AcGround to battery neg

[CampDavid]

I am helping a friend rewire his Ac and Dc systems on an early 80's Ontario 32.

I have installed new Blue Sea Ac Panels and all new tinned and straned ac wiring.

My question is, should I connect the AC ground ( Green wire) from the main breaker to the negative DC electrical buss,

I believe this is an ABYC requirement, I am not sure if I am correct nor do I understand why this would be required.

Fletch

[sailorchic34]

The incoming ground would connect to the ground buss on the blue sea panel. Hot (Black) and Neutral (white) connect to the main breaker. I believe that the ABYC does say connect the AC ground to Boat ground (engine, etc) which normally is also the DC ground.

However some folks think thats not so great. From a personal safety its good, but the AC harmonics can sometimes disrupt DC electronics connected. Plus it assumes that all other boats are wired the same way, Not going to happen in the real world.

Me, except for the Battery charger which for me is normally off ( I've Solar), my AC is completely separate from the DC.. I know cause I've wired it myself. Sometimes the AC ground WILL connect to the DC via the battery changer DC negative, but YMMV

[Blue Stocking]

Next to anchors and guns, this is arguably the most discussed subject on this forum--but choose wisely.
The answer is yes--they do come together, but please read on.

[billwa]

I would imagine it depends on weather your AC is shore power or onboard genset.

Take the classic example of a steel hulled boat.

"earthing" (ie bonding) the genset to the hull (which is required for a electrical compliance certificate in australia) actually makes it more likely to be electrocuted. You need to grab one wire and touch something metal to be electrocuted.

Leaving the genset "floating" would be safer as only an active-neutral fault could possibly cause electrocution. You need to grab two wires.

The DC(-) and all metal appliances and the hull need to be eqipotential bonded for onboard safety, regardless of if you are using a genset or not. In this case, from a safety point of view, while on the boat you are perfectly safe.

Connecting the onboard bonding system to the shore power earth is necessary to prevent electocution if a fault exists at some point when you are stepping from the jetty to the pier or in the water around the boat.

[mitiempo]

It is a fiberglass boat.

ABYC does call for this connection. The theory being that you cannot depend on the shore power ground being properly connected. In the case of a fault in a charger or other AC device it gives it an out - preventing the entire DC system from becoming AC energized.

This does increase the chance of corrosion so a galvanic isolator is recommended.

From ABYC E-11

[goboatingnow]

Install a whole boat ELCI. Do not connect the two. Hey presto safety and isolation of the two electrical systems

Contrary to what's been said, the primary reason
That dc negative is connected to ac earth is to extend the ac earths protection into dc only connected equipment. The classic example is an engine. If this went ac hot, without the interconnect it could remain hot without triggering ac fuses. With the interconnect there's a safety path to blow the ac fuses. The comment re lack of shore earth has nothing really to do with it.

My view is as the first para. Not abyc compliant but a more modern and salient one



Dave

[mitiempo]

Here are the reasons Nigel Calder gives for the connection between AC ground and DC negative. All good reasons I think.