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post #1 of 4 Old 07-16-2015 Thread Starter
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Connecting AC and DC ground via branch bus

Everything I've read, here and elsewhere, says that the AC Green wire must be connected from the main AC panel to the engine negative terminal or the main negative bus. How direct does that connection really have to be?

Is there any reason I can't wire it from the battery charger directly to the nearest negative bus bar, presuming that bar is wired back to the main negative bus and thereby to the engine with sufficient gauge wire all the way? There are no ground loops here.

My AC system has only two circuits: one for an outlet and one for the charger. It is a 30A system and nothing less 10awg wire anywhere except for some very short 12awg runs that came as part of the main panel.



Details to forestall questions and the usual slate of suggestions: There's a galvanic isolator and an ELCI breaker between the shorepower inlet and the main panel. The battery charger circuit also has a GFCI outlet in line (between the panel and the charger) purely to provide GFCI protection for that circuit. The main panel does have a reverse polarity light. There is no voltmeter. There is no inverter.

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post #2 of 4 Old 07-19-2015
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Re: Connecting AC and DC ground via branch bus

short answer - as short as practical....reality - the better connection is the more desired, that is - a quality conductor, appropriately terminated and as the manufacturer specifies.

There is a great deal of opinion on the connection, if ANY, between the two systems. There are two requirements - safety and electrical, then the whole "bonding" of water contact, possible conductors (metallic thru-hulls, anodes, etc). The individual systems have requirements and the whole boat system does as well.

Requirements for home electrical that ties to the electrical grid are NOT always the best method for boats.
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post #3 of 4 Old 07-19-2015 Thread Starter
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Re: Connecting AC and DC ground via branch bus

Hmm. I'm not sure my question was clear or if I just don't understand the answer provided.

I am not asking if I should connect AC green wire to DC ground. I have a galvanic isolator and I'll only be plugged in when I need to charge or run power tools. I am not worried about corrosion. I am worried about safety. I will be connecting them.

My question is: assuming that I am going to make the connection, can I connect the grounding wire on one AC branch to a nearby negative bus bar, or does the connection have to be from the main AC panel directly to the engine (actually engine bus bar)?

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post #4 of 4 Old 07-19-2015
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Re: Connecting AC and DC ground via branch bus

Quote:
Originally Posted by eko_eko View Post
Hmm. I'm not sure my question was clear or if I just don't understand the answer provided.

I am not asking if I should connect AC green wire to DC ground. I have a galvanic isolator and I'll only be plugged in when I need to charge or run power tools. I am not worried about corrosion. I am worried about safety. I will be connecting them.

My question is: assuming that I am going to make the connection, can I connect the grounding wire on one AC branch to a nearby negative bus bar, or does the connection have to be from the main AC panel directly to the engine (actually engine bus bar)?
A 10GA green jumper between the AC Green Bus and DC negative bus, behind the panel, is perfectly adequate and how most builders do it..
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