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Dosheimer asked

Mobile petrol generator on boat: Additional groundig necessary?

Hi!
I am before buying a mobile petrol generator for offshore use on my sailboat for charging my lithium batteries from time to time when there is not enough solar and wind.

The protective earth wire of the 230V shore power plug of the boat first goes through a zink saver (Sterling Saver II / Pro Save E) and then via RCBO and fuse to a Multiplus 12/3000/120-50.

After the zink saver and before the RCBO+fuse the grounding is connected to a big zink anode through the hull (big zink anode fully has permanent seawater contact). Also the Multiplus is connected to this central earthing point in the bilge of the boat.

Question: Do I have to ground the generator iteself in addition i.e. with an additional cable from the generator into the seawater in this setup?

Grounding
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Dosheimer answered ·

this is written in the manual of the generator:
["...the generators were initially designed as an IT system with basic protection by insulation of hazardous live parts according to DIN VDE 0100-410. The generator housing is insulated from the current-carrying L and N conductors. The generator must be grounded in all cases, except for an IT system with an insulated neutral wire and bonding. A grounded IT system requires the use of an insulation monitoring device..."]

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Dosheimer answered ·

just did read about it. I will ask for a professional electrician before buying...

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dc-marine answered ·

Since the generator is onboard the vessel, you do not need to externally ground it to the water/hull. However you need to connect the neutral to the ground inside the generator, so that a ground fault may make is way back to the power source, aka the generator. This is what is referred to as a "bonded neutral" and is the opposite of a "floating neutral" where the neutral and the ground are not connected anywhere. Plugging the generator to your shore power inlet will effectively ground it by using the grounding conductor (green and yellow) of the cord, just like it happens when you connect to shore. The conductive chassis parts of the generator would already be bonded by the manufacturer when assembled.


According to your manual, the neutral (grounded conductor) and the line (ungrounded conductor) are not connected to the housing/ground (grounding conductor). This is done because most mobile generators aren't meant to be powering an electrical installation but rather portable equipment such as power tools or computer. Since you are using the generator as a power source for an installation, the neutral and ground must be bonded at the source, aka inside the generator enclosure.

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Dosheimer avatar image Dosheimer commented ·

Thanks for your response!

My doubt is the additional earthing point in the boat (central boat earthing point) as described in my initioal post.

Could you please check my following thought:

When I would do the described bonded neutral via a connection/bridge between neutral and earthing wire directly at/in the generator and when I do not ground the generator itself into the seawater, the current can flow back from a faulty device within the boat to the generator and will activate the RCBO within the boat. The additional central boat grounding also is connected in this setup (as it has connection with the earth wire of the shore power plug of the boat), but will not play a role as there is no connection between the central earthing point in the seawater throught the seawater to the generator to make something like a ground-loop. Therefore my 30ms 100mA RCBO´s would work.

In this correct? Or can the central earth point within the boat can cause any trouble in this context?

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dc-marine avatar image dc-marine Dosheimer commented ·

This is correct. Your RCB should operate as intended as long as there’s a difference of current between your line and neutral, regardless of where the grounding connects to, as long as the fault can make its way back to the power source. Since your load panel is grounded to the same bus as your shore power inlet and the seawater grounding point, any fault should be able to carry back to the source and trip your protection. A fault being defined as energizing a conductive grounded surface, not just a line wire connecting to a non conducting grounded surface such as chaffed line wire to the fibreglass hull.

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Dosheimer answered ·

Maybe someone knows something about prospective problems because of the connection to the already existing boat´s central grounding point?

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