Installing New Inverter - Do I connect the Ground?

[NickBee]

Hi,

I am installing a 2000W inverter-charger on my sailboat. When testing the 120V on my electric outlet, I notice the Open Ground (this is normal)... nothing is connected.

My question:

When connecting the 120V exit from my Inverter-Charger, Do I connect also the 120V Ground to the common ground of around (the motor)? If so, it's not dangerous when I'll use it in charge mode?

tx
Nick

[dfelsent]

https://stevedmarineconsulting.com/i...installations/

Short answer:
Your inverter should have a ground stud as part of the DC power connections. You need to tie that with quite a heavy wire to your DC ground. This is different from the DC minus from the battery.

[NickBee]

Thanks, very good information on this website.
If I understand well, I don't need to connect the 120V Ground of the Secondary pannel Breakers (After the Inverter) to this DC Ground. Just the ground strud of the inverter to the DC Ground (connected to the main body of the motor).

[smac999]

The green ac ground from the inverter goes to the ac panel ground bus. You should not have an open ground at outlet.

It will also have a chassis ground and dc neg. which both go to dc ground.

The boat should also have a connection between. Dc ground and ac ground.

Also the inverter when inverting needs to join ac ground and Ac neutreal. Marine inverters will do this

[StoneCrab]

So many grounds. I agree with the previous post.

Basically, you need grounds to protect the users if a wire breaks in the appliance or something goes wrong. The AC grounds back up the neutral wires as a return path for the current should something happen. You never want to be part of that return path, so always use three prong plugs and make sure that your outlets are grounded.

The inverter DC side needs to be tied into the ships battery system and DC bonding system. That gets a little more complicated in that you don't just want to be grounding everything everywhere. It will create current paths that you don't want. Sometimes these are called ground loops.

You need DC negative bus bars for return power and a separate system for bonding thru hulls, prop shafts and sensors together so that your boat isn't leaking current into the water around the boat and destroying itself by electrolysis.

If you have all that mastered, we can start a thread on RF grounding and the counterpoise requirements of most radios. These grounding systems will typically have ac and dc components. If you see any weird ground straps with capacitors across a gap, those are draining your RF ground system.

Grounding systems on boats require some imagination.

[NickBee]

Good! Thanks a lot for your reply! I will analyse my actual grounding system and add components accordingly.
Nick

[Davidla]

Originally Posted by dfelsent

https://stevedmarineconsulting.com/i...installations/

Short answer:
Your inverter should have a ground stud as part of the DC power connections. You need to tie that with quite a heavy wire to your DC ground. This is different from the DC minus from the battery.

Sorry but I have to disagree here. You may have a bonding system separate to a 12v DC system, but you will not have a DC ground in any shape or form. There is in effect, no such thing as a DC ground or it is very rare in boat systems and would require a three wire DC system similar to an AC one to be implemented.

Why is there is no such thing as a DC ground? It is incorrect terminology and at the risk of great flaming here is why:
When you look at a simple DC circuit you have a wire leaving the positive terminal of a battery going to (through) a load then returning to the negative terminal of the battery. That is, you have a complete path from positive to negative and no ground circuit involved.
All electrical circuits AC or DC have to leave the source and return to the source to make it work. Yes your negative return wire will have zero volts (because the load used it all up - this is true of all complete circuits BTW).
It is exactly the same in a boat. When you refer to grounding a load on a boat you are simply connecting it back to the Negative battery terminal. Prove it to yourself simply by "grounding your load" as you refer to it, then disconnect the negative battery terminal and check if your load still works. Of course it doesn't because there is no return path to the battery.
You don't have a DC grounding system on a boat - you have a complex path back to the battery negative terminal.
Completely different to an AC circuit which has a hot and neutral wire (analagous to positive and negative DC) and you have a ground wire for safety. Which conducts a shorted neutral wire back to earth (ground, same thing).
One thing you should NEVER do is connect anything related to your DC circuits to your bonding system. Otherwise you are creating a path for electrolysis.

You are correct when you say you need to connect the DC case "ground" wire back to the boat, but it will go to the DC negative circuit. There is no alternative.

[Davidla]

Originally Posted by StoneCrab

You need DC negative bus bars for return power and a separate system for bonding thru hulls, prop shafts and sensors together so that your boat isn't leaking current into the water around the boat and destroying itself by electrolysis.



Grounding systems on boats require some imagination.

At the risk of annoying people, electrolysis is completely different to galvanic corrosion and galvanic corrosion is reduced with a bonding system. A bonding system will do nothing to protect your boat from electrolysis; which is man made versus galvanic corrosion which occurs naturally.
Again

[thomm225]

What if your boat doesn't have a ground?

No motor. Or the outboard is raised?

My inverters our hooked to the batteries only.

[Davidla]

Originally Posted by thomm225

What if your boat doesn't have a ground?

No motor. Or the outboard is raised?

My inverters our hooked to the batteries only.

As I said, your boat does not have a ground, your inverter chassis ground is provided that in the event an AC or DC fault develops which connects to the chassis and thus makes it live, the resultant current flow will pass to the DC negative system. You may or may not have a path to your engine there, but it in effect is still part of the DC negative path. This is why there is an engine DC negative connection back to the battery circuit.
Any other AC fault should be managed by GFCI or RCD depending on your language. The reason the wire for this connection has to be so large is because of the DC current capable of being drawn by the Inverter.

[Sailmonkey]

Originally Posted by Davidla

At the risk of annoying people, electrolysis is completely different to galvanic corrosion and galvanic corrosion is reduced with a bonding system. A bonding system will do nothing to protect your boat from electrolysis; which is man made versus galvanic corrosion which occurs naturally.

Again

How about we call it what it is, stray current corrosion.

Unless you really mean it’ll cause hair removal or production of oxygen

https://en.m.wikipedia.org/wiki/Electrolysis

[Davidla]

Ah, but stray currents can be caused by galvanic corrosion or by incorrect wiring pushing a DC current out of your vessel and the effect of this corrosion is a lot faster than by galvanic. Lets call this electrolytic corrosion?

[thomm225]

Originally Posted by Davidla

As I said, your boat does not have a ground, your inverter chassis ground is provided that in the event an AC or DC fault develops which connects to the chassis and thus makes it live, the resultant current flow will pass to the DC negative system. You may or may not have a path to your engine there, but it in effect is still part of the DC negative path. This is why there is an engine DC negative connection back to the battery circuit.
Any other AC fault should be managed by GFCI or RCD depending on your language. The reason the wire for this connection has to be so large is because of the DC current capable of being drawn by the Inverter.

Just making the point that all boats don't have an engine ground to the water.

My inverters are just hooked up straight to the batteries.

The whole thing is "floating" so to speak.

[Davidla]

Apologies, I thought you were referring to something else. Yes in effect all inverter supplies are floating when not alongside and plugged in to shore power.

[Davidla]

One other thing I forgot to mention in an earlier post. Best practice seems to be that inverter AC loads should have a separate neutral bus from shore power Neutral loads. Makes sense given the use of ground to neutral internal in the inverter when not connected to shore power. This happens as part of the auto transfer in my victron at least.