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meshugga avatar image
meshugga asked

Electrolysis Problem - Autotransformer 120/240VAC-32A

I have recently installed an Autotransformer on my yacht to achieve 115 Vac power. Power is supplied by a 230 Vac Multiplus. According to the installation instructions, I achieved a Ground-Neutral bond by unchecking the Multi's "ground relay" setting and connecting ground relay to earth relay. The Autotransformer works just fine.

However, all my stanchions and other 316 stainless steel deck fittings have now started showing surface rust which is causing rust streaks down the hull. This did not happen prior to installation of the Autotransformer and is obviously unacceptable.

My 230Vac is grounded via 2 large zinc plate anodes through-bolted below the waterline. These anodes are not electrically isolated from the GRP hull. The engines, generator, watermaker, and other DC & AC electrical equipment are also all grounded to these anodes.

Any input/solution will be welcome


Autotransformer
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meshugga avatar image meshugga commented ·
Has anybody else had this problem?

Is this an installation fault or is it an inherent problem with the way the Autotransformer must be connected? Unless I can resolve this, I may need to return the Autotransformer and rather install a 115 Vac Multiplus.

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JohnC avatar image
JohnC answered ·

Hi @Meshugga

I very much doubt that you have an electrolysis issue based on those observations. 316 can appear to 'rust' over time, especially if someone's polished it with mild steel wool. And I'd expect it to continue no matter what you do with your electrical system.

Perhaps you should talk with a stainless supplier expert to see what he says. Or even google it. There are passivation treatments that can be applied too.

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Trevor Bird avatar image
Trevor Bird answered ·

Hello @Meshugga . Isolated deck fittings on GRP can’t have electrolysis corrosion because they are totally isolated. Electrolysis ( stray current corrosion) can only occur in the presence of a current. If those fittings are showing signs of “tea staining”, it can’t be because of the auto transformer.

I am not including stanchions in this because they may be connected to ground through the lifelines but isolated fittings cannot suffer Electrolysis corrosion.

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