Earth ground, boat ground and wiring

[oysteinhermansen]

Boat is Sea Ray 315 (280) with a Volvo KAD300 diesel engine.

I did some checking, using a combinded ohm/volt-meter, to find out how the earth ground was connect in my boat. I found the following.

Shorepower earth: This is sent through a galvanic isolator to the distribution panel in the cabin. All outlets (220v) in the cabin, the microwave and the fridge are connected to "land earth" (shorepower earth). This curcuit has a GFS.


In the engine room there are 2 units which uses 220v (shorepower). This is the battery charger and the water heater. They get 220v from the distribution panel in the cabin, but they do not get earth ground. The ground wire on these units are connected to the engine. And there are no GFS in this curcuit. If I messure the Ohm from engine to negativ 12v (or 12v ground) it is 0 (zero).

In other words: 220v units that are located in the engine room is at the same electrical level as 12 ground (or minus 12v). They are both connected to the enige and from the enige to the sterndrive and further in the water.

Is this the normal way of doing things ? I have not done any changes to the electrical system so I know this is done by Sea Ray design.

What are the upside, and the downside, with this setup when it comes to corrosion ?

 

[fc3]

Unfortunately, European regs are different that US, so can't help you much. On US boats, all shore power items are earthed and the shore power inlet is as you described with a ground fault interrupter. Also, the shore power earth is interconnected to the negative side of the 12 volt system.

Best regards,
Frank

 

[oysteinhermansen]

Unfortunately, European regs are different that US, so can't help you much. On US boats, all shore power items are earthed and the shore power inlet is as you described with a ground fault interrupter. Also, the shore power earth is interconnected to the negative side of the 12 volt system.

Best regards,
Frank

Thanks.

The difference seems to be that in Europe you may disconnect items from shore power earth if you have a local earth. And the engine and sterndrive functions as local earth.

But you answered parts of my question since you said that shore power earth is interconnected to the negative side of the 12 volt system.

/Oystein

 

[le cras]

You should be looking for a high resistance from shore to boat on the earth pin. This could read as an open circuit, and a low resistance from boat to shore.
Of course this will only work with a multimeter that has diode check function.
The “on” boat connection has to be on the boat not the end of the shore power cable, this is the same on all boats with a galvanic isolator.

Internal resistance between ground points (including the water) for the 12, 110v or even 220v could have only the resistance of the cables and connections between them.

Although the low 12v and the higher shore power grounds should be separate this is not always possible.
Depending on the type of water heater, the water heater is full of water and may be heated by a heat exchanger from the engine water, and therefore it would be very difficult to electrically isolate the grounds.
Dual power items are the main reason for common grounds.