Shore power, inverters and RCD/MCB

rogerthebodger

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One more question: Is it necessary to have a reverse polarity indicator on the boat if all my circuit breakers are 2P? By googling it would seem that the answer is "no", but I thought I would double check with the forum.

I also have a reverse polarity indicator consisting to 2 neons green between line (live) protective earth and (red between incoming neutral and protective earth.

Green must be on and red must no off

If reversed reverse polarity , if neither on protective earth fault.

This only applies to the incoming shore power then inverter should no be able to show reverse polarity if wired correctly
 

Alex_Blackwood

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Aliex this is one of my points that it depends on the exact configuration of both inverter and boat

Clearly a an inverter with a center tap output is different to a to one that does not have a center tap.with regard to a protective current path to comply with Kirchoff's law of current flow

Not interested in Paul Rainbow any more
Strongly disagree. Paul talks from experience. I think you will find that he does very much follow the guidance and knows his onions! Nuff sayed 🤫
 

rogerthebodger

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Strongly disagree. Paul talks from experience. I think you will find that he does very much follow the guidance and knows his onions! Nuff sayed 🤫

Cannot agree as I also talk form experience but maybe different experience so we must agree to differ .

Its his attude to anyone who differs due to different knowledge and experience.

Nuff said
 

Tranona

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For what it's worth there's a shaft zinc on my stainless shaft, close to the bronze propeller. No other grounding points on the boat, plastic through hulls all around. From the conversation here I gather this might not be optimal, so I'm furiously flipping through my copy of Calder's book trying to find out why.
Nothing wrong with that and no reason to change. The only reason I used an anode was to ground the 240v as it is a convenient and cheap way to do it. Not connected to the engine or the stern gear. However if I did have a hull anode wired to the shaft via the gearbox I would have used that for the ground.
 

PaulRainbow

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The OP is proposing to fit a Victron Multiplus, from the installation manual (highlighting is mine) :

- In a fixed installation, an uninterruptible grounding can be secured by means
of the grounding wire of the AC input. Otherwise the casing must be grounded.
- In a mobile installation (for example, with a shore current plug), interrupting the
shore connection will simultaneously disconnect the grounding connection. In
that case, the casing must be connected to the chassis (of the vehicle) or to the
hull or grounding plate (of the boat).
 

PaulRainbow

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For what it's worth there's a shaft zinc on my stainless shaft, close to the bronze propeller. No other grounding points on the boat, plastic through hulls all around. From the conversation here I gather this might not be optimal, so I'm furiously flipping through my copy of Calder's book trying to find out why.
If you are not connected to shore power you will not have a path to Earth. A small button anode (as mentioned by Tranona) will provide such a path if no other method exists.

In addition to post #25 the current ISO states :

6.3 The AC protective conductor(s) shall be provided with a final (single) connection to the hull of a
metallic hull craft, or, if the craft has a non-metallic hull, to the main grounding/earthing point of the craft.

You are not legally obliged to comply with the ISO, but it seems silly not to, especially as Victron state the inverter should be grounded.

One more question: Is it necessary to have a reverse polarity indicator on the boat if all my circuit breakers are 2P? By googling it would seem that the answer is "no", but I thought I would double check with the forum.

It looks like it's cheaper to buy an external testing device (e.g. this) than pay for a Blue Sea's panel with a reverse polarity detector.
No legal requirement for you to fit a reverse polarity indicator. A mains neon is a cheap and effective method of providing one if you choose to fit one. Just connect between neutral and earth (neon polarity reversed) if it lights up the polarity is reversed.
 

sailoppopotamus

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Thanks to all for your help, much appreciated. I've read the Victron manual and underlined the bit about the inverter being grounded. As said earlier I'll measure the engine to shaft resistance with my multimeter to make sure that my engine is actually providing a good path to the water, else I'll fit a button anode as suggested next time I haul the boat.
 

RupertW

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Thanks to all for your help, much appreciated. I've read the Victron manual and underlined the bit about the inverter being grounded. As said earlier I'll measure the engine to shaft resistance with my multimeter to make sure that my engine is actually providing a good path to the water, else I'll fit a button anode as suggested next time I haul the boat.
It’s a good idea to measure the resistance but do be aware that a very low resistance will be shown by multimeter even if some part of the connection is bad, but a massive resistance if any loads go on. Normally I’d put a load through the possible bad connection and measure voltage drop and current but I confess I’m not sure whether I’d do that with the prop in the water.
 
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