What happens is entirely dependent on the physical layout of the system. A change in location of one connection can completely change the functioning of the system.
Throw in that the AC grounding system is designed for transient fault safety protection, and that the bonding system is designed to provide a good path for very small currents to the sacrificial anode, it becomes a very challenging engineering problem.
Next the implementation is critical, such as proper metals and good connections. It quickly becomes impossibly complicated and it is boat dependent.
Following standards based on quality collective experience is a good starting point.
Understanding the meaning of grounded vs grounding is also important.
A common vocabulary is also needed. Adopting the standards definition goes helps reduce confusion.
The best example is the use of the word electrolysis, which is confusing. The term Galvanic corrosion is well understood as is Stray current corrosion.
Norman Petersen
-----Original Message-----
From: THOMAS VANDERMEULEN <tvinypsi@gmail.com>
To: electricboats@groups.io
Sent: Fri, Dec 4, 2020 9:30 am
Subject: Re: [electricboats] Grounding.
From: THOMAS VANDERMEULEN <tvinypsi@gmail.com>
To: electricboats@groups.io
Sent: Fri, Dec 4, 2020 9:30 am
Subject: Re: [electricboats] Grounding.
Ryan Scott Dancey says:
(a) "If you have AC and DC power on your boat, and the DC negative is not bonded to AC safety ground, it is possible for stray AC current to enter the DC system. When this happens, AC current may enter the water around a boat and injure or kill swimmers near the boat."
(b) "Electric motors may be electrically isolated from the shaft (mine is; Electric Yacht QuietTorque 10kw). Grounding to the chassis of the engine doesn't do anything useful. My boat is old (1973) and does not appear to have an external grounding plate (future upgrade!) so I am going to have to ground to some other path to earth. My boat doesn't have keel bolts either. The least best, but perhaps only available, option is to ground via a metal through-hull (which brings with it concerns about corrosion)."
(a) If the AC and DC systems are not interconnected, by what pathway do you envision the "stray AC current" would enter the DC system? Also, wouldn't a galvanic isolator in the AC connection to shore (as recommended by ABYC) eliminate the possibility of stray AC entering the water?
(b) By what method is the motor in your QuietTorque system isolated from the prop shaft? (Seems like there must be some pathway, through bolts and motor case for instance, for a connection to be made between motor and water.)
Thanks for any clarifications.
[-tv]
(a) "If you have AC and DC power on your boat, and the DC negative is not bonded to AC safety ground, it is possible for stray AC current to enter the DC system. When this happens, AC current may enter the water around a boat and injure or kill swimmers near the boat."
(b) "Electric motors may be electrically isolated from the shaft (mine is; Electric Yacht QuietTorque 10kw). Grounding to the chassis of the engine doesn't do anything useful. My boat is old (1973) and does not appear to have an external grounding plate (future upgrade!) so I am going to have to ground to some other path to earth. My boat doesn't have keel bolts either. The least best, but perhaps only available, option is to ground via a metal through-hull (which brings with it concerns about corrosion)."
(a) If the AC and DC systems are not interconnected, by what pathway do you envision the "stray AC current" would enter the DC system? Also, wouldn't a galvanic isolator in the AC connection to shore (as recommended by ABYC) eliminate the possibility of stray AC entering the water?
(b) By what method is the motor in your QuietTorque system isolated from the prop shaft? (Seems like there must be some pathway, through bolts and motor case for instance, for a connection to be made between motor and water.)
Thanks for any clarifications.
[-tv]
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