What is the simplest and safest way to automatically make/break a ground to neutral bond in a mobile AC system?
I would like to automatically [make/break a ground to neutral bond] anytime shore power is connected to the RV

The following circuit should work if your inverter/charger unit has separate connections for inverter-out and charger-in.



simulate this circuit &ndash; Schematic created using CircuitLab
When shore power is available, the Neutral and Ground of the RV AC distribution system are &quot;unbonded&quot;. (Provided their only connection is through the relay.)
[The schematic shows the shore power protective ground connected to the RV protective ground. The assumption made is that the shore power protective ground is similar to the actual earth (or water) potential near the RV.]
[The schematic only shows one &quot;Live&quot; line. If there are two live lines, L1 and L2, are used, you will need a larger or separate relay to disconnect the inverter from the shore power, when shore power is available.]
[If the inverter/charger unit does not have separate inverter-out and charger-in connections, the above circuit, by itself will not work, and requires additional circuitry. Please provide the manufacturer and model number for the inverter/charger unit.]

I ran a ground to neutral bond through one of the NC contacts, so that when shore power was not present, the bond was made. This appeared to work. When energized, the bond was broken, when de-energized the bond was restored.

The above circuit does that, but also connects the shore neutral to the RV neutral after the bond is broken, and breaks the connection between RV neutral and shore neutral before the bond is re-established (when shore power is removed).

But the coil could fail someday, and the manufacturer said it should fail in its normal state, not its energized state. I understand that is not a certainty, and therefore will deal with that issue separately.

In the circuit above, if the coil fails, then the shore power L1 will remain disconnected to the RV power L1. [There is another possible failure mode of relays, which is that the contacts become welded together. If this should happen, the RV can still draw from the shore power, but cannot supply power to the shore (or the RV) from the inverter.

When testing this, the coil began bouncing and no power was passed through the contacts.

I have still not seen an accurate circuit diagram of how this test was made. My guess is that there is a problem with design/wiring. There are problems with the diagram you have provided, which are discussed in my answer to your other question.

I called the manufacturer who stated that you can not power an EM coil with the same source that you're running through the contacts.

You most certainly can power the coil of a relay with the same power you send through the contacts, provided the coil is rated for that voltage. If you are getting a constant on-off oscillation, it may be due to mis-wiring. That is, the &quot;door-bell&quot; effect you are seeing is possibly due to the fact that the relay is wired such that when the coil is energized, it opens contacts that break the circuit powering the coil. The coil then de-energizes, closing the contacts, allowing power to be applied to the coil again, and the process repeats. This is a design or wiring issue, and in no way negates the fact that a relay can be powered by the same power source that is applied to its contacts. It just has to be done right.