Electrical System Grounding

Sep 11, 2013
242
Catalina 25 6106 Lake Erie Metro Park
I'm in the process of rewiring my Catalina 25 and I'm curious about grounding both the 120 VAC and the 12 VDC. My Pearson boat had ground wires EVERYWHERE, from the negative side of the battery and the 120 VAC ground, all of which terminated at the cast iron keel. Is this accepted practice? The Catalina's rather rudimentary electrical system has NO grounding to the (lead) keel that I can see.
Should I ground accordingly or not?

Thanx,

Tom G
 
Sep 11, 2013
242
Catalina 25 6106 Lake Erie Metro Park
Thank you Davidasailor, very interesting article.
From that I take it I should connect the green earth wire of the 120 VAC system through an isolator to the keel and the negative side of the battery directly ?
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
From that I take it I should connect the green earth wire of the 120 VAC system through an isolator to the keel and the negative side of the battery directly ?
There are 2 concepts that get easily confused. Bonding refers to keeping all the underwater metals at the same electrical potential to prevent corrosion. Grounding refers to providing a safe path to ground in the event of a short or some other device failure.

For the AC system the ground wire as it enters the boat should go to a galvanic isolator and then to a common bus bar near the AC panel. At this bus bar all of the circuit grounds are connected. From the bus bar, a single ground wire should go to an underwater metal that is substantial, a keel or an engine block.

There should be a similar set up with the DC system. A common ground bus with one connection to an underwater metal at the same point the AC ground is connected. The idea is to have them connected with a path to ground.

A good resource is Charlie Wing's book Boatowner's Electrical Handbook. Another good resource is the MarineHowTo.com website.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
The ABYC standards on this are quite clear..


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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Sep 11, 2013
242
Catalina 25 6106 Lake Erie Metro Park
That makes sense, billjoye. I was curious about grounding to the keel since it is, as you pointed out, encased on Fiberglas and paint. That being said, is there any point in galvanic isolation?

Tom G
 
Sep 11, 2013
242
Catalina 25 6106 Lake Erie Metro Park
MainSail:

If I’m reading this correctly, what the specifications are directing is that the DC and AC grounds should be connected together even though there’s no way of grounding to an engine, iron keel, etc. in other words, connect the grounds and just let it go at that?

Tom G
 
May 7, 2011
205
Catalina 30 Lake Lanier
An AC (L or N) to G short will only be energised when plugged into a power source. If Shore Power, then the safety ground will take care of it. I am under the impression (but no direct knowledge) that a generator ground will also handle it. We added an AC ELCI main breaker specifically for this reason. It will detect the current imbalance and disconnect.
 
Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
Many of these responses seem to be referring to AC at the dock, versus AC from an inverter. We rarely are connected to shore power, but we have an inverter to provide the rare AC requirements underway or on the hook/mooring. But, we are having problems with the GFCI tripping on the inverter. We have both the DC and AC grounded directly to the engine mounts. Ours is a steel hull.
 
Sep 11, 2013
242
Catalina 25 6106 Lake Erie Metro Park
Just to clarify:
1) My concern is in regard to shore power connection only.
2) We have no generator or inverter, our outboard motor has its own starting battery, completely separate and isolated from the house batteries.
3) At this point the AC ground and the DC common (negative side of the batteries) are NOT connected.

So I coughed up $140 for a galvanic isolator and installed it as described in the instructions: between the shore power ground and the boat's AC ground bus.
My GFCI outlets are live, but my plug in electrical tester for outlets indicates an open ground condition and the reverse polarity LED on the breaker panel was lit. I bypassed the galvanic isolator and the tester showed correct orientation and the reverse polarity LED went out.

What did I do wrong?

Tom G
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
My GFCI outlets are live, but my plug in electrical tester for outlets indicates an open ground condition and the reverse polarity LED on the breaker panel was lit
When a GI is installed, it blocks the ground connection until it doesn't, which is what it is designed to do. There are a series of diodes in the GI that prevent low voltage current flow. However, when there is a short to ground the voltage will be higher and the current will flow popping the circuit breaker on the power pedestal. On shore, the ground and neutral wires are connected at the circuit breaker panel. On a boat they should not be connected on board. Since the ground wire appears to be disconnected, an open circuit will appear between the hot wire and ground, on shore a DVM will show voltage between the hot and ground, and between the hot and neutral.

Which GI did you purchase for $140?
 
Sep 11, 2013
242
Catalina 25 6106 Lake Erie Metro Park
Added note: AC ground and DC 0 volts (negative side of batteries) are connected together and grounded to the keel. A separate wire runs from the AC ground bus to the keel and a separate wire runs from the DC 0 volts to the same point on the keel.

Tom G
 
Oct 22, 2014
352
Pearson P303 #221 RockPort Maine
As mainsail stated:
The ABYC standards on this are quite clear..
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.

Here's some added info to find stray current too! I installed a switch with an AM meter between AC and DC grounds. Remember, it's important to isolate where your problem current is coming from AC or DC. Hope this helps!
Capt. Rob
 

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Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Galvanic Isolator by Yandina. $139 on Amazon.
Attached are pix....
That's what I thought. The Yandina GI is not a fail safe GI. If there is a short and the diodes fail, then there is no AC ground. In a fail safe GI if the diodes fail, the galvanic protection goes away, but the AC ground functions.
See: http://www.yandina.com/galvanicIsolator.htm In practice this means you should regularly test the GI to make certain it hasn't failed.