a boat mechanic knows Im about to have this hb wired, he mentioned something about the inverter and the bank of battries and making sure there was complete or solid ground, he went on to talk about the acid and reaction from these battries, inverter and charging system.

can someone give me any additonal info I need to speak with the electrician about on this issue, It made me wonder if more grounding kept this (eletrolosis) (sp) if this is the correct term, minimized by more grounding, excuse my inability ask the question properly, hoping someone may understand what Im asking

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"Come OOON Back............

Obviously you are confused because you are talking about two different things, grounding and galvanic corrosion (not electrolysis)

 

I assume that you have both an Alternating Current (120V AC) system and a 12 V Direct Current (DC) system.   Your DC system should be grounded at the engine block, meaning the negative wire from the battery (black wire) should be connected to the engine block.  That is the only place it should be grounded!  This is extremely important to prevent galvanic corrosion.

 

Your AC system has three wires, a black (hot side) a white (neutral side but just as hot as the black) and a green wire.  The green wire is the grounding wire and is connected to the engine block as well.  This is the only place the green wire should be grounded. 

 

An inverter takes 12 V DC and converts it to 120 V AC so when you are not on shore power or a generator you can run some AC appliances, such as your TV. 

 

I don’t want to write a long essay here so here is a link to read up on DC and AC systems.

http://newboatbuilders.com/pages/electricity.html.

 

There are several good books on this; I recommend Nigel Calder’s book Boatowner’s Mechanical and Electrical Manual.    Another good one is Ed Sherman’s book Powerboater’s Guide to Electrical Systems.  Both are excellent.  I know both the authors and their writing style makes it easily understandable.

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Ike
"Don't tell me I can't. Tell me how I can!"
New Boat Builders Home Page
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thanks ill research the books you mentioned and your right i knew i used the wrong term, the mechanic did mention the boat engine was by far the best ground, not sure why the hull isnt as good I know the engine is 20 plus inches in the water, but thats all imaterial ill see that the grounding takes place like you mentioned. perhaps by this time next year ill have this basic info you guys have gained through the years.

looks like the only thing Ill run off the inverter will be the tv, satalite and perhaps a fan, so perhaps your book will give me the # of batteries size etc and the size inverter I should go with

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"Come OOON Back............

A metal hull should never be used as ground.  The reason is because if you get a ground fault, (that is, a short to ground ) then you have current flowing in the hull. In the case of DC that means severe galvanic corrosion problems. Not just on your boat, but all the boats around you as well   If you have an AC fault to ground, then there is 120V AC on the hull.  This is a serious shock hazard for anyone touching the boat, and anyone in the water near the boat. This is why the AC green grounding wire is grounded to the block but not connected to the white neutral wire anywhere on the boat like it is in household systems. If you have an AC system you should also install GFCI (ground fault circuit interrupters) on the boat to prevent accident shock hazards.

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Ike
"Don't tell me I can't. Tell me how I can!"
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So there is no electrical connection between the engine block and the hull on a metal hulled boat? What about motor mounts, and drive mounts? Certainly these are not electrically insulated are they?

I'm new to this boating thing and really don't know.

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Superdad

I believe the motor mounts are insulated with rubber, I don't think there is anywhere were the motor is ground to the hull.

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Mike <BR>lake texoma, 1995 44 gibson standard

Your engine should be isolated from the hull for two reasons. One is the electrical isolation. The other is noise. If you have solid mounts that are connected directly to the engine beds then all the noise of that engine is transmitted directly to the hull which then acts like a great big drum. There should be rubber mounts between the engine and the engine beds. Sometime these are solid rubber, sometimes they are filled with a fluid, usually an oil. This helps dampened engine shake and reduces noise.

Here is a link to a site that sells engine mounts. Engine mounts This is just to illustrate. Just Google Marine Engine Mounts and you will get lots of hits. But if you look at the description they all say, "eliminates metal to metasl contact"

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Ike
"Don't tell me I can't. Tell me how I can!"
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Edited: 11/08/2007 at 06:07:03 PM by Ike

Grounding your AC to the engine block isn't going to do much for the safety of the system; especially if the engine is not grounded to the hull. In the event of a ground fault you could have a "hot" engine to the tune of 120 volts. Could be deadly.

It's my understanding the AC should be grounded ashore; and for safety to the boat's grounding system through a galvanic isolator. A nice loud alarm could alert you to any problems.

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Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

Admiral, you are right, the AC should be grounded ashore. And yes you should use an isolator, but the question was about where it should be grounded on the boat and the answer is, the dc negative should be grounded to the engine block, and the AC GREEN wire (and only the Green Wire) should be connected to the engine block. Here is what the ABYC standard says.

11.18.2. DC Grounding Conductor
11.18.2.1. A DC grounding conductor shall
not be smaller than one size under that required for
current carrying conductors supplying the device and
not less than 16 AWG. (See FIGURE 18 and
FIGURE 19.)
11.18.2.2. Routing - The DC grounding
conductor shall be routed from the device to the
engine negative terminal or the DC main negative bus
by one of the following means:
11.18.2.2.1. The DC grounding conductor shall
be routed together with the current carrying
conductors as a third wire
11.18.2.2.2. The DC grounding conductor shall
be routed as a separate conductor.
11.18.2.3. The DC grounding conductor shall
be connected to a DC grounding bus in accordance
with E-11.18.2.5.
11.18.2.4. Connections - DC grounding
conductor connections shall be made in accordance
with E-11.16.3.

For AC

11.5.3.3. The main AC system grounding bus
shall be connected to
11.5.3.3.1. the engine negative terminal or the
DC main negative bus on grounded DC systems, or
11.5.3.3.2. the boat's DC grounding bus in
installations using ungrounded DC electrical systems.

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Ike
"Don't tell me I can't. Tell me how I can!"
New Boat Builders Home Page
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Agree completely. My feeling however is that if the engine is NOT grounded to the water (somehow); using the engine as a 120v "ground" would be faulty logic, and dangerous. Especially with an aluminum hull.

Generally the engine IS grounded to the water through the drive train, or a grounding plate. Maybe this is why some outdrives get so badly eaten up?

-------------------------
Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw