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Old 14-06-2012, 20:27   #1
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Engine grounding

We have a Hunter 410 with a Fisher Panda generator. It has it's own starter battery, not part of the of the boat charging system. My question is the genset engine ground is to the prop shaft strut thru bolt. Is that a normal place for a ground or is there a better place?

I also found a breaker box for the 120v from Square D. That seems odd for a boat installation. There is a reverse polarity problem when the generator is running. Any opinions?
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Old 15-06-2012, 06:30   #2
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Re: Engine grounding

Quote:
Is that a normal place for a ground or is there a better place?
The short answer is no, this is not the normal place for a ground, and the quality of the "ground" is questionable.

It is good marine electrical system practice, and an ABYC Standard, to have a single vessel ground. There may be "auxiliary" ground busses for convenience; e.g., on a flying bridge, in an engine compartment, etc., but all of these auxiliary ground busses are tied back to the vessel ground with appropriately sized conductor.

This is truly a complex issue that involves an understanding of DC electrical system design, galvanic corrosion, stray current corrosion, radio frequency grounding, lightning protection, and on and on!!

If I was your electrician, I would:
1. Remove the bogus "ground" from the strut.
2. Tie the B- from the genset starting battery to the vessel ground that includes the B- from the house bank and the propulsion engine starting battery.
3. Tie the genset engine block to the propulsion engine block with the same sized conductor as in #2 above.

From the ABYC Standards:
E-11, Fig 18 Grounding and Bonding .pdf

Quote:
I also found a breaker box for the 120v from Square D. That seems odd for a boat installation. There is a reverse polarity problem when the generator is running.
There is a requirement for a circuit breaker at the output of the genset. You did not state if the installed breaker was single or double pole. In any case, it is my opinion, that Square D circuit breakers do not belong on vessels <100' LOA!

If I were your electrician, I would:
1. Remove the Square D breaker and install an appropriately sized Blue Sea Systems double pole circuit breaker. 30A is p/n 8077 and 50A is p/n 8079. If the area is a potentially wet one; e.g., in the lazarette of a sailboat, the breaker needs to be in a drip proof enclosure.
2. Ensure that the the neutral and the safety ground are tied together in the genset electrical connection box.

Hope this helps.
Charlie
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Old 15-06-2012, 07:09   #3
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Re: Engine grounding

Quote:
Originally Posted by CharlieJ View Post
The short answer is no, this is not the normal place for a ground, and the quality of the "ground" is questionable.

It is good marine electrical system practice, and an ABYC Standard, to have a single vessel ground. There may be "auxiliary" ground busses for convenience; e.g., on a flying bridge, in an engine compartment, etc., but all of these auxiliary ground busses are tied back to the vessel ground with appropriately sized conductor.

This is truly a complex issue that involves an understanding of DC electrical system design, galvanic corrosion, stray current corrosion, radio frequency grounding, lightning protection, and on and on!!

If I was your electrician, I would:
1. Remove the bogus "ground" from the strut.
2. Tie the B- from the genset starting battery to the vessel ground that includes the B- from the house bank and the propulsion engine starting battery.
3. Tie the genset engine block to the propulsion engine block with the same sized conductor as in #2 above.

From the ABYC Standards:
Attachment 42318



There is a requirement for a circuit breaker at the output of the genset. You did not state if the installed breaker was single or double pole. In any case, it is my opinion, that Square D circuit breakers do not belong on vessels <100' LOA!

If I were your electrician, I would:
1. Remove the Square D breaker and install an appropriately sized Blue Sea Systems double pole circuit breaker. 30A is p/n 8077 and 50A is p/n 8079. If the area is a potentially wet one; e.g., in the lazarette of a sailboat, the breaker needs to be in a drip proof enclosure.
2. Ensure that the the neutral and the safety ground are tied together in the genset electrical connection box.

Hope this helps.
Charlie

Ditto!!!
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Old 15-06-2012, 07:36   #4
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Re: Engine grounding

This is NOT normal for grounding to the "engine". A bare starter bolt perhaps...

I ALSO ground my alternator BTW, with a "separate" smaller - wire, not relying solely on the engine's main battery - wire. This is a more reliable, low loss connection.

Unless bonded, the strut is not normally connected "electrically" to the shaft at all, as the rubber lined cutlass bearing separates it from the shaft.

In my case, I isolated the engine from the AC and DC system (except when its running), by installing an on off switch in the black - wire, as well as the red + one. I shut off both during the 99.9% of the time that its not running. This minimizes any stray current, that eats zincs.

For galvanic protection of the shaft / strut / and prop... The one shaft zinc alone does the job for a year. It is bonded internally from a bolt on the strut's inside surface, to the shaft "brush". This provides contact between the shaft and strut. If you're not using a shaft brush and bonding wire, your strut is not protected by the shaft's zinc at all.

These changes have eliminated my early problems with rapid zinc consumption from 16 years ago, and all underwater metal is stable.

I also isolated my mast's lightning ground from the AC and DC system, as well as aft bonding wire. This required that I isolate things like the base of the VHF antennae, which is common with the DC-. By using diodes to connect the SSB radio's copper strap to the grounding plate, it transmits RF energy, but NOT DC current.

This was partially after consultation with Stan Honey, 15 years ago, who helped diagnose my problems. I was an ABYC member while building our boat, and had wired it with ONE common ground, as ABYC specified. In my case, this created a battery of stray currents that was eating zincs at an astronomical rate! I was also OVER zinced at the time. My one shaft zinc is now all that I use, (for the drive train), and the copper plate, as well as rudder hardware remain unprotected.

What works on one boat will not necessarily work on another. You may need to experiment. Bear in mind that the ABYC standards are a great starting point, but may not work for you. Their orientation seems to be toward safety of the "occupants", and minimizing a manufacturer's liability, as opposed to safety of the diver under the boat...

For me, "being" the manufacturer, (can't sue myself), and diving on the bottom every two weeks to wipe off the slime, I was more concerned about zinc consumption, (requiring more marina dive time), and my safety IN the water, than IN the boat, (which has all double insulated AC accouterments). Bear in mind... I do check for proper ground to the dock's AC pedestal, (with a small testing plug in device), every time I hook back up, or at a new marina. If I feel the need, a flip of a switch turns the "safety ground" back on.

In any case, there are a lot of ways to wire these boats up, and some careful prioritizing and experimentation may be called for.

Best of luck,

M.
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