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: 10427
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Bonding/Grounding an AC System

Postby Bill Edmundson » Fri Feb 27, 2015 8:34 pm

:? :cry: :roll: :shock: :? I've decided what I'm going to do, right or wrong. The main DC panel will have a line to the earth ground. All metal parts associated with the fuel tanks will go to earth ground. The AC system will ground through shore power. When I'm on the generator, it will use the shore power cable. The generator will attach to the earth ground.

I confess! I started this. The more I read the worse it gets. It seems we're literally in the same boat on this. I don't think there are any experts, just opinions.

Anyway, I'll have a static ground for the DC and a place for a ground fault to go on the AC side.

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

User avatar
jamundsen
Posts: 1494
Joined: Tue May 26, 2009 12:47 pm
Location: Lakeland, Fl
Contact:

Re: Bonding/Grounding an AC System

Postby jamundsen » Sat Feb 28, 2015 9:20 am

After reading all this I think I'm going to build a row boat. :lol:
John Amundsen
Monte Carlo
Lakeland,Fl

Work tends to get in the way of boat building

User avatar
chugalug
Posts: 1061
Joined: Sat Nov 29, 2014 5:01 pm
Location: top of mn.

Re: Bonding/Grounding an AC System

Postby chugalug » Sat Feb 28, 2015 10:09 am

:D You'll have to let us know how it works out for you ;then you're the expert!Iwould have thought you could have found something about it on the Jamestown Distributor site.They have lots of videos on things.Maybe you'll have to drag around a few zinc guppies too. :?:was just on Jamestown how to's had interesting article on GFCI's
Working on regular-sized Bo-Jest


"If it's not crooked,It's not mine

User avatar
kens
Posts: 4441
Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: Bonding/Grounding an AC System

Postby kens » Sat Feb 28, 2015 8:48 pm

All you guys are correct, Ray, Bill, you guys are just as expert as the engineers that write the white papers.

I will attempt to simplify my experiences,

The 'ground' is required to return a circuit that makes a device work. We all understand that. Leave this part alone, there is little discussion here. A light bulb dont work without a ground. ( AC or DC dont matter here) its irrelevant for discussion here. A ground is the return circuit, period. (for discussion)

The grey area is 'bonding'. This is the part that confusses us all. Think this way:
Take the science experiment of the lemon and the penny, to make a small battery. You guys remember that? (or any similar kitchen battery experiment)
This little lemmon/penny battery is in-sufficient to light up any bulb or activate any device, but the voltage can be measured. Correct????

Well, there you have it, it is called a 'stray voltage'

This 'stray voltage' is in fact enough to promote galvanic corrosion. There aint no light bulbs gonna come on, BUT, you might see some insideous corrosion in places you never thought of.
"BONDING" is the solution to dilute the effects of the lemon/penny battery,
And in the boat world salt water is the duplicate of the lemon. It is the acid to make the kitchen battery work. Fresh water not so much so. But, salt water is a conductor. Pure clean water, H2o, is a insulator. Maybe this confuses folks because water is a insulator. It is only the minerals suspended in the water that make a conductor (i,e. the battery acid)

The main reason you do 'bonding' is because the water your boat floats in aint pure H2o.
And in Bills case, if he grounds to shore power, then he is reliant upon the marina's maintenance and protocol to be the 'bonded' ground.
Who do you trust????
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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 » Sun Mar 01, 2015 12:05 am

The problem with all of this is bonding works to protect from corrosion sometimes and other times is actually causes it. A properly bonded system will protect the submerged metal items from stray voltage produced inside the hull. Perhaps this is a bad bilge pump or a terminal strip that has gotten wet or another electrical fault of some type. The stray voltage will be attracted to the bond line because it is the path of least resistance and flow out without causing any corrosion. That's good!

BUT if the stray voltage is coming from another boat nearby or a fault on a dock it will enter bonding system at the ground plate and flow to the least noble metal. It does this because the bond line offers less resistance for the electricity than flowing through the water.. SO the bonding system has "attracted" the stray current!' The least noble metal is usually a prop, aluminum O/B or hopefully zincs mounted somewhere and they will corrode. But had the system not be bonded this this would not have occurred. So I guess the question in this situation is who do you trust more - your wiring job or someone else’s? This is why many preach the “unbond and isolate” method.

But lets say you went with bonding and know your wiring is all perfect, all the boats around you at the marina are 100 percent perfect and the dock also is fully in compliance. GREAT, nothing can go wrong now!

Well, hold on skipper all is not well. Because now you have your submerged metal bonded and the boat next to you is bonded AND those bond lines are connected to the shore power by the green wire of the AC system. That means you boat’s underwater metal is directly connected to his. So what, you say? Because now we have formed a galvanic cell with one boat serving and the anode and the other the cathode. Even if the submerged metals are the same they will still suffer damage by what is called “impressed-current corrosion” due to the presence of a voltage field in the water.

So now what? Simple, get out your wallet. Go online and order either a galvanic isolator or galvanic transformer. These allow AC to pass through the shore power line but block the DC which is what is causing the problem. OR unbond and isolate. WAIT - that doesn’t work with an O/B or O/I because we can’t unbond the submerged outdrives from the rest of the interior bonded items.

So what is the answer? Damn if I know....................... :?
So Many Rivers,
So Little Time....

User avatar
chugalug
Posts: 1061
Joined: Sat Nov 29, 2014 5:01 pm
Location: top of mn.

Re: Bonding/Grounding an AC System

Postby chugalug » Tue Mar 03, 2015 11:30 am

App http://www.circuitwizard.bluesea.com help? Also check article on web letter #101
Working on regular-sized Bo-Jest


"If it's not crooked,It's not mine

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 » Sun Mar 08, 2015 9:23 pm

Still been obsessing about the AC/DC ground/bond thing. Spent several more hours trying to better understand the forces at work. Here is my thoughts as they relate to the system in my boat (your boat may well be different). I know this is NOT to ABYC code but struggling to see why it is not a viable solution.

As I see it there are two major concerns – corrosion and electrocution. First, I will address electrocution.

Did some checking this weekend and confirmed my DC ground is NOT connected in any way to the AC white or green. Also, the AC white is NOT connected to the AC green. The greens are all hooked together but essentially go nowhere. I know this is not right but left it that way because I could not see any possible way I can touch an AC device and at the same time another item that is grounded. No AC units are in arms length of another and there are no exposed DC grounds within reach of the AC equipment. There is lots of wood, a little plastic and next to no metal - none of which is grounded. For the life of me can't see how a failure of one of the AC devices could lead to a electrocution when there is no return path to ground.

I understand there is a possible fire hazard IF the battery charger shorted out and sent high amp 12v through the small AC green wiring (bond) as it tries to go to ground. But in my case the green goes nowhere. I guess the exposed metal of the AC devices (like the water heater case) could be energized with 12 volts but if it can't go to ground to me it seems like there would be no load to cause heat.

One side of my brain says I should add a ground plate to the hull exterior and tie the green AC side to it. This would provide a path for an AC fault in any of the devices to go to ground. I would though need to add a Galvanic Isolator to prevent “impressed-current corrosion”. But the other side of my brain says I have already decided a fault in the boat won't cause a shock (see above) so is this necessary? PLUS if the ground plate receives an AC fault and transmits 120V outside the hull into the water it will be creating a serious hazard for anyone swimming along side the boat – which we do often. So now the “safety feature” may well electrocuted me!

ANYONE – any thought on this? If this logic is flawed PLEASE point it out.

Now for corrosion-

Corrosion is really only a big concern if you plan to regularly moor at a location where there are other boats – like a marina - or if you sit in the water and have a shore power charger to maintain a battery. If that is not the case it shouldn't be a problem but my use may well include this.

Since I have decided to isolate my DC side from the AC side (no bonding) AND the outboard represents my only submerged metal surface stray current can't shortcut through the hull (only one entry or exit point) nor can a galvanic cell form because of dissimilar metals (other than within the engine itself and for that it has zincs). Also since the AC system is NOT connected to any submerged metal “impressed-current corrosion” cannot occur. So, in my mind, the corrosion problem is not a concern.

But again this is just my layman's thoughts on how this all works. Would appreciate other opinions.
So Many Rivers,
So Little Time....

User avatar
chugalug
Posts: 1061
Joined: Sat Nov 29, 2014 5:01 pm
Location: top of mn.

Re: Bonding/Grounding an AC System

Postby chugalug » Mon Mar 09, 2015 5:58 am

:D Jamestown Distributors web site has articles on gfci's and electric set ups if you look in their info archives.Saw one recently about stray voltage and swimmers.
Working on regular-sized Bo-Jest


"If it's not crooked,It's not mine


Return to “Electric Power & Systems”

Who is online

Users browsing this forum: No registered users and 2 guests