ECN Forum Forums General Topics of the Trade General Discussion Area Wiring boat lifts to avoid electrolysis

There is a discussion going on over on one of the boat discussion groups about elevator style lifts that have metal in the water all the time. When this is connected to the service grounding electrode system, it tends to become the best electrode and if the metal is aluminum, it will erode away.
There are lots of ideas about how to legally mitigate the problem. The easiest one is to simply unplug the whole thing when it is not being used but that still leaves it connected when you are out in your boat. That mitigates most of the damage but not all of it. My first thought is why don't they use double insulated motors so they would not need the grounding conductor in the first place but those motors do not seem to exist in normal circles. (120/240 6 wire motor at 1hp or so).

The other thought is a 3 or 4 wire contactor/switch that disconnects all wiring when the motors are actually running as part of a "Gem" style controller. (uses a gate opener clicker)

Any thoughts here?

Greg:

I have not heard of any electrolysis issues related to boat lifts in my neighborhood, but I'll ask & look around. I have a 'down the block' neighbor that owns a bulkhead etc. business, and he installs lifts. Another neighbor is a EC that does a lot of work on docks/lifts.

Your thought of a "remote" contactor and opening the EGC with the supply sounds interesting. Now...should we get into 'make-break' debates?

The ones with the problem are aluminum in salt water, typically the "elevator" style where the frame is always in the water.
I would not own one, simply because of the marine fouling problems but people do.
I think the real answer is to separate the <service> bonded parts from the part that is in the water by double insulating the motor or electrically isolating it from the frame.
That is something that would have to be coordinated between U/L and the manufacturer I suppose.

I think on an existing installation I would start by making sure my electrodes at the house are doing their job. This may not be as big a problem when the electrode is a city wide metal water system. Folks up north may not really see it that much. I suppose if you drove additional electrodes down near the dock it would mitigate voltage differentials but dissimilar metals in the electrolyte (salt water) might create it's own problem. Do they make aluminum ground rods

Living by the coast, and observing what salt in the wind can do to unprotected aluminium, (without the help of any electrolysis), I would think that protective coatings on the exposed metal would be the only hope.
I know nothing about boats, but are these aluminium lifts really designed for salt water use?

They use aluminum because steel just will not hold up in salt water, even galvanized. As I said, I would not use that style at all, my lift has no metal in the water but they do seem popular, particularly for small boats and jet skis.

Can you put another electrode in the water and use cathodic protection?

That is the issue. The anodes are eaten away very fast. If they do not stay on top of them the lift starts eroding away.

Sacrificial anodes are the way to go. As long as you replace them as needed the Aluminum will last quite a while.