Hi all,
This was a previous discussion multiple times it appears. I'll post my very lengthy previous reply below for reference, but here's the 'short' answer ...as it were :-) ... in OP's context.
First, who am I? Not that it makes me right of course but I taught for a little over three years at a local electrical trade school, ultimately as the lead electrical instructor. Grounding and electrical safety was _my_ class, plus I taught the AC motors class a few times. I have 25+ years in the field designing, building and configuring (up to) 100KVA outdoor electrical systems, and I've performed many other electrical design functions, small and large. I was responsible for stage, sound and lights, specifically the electrical configurations, including specifically grounding, at an outdoor professional sports stadium, for the US Navy's 4th of July celebrations, at a major university, many large festivals, etc.
Plus I'm an electric boater.
So:
1) According to ABYC for DC you should have two wire systems (unlike for standard AC) _and_ ground referencing*.
* The most negative battery terminal is connected electrically to the water**.
** As a practical matter, fresh water is not really a very good conductor, but it's still, per ABYC E-11, the correct way.
2) How you should get there is kind of up to you. Opinions seem to vary*.
* Chemists will say you want suitable anode material, people usually use a Zinc anode on the prop shaft**, for a negative ground system.
** The Galvanic Table says Magnesium or Aluminum should work pretty good too chemistry-wise. But OP asked what people are actually doing.
3) Once (if?) you make that 'Earth' path available for lightning, you should look at the exact physical configuration**. Lightning _will_ first seek the absolute highest conductor on your boat***. Like the top of a mast* for instance. It's a remote chance, but spectacularly dangerous. One solution I've seen used is a chain hung off a side stay into the water.
* A _wet_ wooden mast _should_ be considered a conductor. IDK about wet carbon fiber... definite maybe. If you've got wires going up it, it conducts lightning.
** If a lightning bolt finds a motor winding in it's path, that motor will probably cease to function. Possibly explode into flames.
** Disregard anything considered 'insulation' in the actual electrical system re: lightning. It's going pretty much straight through any of that folly in milliseconds.
4) ALL USER ACCESSIBLE CONDUCTIVE PARTS _MUST*_ BE ELECTRICALLY CONNECTED TO EARTH**.
Did I say that loud enough?
* Especially if you have 120 and or 208/240 VAC. 'Low Voltage,' systems (aka <50V) _MIGHT_ get a pass, but 'best practices' was mentioned. Just ground everything.
** Per basically all modern electrical codes, grounding is meant to activate overcurrent protection, which is _also_ required, (for fire prevention***.)
*** Fire prevention is probably pretty important on a fiberglass boat. Electrical deaths are usually related to fire, and not shock.
5) ABYC requires the positive terminals of the DC supply(s) to have the overcurrent protection devices*.
* (The US) NEC has a whole chapter on motors. Typically, overcurrent protection, _plus_ overload protection is required. It gets complex with so many types of motors and controllers available. The overcurrent protection (fuses or breakers) protect the wires, and overload protection protects the motor's windings. This is how (competent) industry does it.
6) For 'Grounding,' you want one and only one path to 'Earth' from any point in the system. Otherwise, it forms a loop*.
* Any changing magnetic field through a conductive loop** _will_ induce current. This is a law of physics, not electrical code. Currents forced through your boat's 'anode' will tend to dissolve it!
** Minimizing loop area becomes best practice if you can't avoid loops***.
*** Isolating the shore power ground from the boat's grounding system is recommended. Then you won't have a loop. If you can't envision this loop, you don't (yet) know what you're doing. Loops can be sneaky little buggers too. 'Neutral' wires are grounded conductors, as a for instance...
7) Battery chargers virtually always have a transformer that isolates the battery side. An Ohmmeter can confirm that yours does*.
* Measure resistance from each prong on the power plug to all outgoing battery conductors**, only if they're all open circuits, is it isolated.
**That's effectively six measurements total with a three prong plug and two battery clamps.
If you don't understand grounding and isolation, you don't (yet) know what you're doing. Start there.
I hope this helps. Below is a more detailed reply to a recent similar post:
Good luck, and fair winds and following seas amigos!
Dave
fitunderground via groups.io <fitunderground=yahoo.com@groups.io>
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Thu, May 5 at 12:53 PM
Hi all 👋🏼 does anyone know of or could recommend someone experienced in installing electric sail drives or an ABYC specialist that has existence with electric drive systems? I'm open to doing online or phone, although I'd prefer someone local (Southern California), that could help me finalize my electrical plan and figure out what else I need for safety.
The previous threads have confused me more than they've helped (mostly due to my lack of knowledge and experience) but I'm starting to struggle with the final pieces for grounding, galvanic isolation and if I should keep my 12v (house) and 48v (motor) banks floating. I would greatly appreciate any and all recommendations or advice. Thanks!
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