Galvanic isolators

[landyhubbard]

I fitted a galvanic isolator to my boat's shore supply last year, mainly because I read somewhere that said that it was necessary to ensure propper operation of the RCD, and obviously there are the claimed advantage that it protects the boat against stray current leakage. A friend of mine is fitting a shore supply to his boat, for occasional use when he visits marinas. He keeps his boat on a mooring so it won't be plugged in most of the time. He has been told by an "electronics expert" that the galvanic isolator is unnecessary and could be positively harmful- is he right?

 

[pvb]

Not harmful...

Fitting a galvanic isolator certainly wouldn't be "harmful", but a galvanic isolator isn't essential if there's only very occasional use of shorepower.

 

[Nautorius]

Hi,

Galvanic Isolators are only critical in a metal (Steel or Aluminium) hull or when shore power permanently connected. If on a swing mooring he should be fine, as long as shore power time limited. Does he have Bravo 3 outdrives? If he does, regardless of where it is moored I would fit one as they tend to disappear rather quickly when plugged in!

Cheers

Paul /forums/images/graemlins/laugh.gif

 

[Roach1948]

I thought a galvanic isolator was to stop Earth leaks through the 12v system - So if no battery charger is permanently attached to the 12v system, my understanding is that an isolator is not required.

 

[john_morris_uk]

[ QUOTE ]
I thought a galvanic isolator was to stop Earth leaks through the 12v system - So if no battery charger is permanently attached to the 12v system, my understanding is that an isolator is not required.

[/ QUOTE ]The 12v system might be a bit of a bit of a red herring as some boats cathodic protection is connected to the boats 12v negative and some are not. For example in our boat, the cathodic protection is completely isolated from the ships 12v system as there is special insulation fitted between the engine and the gearbox.

In a boat where the 12v system is also connected (often unavoidably) with the cathodic wiring, and the boat spends a lot of time plugged into mains power, then a galvanic isolator makes a lot of sense. The galvanic isolator ensures that stray currents through the mains lead cannot exacerbate or nullify the correct action of the anodes fitted to your hull and underwater gear.

Hope that this makes sense and clears up a possible confusion.

 

[VicS]

[ QUOTE ]
I read somewhere that said that it was necessary to ensure propper operation of the RCD,

[/ QUOTE ] You have your logic about the primary purpose of the galvanic isolator (GI)and its secodary benefits round the wrong way.
The purpose of the GI is to block current originating from low voltage sources that cause galvanic corrosion if shore power is left plugged in for prolonged periods.
It is the earth connection itself is what ensures that the RDC will operate. At least the shoreside RCD.
To ensure full protection and correct operation of the on board RCD it is important that the 12 volt negative and the major metal items on board are connected to the earth.

Your friend's "electronics expert" is right about there being no need to fit a GI on a boat kept on a mooring (or not normally left plugged in) but wrong about one being harmful.

For more details take a look at http://www.yandina.com/galvanicIsolator.htm While you are there also read the section dealing with the debate about fitting a capacitor as well, and also the Installation instructions in the "Manuals" section of the site