Question about inverter earth connection to boats earth or bonding system

[Tim-JS]

Hi,

I’m about to install a Sterling Power inverter / charger, which they call a "combi".

I’ve read all the inverter installation threads i can find, but there’s one area i’m not 100% sure about so thought it would be prudent to check with the hive .

One end of the unit has the AC input and output, and the other has DC positive and negative along with an external earth point.

The installation instructions have a diagram showing that the earth needs to be connected to “boats earth or bonding system”.

The house bank and inverter are towards the front of the boat, and the engine and its earth are towards the rear.

Is it OK to use the continuity that exists between the house DC negative and the earth on the engine, or do I need a new stand alone cable directly between the earth on the unit and the earth on the engine ?

And if the former is acceptable, is there a preferred point to access this, eg:

• simply connect the earth and DC negative together on the unit (obv i’ll have the DC negative on the unit connected to the load/charge side of the shunt).
• have a separate cable from the earth on the unit to the load/charge side of the shunt
• have a separate cabe from the earth on the unit directly to the house DC negative (ie bypassing the shunt)

In case it’s significant:

• The SP documentation confirms “When the Combi is in inverter mode the 'through the box' earth line is automatically disconnected from the input earth and joined to the output neutral, complying with the natural earth inverter requirements”
• I intend to keep the inverter output circuit separate from the shore connected AC circuit, and it will have its own RCCB & MCB consumer unit and “inverter only” sockets

Hope this makes enough sense.

Thanks, Tiim.

 

[VicS]

Hi,
I’m about to install a Sterling Power inverter / charger, which they call a "combi".
>
>
Is it OK to use the continuity that exists between the house DC negative and the earth on the engine, or do I need a new stand alone cable directly between the earth on the unit and the earth on the engine ?

Thanks, Tiim.

It should be earthed directly to the main earthing point as indicated in the installation instructions.

.

 

[PaulRainbow]

Hi,

I’m about to install a Sterling Power inverter / charger, which they call a "combi".

I’ve read all the inverter installation threads i can find, but there’s one area i’m not 100% sure about so thought it would be prudent to check with the hive .

One end of the unit has the AC input and output, and the other has DC positive and negative along with an external earth point.

The installation instructions have a diagram showing that the earth needs to be connected to “boats earth or bonding system”.

The house bank and inverter are towards the front of the boat, and the engine and its earth are towards the rear.

Is it OK to use the continuity that exists between the house DC negative and the earth on the engine, or do I need a new stand alone cable directly between the earth on the unit and the earth on the engine ?

And if the former is acceptable, is there a preferred point to access this, eg:

• simply connect the earth and DC negative together on the unit (obv i’ll have the DC negative on the unit connected to the load/charge side of the shunt).
• have a separate cable from the earth on the unit to the load/charge side of the shunt
• have a separate cabe from the earth on the unit directly to the house DC negative (ie bypassing the shunt)

In case it’s significant:

• The SP documentation confirms “When the Combi is in inverter mode the 'through the box' earth line is automatically disconnected from the input earth and joined to the output neutral, complying with the natural earth inverter requirements”
• I intend to keep the inverter output circuit separate from the shore connected AC circuit, and it will have its own RCCB & MCB consumer unit and “inverter only” sockets

Hope this makes enough sense.

Thanks, Tiim.

You are confusing protective Earth and DC negative. Forget about the DC systems, DC negatives and "engine Earth"

Your inverter sockets should all have their Earth connections taken back to the consumer units Earth busbar. The inverter output Earth and case Earth should also go to the consumer units Earth busbar. You must have a wire from the consumer units Earth busbar to the water. The connection to the water can be the hull of a metal boat, the vessels ground plane (if it has one) the main hull anode (if it has one) or a small anode, fitted for the purpose of providing a PE connection.

If the current shore power Earth is connected to the water, you should use this same connection for the inverter. In this case you can connect the inverter PE circuit to the Earthing point, or to the shore power consumer unit busbar.

All Earth wiring must be the same size/rating as the current carrying wires, i would use 2.5mm arctic flex throughout.

Do not rely on connecting the Earth to anything other than the above.

 

[Alex_Blackwood]

You are confusing protective Earth and DC negative. Forget about the DC systems, DC negatives and "engine Earth"

Your inverter sockets should all have their Earth connections taken back to the consumer units Earth busbar. The inverter output Earth and case Earth should also go to the consumer units Earth busbar. You must have a wire from the to the consumer units Earth busbar to the water. The connection to the water can be the hull of a metal boat, the vessels ground plane (if it has one) the main hull anode (if it has one) or a small anode, fitted for the purpose of providing a PE connection.

If the current shore power Earth is connected to the water, you should use this same connection for the inverter. In this case you can connect the inverter PE circuit to the Earthing point, or to the shore power consumer unit busbar.

All Earth wiring must be the same size/rating as the current carrying wires, i would use 2.5mm arctic flex throughout.

Do not rely on connecting the Earth to anything other than the above.

Thought you might pick that up. The terminology in some of the posts regarding Negatives, Earths and Neutrals, amongst other things . is somewhat sloppy!
I would again reiterate that if the OP is in anyway unsure he must consult a professional.

 

[Tim-JS]

Hi,

Thanks all for the info.

@Vic, if I read the diagram in the SP installation instructions as “logical” rather than “physical”, they all appear to be connected together ? (FYI my boat currently has the DC negative connection to the engine earth from the starter battery rather than the house, and house and starter DC negatives are connected together.)


@PR, thanks, I agree I’ve not made the full picture clear so my question may be “confusing protective earth and DC negative” with no hint at why (the hint being that I thought my engine block has an electrical connection to the water(?), and all my DC negatives are connected to the engine block.)

(Please pardon my layman’s terms...)

My boat is from 2007 and from the owner’s manual and what I can see physically, doesn’t currently appear have (what i call...) a consumer unit with RCCD protection. I think this is/was considered acceptable (in 2007) because the only time there is 230V is when connected to shore power and the (European) shore supply includes the RCCD protection?

When I install my inverter, there will now be another source of 230V, so I need a protective earth for this too.

My thoughts were that if the "common ground" on my engine block is electrically connected to the water, this appears to be the most logical ground to use for the new AC inverter & its circuit.

And if this is the case, this lead me to the question of whether to use a new stand alone (2.5mm, thanks) “Inverter AC circuit” ground connection, or whether it would be OK to connect to the much thicker DC negative connections that are already connected to this ground, as the installation diagram appears to suggest?.

@AB, very good point but I’d also like to understand, not least because my experience suggests “professional” isn’t a 100% guarantee either .

Hope this makes enough sense and again thanks all for sharing your wisdom.

Thanks again, Tim