Re: Inverter/Charger wiring advise


greatketch@...
 

John,

If you are not sure about the status of the AC Safety Ground, you really should have a qualified electrician review your plans. What I write below is based on what I think is a good understanding of the matter, but I wouldn't want to risk your life on it...

AC Currents are (almost) never the source of stray current corrosion. To be sure, AC wiring CAN carry DC currents that can be serious sources of stray currents.  This is why AMEL separated the DC Negative from the AC Safety Ground and Bonding system.

A couple things about the AC Safety Ground.  It is normally connected to the AC Neutral only at the source of power. This is done so it can provide a low resistance path to carry any leakage current back to the source of power and safely away from people.

When your source of power is shore power the AC Safety Ground and the AC Neutral are connected only on shore, never on the boat.  A boat that has no isolation transformer, nor inverter, nor generator would never have the Neutral and Safety Ground connected together on the boat.

If your source of shore power comes into the boat through an isolation transformer, the transformer becomes the "source of power" and the AC Safety Ground and Neutral are connected together there.  

When the generator is running, it connects the AC Safety Ground and Neutral together inside the generator.

Same with an inverter.  When it has an external source of power, it passes the AC Safety Ground on through.  When it turns on and becomes the "source of the power" it connects the AC Safety Ground and Neutral so any leakage from the Hot wire has a way to get back to the source of power without going through people.

The inverter case is connected to the AC Safety Ground in the event of a inadvertent connection between the Hot wire and the case so that voltage can be drawn off before it becomes dangerous to people.

Without a connection back to the inverter when the inverter is the source of power, the AC Safety Ground becomes worse than useless.  If there was an insulation fault that connected the Hot wire to the case of, for example, your microwave, the AC Safety Ground would not be able to drain off that voltage because it could not supply a path for the current back to the source.  In that case the entire bonding system would become charged to the same voltage as the Hot wire with no way for the current to get back to the inverter. Now to put this in perspective, it is very unlikely on the boat that you could find a way to complete that circuit with your body...  but "very unlikely" is not the same as "not possible."


Bill Kinney
SM160, Harmonie
North Bimini, Bahamas.

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