Shore power and galvanic corrosion

[roaringgirl]

I want (need) to connect to shore power for the southern hemisphere winter - I'm not getting enough from solar, and I need to run a dehumidifier. I have a 3kVA victron multiplus charger/inverter, I didn't install it myself, so I'll need to rummage to check the wiring for shore power. There is a galvanic isolator in the wiring between the boat's shore power socket and the inverter. The shore power post has an RCD.

I have some options:
1. Connect the boat to shore power and use it in "charger only" mode - this will keep the batteries topped up, and supply 220V ac to the outlets on the boat. Presumably this means that my anodes will be connected to the earth of every other boat on the dock, so my anodes will be at the mercy of everyone else's electrical systems (how effective is a galvanic isolator?)

2. Connect the boat to shore power, and leave the inverter/charger switched off - the PV will keep up with the 12V needs on board and the shore power will do for the cooktop and the dehumidifier. What happens to the earths in this case? If I'm not using the inverter unit at all, is my earth still provided by the engine block (and my anodes) or is it being provided by the shore post - and will my anodes therefore be safe from everyone else's systems?

3. Run a cable from shore power to a single AC outlet inside the boat, bypassing my boat and all the earthing/anode issues associated with it. This will be a bit more fiddly to live with, but might be better I can't protect my anodes any other way.

Please advise - I'm just trying to think this one through and I'm not sure how the earthing works and how my decisions will affect the longevity of my anodes (and then the destruction of important things!)

 

[Alex_Blackwood]

I want (need) to connect to shore power for the southern hemisphere winter - I'm not getting enough from solar, and I need to run a dehumidifier. I have a 3kVA victron multiplus charger/inverter, I didn't install it myself, so I'll need to rummage to check the wiring for shore power. There is a galvanic isolator in the wiring between the boat's shore power socket and the inverter. The shore power post has an RCD.

I have some options:
1. Connect the boat to shore power and use it in "charger only" mode - this will keep the batteries topped up, and supply 220V ac to the outlets on the boat. Presumably this means that my anodes will be connected to the earth of every other boat on the dock, so my anodes will be at the mercy of everyone else's electrical systems (how effective is a galvanic isolator?)

2. Connect the boat to shore power, and leave the inverter/charger switched off - the PV will keep up with the 12V needs on board and the shore power will do for the cooktop and the dehumidifier. What happens to the earths in this case? If I'm not using the inverter unit at all, is my earth still provided by the engine block (and my anodes) or is it being provided by the shore post - and will my anodes therefore be safe from everyone else's systems?

3. Run a cable from shore power to a single AC outlet inside the boat, bypassing my boat and all the earthing/anode issues associated with it. This will be a bit more fiddly to live with, but might be better I can't protect my anodes any other way.

Please advise - I'm just trying to think this one through and I'm not sure how the earthing works and how my decisions will affect the longevity of my anodes (and then the destruction of important things!)

Option 1 The GI will isolate the earth loop from the shore supply, unless there is a fault. Your inverter will have an earth connected but this is not part of the shore supply loop. That is a simple answer. No doubt you will have all the experts along shortly with more detailed descriptions.

 

[Tranona]

Option 1. What thousands of people do without any problems. Your anodes will not be connected to the 220v. They should only be connected to the items they are protecting and nowhere near the 220v. Most GRP boats only require one anode for the propeller/shaft or if a saildrive for the drive housing and possibly propeller, none of which have a connection to 220v.

 

[vyv_cox]

As you have said, it is the earth connection to the power supply, and thence to other boats, that is potentially the problem. Most(all?) galvanic isolators disconnect the earth but some also disconnect the 220 volt supply in the event of problems. There is a threshold of, I think, about 1 volt on the earth so that it functions for safety purposes but otherwise disconnects to avoid unwanted corrosion. I assume you can check yours to know which you have.

 

[roaringgirl]

Urgh, I'll have to take the headlining down in the heads to look at the GI unit!

 

[Alex_Blackwood]

Urgh, I'll have to take the headlining down in the heads to look at the GI unit!

Strange place to put it! have you considered moving it if you have to take the headlining down? They can go wrong.

 

[William_H]

Permanent connection to mains for a boat witha GI is quite common and apparently without problems. However the whole matter is a bit of a dark art. YOu should be ok with mains connected 24/7 however if youb are concerned easiest is to run the dehumidifier on a single lead from jetty supply with no other connection or earth. Assuming dehumidifier is all plastic so called double insulated. ol'will