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Old 09-21-2016, 10:43 PM   #1
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BAD GROUND reading when running generator

HI All,

I was checking the 110v outlet circuits when I was running my genset and I was getting a BAD GROUND reading with one of the plugin type circuit checkers. Switch to Shore power and all is good, switch back to the generator and get the BAD GROUND reading again. I looked at my transfer switch, looked inside the power box on the generator and did not see anything obvious, but I am going to keep trouble shooting.

Any thoughts on this?

Morning Star
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Old 09-22-2016, 12:19 AM   #2
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The generator ground is not connected to the neutral. If this is the case you can measure 120 vac between hot and neutral and aprox. 67 vac between either hot and ground and between neutral and ground.

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Old 09-22-2016, 02:17 PM   #3
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To expand a bit further, 120VAC ground and neutral should be connected together *At the source*. So they must not be connected inside the boat when the boat is running off shore power. When on shore power, the connection between neutral and ground is made inside a shoreside breaker panel. When running on the boat's internal generator, ground and neutral need to be connected together usually in or near the generator distribution panel. This can be done a few different ways but usually resides in or near the switch that changes over from internal power to shorepower. Its possible a wire or switch is broken, or somebody did some rewiring and inadvertently disconnected it. Whetever the reason, it must be fixed. Not having this connection when running on the generator is extremely hazardous, because right now there is probably no AC safety ground anywhere on the boat when running on the generator.

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Old 09-22-2016, 03:03 PM   #4
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kchance has it right. I would hope the ground connection would be made and broken automatically with the transfer switch.
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Old 09-22-2016, 03:38 PM   #5
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Actually the generator transfer switch disconnects both white neutral and black hot.
So physically bond (connect) the gen ground to neutral in the gen control box, is good and should be done.

When the transfer switch opens, the gen neutral is disconnected, so the ground to neutral bond is broken to the ship's electrical wiring.

End of story.
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Old 09-22-2016, 10:38 PM   #6
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Who ever installed the gennie should have connected the neutral and frame ground together. When gennies are shipped, this connection is normally not made at the factory. Sounds like you need to add a jumper. Common issue.

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