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Old 02-12-2018, 18:35   #1
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Earth Leakage Protection/ Residual Current Device.

I am vaguely aware that there is a technical difference between both devices but both are designed to prevent electric shock. (In Ausralia I think RCDs have superseded ELPs)


I am also aware neither device installed in the house meter box (at the front of the house) will give protection to someone working in the backyard shed. (Apparently it is a sackable offense for any mining company employee to use a power tool unless that tool is plugged in to a safety device)


Now my question: Will either of those devices work on a yacht at sea? (I'm worried about lack of "earth")


Clive
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Old 02-12-2018, 18:39   #2
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Re: Earth Leakage Protection/ Residual Current Device.

can't get a better earth / ground than the ocean a few feet away
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Old 02-12-2018, 18:49   #3
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Re: Earth Leakage Protection/ Residual Current Device.

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Originally Posted by coopec43 View Post
I am vaguely aware that there is a technical difference between both devices but both are designed to prevent electric shock. (In Ausralia I think RCDs have superseded ELPs)


I am also aware neither device installed in the house meter box (at the front of the house) will give protection to someone working in the backyard shed. (Apparently it is a sackable offense for any mining company employee to use a power tool unless that tool is plugged in to a safety device)


Now my question: Will either of those devices work on a yacht at sea? (I'm worried about lack of "earth")


Clive
Recent changes now require RCDs on inverters for caravans and boats. Probably a good idea in a wet environment.
http://www.enerdrive.com.au/product/...-inverter-kit/
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Old 02-12-2018, 18:59   #4
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Re: Earth Leakage Protection/ Residual Current Device.

[QUOTE=swampbush;2773635]Recent changes now require RCDs on inverters for caravans and boats. Probably a good idea in a wet environment.
RCD-GPO Inverter Kit - Enerdrive Pty Ltd[/QUOTE

I think you've answered my question. If they work in a caravan which is insulated from the "earth" by road tyres then they should work on a yacht

Does the chassis of the caravan the become the earth? Is that how it works?


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Old 02-12-2018, 19:29   #5
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Re: Earth Leakage Protection/ Residual Current Device.

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can't get a better earth / ground than the ocean a few feet away

But not very useful to protect for electrical faults with on-board sources. That's what the "green/yellow" wire is for.
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Old 02-12-2018, 19:37   #6
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Re: Earth Leakage Protection/ Residual Current Device.

Gfi's, rcds, Elcis Don't need a ground or ground wire to work.

They measure current difference between hot and neutral. Which should be 0.

Nothing to do with ground. Likly the missing current is going to a ground. But that is not measured.

They are required on boat shore inlets when plugged into a dock.
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Old 02-12-2018, 21:22   #7
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Re: Earth Leakage Protection/ Residual Current Device.

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Originally Posted by smac999 View Post
Gfi's, rcds, Elcis Don't need a ground or ground wire to work.

They measure current difference between hot and neutral. Which should be 0.

Nothing to do with ground. Likly the missing current is going to a ground. But that is not measured.

They are required on boat shore inlets when plugged into a dock.
Thanks for that.
This is an interesting article about the safety device on portable generators.
http://www.powersafe.net.au/pdf/duosafety.pdf


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Old 02-12-2018, 22:04   #8
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Re: Earth Leakage Protection/ Residual Current Device.

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Originally Posted by coopec43 View Post
Thanks for that.
This is an interesting article about the safety device on portable generators.
http://www.powersafe.net.au/pdf/duosafety.pdf


Clive

I worked for a company that made generators, among other things, for nearly 16 years in my younger days. Back then we laughed at anyone that suggested fitting an RCD to a genset used in a portable capacity. RCD's don't work if you have a "floating" supply as is the norm from a genset. But the do-gooders stepped in and demanded RCD protection. To achieve earth leakage protection on a generator one has to effectively make it more hazardous by earthing one of the live connections. This is usually done using an earth stake which kind of negates the whole portability issue of a portable generator.


If you have a floating supply, in order to electrocute yourself you either need to hang onto both wires at once (ensuring that the current passes through your heart) or you need two faulty appliances - one with one side of the circuit grounded to the chassis, and the other with the other side of the circuit grounded to the chassis and then you need to touch both appliances at the same time.


On land, where the neutral is the sum of currents of the supply line phases and generally uses the actual earth (as in the planet) as a conductor in polyphase AC generation systems, then there's no getting out of the need to earth the neutral supply line and an RCD makes perfect sense. On a boat, the need probably isn't so clear cut when not plugged into shore power.
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Old 03-12-2018, 10:24   #9
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Re: Earth Leakage Protection/ Residual Current Device.

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Originally Posted by OldMan View Post
But not very useful to protect for electrical faults with on-board sources. That's what the "green/yellow" wire is for.
The green/yellow wire has to pass the fault somewhere. The connection on the boat from the green/yellow wire to the DC negative provides the path for the fault to earth.
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Old 03-12-2018, 11:08   #10
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Re: Earth Leakage Protection/ Residual Current Device.

On a wheeled vehicle, there is no true earth / ground.

Chassis / engine bock is tied into DC negative return.
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Old 03-12-2018, 13:57   #11
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Re: Earth Leakage Protection/ Residual Current Device.

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The green/yellow wire has to pass the fault somewhere. The connection on the boat from the green/yellow wire to the DC negative provides the path for the fault to earth.

The topic is 'yacht at sea', i.e. the power source is on the vessel, not on land.



The green/yellow wire passes the fault to the source at the neutral/ground bond. No earth involved.
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Old 05-12-2018, 20:20   #12
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Re: Earth Leakage Protection/ Residual Current Device.

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Originally Posted by mitiempo View Post
The green/yellow wire has to pass the fault somewhere. The connection on the boat from the green/yellow wire to the DC negative provides the path for the fault to earth.
Actually, there is no "fault to earth" path on a boat with no electrical connection to the shore. There is a very high resistance path from seawater to earth (below the sea). It's better to visualize a boat as being an aircraft in flight. You may, if you like, fill a bucket with dirt, stick a copper rod in it, and call it "ground." But it won't do anything.

The shock/electrocution factor occurs when a person comes between two points with a difference of potential: a voltage. If the generator or inverter is on board, one must come into the path of the electrical source -- across both "sides" of the circuit.

Providing a path for either side of the source power circuit to pass current to some common conductor - like the battery negative terminal - only increases the hazard that a person will be placed between one side and the other of the generating source.

The reason "mains" power has the neutral side grounded is to provide a discharge path for transient voltages, such as lightning. In the early days of AC power distribution, that path to ground (which we just call "ground") was not provided, and the entire circuit "floated" above ground. When lightning struck the distribution systems anywhere, it charged the entire network and caused arcing and fires in multiple locations (there were stories of lightning flying around inside homes). So, the compromise was to connect one side of the circuit to a local ground reference. That solved one problem, but now the ungrounded side of the circuit ("hot") had a potential to ground, and the risk of electrocution if a person touched that side while grounded himself. So a safety ground was later added to provide an alternate path.

The third path: "safety ground" -- that third prong on the plugs, was added later to keep the exposed conductive parts on appliances at the same potential as the path current would take to ground - to provide a preferential path around a human who might contact an accidentally energized surface. It only serves a purpose when connecting to shore power, and if you install an isolation transformer, the safety ground will terminate at the transformer primary and not be carried through to the boat's AC power receptacles. If you are generating your own power, you don't have the risk of a surge from a distribution system being hit by lightning miles away, so you can omit the neutral-to-ground connection altogether. On a boat, generating its own power from a generator, inverter, or through an isolation transformer, that third prong for the safety ground does nothing.

By the way, the preferred term is "common" to refer to connections to a single point of potential - in order to avoid the misconception that there is any earth grounding involved. "Chassis common" for example, not "chassis ground." But you can call it chassis ground if you connect it to the rod in that bucket of dirt you carry on board.
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Old 05-12-2018, 22:14   #13
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Re: Earth Leakage Protection/ Residual Current Device.

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Originally Posted by OldMan View Post
The topic is 'yacht at sea', i.e. the power source is on the vessel, not on land.



The green/yellow wire passes the fault to the source at the neutral/ground bond. No earth involved.
yes. both the gen and the inverter need to have a N to G bond in order to clear the fault. (only the one providing the power should have the bond at that time)
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Old 06-12-2018, 04:43   #14
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Re: Earth Leakage Protection/ Residual Current Device.

Thank you Capt Pat and others who took the time to respond to my query regarding ELP/RCD.

After reading your post Capt Pat I think I've almost got it but as it is late at night I'll go over it again in the morning. Maybe if I can follow that it will also explain why I need to bond "earth?" all my skin fittings?


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Old 06-12-2018, 05:27   #15
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Re: Earth Leakage Protection/ Residual Current Device.

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Originally Posted by Cpt Pat View Post
Actually, there is no "fault to earth" path on a boat with no electrical connection to the shore. There is a very high resistance path from seawater to earth (below the sea). It's better to visualize a boat as being an aircraft in flight. You may, if you like, fill a bucket with dirt, stick a copper rod in it, and call it "ground." But it won't do anything.

The shock/electrocution factor occurs when a person comes between two points with a difference of potential: a voltage. If the generator or inverter is on board, one must come into the path of the electrical source -- across both "sides" of the circuit.

Providing a path for either side of the source power circuit to pass current to some common conductor - like the battery negative terminal - only increases the hazard that a person will be placed between one side and the other of the generating source.

The reason "mains" power has the neutral side grounded is to provide a discharge path for transient voltages, such as lightning. In the early days of AC power distribution, that path to ground (which we just call "ground") was not provided, and the entire circuit "floated" above ground. When lightning struck the distribution systems anywhere, it charged the entire network and caused arcing and fires in multiple locations (there were stories of lightning flying around inside homes). So, the compromise was to connect one side of the circuit to a local ground reference. That solved one problem, but now the ungrounded side of the circuit ("hot") had a potential to ground, and the risk of electrocution if a person touched that side while grounded himself. So a safety ground was later added to provide an alternate path.

The third path: "safety ground" -- that third prong on the plugs, was added later to keep the exposed conductive parts on appliances at the same potential as the path current would take to ground - to provide a preferential path around a human who might contact an accidentally energized surface. It only serves a purpose when connecting to shore power, and if you install an isolation transformer, the safety ground will terminate at the transformer primary and not be carried through to the boat's AC power receptacles. If you are generating your own power, you don't have the risk of a surge from a distribution system being hit by lightning miles away, so you can omit the neutral-to-ground connection altogether. On a boat, generating its own power from a generator, inverter, or through an isolation transformer, that third prong for the safety ground does nothing.

By the way, the preferred term is "common" to refer to connections to a single point of potential - in order to avoid the misconception that there is any earth grounding involved. "Chassis common" for example, not "chassis ground." But you can call it chassis ground if you connect it to the rod in that bucket of dirt you carry on board.

Great Post a comprehensive explanation
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