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Old 24-02-2011, 18:17   #1
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ground continuity

Should I be seeing continuity between my 110AC green ground and white neutral wires? I'm not seeing a shared connection on the boat.

I installed a GFI outlet last spring, and all has been fine, but noticed the trip indicator lite is always on in both the tripped or reset condition. Thinking the GFI was bad, I unhooked it to replace, then out of curiosity checked continuity on the bare wires. I was getting a tone when touching the DVM leads to the white and green wires. When I unhooked the shorepower cord from my boat, the continuity tone stopped.



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Old 24-02-2011, 18:21   #2
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Re: ground continuity

Many shore side systems use a common buss for the ground and neutral... that's why we have zincs!
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Old 24-02-2011, 18:38   #3
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Re: ground continuity

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Many shore side systems use a common buss for the ground and neutral... that's why we have zincs!
That's code, neutral & ground must be bonded together. If you've ever wondered why some AC appliances are "polarity conscious", it's because they're using the neutral as ground. If the AC system isn't bonded properly, these appliances can become a shock hazard.
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Old 24-02-2011, 18:42   #4
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Re: ground continuity

I shoulda left the "many" off huh?
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Old 24-02-2011, 19:12   #5
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Re: ground continuity

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Many shore side systems use a common buss for the ground and neutral... that's why we have zincs!

Yes, I'm aware of that and also that my boat has no common connection between the 2, which explains why the no tone when shorepower cord disconnected. I just wasn't sure what to expect when going thru the galv. isolator. So my findings are correct then, right?

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Old 24-02-2011, 19:23   #6
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Re: ground continuity

Electrolysis
This site might help you check out your AC system.

An isolation transformer is much safer, but more expensive of course.
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Old 24-02-2011, 19:53   #7
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Re: ground continuity

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I shoulda left the "many" off huh?
Well, no harm, no foul , as I'm sure some places may not meet this requirement... intentionally or otherwise.

I should have clarified my statement as well. The National Electrical Code (NEC, US) & Canadian Electrical Code (CEC) do not regulate electrical systems installed on boats or aircraft. What's required in these cases is most likely regulated by Transport Canada here, & apparently the Coast Guard in the US.
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Old 24-02-2011, 20:21   #8
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Re: ground continuity

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Originally Posted by US1Fountain View Post
Yes, I'm aware of that and also that my boat has no common connection between the 2, which explains why the no tone when shorepower cord disconnected. I just wasn't sure what to expect when going thru the galv. isolator. So my findings are correct then, right?

Thanks
Your boat shouldn't, which is why GFI's don't like generators which sometimes float the neutral on boats. I'm not an electrical engineer, but I understand the concept, so I'll TRY to explain (any EE's feel free to step in here)......

AC current (think 120V) has to run in a circuit and polarity is switched back and forth. DC (think 12V systems) have constant polarity. Your underwater metals are (hopefully) bonded to the DC ground.... I'm not getting into galvanic isolators here.... IF, the AC neutral gets grounded and there is an interconnection to the DC ground, you get 2 issues: a shock hazard between metallic objects and sea water, and electrolysis of your underwater metals.

Zincs are installed as a sacrificial anode to protect the harder (more noble) metals of props, shafts, through hulls etc. I have chased grounded neutrals down to silly things like microwave ovens and televisions.

So.... (here we go again with the "many") Many boats do not connect the AC neutral and ground as it shouldn't be, so to the OP, your boat seems to be wired correctly based on your findings. My apologies if the concept in my head didn't make it out in type!
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Old 24-02-2011, 20:28   #9
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Re: ground continuity

Thanks! Appreciate the replies.
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Old 24-02-2011, 21:07   #10
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Re: ground continuity

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So my findings are correct then, right?
Ac Neutral and AC protective ground should not be connected togther on the boat, so once the cord is disconnected is should be open circuit.

( Note this statement isnt true for onboard power generation devices)

Dave
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