When on inverter am I using the batteries?

MrWizard wrote:
It's happen before, with other members
Usually with more extensive and expensive repair costs

Always always unplug shore power before starting generator

Turn off shut down generator before plugging into shore power

I 'harp' on this, I'm adamant about it, it's prevents damage and is a safety issue
But some people disagree
Until the flying Sparks, happens to them

This should never ever happen with a properly configured coach. For very old coaches or ones with suspect or incorrect wiring it is absolutely possible to have a problem. However, stopping the generator or turning off the inverter is masking the underlying problem which is very dangerous. The only way for what you describe to happen would be if the coach were mis-wired or had seriously defective transfer switches. A common cause of this is a mis-wired neutral line. The neutral line for a “self-derived system” is bonded to ground at a single point. This is called a NG bond. However, when the coach is connected to shore power it (by NEC code) cannot have a NG bond because that NG bond is done at the central electrical panel. In the NEC the ground line is never to be a “current carrying” conductor. It is only to be used for a safety ground to prevent shocks caused by miswiring or defective equipment. The generator transfer switch has the required NG bond as does the internal transfer switch inside inverters. If a coach has a generator that “sparks” or “causes damage” when the coach is connected to shore power then by definition that would mean at a minimum dangerous voltages would be present at the EXPOSED end of the shore power cord while the generator is running. This is very dangerous indeed and not due to the shore power connection. The same thing occurs with a mis-wired or defective inverter. The solution to the problem is not to do gymnastics such as turning off all other sources of power when switching it is to correct the underlying wiring problem. Some inexpensive inverters use a method that will cause 120 VAC to be present on the neutral line and 0 VAC on the "hot" line. This is to simulate a negative voltage on the positive side. The reason for this is it is much less expensive to create an oscillating positive voltage rather than create a negative voltage on the hot line as is normally required for AC power. Again, if there is a incorrectly NG bond this can mean that the chassis is actually "hot" during inverter operation. This is a very bad situation indeed. Finally, a mis-wired coach plus a mis-wired shore power connection can create a hot skin condition and that can cause problems as well. It is best to invest in a protection system to prevent that sort of issue.