Fail Safe Installation of a DYI Galvanic Isolator?

[dreuge]

Dear Maine Sail,

I have read many discussion regarding the need, use, and installation of galvanic isolators. I don't understand why one should NOT install the galvanic isolator at the junction between the DC ground and the AC green ground. Installing at the DC/AC junction seems like a "fail safe" installation. The green AC safety ground is never broken therefore it always remains a fail safe.
In this case, one could purchase a more affordable non fail-safe GI or use a decent 50A DYI galvanic isolator (which can be made for under $20). Any failure of the GI would only isolate the DC ground from the AC safety ground, which is probable the case for most sailboat under 40' anyway. More important, I would guess, is the use of GFCI protection on all AC circuits.

 

[IStream]

Well, for one thing it defeats the main purpose of the galvanic isolator, which is to isolate the boat from small external potentials that can eat your zincs. If you don't break the green AC ground wire with the GI, it does nothing in this regard.

 

[dreuge]

Well, for one thing it defeats the main purpose of the galvanic isolator, which is to isolate the boat from small external potentials that can eat your zincs. If you don't break the green AC ground wire with the GI, it does nothing in this regard.

Thanks for you reply, but let me remind you that it is the bonding of the AC and DC grounds which can lead to excessive galvanic corrosion. Placing a GI on the DC ground side of the AC/DC ground junction will isolate the DC ground system from the AC green ground thus isolating the connection to your engine, shaft, prop, and zincs as desired. There maybe be other reasons for not installing the GI as proposed, but it will provide the galvanic isolation.

 

[Johnb]

My read on it is that the GFCI will protect against current leakage from live and/or neutral to ground but does nothing to prevent current flowing between the incoming AC "ground" (which may have a voltage difference relative to the local ground, sea water etc) and the water surrounding your boat. It is the current that flows between the incoming AC ground and the surrounding water that does the damage.

If you could be entirely sure that there is no connection between AC ground and DC ground anywhere on the boat, other than the point at which they are officially connected, then what you say would be valid, but I suspect that in real life you are better off installing the galvanic isolator where it is supposed to be. And not using any homemade ones.

 

[IStream]

Thanks for you reply, but let me remind you that it is the bonding of the AC and DC grounds which can lead to excessive galvanic corrosion. Placing a GI on the DC ground side of the AC/DC ground junction will isolate the DC ground system from the AC green ground thus isolating the connection to your engine, shaft, prop, and zincs as desired. There maybe be other reasons for not installing the GI as proposed, but it will provide the galvanic isolation.

It's the DC from the other boats that it's isolating you from.

 

[Maine Sail]

If you want to install a GI, and meet applicable safety standards, it is installed immediately after shore power inlet. This is an ABYC requirement as well as an ISO/RCD requirement. Installing it in any other location removes the bouncer from the bars entrance and this means the bouncer can be quite easily bypassed.

If you really want to protect you boat unplug or install an isolation transformer.

 

[thinwater]

I've always felt like most boats with solar panels really don't need to be plugged in when unoccupied. On less thing.