Originally Posted by PigPen
On the shore power side of things, you're starting with a bond. Most people seem to run the shore power directly into an inverter/charger so that it can charge the batteries while supplying power. In this case, you wouldn't want the inverter to have it built in based on what you are saying.
Just to make sure we're on the same page, I think what you're describing is a topology like the following. I've put in arrows to illustrate the energy flows.
You're right: some inverter-charger devices will offer a built-in ground-neutral bond. It isn't an inherently good
feature; it's the design of the system around it that makes it good or bad.
If we think of only the batteries and the grid-supplied shore power, a built-in automatic bond in the inverter-charger would be really convenient. It'll bond when shore power is disconnected, and open when shore power is connected. Great!
The catch is this: what happens when the shore power cord is plugged to a generator? What provides the ground-neutral bond?
The inverter-charger won't provide the bond: its logic is "if there's power at my ac input, disconnect the bond." The inverter-charger doesn't actually know or test whether the ac input circuit provides a bond. (note: I'm generalizing. It'll be important to confirm by checking the owner/user/installer manuals of any specific device before use.)
The generator may or may not provide the ground-neutral bond. I'm most familiar with the Honda portable inverter generators (EU2000 and EU7000) and know that these from the factory do not provide a bond. It has been reported that other generators do provide a bond. The point is, bonding isn't standardized in the industry and we can't make an assumption.
When considering the portable generator scenario one might say "the automatic bond in the inverter-charger did the wrong thing! It's bad!" I would say just be aware of and understand the issue and plan accordingly.
For the specific case described here (topology as above, inverter-charger with automatic bonding, possibility of plugging shore power to a generator with unknown bonding), here's one simple idea. Several years ago Mike Sokol proposed building a ground-neutral bond plug
. Make one and tether it to the male plug end of the shore power cord. Each time the shore power cord is plugged into a power source it'll be there and remind you to ask yourself "am I plugging into a generator? Plug in this bond plug to the generator too, to ensure that the ground-neutral bond is provided."