Slowtack
Well-Known Member
I am looking at buying a small inverter (300W) to run laptop and other small loads on board. It has an earth connection. Can this be (a) ignored or (b) connected to the 12V negative?
Inverter Earth
- Thread starter Slowtack
- Start date
VicS
Well-Known Member
It should be earthed in the same way that a shore power supply is earthed to the boat ie to the main metal lumps anodes and the 12v -ve
Csail
N/A
Sterling say earth to battery N
colinmi
Well-Known Member
It needs to be connected direct to the earth on the shore power.
Do not just connect it as vic says to the big metal lumps. This is dangerous and could result in the big metal lumps becoming live, in the event of a fault occuring.
Yes the big metal lumps should be earthed, but not used as an earth for other equipment connected to the mains.
Do not connect it to the battery negative. This connection should already be made much earier in your system.
Hope this helps
Colin
Do not just connect it as vic says to the big metal lumps. This is dangerous and could result in the big metal lumps becoming live, in the event of a fault occuring.
Yes the big metal lumps should be earthed, but not used as an earth for other equipment connected to the mains.
Do not connect it to the battery negative. This connection should already be made much earier in your system.
Hope this helps
Colin
Jonny_H
Well-Known Member
[ QUOTE ]
It needs to be connected direct to the earth on the shore power.
[/ QUOTE ]
[ QUOTE ]
Do not just connect it as vic says to the big metal lumps
[/ QUOTE ]
[ QUOTE ]
Do not connect it to the battery negative
[/ QUOTE ]
What happens when not connected to shore power if your not meant to earth to -ve on battery or an earthed 'metal lump' (engine block presumably?)
If your connected to shore power there is no need for an inverter surely /forums/images/graemlins/confused.gif
Jonny
It needs to be connected direct to the earth on the shore power.
[/ QUOTE ]
[ QUOTE ]
Do not just connect it as vic says to the big metal lumps
[/ QUOTE ]
[ QUOTE ]
Do not connect it to the battery negative
[/ QUOTE ]
What happens when not connected to shore power if your not meant to earth to -ve on battery or an earthed 'metal lump' (engine block presumably?)
If your connected to shore power there is no need for an inverter surely /forums/images/graemlins/confused.gif
Jonny
Richard10002
Well-Known Member
If I've understood what I've discovered here and in a variety of books, as far as the boat is concerned, an inverter, or a generator, should have the earth connected to its' own negative, so that any leakages get back to where they came from, rather than passing through people to the big wide world, (Earth), which may be at a different potential to the boat.
I'm not giving advice here, just testing my knowledge ... someone else can give the advice /forums/images/graemlins/smile.gif
I'm not giving advice here, just testing my knowledge ... someone else can give the advice /forums/images/graemlins/smile.gif
Slowtack
Well-Known Member
I'm a bit confused now. The main anode is a "tear drop" type bolted to the GRP hull and wired to the engine block which is itself connected to the 12V negative.
I plan to run this from battery/engine alternator.Is it OK to connect the inverter earth to the 12v negative then?
I plan to run this from battery/engine alternator.Is it OK to connect the inverter earth to the 12v negative then?
Richard10002
Well-Known Member
hope you're not asking me /forums/images/graemlins/smile.gif
My understanding is that, on a boat, the inverters earth would be connected to the negative inside its' AC socket. But dont do this based on me saying it.
My take on electricity is that it is a closed system, and all the electrons should end up back where they started. Any which get out, and are able to go somewhere else, or try and get back to where they came from via a different route, are dangerous, because they might go through people.
My understanding is that, on a boat, the inverters earth would be connected to the negative inside its' AC socket. But dont do this based on me saying it.
My take on electricity is that it is a closed system, and all the electrons should end up back where they started. Any which get out, and are able to go somewhere else, or try and get back to where they came from via a different route, are dangerous, because they might go through people.
rachapman
Member
AFAIK an earth connection is to protect the user in a situation where the equipment casing becomes live due to a fault condition, with the idea that it will create a short circuit and blow the supply fuse to the equipment.
So connecting to the battery -ve should achieve this.
And the inverter supply lead should be fused.
Regarding our inverter, this year I permanently mounted it and I've connected the earth to the battery -ve input with a short jumper. Inverter works, but I don't know how I'd test whether the earth protection works other than by chucking water over it.
So connecting to the battery -ve should achieve this.
And the inverter supply lead should be fused.
Regarding our inverter, this year I permanently mounted it and I've connected the earth to the battery -ve input with a short jumper. Inverter works, but I don't know how I'd test whether the earth protection works other than by chucking water over it.
rogerthebodger
Well-Known Member
[ QUOTE ]
nverter, or a generator, should have the earth connected to its' own negative,
[/ QUOTE ]
That is correct but not the whole story.
At least a fuse or overload breaker should be in the live side between the invertor output and the appliances. Better still is to use a RCD connecter in both the live and neutral with the earth / neutral connection on the invertor side of the RCD.
IMHO a connection of the earth point on the invertor to an earthing point earth plate / anodes is pointless on most boats except metal boats (I have a steel yacht) which are a very special case.
nverter, or a generator, should have the earth connected to its' own negative,
[/ QUOTE ]
That is correct but not the whole story.
At least a fuse or overload breaker should be in the live side between the invertor output and the appliances. Better still is to use a RCD connecter in both the live and neutral with the earth / neutral connection on the invertor side of the RCD.
IMHO a connection of the earth point on the invertor to an earthing point earth plate / anodes is pointless on most boats except metal boats (I have a steel yacht) which are a very special case.
colinmi
Well-Known Member
Oh dear
What a mess. Everyone seems to have a bit of an handle on it, but not a proper understanding. The old saying "a little bit of knowlege is a dangerous thing" comes to mind.
Lets look at the systems as seperate entities and leave out how they should be connected to each other till later.
The question was how to earth the inverter. The mains supply to the invertor will either come form the shore supply or a generator. In either case a 3 core cable should be used...live, neutral and earth. Simple as that. Thats how it should be earthed.
Now whats connected to what.
Shore supply....Somewhare back in a corner of the marina,, or out in the street there is a big grey transformer that belongs to the supply authority. In the core of the transformer secondary winding, the earth and neutral are connected together. This is the only connectioin that should exist between earth and neutral.
Generator....In the windings of the generator, the earth and neutral are connected together. Again, this is the only place where this connection should exist.
Earth safety bonding...All of the metal componets in a boat should be connected to the shore power or generator earth wire (where practical to do so).
DC system.... There is no requirement for a safety earth on this system. The negative wire is often reffered to as an earth, because it can be connected to the body of say the engine block so that only one wire is required. But its not really an earth in the same sense of the mains system.
Anodes...A single core cable is run from the anode(s) to all of the metalwork in the boat that you deem requires protection from corrosion. ie fuel tanks, engine blocks, sea cocks (although there is an arguement aginst connecting sea cocks) water tanks etc.
What connection should be made between systems...The battery(s) negative terninal should be connected to the shore supply earth, the generator earth and the anode(s). This conncetion should be made as far back in the systems as possible and with a substantial cable.
Now the disclaimer...Im not claiming to be an expert on this subject but I am an electrical engineer and I have rewired my own boat, new generator, invertor, charger, mains and 12v systems. Everything works and I am confident everything is safe.
There are lots of books on the subject, but the question was how to earth the invertor. See my first sentence. That is the correct way to do it. Using other lumps of metal as the safety earth is not safe and could result in fire or risk of electric shock.
Hope this helps
Colin
Colin
What a mess. Everyone seems to have a bit of an handle on it, but not a proper understanding. The old saying "a little bit of knowlege is a dangerous thing" comes to mind.
Lets look at the systems as seperate entities and leave out how they should be connected to each other till later.
The question was how to earth the inverter. The mains supply to the invertor will either come form the shore supply or a generator. In either case a 3 core cable should be used...live, neutral and earth. Simple as that. Thats how it should be earthed.
Now whats connected to what.
Shore supply....Somewhare back in a corner of the marina,, or out in the street there is a big grey transformer that belongs to the supply authority. In the core of the transformer secondary winding, the earth and neutral are connected together. This is the only connectioin that should exist between earth and neutral.
Generator....In the windings of the generator, the earth and neutral are connected together. Again, this is the only place where this connection should exist.
Earth safety bonding...All of the metal componets in a boat should be connected to the shore power or generator earth wire (where practical to do so).
DC system.... There is no requirement for a safety earth on this system. The negative wire is often reffered to as an earth, because it can be connected to the body of say the engine block so that only one wire is required. But its not really an earth in the same sense of the mains system.
Anodes...A single core cable is run from the anode(s) to all of the metalwork in the boat that you deem requires protection from corrosion. ie fuel tanks, engine blocks, sea cocks (although there is an arguement aginst connecting sea cocks) water tanks etc.
What connection should be made between systems...The battery(s) negative terninal should be connected to the shore supply earth, the generator earth and the anode(s). This conncetion should be made as far back in the systems as possible and with a substantial cable.
Now the disclaimer...Im not claiming to be an expert on this subject but I am an electrical engineer and I have rewired my own boat, new generator, invertor, charger, mains and 12v systems. Everything works and I am confident everything is safe.
There are lots of books on the subject, but the question was how to earth the invertor. See my first sentence. That is the correct way to do it. Using other lumps of metal as the safety earth is not safe and could result in fire or risk of electric shock.
Hope this helps
Colin
Colin
rogerthebodger
Well-Known Member
I agree it is a mess.
[ QUOTE ]
The mains supply to the invertor will either come form the shore supply or a generator. In either case a 3 core cable should be used...live, neutral and earth.
[/ QUOTE ]
The supply to am invertor is DC either 12V or 24V as the case may be. The output from the invertor will be mains and having built several yachts have found that the neutral and earth (case of most invertors) are not connected and neither are the earth and neutral of generators are connected by manufactures.
[ QUOTE ]
What connection should be made between systems...The battery(s) negative terninal should be connected to the shore supply earth, the generator earth and the anode(s). This conncetion should be made as far back in the systems as possible and with a substantial cable.
[/ QUOTE ]
If you connect all earths together particular the shore power earth, and the anodes this will cause a problem unless a galvonic isolator is not fitted and if shore power is used the shore power earth should not be connected at the boat at all(you in effect say this in your posting)
My point about not connecting the mains earth to any part of a GRP or wooden boat is that you are insulated fron the earth anyway so no current can flow to earth through you so no shock (much different to when at home)
[ QUOTE ]
Shore supply....Somewhare back in a corner of the marina,, or out in the street there is a big grey transformer that belongs to the supply authority. In the core of the transformer secondary winding, the earth and neutral are connected together. This is the only connectioin that should exist between earth and neutral
[/ QUOTE ]
Unless you use an isolating transformer in which case the secondary neutral and earth must be connected and it becones the same as a generator / invertor connection.
[ QUOTE ]
The mains supply to the invertor will either come form the shore supply or a generator. In either case a 3 core cable should be used...live, neutral and earth.
[/ QUOTE ]
The supply to am invertor is DC either 12V or 24V as the case may be. The output from the invertor will be mains and having built several yachts have found that the neutral and earth (case of most invertors) are not connected and neither are the earth and neutral of generators are connected by manufactures.
[ QUOTE ]
What connection should be made between systems...The battery(s) negative terninal should be connected to the shore supply earth, the generator earth and the anode(s). This conncetion should be made as far back in the systems as possible and with a substantial cable.
[/ QUOTE ]
If you connect all earths together particular the shore power earth, and the anodes this will cause a problem unless a galvonic isolator is not fitted and if shore power is used the shore power earth should not be connected at the boat at all(you in effect say this in your posting)
My point about not connecting the mains earth to any part of a GRP or wooden boat is that you are insulated fron the earth anyway so no current can flow to earth through you so no shock (much different to when at home)
[ QUOTE ]
Shore supply....Somewhare back in a corner of the marina,, or out in the street there is a big grey transformer that belongs to the supply authority. In the core of the transformer secondary winding, the earth and neutral are connected together. This is the only connectioin that should exist between earth and neutral
[/ QUOTE ]
Unless you use an isolating transformer in which case the secondary neutral and earth must be connected and it becones the same as a generator / invertor connection.
Richard10002
Well-Known Member
[ QUOTE ]
The question was how to earth the inverter. The mains supply to the invertor will either come form the shore supply or a generator. In either case a 3 core cable should be used...live, neutral and earth. Simple as that. Thats how it should be earthed.
[/ QUOTE ]
Colin,
I think you need to look at this part of your advice again...... the invertor is supplied by the boats' 12v system, not by shore supply or generator. The supply will be either directly from a battery, or via one of those cigarette lighter type sockets.
Richard
The question was how to earth the inverter. The mains supply to the invertor will either come form the shore supply or a generator. In either case a 3 core cable should be used...live, neutral and earth. Simple as that. Thats how it should be earthed.
[/ QUOTE ]
Colin,
I think you need to look at this part of your advice again...... the invertor is supplied by the boats' 12v system, not by shore supply or generator. The supply will be either directly from a battery, or via one of those cigarette lighter type sockets.
Richard