Inverter Grounding Problems

[Maine Sail]

Good point!

Electrically it does not matter much "where" it goes as the AC protective Earth bus and the DC ground bus are at the same potential because they are tied together. Where it matters is being sure you maintain the proper wire size to shunt a fault to Earth and tip a fuse or breaker before igniting a wire..

 

[Bill Roosa]

You do want to be mindful of creating multiple ground circuits to the various ground busses.
The wire diagram should look like a spider for each load to ground buss (2 spiders AC and DC) and not have any connections between the spider legs. The two busses should only be connected at one point also.

 

[Witzend]

You do want to be mindful of creating multiple ground circuits to the various ground busses.
The wire diagram should look like a spider for each load to ground buss (2 spiders AC and DC) and not have any connections between the spider legs. The two busses should only be connected at one point also.

Yea, that was my first concern, creating a ground loop. I also question why the DC and AC grounds are connected together in the first place? Doesn't this open yourself to the possibility of putting AC on the DC ground? Say with hooking up to a marina with the ground and hot swapped. I have seen it before.

 

[Witzend]

I checked to see if my AC and DC grounds are connected. They are not.
So the question is: Is my boat wired incorrectly?

 

[kenn]

I checked to see if my AC and DC grounds are connected. They are not.
So the question is: Is my boat wired incorrectly?

Potentially yes. On the boat, AC ground and DC ground should be electrically connected.

If you have a galvanic isolator, where is it installed?

 

[Witzend]

Potentially yes. On the boat, AC ground and DC ground should be electrically connected.

If you have a galvanic isolator, where is it installed?

Yes there is one, I will have to see how it is wire in. Never really chased it out before.

So why do you want to connect the AC ground to the DC ground?
What are the reasons?
I can think only of reasons why I would not want it connected. Such as opening yourself to the possibility of putting AC on you DC ground.

 

[Witzend]

http://marinesurvey.com/yacht/ElectricalSystems_AC.htm#Grounds

Grounds and Grounding
One of the least understood aspects of a boats electrical system, and the most troublesome, is the proper method of grounding. That we often get questions of whether AC or DC electrical equipment should be grounded to the boat's bonding system is illustrative of this point. AC and DC grounding systems are two separate systems, for distinctly different reasons. If you don't understand these systems, you run the distinct risk of creating a disaster. Actually, there are four separate ground systems: DC ground, AC ground, AC grounding (or bond), and the vessel's bonding system. You can add to this lightning and HF radio grounds as well. Do you know the principles of each? Are you sufficiently confused to discourage you from doing your own wiring? I hope so. For unless you understand each thoroughly, you're headed for trouble.

 

[Maine Sail]

I checked to see if my AC and DC grounds are connected. They are not.
So the question is: Is my boat wired incorrectly?

All Catalina's leave the factory wired to current USCG, ABYC and NMMA wiring standards and there SHOULD be an AC/DC ground tie. Our 310 had one. Usually a single green 10GA wire between the AC portion of the panel and the DC Bus..

If your boat does not have an AC/DC ground tie then no it is not wired correctly.

 

[kenn]

So why do you want to connect the AC ground to the DC ground?
What are the reasons?
I can think only of reasons why I would not want it connected. Such as opening yourself to the possibility of putting AC on you DC ground.

Actually, that's why you want AC and DC grounds connected. Without the connection between the AC ground and the boat, it's possible to have a fault where the AC hot touches the boat ground, and the boat is now hot. ( This is part of how an ESD hazard is created)


http://marinesurvey.com/yacht/ElectricalSystems_AC.htm#Grounds

http://marinesurvey.com/yacht/ElectricalSystems_AC.htm#Grounds

Here's the next paragraph:

The AC ground and grounding systems are "free floating," meaning that they do not ground on the vessel, but only to shore. The ground, or neutral, is a current carrying conductor, and is the source of many troubles because people do not regard it as such. The grounding, bond or green wire is the "safety" intended to channel current safely to ground in the event of a short circuit. Both of these circuits are capable of conducting current and can be the source of electrolysis when there are system faults with the dock or marina wiring. This is very easy to test for.

This paragraph is close to gibberish. The sections I highlighted in red... oh man... neutral is NOT called ground, the AC ground is NOT called bond. Confusion central.

That's as far as I read. He might be smart, but it's not evident from that paragraph. Absolutely don't take this guy as authoritative on the subject of boat wiring, til his editor pays a visit.

My go-to sources are ABYC, Nigel Calder, Ed Sherman (ABYC instructor) and of course MaineSail.

 

[Bill Roosa]

The definitions for 220 volt circuits (110 is just one or the other "hot")
+110 volts AC - red - hot
-110 volts AC - black - hot (180 degrees out of phase with the red hot so 220 between them)
0 volts AC- neutral - white the 'return current carrying "ground"' for 110 volt AC circuits
0 volts AC/DC - safety ground - green or bare copper not a current carrying conductor

12 volts DC + red (oops we have a problem on 220 rigged boats on 110 boats the hot at the shore power outlet changes color on the boat to black so 110 boats are OK color wise)
0 volts DC - black (this is where we have some issues on a 110 wired boat)
0 volts DC bonding - green not a current carrying conductor
0 volts lightning ground - green not a current carrying conductor
All the grounds/bonding should connect a a central location
The neutral should connect to either the ground on the shore power at the end of the dock or for all on board sources of AC at the source

 

[Stu Jackson]

I checked to see if my AC and DC grounds are connected. They are not.
So the question is: Is my boat wired incorrectly?

witz, where did you look? Really, this not a trick question and I am not trying nor intending to be insulting in any way shape or form.

Maine Sail noted how Catalinas are wired. Mine's fine.

So where is it that you do NOT have an AC and DC ground connection? Was you boat purchased new or did it have a PO?

 

[Witzend]

I Ohmed between the AC and DC Bus bars... Open. I need to get back to the boat and see if the Galvanic Isolator has replaced this connection.

 

[Stu Jackson]

witz,

Unless I'm really missing something BIG picture, the GI shouldn't have anything to do with it.

 

[Maine Sail]

I Ohmed between the AC and DC Bus bars... Open. I need to get back to the boat and see if the Galvanic Isolator has replaced this connection.

The GI does not replace that connection. The AC/DC ground tie is still required.... I suspect someone disconnected it somewhere along the way...

 

[Witzend]

Thanks for the info, I will reconnect, but my gut is telling me to keep the systems separate. I understand the possibility of the AC hot coming in contact with some casing that is on the DC Ground and then making that hot, but I think it is equally or more likely that you plug into a marina that has it's ground hot. I guess the best protection is before you connect up, get the meter out and make sure it is wired correctly.

 

[kenn]

I think it is equally or more likely that you plug into a marina that has it's ground hot.

Hard to say with certainty. Given that the grounded twist-lock has been a shore-power standard for many years, I'm inclined to expect correct marina wiring in just about all but the most decrepit mon'n'pop marinas. If anything, I'd be more worried about failing connectors leading to high-resistance connections (... leading to connector burn-up) or disconnected grounds.

But as you said, it's easy enough to check all this when you first hook up.

Witz, if every boatowner put as much thought into their AC system as you are, there would be fewer problems. As you know, that's not the case, and marine shorepower systems require more checking and maintenance than land-based AC wiring. Our only course is to codify safe practices into published standards and then insist on their application.