Bonding System Question?

[aboutgone]

I am in the process of rewiring my CSY 44. In regards to the bonding of the AC systems, I have read that you bond them to any wet surface (engine block/ thru hull).
But isn't that where the D/C is grounded to? Shouldn't I keep the two separate?
I have a 10'X 2''X .250'' copper bar stock on my hull near the keel for lightning protection. Can I use that for an isolated bonding system, or should I use it only for lightning protection? Thanks .................Ed

[s/v Jedi]

Hi Ed,

You can connect your AC ground at that plate. When I write that you should keep battery negative away from AC ground there will be flocks of posters following up with why you should interconnect the two but the experts never agree on the matter.

Take special care with ground from shore power. You need so protection against galvanic corrosion there.

cheers,
Nick.

[GordMay]

Excerpted from ABYC E-11

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.


11.7.2.2.1.4. The shore-grounding (green) conductor is connected, without interposing switches or overcurrent protection devices (See E-11.5.3.5.), from the shore power inlet to

11.7.2.2.1.4.1. an optional galvanic isolator, and then to

11.7.2.2.1.4.2. all non-current carrying parts of the boat’s AC electrical system, including

11.7.2.2.1.4.3 the engine negative terminal or its bus.

See the diagrams (figures) at ➥ http://www.paneltronics.com/atimo_s/...11Excerpts.pdf

[CharlieJ]

Ed-
Discussions about "bonding" and "grounding" usually go off track because of terminology and lack of understanding regarding the terms.

I am in the process of rewiring my CSY 44. In regards to the bonding of the AC systems, I have read that you bond them to any wet surface (engine block/ thru hull).

The bold sentence shows some popular misconceptions. OK, here goes. Shoreside. "bonding" of AC systems as covered in the National Electrical Code (NEC) covers many, many pages. Essentially it entails connecting all the metal, non-current carrying, components in the electrical system together "...to establish electrical continuity and conductivity." The bonding system is then connected to the service ground.

Aboard a vessel that is in compliance with the ABYC Standards we have:

E-11.15.3.2 All exposed, electrically conductive, non-current carrying parts of fixed AC electrical equipment and appliances intended to be grounded shall be connected to the grounding conductor.

The subtle difference is that this grounding conductor is connected at one place on board to the vessel ground (B-) AND it is connected to the neutral at the transformer that supplies the marina/dock. (I am not considering an isolation transformer and its ramifications in this, already, confusing discussion.)

But isn't that where the D/C is grounded to? Shouldn't I keep the two separate?

Gord has cited the proper section from E-11; the AC safety ground (green wire) bus is to be connected ("bonded") to the vessel ground (B-) at one and only place to provide safety should an AC hot (Line) ever come in contact with the DC system. This connection will provide a redundant path back to ground and cause a circuit breaker in the AC circuit to open. Galvanic corrosion issues are handled with a galvanic isolator.

I have a 10'X 2''X .250'' copper bar stock on my hull near the keel for lightning protection. Can I use that for an isolated bonding system, or should I use it only for lightning protection?

Again, the bold phrase is unclear. The following diagram from E-11 shows that there are several "grounds" that serve different purposes. These grounds are all tied together. They are separated because many of them are there to provide an equipotential connection and are not intended to carry appreciable current; e.g., the "bonding system" that bonds all of the underwater fittings on a vessel and then connects them to a sacrificial anode to provide cathodic protection. The battery negative return (B-), on the other hand, is designed to carry significant current.

I hope this has helped

E-11; Fig. 18; Grounding Systems.pdf