Mike Dolt Enterprises
Mike Dolt Enterprises
User: hardworkingstiff, Location: Wilmington, NC
Asked on: Tuesday, April 19, 2011 at 6:15 am EDT
Answered on: Tuesday, May 14, 2024 at 4:22 am EDT
Question: I've heard of a few problems with corrosion in marinas. Reading articles on the WEB about it seems to indicate that although the grounding system of the marina wiring is involved, it is usually not the cause.Thinking about this some more, I had the thought that the only reference to ground with the electrical system are the ground rods at the service disconnect and the grounding system of POCO.So, what happens if the POCO grounding starts to develop some resistance and the water the boats are in becomes a competitive parallel path back to the substation? The boats are supposed to have the engines bonded to the AC ground conductor and that would allow any metal on the boat in contact with the water to carry AC current from the AC grounding system into the water and back to the substation. Any degradation of the AC system neutrals or grounding connections would tend to raise the current flow on the marina ground conductors going to the boats.In general, I've always been taught/told that AC current does not cause corrosion. I've read some people say that's not quite true, but the current level has to be pretty high. Usually, electrically induced corrosion is from a DC source (that's how dissimilar metals corrode, they set up a DC cell).The question I would like to throw out for comments is, under what conditions would the marina wiring actually cause the zincs on the boats to corrode? Please understand this is not a question of how the AC ground system is part of the corrosion cells formed when boats are in conductive water and plugged into a common grounding system.Thanks in advance for any comments.
Possible Conditions for Marina Wiring-Induced Zinc Corrosion
Under certain specific conditions, the marina wiring system can contribute to zinc corrosion on boats:
High Neutral-to-Ground Resistance
If the neutral-to-ground resistance in the POCO grounding system increases, it can cause a voltage drop between the neutral and ground at the marina service disconnect. This voltage drop can establish a potential difference between the boat's AC grounding system and the surrounding water.
Conductive Hull and Underwater Metals
If the boat's hull and underwater metals are conductive (e.g., steel, aluminum), they will be in contact with the water. This provides a path for AC current to flow from the boat's AC grounding system into the water and back to the substation via the POCO grounding system.
High AC Leakage Currents
If there are high leakage currents in the marina's electrical system, such as from damaged wiring or equipment, this can increase the amount of AC current flowing through the boat's grounding system and into the water.
Electrolytic Cell Formation
When AC current flows through the water, it can create an electrolytic cell between the boat's underwater metals and the zinc anode. This electrolytic cell can lead to the corrosion of the zinc anode.
How it Works
1. The high neutral-to-ground resistance establishes a voltage potential between the boat's AC ground and the surrounding water.
2. Conductive hull and underwater metals provide a path for AC current to flow from the boat's grounding system into the water.3. High leakage currents increase the amount of current flowing through the boat's grounding system and into the water.
4. Electrolytic cell formation between the boat's underwater metals and the zinc anode causes the zinc anode to corrode.
Note:
It's important to emphasize that this type of corrosion is uncommon and requires a combination of specific conditions. Additionally, the effects of galvanic corrosion (DC currents) between dissimilar metals in the water are typically much more significant. Flag for review