Safety Shore based power

[ArranP]

I am intending to install Victron Pheonix Inverter to be the exclusive provider of AC power on my boat with a seperate charger for charging the house bank from AC shore power. I am assuming negates the need for a isolation transformer as the AC power is only connected to the battery charger not the inverter.

However it has been suggested to use a Multiplus Inverter instead of the Pheonix. The Multiplus has a battery charger built into it. The problem I am considering is when the AC shore power connects to the Multiplus inverter, the boats ground plates will be connted to the shore based earth and thus could paralise someone in the water within the vicinity of my boat.

Where as with the Pheonix Inverter there is no connection to the AC shore based power, instead the AC power is connected only to the seperate battery charger.

[fxykty]

You want to isolate the shore earth from the boat ground. If you want to avoid using an isolation transformer then why not a galvanic isolator like this: https://www.victronenergy.com/isolat...anic-isolator?

[smac999]

The separate charger and inverter is the way to go of you want to travel the world. As a good charger will take 120 - 230v and 50-60hz. So you can charge in any country and the inverter will make correct power for your plugs no mater where you are. The multiplus does not. The charger needs to be big enough to handle all the loads plus charge though. So you might need 200a of chargers.

If you are not traveling. The multi is fine and has some advantages. They are on 1000’s of boats. You’d want a galvanic isolator or iso transformer.

[SailingHarmonie]

Your strategy of charger separate from inverter is a valid one, but you need to be sure that the charger is galvanically isolated from the boat’s electrical system. Not all are.

Also, the charger does not need to be sized for peak load, only the average load, letting the batteries buffer the peaks out of the inverter.

[boatpoker]

Originally Posted by ArranP

when the AC shore power connects to the Multiplus inverter, the boats ground plates will be connted to the shore based earth and thus could paralise someone in the water within the vicinity of my boat.

I'm assuming you are in salt water ... There are no recorded incidents of electrocution in salt water from vessel AC current. It is a fresh water phenomena.

[Fuss]

that’s right, the simple reason is that in fresh water a salty person provides a better path… however an iso transformer is a good idea.

[GordMay]

Originally Posted by boatpoker

I'm assuming you are in salt water ... There are no recorded incidents of electrocution in salt water from vessel AC current. It is a fresh water phenomena.

Originally Posted by Fuss

that’s right, the simple reason is that in fresh water a salty person provides a better path… however an iso transformer is a good idea.

In fact, electrical conductivity* [measured in microsiemens per centimeter (uS/cm)] is how we measure of the salinity [or purity] of water.

Freshwater is usually between 0 and 1,500 uS/cm [depending upon TDS - Distilled Water ≈0.5-3 uS/cm], and typical sea water has a conductivity value of about 50,000 uS/cm.
Hence sea water is as much as a million times more conductive than [pure] fresh water.
Ironically, the more polluted the water, the less likely is electrocution.


Conductivity of human tissue [S/m] ➥ https://www.researchgate.net/figure/..._tbl1_43148155
1 S/m = 1,000 uS/m

The electrical conductivity, of the human body, varies for different organs, like muscle, liver, and blood. The skin is the least conductive part, at about 10,000 uS/cm.
Hence the human body is over six times more conductive than fresh water, but only one fifth as conductive as sea water.

* Conductivity is formally defined as the reciprocal of resistivity, measured in Ohms [Ω]. Water can conduct electricity, because of the ion concentration within the water, which comes from dissolved solids and inorganic materials, like carbonate compounds, chlorides, and sulfides like sodium [salt]. The conductivity range also depends on the ion’s potential to bind with water.

[markcouz]

Very interesting read, thanks for that info.

What would be the risk of shock due to nearby lightning strike in salt water? If I am swimming and see a storm approaching I get out of the water - is that maybe unnecessary?

[fxykty]

Originally Posted by markcouz

Very interesting read, thanks for that info.

What would be the risk of shock due to nearby lightning strike in salt water? If I am swimming and see a storm approaching I get out of the water - is that maybe unnecessary?

Unless you get a direct hit or extremely near miss I would assume the shock is minimal. However, even your head above water raises your risk of getting struck by lightning, so the short answer is leave the water when a lightning storm approaches.