Inverter installation questions - neutral, ground, GFCI, etc.

[prskier17]

Hello, I recently completed some upgrades with my electrical system and am now a bit uncertain with my inverter.

Here are the relevant sailboat details:
- Sailboat is 2019 Corsair 970 trimaran
- There is NO grounding plate, or any metal objects in contact with the water on this boat, with the exception of a 9.9hp Honda outboard when it is lowered.
- There is no keel on this boat, rather a fiberglass retractable daggerboard.
- There is no shore power on this boat and I will not be adding it.

The electrical system includes:
- 2x 100Ah Renogy LiFePo batteries for house
- 18Ah AGM battery for starting outboard
- 200W of 12vdc solar
- Renogy DC-DC MPPT charger
- Renogy 1000W inverter - https://www.renogy.com/1000w-12v-pur...e-new-edition/

Attached is the diagram of this system. Not shown in that diagram, I do have the inverter chassis ground wired to my DC-negative bus. Here's were I have some uncertainty. The inverter does not have an internal AC Neutral to ground bond. The manual states: "The neutral (common) is not bonded to the chassis ground. Therefore, when chassis is connected to ground, the neutral conductor is not grounded. At no point should the chassis ground and the neutral conductor of the inverter be bonded. Bonding the chassis ground and the neutral conductor of the inverter or connecting the inverter to household AC distribution wiring will damage the unit and void the warranty. For more information regarding grounding, users and/or installers must consult with the Local and National Electric Codes (NEC) for more specific grounding regulations and suggestions as they can change per scenario."

I have been searching and reading for this scenario and believe several details need to be considered:

1. My boat is not grounded.
2. I do not utilize shore power.

Given this, is a floating neutral OK? I have a (minimal) understanding of what is written for marine electrical, but the references I've found always include shore power and ground bonding to inboard engines, etc. It seems my boat is isolated. I also sail in freshwater. Any insight into my situation would be much appreciated.

[Statistical]

As long as you don't connect to shorepower (or generator) you are fine. The manual is unfortunately using vaguely written terms but to be clear there are two seperate grounds.

The DC grounding connector. There is a lug on the chasis of the inverter. This is for attaching a DC (not AC) grounding connector. This provides a backup protection in case the DC negative connection fails or the case becomes energized with DC power through an internal fault. So in your DC diagram above you would have a third wire connecting the inverter. Ideally this goes to a seperate DC grounding bus with all other ground lug connections which is then connected to the primary DC negative bus which is connected to the DC negative on the battery. However on smaller systems the DC grounding connector can be connected to the DC negative bus directly. It may seem weird that you have two DC connections (DC ground and DC negative) going the same place but much less AC ground the DC ground is a non current carrying conductor. It is simply a safety measure and would only carry current in an emergency. If the case became energized without a DC ground conductor if you touched it while say standing in bilge water you would become the DC ground conductor.

The AC ground (third pin on NEMA outlets). The AC ground and neutral are bonded internally already in the inverter. There isn't anything else you need to do and in fact as the manual indicates you should NOT connect AC ground to DC ground/neg. You also if using AC wiring not just the built in outlets should never connect AC ground to AC neutral anywhere on the boat. AC ground and neutral should only happen at one location and that is the source in this case the inverter.

Note due to #2 and the lack of neutral-ground switch this inverter can NEVER be connected to shorepower or generator. It can't be used for other reasons as well (no ability to sync to the grid AC timing). Now from your described situation that likely isn't a problem just keep in mind in the future if you ever do upgrade to shorepower or generator this inverter can not be connected to same circuits powered by shorepower or a generator. It could be used as an isolated inverter for circuits powered only by this inverter through battery. If all that seemed overly complex you can ignore it just keep in mind if someday you add shorepower or generator you need to revisit your design but you are fine until then.

Side note: I am fairly certain this inverter is not creating a floating neutral and that inside the inverter the AC neutral and AC ground (not DC ground) are connected. The wording in the manual is vague but it is saying the neutral and AC ground are not and should not be connected to DC ground. One way to verify is to use a multimeter and test for connectivity between the neutral and ground on the outlet. Likewise a connection between AC ground and DC negative or DC ground will show no connectivity.

[prskier17]

@statistical, thank you for the detailed response! My diagram had an omission and I do have a ground wire connecting the chassis lug to DC negative (updated diagram attached). Per the inverter manual, I used a 14ga wire for this but I'm wondering if I should increase this to 6ga?

I will test for continuity between the AC Neutral and AC Ground, thank you for that information.

I understand that I cannot use this setup with any other source (shore power or generator) and this is not an issue.

Again, thanks of the detailed response!

[Statistical]

Originally Posted by prskier17

@statistical, thank you for the detailed response! My diagram had an omission and I do have a ground wire connecting the chassis lug to DC negative (updated diagram attached). Per the inverter manual, I used a 14ga wire for this but I'm wondering if I should increase this to 6ga?

I will test for continuity between the AC Neutral and AC Ground, thank you for that information.

I understand that I cannot use this setup with any other source (shore power or generator) and this is not an issue.

Again, thanks of the detailed response!

No problem.

ABYC standard which I think is reasonable is the ground conductor should be no smaller than one size smaller than the positive conductor.

11.17.2 DC Grounding Conductor
11.17.2.1 A DC grounding conductor shall not be smaller than one size under that required for current carrying
conductors supplying the device and not less than 16 AWG (see FIGURE 5 and FIGURE 11).
11.17.2.2 ROUTING
11.17.2.2.1 The DC grounding conductor shall be routed from the device to the engine negative terminal or the DC
main negative bus by one of the following means:
11.17.2.2.1.1 the DC grounding conductor shall be routed together with the current carrying conductors as a third
wire; or
11.17.2.2.1.2 the DC grounding conductor shall be routed as a separate conductor.

11.17.2.2 seems highly redundant to me given I can't imagine a realistic scenario which doesn't fit one or the other of the allowing routing methods.

[prskier17]

The DC inverter leads are 4ga. I'll replace the chassis ground with 6ga. Thanks!

[smac999]

most smaller inverters. like anyone with a socket instead of a terminals for hard wiring. has a floating ground.

so do most portable gennys. any boat using a honda 2000 etc on the swimgrid. is making the whole boat a floating ground.

if it wasn`t safe... they would not be sold that way.