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@JBPohle, where are the neutrals abandoned? If the neutrals are abandoned at the ELCI, then nothing inboard of the ELCI should be able to trip it, so that would be a clue that the issue is somewhere outboard of the ELCI -wherever that's installed. Are you able to provide even a rough pencil sketch of how your shore power comes in to the boat, where the ELCI is, where the neutrals have been abandoned, and how your AT is connected to the Quattro? Again, rough is fine, I'm just trying to get an image of the whole problem.

@JBPohle sorry for the delay; I'm working on getting someone more familiar with how the Autotransformer does what it does, particularly when in this particular configuration, to weigh in on this. My current working theory is that since the Autotransformer is using the created neutral to balance the output legs -meaning that at any given time there can be a significant amount of current on the created neutral- then it makes sense that you're getting a voltage reading between the created neutral and ground.

Again, however, that's my working theory but I'm inquiring with minds greater than mine -and more familiar with both the 230v Quattro and how the Autotransformer works with it- before giving that as a definitive answer. I'll report back here later today and either Alan or I will respond to you via email as well!

Hi @JBPohle,

I run a similar setup to you in USA RV parks.

The first thing I notice is that you are not on a traditional 240V split-phase service. What you have is two 120v legs coming from a 120/208V three-phase service. This is code-legal since 2008 at RV parks and marinas in USA.

Unfortunately, it mean the L1-L2 voltage is low, and since your AT makes a new "derived neutral" at the halfway point, you get low voltage on your house side, too. You got lucky at this marina: the starting voltage was higher than usual. Somewhere, you'll find one that starts out nominal (208V) and then sags to 200V when everyone loads up the marina on a hot day, and then you'll be sending 100V to your appliances! Not so great. This is an unavoidable issue with this design, unless you are willing to add other components to your setup. (If you are interested in that, please start a new question about it and I will explain some of the options.)

Anyway, the next thing to note is that you definitely can't connect your derived neutral to your shore supply ground. The ground wire is a safety conductor, not a carrying one. The ELCI will trip the moment 10 or 15mA flow down that wire. Even if the measured voltage between your derived neutral and the shoreside ground were 0.5V, you'd trip it.

I think 60VAC measured is too high, though, and it makes me wonder if something else is also going on.

The first thing I would do is check to see if you have an inadvertent neutral-safety ground bond on your house load side. Do this when you are not on shore or generator, with the inverter's internal N-G bond relay open, and with the inverter's control signal to the AT not triggering the N-G bond relay inside the AT. You may have an appliance that is wired incorrectly.

If you see that all okay, the next thing you might do is put a low-Z meter on that pair of wires. Sometimes stray capacitance can build a "phantom voltage" on unused conductors. It may be fooling you, and the real potential there may be very low (but likely still enough to trip the ELCI; see above). The hassle here is that you may have to borrow a meter with a low-Z measuring mode. Or you could use it as an excuse to upgrade!

The last thing I'll mention is that the voltage split that your AT produces will indeed shift as the loads imbalance the two sides of the coil. That you observed that is normal and is not part of any problem you may have.

Caveat: I am not an electrician. However, most electricians also have no clue when you ask them for help with a system like this.

John,

I was waiting for someone else to verify my math before I came back again. It checks out: your neutral-to-ground voltage of ~60V is what you should expect when you are on a 208/120V shore supply. The phase angle of the two legs (120deg) creates this difference between your derived neutral and the shore ground (and the shore neutral).

I wouldn't worry about any of the readings you're seeing.