question

animaashi avatar image
animaashi asked

Why do we have shorts and stray voltage while on shore power?

We are operating a sailboat with a Victron Multiplus 24v 3000Va charger/inverter onboard. We have recently been hauled out of the water for work and we now have some strange things going on. While we are on inverter power everything appears to be ok. When we plug in and switch the shore power on (3 pole switch/breaker) then we have 75vac between hot and ground, and 48vac between neutral and ground. There is 48vac between the grounded components of the boat and the dirt. This is happening regardless of if the multi-plus is active or not (when on shore power and the incoming 3-pole switch is closed). There are no shorts between hot & ground or neutral and ground on the plug side of the shore power switch. There are also no shorts between hot and ground on the boat side. This was determined by turning everything off and testing with a multimeter. This is perplexing and I am thinking that the multi-plus has failed or that there is a problem with the shore power. However the shore power tests just fine as well with no shorts and voltage only between hot and neutral, and hot and ground. Currently the chassis of the Multiplus is not tied to the ship's ground I will be working on that today, it is bonded however through the ac input line. We have an ELCI after the multi-plus which does not trip. The Multi-plus is wired directly inline from the switch for shore power, and is wired directly to the ELCI, which then goes back to the distribution busses.


Update: grounding the chassis of the multi-plus to the ship's ground has not resolved the issue.

Thank you.

MultiPlus Quattro Inverter ChargerGroundingshorepowersafety
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5 Answers
kevgermany avatar image
kevgermany answered ·

I think you need to get it checked by an electrician.

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animaashi avatar image animaashi commented ·
The multi-plus itself? Or the entire install? I had a guy up here the other day who was scratching his head as this makes no sense.
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snoobler avatar image
snoobler answered ·

Floating ground. With the boat out of the water, the hull is no longer grounded.

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animaashi avatar image animaashi commented ·
I do not believe that the ground is floating. The multi-plus will close the connection between the ship's ground and the panel ground and open it's own ground to neutral connection which should be bonded at the panel. Therefore the boat should be grounded by the shore power connection. Now I am not getting any continuity between neutral and ground on the shore power side, could this be causing the issue?
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snoobler avatar image
snoobler answered ·

What is the hull's grounding plate connected to?



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animaashi avatar image animaashi commented ·
The DC negative bus bar is grounded and bonded to everything else. The AC bus is grounded to the negative bus bar, the inverter chases is grounded to the DC bus. The Ground bus is connected to everything and is performing the grounding by proxy for the shore power. I don't understand why we are having this issue, we're nothing more than a fancy tree house with an extension cord at the moment.
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kevgermany avatar image
kevgermany answered ·

The multiplus has an internal automatic connection between neutral and ground for off grid use. That would explain the disconnection between neutral and ground.


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Daniel Swaab avatar image
Daniel Swaab answered ·

@Animaashi I seem to run into the same issue ; Did you ever find a solution?

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