Common Ground without an engine...

[GilStump]

Hey guys n gals

I am installing an electric motor into my Fiberglass 1977 Orion S&S 35. All I have read about grounding says that the engine's negative is the common ground for both DC and AC. My new motor's shaft is isolated. I thought of connecting a bus to a keel bolt, but then I will also give myself lightning protection this way. Wouldn't a strike potentially frizzle everything connected to the common ground? My raw water intake is bronze and I wonder if I could better isolate the common from the lightning by bonding to this thru-hull? If I put a galvanic isolator on the AC end, will this be enough to keep my thru-hull from getting eaten alive by stray current? Or should I bite the bullet, haul out and install a grounding plate? I don't want to do this....

Also, when choosing a common bus for the whole boat, how do you know what size to get?

Thanks!

[mitiempo]

Gil

If your shaft is isolated I think you would treat it the same as a boat with outboard power. The ground is the negative battery post. Keep the AC separate from the DC. Through hulls can be bonding grounds or lightening grounds but not electrical grounds. As far as lightning, it goes where it wants.

[GilStump]

There are two battery banks. A 48v for the Elec motor and a 12v for house. Should they be grounded together using the negative post? Where should the AC ground go in that case?

[mitiempo]

They 2 battery grounds should be connected. The AC ground should not be connected to the batteries. This means the safety ground is the green wire from the shorepower supply on the dock. A galvanic isolator is not required as the AC and DC grounds are not connected.

Bill or MaineSail will hopefully comment.