Richard10002
Well-Known Member
(Apologies to David /forums/images/graemlins/wink.gif )
I’m sure lots of us are confused about this stuff, and I am really trying to understand it, but it’s not easy when there seem to be 2 schools of thought.
Following on from my queries regarding earthing an on board generator, where I asked if I should do what the instructions say and connect the earth to a “stake stuck in the ground”, (in our case, a wire in the sea) – which does not seem to be a good idea.
Some said that the earth wire on the boat supply cable should be tied to the negative in the plug at the generator, and others said that nothing should be done, so the earth wire is not connected to anything, (thus leaving the system “floating”).
I have read the following book, (the following paragraph many times!)….. so:
From The 12 Volt Bible for Boats Page page 132, (Second Edition Adlard coles),
Quote
“All of this can be sorted out very fairly simply. As for the earthing wire, its’ purpose in an electrical system must be clearly understood. It’s required to provide an electrical path for AC fault current to get back to its’ source of power, (whatever that may be), so that people on board don’t get a shock in the event of a short circuit to the casing of a piece of AC electrical equipment. If a boat has an AC generator, a DC to AC inverter, or is equipped with what is known as an isolation transformer, these items are considered AC power sources and the green/yellow wire, and blue “neutral” wire in the three wire AC line are connected together at these devices. But, for all other installations, such as the simple AC circuit used to feed an on-board battery charger, and perhaps a few convenience outlets, the green/yellow wire must be carried back to the source of power on the dock, and ultimately back to land. All of this is accomplished via the shore power cord.”
Unquote
It seems then that the earth wire is a kind of 2nd “neutral” wire which shunts leaked power back to “earth”, from where it finds it’s way back to the power station in the case of shore based AC power, or back to the generator or inverter in the case of our boat AC power.
My logic tells me that sending fault current to neutral at the generator must be right … as it mimics a miniature version of the land based system. Alternatively, a car is a “floating” system, albeit 12v rather than 240v, so this kind of makes sense, but not as logically as the other.
It also suggests that, if you get a qualified marine electrician on board, he may be of the “floating” school, or he may be of the “send it all back to the power source” school and, actually, there is a choice over which system/method to apply, neither of which is wrong.
Am I right in thinking that there is a choice, which is why there are differing opinions, none of which are wrong?
In my case, the generator I am going to buy will have a continental 2 pin socket, so there is no earth “hole”…. Which begs the follow on question:
How do they provide a path to earth in European land based systems, where the power cord, plug, and socket, only have two wires, pins, holes, respectively… i.e. there is no earth wire.
Richard
I’m sure lots of us are confused about this stuff, and I am really trying to understand it, but it’s not easy when there seem to be 2 schools of thought.
Following on from my queries regarding earthing an on board generator, where I asked if I should do what the instructions say and connect the earth to a “stake stuck in the ground”, (in our case, a wire in the sea) – which does not seem to be a good idea.
Some said that the earth wire on the boat supply cable should be tied to the negative in the plug at the generator, and others said that nothing should be done, so the earth wire is not connected to anything, (thus leaving the system “floating”).
I have read the following book, (the following paragraph many times!)….. so:
From The 12 Volt Bible for Boats Page page 132, (Second Edition Adlard coles),
Quote
“All of this can be sorted out very fairly simply. As for the earthing wire, its’ purpose in an electrical system must be clearly understood. It’s required to provide an electrical path for AC fault current to get back to its’ source of power, (whatever that may be), so that people on board don’t get a shock in the event of a short circuit to the casing of a piece of AC electrical equipment. If a boat has an AC generator, a DC to AC inverter, or is equipped with what is known as an isolation transformer, these items are considered AC power sources and the green/yellow wire, and blue “neutral” wire in the three wire AC line are connected together at these devices. But, for all other installations, such as the simple AC circuit used to feed an on-board battery charger, and perhaps a few convenience outlets, the green/yellow wire must be carried back to the source of power on the dock, and ultimately back to land. All of this is accomplished via the shore power cord.”
Unquote
It seems then that the earth wire is a kind of 2nd “neutral” wire which shunts leaked power back to “earth”, from where it finds it’s way back to the power station in the case of shore based AC power, or back to the generator or inverter in the case of our boat AC power.
My logic tells me that sending fault current to neutral at the generator must be right … as it mimics a miniature version of the land based system. Alternatively, a car is a “floating” system, albeit 12v rather than 240v, so this kind of makes sense, but not as logically as the other.
It also suggests that, if you get a qualified marine electrician on board, he may be of the “floating” school, or he may be of the “send it all back to the power source” school and, actually, there is a choice over which system/method to apply, neither of which is wrong.
Am I right in thinking that there is a choice, which is why there are differing opinions, none of which are wrong?
In my case, the generator I am going to buy will have a continental 2 pin socket, so there is no earth “hole”…. Which begs the follow on question:
How do they provide a path to earth in European land based systems, where the power cord, plug, and socket, only have two wires, pins, holes, respectively… i.e. there is no earth wire.
Richard
