Inverter on board

sailaboutvic

sailaboutvic

Well-Known Member
Joined
26 Jan 2004
Messages
9,972
Location
Northern Europe
Visit site
I'm looking at buying a 3000w inverter most have a earth connection, talking to some who have them the earth isn't connected,
what the view on connecting the earth and where too ?
 
If it doesn't have an Earth connection, don't buy it. Inverters must be Earthed, anyone who doesn't correctly do so is an idiot.

If you shore power Earth is grounded on the boat, connect it to that point. This can be the hull of a metal boat, the ground plane (if fitted), a hull anode or any other below the water metalwork. Basically, it needs to be connected to the water, therefore the Earth.

There is a little more to fitting an inverter. Do you plan to have it connected to onboard systems (existing sockets etc) through the boats consumer unit, or to have it "freestanding", where you just plug things into the inverter itself ?
 
PaulRainbow said:
If it doesn't have an Earth connection, don't buy it. Inverters must be Earthed, anyone who doesn't correctly do so is an idiot.

If you shore power Earth is grounded on the boat, connect it to that point. This can be the hull of a metal boat, the ground plane (if fitted), a hull anode or any other below the water metalwork. Basically, it needs to be connected to the water, therefore the Earth.

There is a little more to fitting an inverter. Do you plan to have it connected to onboard systems (existing sockets etc) through the boats consumer unit, or to have it "freestanding", where you just plug things into the inverter itself ?
Click to expand...
At the moment I will probably just use it through the socket until I get around to doing some wire tidy up and corrects what others have done but at some point I will connect up to the boat onboard system , the In board Gen is connected to the a anode , I guess I could connect it to the same Anode or at less to the Gen earth or what ever the most convenient Paul.
 
The external earth terminal should be connected to the boat's main earth terminal / ground plate / metal hull.

Be aware that the AC outputs of many portable inverters do not have a "line" and earthed "neutral" but rather something reassembling a "centre tapped" earth in which both live conductors are at 115 volts relative to earth. If you intend integrating your inverter with an existing shorepower system . either with a change over switch (aka "transfer switch") or by plugging in via the shorepower inlet connector you should ensure that it is one intended for boat use or at least has an earthed neutral.

RCDs may not work as intended with the pseudo centre tapped system and single pole switches or mcbs will not fully isolate equipment.

If in doubt get advice from a fully qualified marine electrician
 
Last edited:
When you talk about an "Earth Connection" of the Inverter do you mean a connection to the metal case of the inverter.

As Paul says there is a little more to fitting an inverter as the earth output needs to be connected to the neutral ( depending on exact type of inverter output)

This is to provide an alternative path so the RCD if fitted would work corrected.

I an unsure what a case earth connection acture does unlike a case of an appliance which will protect against an internal short. An internal short to the case of an inverter will not cause an external RCD to trip but could cause any internal protection circuit to shut the inverter down. This of cause depends on the exact internal design of the inverter.
 
sailaboutvic said:
At the moment I will probably just use it through the socket until I get around to doing some wire tidy up and corrects what others have done but at some point I will connect up to the boat onboard system , the In board Gen is connected to the a anode , I guess I could connect it to the same Anode or at less to the Gen earth or what ever the most convenient Paul.
Click to expand...

Using it as you describe, you can Earth it to the same anode as the genset.

If you decide to connect it to the boats systems you'll need to bond neutral and Earth together at the inverter, as you do with the genset, so make sure that's possible with the inverter you choose.
 
Rogershaw said:
When you talk about an "Earth Connection" of the Inverter do you mean a connection to the metal case of the inverter.

As Paul says there is a little more to fitting an inverter as the earth output needs to be connected to the neutral ( depending on exact type of inverter output)

This is to provide an alternative path so the RCD if fitted would work corrected.

I an unsure what a case earth connection acture does unlike a case of an appliance which will protect against an internal short. An internal short to the case of an inverter will not cause an external RCD to trip but could cause any internal protection circuit to shut the inverter down. This of cause depends on the exact internal design of the inverter.
Click to expand...
Yes the case earth .
 
PaulRainbow said:
Using it as you describe, you can Earth it to the same anode as the genset.

If you decide to connect it to the boats systems you'll need to bond neutral and Earth together at the inverter, as you do with the genset, so make sure that's possible with the inverter you choose.
Click to expand...
Going one stage further,
re connect it to the onboard system ,
If I wire it say from the socket to the shore power wires , i.e. Plug it into the shore power socket , will that be safe to do so?
In which case there never be a chance of the shore power and the inverter being connected at the same time plus all points inside the boat will have power from the inverter .
 
sailaboutvic said:
Going one stage further,
re connect it to the onboard system ,
If I wire it say from the socket to the shore power wires , i.e. Plug it into the shore power socket , will that be safe to do so?
In which case there never be a chance of the shore power and the inverter being connected at the same time plus all points inside the boat will have power from the inverter .
Click to expand...

I've wired ours through a double pole 16a 2 way + off changeover switch so can connect either shore power socket or inverter but not both.
 
sailaboutvic said:
Going one stage further,
re connect it to the onboard system ,
If I wire it say from the socket to the shore power wires , i.e. Plug it into the shore power socket , will that be safe to do so?
In which case there never be a chance of the shore power and the inverter being connected at the same time plus all points inside the boat will have power from the inverter .
Click to expand...

With the right inverter, with neutral and Earth bonded at the inverter it might be safe.

Not a great way of doing it though. Yes, everything in the boat will have power, but through a 13 amp plug. You'll also want to remember to turn the battery charger off, plus the water heater and any other heavy current devices off.

How is the genset wired ?

You'd be better off with a decent inverter that's designed to be properly installed, connected to a 3 way changeover switch, genset, shore power , inverter and off. Genset and inverter both having neutral and Earth bonded at source and also grounded to the water.

If you don't want to do it that way and fit a cheap inverter with a socket or two, either just plug into it or fit a couple of sockets that are dedicated for inverter use and connect to a cable plugged into the inverter. n this case, Earth the case but do not bond neutral and Earth at the inverter.
 
PaulRainbow said:
With the right inverter, with neutral and Earth bonded at the inverter it might be safe.

Not a great way of doing it though. Yes, everything in the boat will have power, but through a 13 amp plug. You'll also want to remember to turn the battery charger off, plus the water heater and any other heavy current devices off.

How is the genset wired ?

You'd be better off with a decent inverter that's designed to be properly installed, connected to a 3 way changeover switch, genset, shore power , inverter and off. Genset and inverter both having neutral and Earth bonded at source and also grounded to the water.

If you don't want to do it that way and fit a cheap inverter with a socket or two, either just plug into it or fit a couple of sockets that are dedicated for inverter use and connect to a cable plugged into the inverter. n this case, Earth the case but do not bond neutral and Earth at the inverter.
Click to expand...
We may be getting our wires cross here , my first question was about earthing the inverter casing , these inverters which are sold on places like Amazon have a connection on the case , this is what the question was about .

My through was at some point once we leave the marina and shore power will no longer needed till the following winter ,
So by remove the shore power wires from the RCD and wire the inverter to the RCD , In which case it will take the same path as main electric but coming from the inverter rather then the mains .
Am I missing something?
My own concern was the earth for the inverter casing as most people who have these inverter on boat seen to be split if the case need to be earth or not and where to earth it to,
Reading an earlier post Paul you seen to think it be find to use the same anode the Gen earth is wired to .

Why turn the hot water heater off ? One reason for the inverter is to heat up the water while at anchor, when the batteries are fully charged and we have power to waste.
 
Last edited:
sailaboutvic said:
Which is why I'm asking the question .
Don't worry
Click to expand...
The answer to your original question is. " Yes, the earth terminal on the outside of the inverter must be earthed to your boat's main earthing point , which itself should have a connection to the water ... by an external earthing plate, a metal keel. or the hull in the case of a metal hull boat." ( I'm not happy about using the anodes. The anode wiring should be for the anodes only. Stray currents are bad enouh for anodes without connecting equipment to them that may cause stray currents)

BUT

There is more to earthing an inverter than just earthing the case and chassis.

If you are going to connect the inverter to your boats shorepower system , whether that be via a 2 pole change over switch or via the shorepower inlet connector, its output should be a "line" or "live" , an earthed "neutral" and an earth ........... just like the shorepower supply and the supply to your house etc

An inverter intended for use on a boat will be, or can be, configured like that .... A Victron Phoenix inverter is a good example

Portable inverters from Amazon ebay etc are mostly not configured like that. They most likely have two live output connections and the equivalent of a centre tapped earth. Each of the live conductors will be 115 volts relative to the earth.. Two pole switching and mcbs should be used with such an arrangement .

If you have a portable inverter without a proper L, N and E output earth rthe case and use it only as a separate supply for just one piece of equipment at a time plugged into it directly.
 
VicS said:
The answer to your original question is. " Yes, the earth terminal on the outside of the inverter must be earthed to your boat's main earthing point , which itself should have a connection to the water ... by an external earthing plate, a metal keel. or the hull in the case of a metal hull boat." ( I'm not happy about using the anodes. The anode wiring should be for the anodes only. Stray currents are bad enouh for anodes without connecting equipment to them that may cause stray currents)

BUT

There is more to earthing an inverter than just earthing the case and chassis.

If you are going to connect the inverter to your boats shorepower system , whether that be via a 2 pole change over switch or via the shorepower inlet connector, its output should be a "line" or "live" , an earthed "neutral" and an earth ........... just like the shorepower supply and the supply to your house etc

An inverter intended for use on a boat will be, or can be, configured like that .... A Victron Phoenix inverter is a good example

Portable inverters from Amazon ebay etc are mostly not configured like that. They most likely have two live output connections and the equivalent of a centre tapped earth. Each of the live conductors will be 115 volts relative to the earth.. Two pole switching and mcbs should be used with such an arrangement .

If you have a portable inverter without a proper L, N and E output earth rthe case and use it only as a separate supply for just one piece of equipment at a time plugged into it directly.
Click to expand...
Thank you Vic that explains it.
The inboard Gen (FP ) as an earth to one of the Keel bolt and once I buy and fitted the new inverter I will earth the case to that bolt .
Sorted ....


My reason for wanted to connect the inverter to the onboard power wiring was NOT to have multiple things running at the same time , but so I don't have an long extending wire running along the boat from the inverter to the galley which will be quite a way from the inverter plus it mean we can use any socket we like , plus I don't have to separate wires up things like the hot water heater to plug into the inverter.
Then there the risk of tripping over it, breaking it, plus its untidy .

I assume that as the shore power once enter the boat goes through a RCD before it wired into a pole switch (Shore power/Gen/ Off) then into a second RCD on the main switch board before going to the AC bus bars . It be fine to just wire it into the shore power RCD ( without the income shore socket wired to it ) and let it use the same path as the shore power and Gen .
but before doing so I wanted to ask the knowledgable guys here for their advise .
Even if to some my question sound stupid to them.

Surly that be the best way forward then just start wiring stuff up.
 
VicS said:
The answer to your original question is. " Yes,
Click to expand...
Was post #2 not clear enough ?

"Inverters must be Earthed, anyone who doesn't correctly do so is an idiot. "

the earth terminal on the outside of the inverter must be earthed to your boat's main earthing point , which itself should have a connection to the water ... by an external earthing plate, a metal keel. or the hull in the case of a metal hull boat." ( I'm not happy about using the anodes. The anode wiring should be for the anodes only. Stray currents are bad enouh for anodes without connecting equipment to them that may cause stray currents)
Click to expand...

A metal keel ? Do we have bare metal keels ? I don't, i antifoul mine.

If the boat is GRP and no no external ground plane, where does one connect the Earth, if not the anode ?

If it's a metal hull and you connect it to the hull, is it not connected to the anodes, that are bolted to the hull ? The hull will be painted, so how is there continuity to the water, if not through the anodes ?

The Earth wire is a non current carrying conductor, it's perfectly permissible to connect it to the anode.

There is more to earthing an inverter than just earthing the case and chassis.
Click to expand...

There's a bit more to fitting inverters than you think too. The rest of your explanation is flawed and lacking.
 
sailaboutvic said:
Thank you Vic that explains it.
The inboard Gen (FP ) as an earth to one of the Keel bolt and once I buy and fitted the new inverter I will earth the case to that bolt .
Sorted ....


My reason for wanted to connect the inverter to the onboard power wiring was NOT to have multiple things running at the same time , but so I don't have an long extending wire running along the boat from the inverter to the galley which will be quite a way from the inverter plus it mean we can use any socket we like , plus I don't have to separate wires up things like the hot water heater to plug into the inverter.
Then there the risk of tripping over it, breaking it, plus its untidy .

I assume that as the shore power once enter the boat goes through a RCD before it wired into a pole switch (Shore power/Gen/ Off) then into a second RCD on the main switch board before going to the AC bus bars . It be fine to just wire it into the shore power RCD ( without the income shore socket wired to it ) and let it use the same path as the shore power and Gen .
but before doing so I wanted to ask the knowledgable guys here for their advise .
Even if to some my question sound stupid to them.

Surly that be the best way forward then just start wiring stuff up.
Click to expand...

Vic, i didn't say your question (or you) was stupid. I said anyone who doesn't connect the Earth is an idiot, meaning those who you say told you they don't have theirs connected.

I thought i was clear in post #2 and #6

I've posted several long explanations of how inverters should be wired, recently.
 
PaulRainbow said:
Using it as you describe, you can Earth it to the same anode as the genset.

If you decide to connect it to the boats systems you'll need to bond neutral and Earth together at the inverter, as you do with the genset, so make sure that's possible with the inverter you choose.
Click to expand...

Paul the OP's question was about the earth point of the inverter case.

I totally agree on the neutral and installation earth line as the OP has with his generator, this allows a return of any leakage current creating a difference in the line and neutral causing the RCD to trip

The question I have is the earth you you refer to the case earth point or the neutral/earth point.

If there is an internal short inside the inverter to the earthed case I cannot see how the RCD will trip as the leakage is before the RCD so no difference in L/N

Or are you saying that the case earth and the neutral/external earth line are connected together if so how will it make it safe from intserna shore.

If you are saying the neutral/external earth point should be connected to the sea I would agree with that as it provides an alternative path for any Line/neutral leakage so the RCD will trip if the internet boat earth is comprised.
 
PaulRainbow said:
Vic, i didn't say your question (or you) was stupid. I said anyone who doesn't connect the Earth is an idiot, meaning those who you say told you they don't have theirs connected.

I thought i was clear in post #2 and #6

I've posted several long explanations of how inverters should be wired, recently.
Click to expand...
Hi Paul
I didn't read the posting to say I or my posting was stupid :) and I agree with your comments , I only said what some cruisers who have these type of inverter have said .

Paul you always given me good advise on here and privately so I was taken a bit back with #13 comment and pulling out of the conversation . ( good to see your back ) Because it's become Dangerous,
The reason I posted is because of just that electricity is Dangeroue if done wrong,
So I rather post question even if it make me look stupid and get it right the first time then just wire stuff up and hope for the best.
Hope you understand .

Now going back to the boat a Moody 42 by the way , yes it's GRP I not looked lately but it my memory service me right there one earth on one of the keel Bolts and another on a long anode ( sea cocks are not bonded )
I'm guess one from the Gen and the other from the AC bus , I going to have to try and trace them back , not a easy job , mean lifting all the boards and moving stuff around .
Once that is done I can then decided where to put the earth for the case .
keel is copper coated although the bulb under the keel isn't , luck if there any AF on it , has it stand on it and get a splash of AF a few mins before launch.

After every thing that's been said I might have to just wire two sockets each side of the saloon and just plug them into the inverter and have another lead from the hot water heater which plug into the inverter then I won't have to worry how the AC is wired and if wiring through the shore power lead is or isn't safe .
 
You must log in or register to reply here.

Share this page

Top