We have a boat docked at a marina with a 208/120V shore supply delivered on a standard 4-wire NEMA 14-50 receptacle.
The boat brings the shore L1, L2, and G directly into a 240V hybrid inverter with a battery. The shore neutral is unused. In normal operation, the inverter simply passes through the shore power to its output and otherwise does nothing, which is all we are concerned with right now.
On the output side of the inverter, L1 and L2 are wired to an autotransformer. The AT has a center tap on the coil so that a split-phase can be derived. The coil is rated to sink 30A continuous on the center tap and so can support a substantial imbalance in the house loads.
With a 240/120V supply, the AT re-produces a "new neutral" on the output side that approximately matches the original shore neutral, which means it also approximately matches the shore ground. Observed voltage between AT neutral output and shore ground is never more than a few volts, with some variation depending on the load imbalances.
In the 208/120V marina, the AT can only make 104V on each output leg, since of course it just divides in two. Leaving that aside, though, the AT neutral output is being observed at roughly 60V potential with respect to the shore ground.
Does this 60V potential make sense given the phase angles of the shore supply?
The boat brings the shore L1, L2, and G directly into a 240V hybrid inverter with a battery. The shore neutral is unused. In normal operation, the inverter simply passes through the shore power to its output and otherwise does nothing, which is all we are concerned with right now.
On the output side of the inverter, L1 and L2 are wired to an autotransformer. The AT has a center tap on the coil so that a split-phase can be derived. The coil is rated to sink 30A continuous on the center tap and so can support a substantial imbalance in the house loads.
With a 240/120V supply, the AT re-produces a "new neutral" on the output side that approximately matches the original shore neutral, which means it also approximately matches the shore ground. Observed voltage between AT neutral output and shore ground is never more than a few volts, with some variation depending on the load imbalances.
In the 208/120V marina, the AT can only make 104V on each output leg, since of course it just divides in two. Leaving that aside, though, the AT neutral output is being observed at roughly 60V potential with respect to the shore ground.
Does this 60V potential make sense given the phase angles of the shore supply?
