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wyb2 · 09-06-2017, 20:36

1st question (see picture): What is this braided uninsulated cable keeps popping up everywhere in the bottom of the boat? I assumed it was DC ground, but I haven't found anywhere that it actually connects to anything. Being low in the boat, anywhere it was resting against the hull has disintegrated from corrosion. I've been removing it as it clearly isn't doing whatever it was supposed to do. RF grounding maybe? All systems working fine without it, don't have an SSB (or know the first thing about them).

2nd question: Been reading about grounding requirements as I am installing an inverter. My understanding is AC ground (both shore and inverter) must be tied to DC- for safety, and DC- should only connect to the water at 1 point (engine/trans/prop shaft). It sounds like a galvanic isolator is a good idea to prevent corrosion when plugged in at a marina, but not a safety item. So I guess part a) is the above all correct? and part b) is a galvanic isolator a consideration for inverter power?

**Paul Elliott** · 09-06-2017, 23:09

Quote:

Originally Posted by wyb2

1st question (see picture): What is this braided uninsulated cable keeps popping up everywhere in the bottom of the boat? I assumed it was DC ground, but I haven't found anywhere that it actually connects to anything. Being low in the boat, anywhere it was resting against the hull has disintegrated from corrosion. I've been removing it as it clearly isn't doing whatever it was supposed to do. RF grounding maybe? All systems working fine without it, don't have an SSB (or know the first thing about them).

2nd question: Been reading about grounding requirements as I am installing an inverter. My understanding is AC ground (both shore and inverter) must be tied to DC- for safety, and DC- should only connect to the water at 1 point (engine/trans/prop shaft). It sounds like a galvanic isolator is a good idea to prevent corrosion when plugged in at a marina, but not a safety item. So I guess part a) is the above all correct? and part b) is a galvanic isolator a consideration for inverter power?

Don't know for sure about the braid, but it could have been part of an RF ground system. As you can see, braid isn't such a good idea on a saltwater boat because the fine wires are prone to corrosion. If you figure out what that braid was for and you want to replace it, you should consider copper foil / tape (the thicker the better).

As for a galvanic isolator, no, it's not a safety item, but it is still a very good idea when you have a shore power connection. The isolator can keep your zincs from rapidly eroding if you would have stray current because of improper grounding of neighboring boats or marina wiring. The zincs protect your underwater metal, from the effects of this stray current, so you want minimize it. Isolators do this pretty well. Stray current in a marina is a very common problem.

wyb2 · 10-06-2017, 09:23

Thanks. I highly suspect we currently do not have an isolator and, even though we will be spending very little time plugged in, may fit one as they are low cost and appear easy to install.

Thinking more about it, I can't imagine an isolator would serve any function on inverter power. It's preventing your grounding wire also serving as a DC connection to other underwater metal, and using up your zincs accordingly. However on inverter power there is no additional underwater components being potentially added to the DC- via the AC ground, so it should be a non-issue.

**Paul Elliott** · 10-06-2017, 09:37

Yes, the isolator is *only* wired to the shore power connection. It makes no difference when the inverter is providing your AC.

It's possible that your shore power situation has proper grounding, and your boat as well as any neighbors are perfectly set up. In that case, an isolator isn't needed. There are tests you can run so see if you have a stray current problem. But since in a marina you have no real control over your neighbors, the isolator may be a valuable addition.

When my boat was in San Francisco, I almost never used shore power, letting my solar panels keep the batteries topped off. Now that we're in Washington, where it gets cold, I run a small electric heater in the winter to keep the condensation under control. I installed an isolator because of this and it has helped with the zinc erosion.

hellosailor · 10-06-2017, 10:09

While that is generally referred to as "grounding braid strap" a PO might have installed it as part of a radio counterpoise, or as a bonding system between metallic thru-hulls and other underwater metal parts. Bonding and grounding being slightly different concepts.

The rotted green sections kinda prove that tinned copper isn't invulnerable after all, huh?