Electrical ground

[moonshadow]

As I am working my way through a stray current issue I found that I am confused about the electrical ground setup on my 469. I was under the impression that the 12 volt and the AC (120 v in my case) shared a common ground. However it turns out that is not the case. One of by DC items on my boat ran the neg wire to an AC ground in error leading to some stray current damage that luckily was identified early, preventing a major problem.
One of the confusing parts is that my boat was wired using the “old” wire color scheme and parts were wired using the “new” color scheme. So black wired can be different purposes.
Lesson learned: best to check with electrical testing before assuming black is a 12v ground.
And: probably a good idea to spend more time learning how to really read the electrical diagram.

[zaphod]

ABYC recommends connecting the DC negative to the AC ground, but european boat builders appear to disagree. On our 39i they are not connected. I toyed with the idea of bringing our boat into compliance with abyc, but decided to leave it as designed. It seems to me the chances of galvanic corrosion are much lower if you keep the systems separate, and therefore no need for things like galvanic isolators. I have yet to hear a compelling reason ABYC thinks they should be connected.

[moonshadow]

I do think that could be part of my confusion. It appears that aybc standards don’t always apply as you described.

[Trevor]

I agree with Zaphod. Galvanic corrosion much more likely with mains earth and DC earth connected.

[moonshadow]

Trevor, my experience seems to support you.