a marina having a galvanic reaction. The start of that is 1 or more devices (boat, power box, extension cord) with a 'stray voltage' i.e. a fault. In our aviation the stray voltage may show up as noise in the radio, in the marina it may be galvanic corrosion. One way to bleed off stray voltage is to provide 'bonding'.
An even better way to deal with stray voltage is to find the fault and fix it.
But, that is not always possible.
Sometimes you can measure millivolts and never figure out where it is coming from.

Sometimes you hear of fishing boats that simply cannot catch fish. Mostly, they are outboards, and boats with terrible corroded electrical system.
Whats the fish got to do with that you say???
.......The boats system is grounded to the outboard, which has a alternator, which is to the motor , which has its lower unit in the water, spreading out its corroded systems stray voltage all around the boat. Fish can sense that and run like hell.
Call it galvanic corrosion, call it scaring the fish, either way, good clean grounds minimize all this commotion.

Good clean grounds minimize the 'potential', and 'bonding' drains off all leftover potential.
Stray voltage promotes corrosion, which starts the whole process all over again.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

User avatar
Lowka53
Posts: 1938
Joined: Fri May 14, 2010 11:47 pm
Location: Ogden, Utah-Jubilee build
Contact:

Re: Bonding/Grounding an AC System

Postby Lowka53 » Thu Feb 26, 2015 6:25 pm

:? I worked in navel electronics while in the navy I have read and reread all these book on systems and it is Greek to me no one person seems to have the same answer and all go into mulitpul details trying to explain themselves. bottom line is do you want to have the chance of throwing an 110 ac current into the surrounding waters. If I remember right most portable generators are closed circuits to begin with not requiring a ground some of the big one in the military was grounded but it was not the rule for all. So in my option and not a expert one that you would be fine using a closed system by all means do not ground to the same system as your dc set up :shock: :?
Don't be afraid to attempt anything. You might surprise your self in the attempt.
http://www.facebook.com/Home.Made.Boat.Building
Bon Voyage-"Wild Flower" 40' house boat being built
14' Mr John-being built
32' Supper Huck-in design

Rod H

User avatar
steveh41
Posts: 570
Joined: Mon Jun 14, 2010 7:16 pm
Location: Catheys Valley, CA
Contact:

Re: Bonding/Grounding an AC System

Postby steveh41 » Thu Feb 26, 2015 7:02 pm

Found a simple diagram of AC-DC bonding for boats...

http://assets.bluesea.com/files/resourc ... ection.pdf

It shows interconnection of the AC and DC bonds with discussion of reasons. It seems there are several ways to skin this; just have to find one that makes sense and stick to it.
The longest journey begins with a single step… then repeat as necessary!

User avatar
raymacke
Posts: 732
Joined: Mon Apr 25, 2005 7:07 pm
Location: Marissa, IL
Contact:

Re: Bonding/Grounding an AC System

Postby raymacke » Fri Feb 27, 2015 8:06 pm

Ok! Who started this thread? It is making my head ache!

This has sent me back to the books for a review as it has been over five years since I tried to understand all of this. I have looked at several sources on information but Charlie Wing’s book “Boatowners Illustrated Handbook of Wiring” is the main resource. But the chapter starts out saying, “Bonding is a controversial, and often poorly understood wiring practice.” Doesn’t inspire confidence does it. Also, there is a debate whether to bond or “not bond and isolate.” This is my understanding of the situation. If anyone see something wrong PLEASE point it out! –

When speaking of boat electrical systems, “bonding” is normally referring to the DC side not the AC. As kens said the “ground wire” is the return current wire of DC system and is not the same as a bonding wire. The bonding wire is considered a “non-current carrying conductor” and is a bare or green wire. To confuse the issue the term “ground” (not grounding wire) is defined as “the potential, or voltage, of water in which the boat is immersed.” I would call it the “earth ground” just because I feel it better clarifies what it is. It also states the “bonding” conductors are separate and in addition to the “ground wires” of either the DC or AC systems.

The purpose of the bonding line is to connect all exposed metallic non-current carrying parts to the ground (negative) side of the DC system. It is usually depicted as a heavy line running down the length of the hull with cables branching off it to connect various items. Included are engine, metal fuel tanks, a ground plate, any zincs installed on the outside of the hull, sail boat mask if metal, any metal through the hulls, the negative pole of the batteries, any electrical panels that are metal and so on. Also, it states the green wire of the AC system should indeed be connected to the bond line. That surprised me as I didn’t remember it that way but that is what it says. The idea is stray voltage from any of these will be directed to the earth ground at the ground plate.

The controversy stems from the possibility of this system actually encouraging stray-current corrosion. It seems it more or less becomes a galvanic cell and can attracting stray current, emitting stray voltage or even producing it. The system needs to have sufficient zincs employed to serve as sacrificial metal. The less noble metal, in this case the zincs, become the receiving side of the stray current and this is important because the receiving side is the one that will be deteriorated by stray current corrosion. Also, there is a controversy about bonding metal “through the hulls” on a wooden boat. Many contend the electro-chemical process going on can dangerously soften the wood around the fitting. Nice.

The alternative is not to bond and isolate. What is meant by this is underwater metal items are isolated and not bonded. On an I/B the prop and shaft are isolated by using an insulating coupling and a zinc added to them for protection if needed. The motor and other exposed metal surfaces on the interior of the hull are bonded together but not connected to anything that can conduct any stray current to the outside wetted hull. The one exception is a ground plate to attach to the radio and mask if so equipped. My understanding is this still works because for a galvanic cell to be created you need to have a entry AND exit point for current to flow. With this there is just one point – the ground plate as everything else is isolated. One of the arguments against this method is there is minimal lightning protection. But the counter argument is if you use a large grounding plate it will serve sufficiently.

But now the real world I live in. For O/B or I/O boats isolation is not possible – just can’t separate the wetted outdrive from the DC electrical system. The ground side of the engine is the ground side of the entire DC system. So bonding and adding zincs seems to be the only solution. But is it?

For me I thought there was another. I have no through the hulls. I have no grounding plate. The only metal in the water I have is the outboard, which is protected by zincs. So in my estimation I have only one entry/exit point and a galvanic cell cannot be formed. Am I missing something here or is this correct?

Also, I do not have my DC and AC ground or bonding systems connected and hadn’t plan to do so – and this is why. When I introduce shore power I have now added a possible second point of entry. If the bond wire from the DC side is connected to the green wire of the AC side, current could then flow from the outboard through the bond system and out to the shore power earth ground (green wire). If I understand correctly this can be remedied by a Galvanic Isolator, which allows AC current to flow but blocks DC current. But if I keep the system separate do I need this?

I could go ahead and bond the DC items but what do I really have. There is the outboard and the battery but I really can’t think of anything else that has a metal housing I need to attach. My tanks are plastic so I don't have to worry about them so is there then a point then?

So I am think with my present system it is effective in preventing stray current corrosion but there are a couple of problems. The first there is zero lightning protection. And I think each person has to weigh and make a decision about this. Do the research – this is a whole other complex problem.

The other is situation maybe my Achilles’ Heel and if I didn't have one I believe I would be good to go. BUT the only place I can see a possible problem caused by the bridging of the two electrical systems is the shore power charger. I need to check and see if the AC and DC sides are totally electrically isolated. If they are not I have the two access points that should be avoided.

So I think I am on the right track and then steveh41 post the above link ( Thanks a lot steve - I hate when facts get in the way of my thought process :shock: ) - http://assets.bluesea.com/files/resources/technical_briefs/grounding_circuit_protection.pdf Take a look as this is important if you have a built-in charger. BTW - I can find nothing in Wing's book about this.

So now it appears, since I do have an on board charger, I do indeed need to bond both the AC & DC sides. I also need to provide a cable capable of handling 50 amps (my fuse size) between the charger and the DC busbar at the battery. I do then need the ground plate to attach to the bond line. I do need to separate my AC white and green wires in to two separate busbars.

At least I think that is what is needed. Like I said this is complicated stuff. Happy to hear others thoughts and opinions on this. Like I said if you se something wrong in my long winded post PLEASE correct me. I certainly do not want to be offering bad info.
So Many Rivers,
So Little Time....


Return to “Electric Power & Systems”

Who is online

Users browsing this forum: No registered users and 2 guests