No connection between AC grounding wire and DC earth.

Catalina36 said:
I've never understood the need to connect AC earth to the sea. The AC circuit already has a dedicated earth wire like any other AC circuit and is also protected by an RCD. The boat is only connected to mains AC when alongside and as such it's connected to AC earth. If I put a battery charger on my car I don't feel the need to drive an earth pole into the adjacent flower bed and connect the AC earth to it. Same applies when on a campsite with a mains power supply. I see no difference just because the boat is floating in water. Perhaps someone who knows could explain.
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Your car charger is grounded through the power supply, as is your caravan or tent hookup. Your boat is when it's connected to the shore power, assuming the shore power is working correctly.

You find find anyone swimming in your flower bed, your caravan awning or your tent. You might see a swimmer in the water near your boat. Very tiny currents can disable a swimmer and cause drowning.

Don't forget, there are lots of boats with inverters and/or generators too, when at sea they need to be suitably earthed too.

For the real reason the AC grounding is connected to the water, Google "Electric shock drowning".
 
PaulRainbow said:
Your car charger is grounded through the power supply, as is your caravan or tent hookup. Your boat is when it's connected to the shore power, assuming the shore power is working correctly.

You find find anyone swimming in your flower bed, your caravan awning or your tent. You might see a swimmer in the water near your boat. Very tiny currents can disable a swimmer and cause drowning.

Don't forget, there are lots of boats with inverters and/or generators too, when at sea they need to be suitably earthed too.

For the real reason the AC grounding is connected to the water, Google "Electric shock drowning".
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Thanks, but I'm even more confused now. If the idea is to protect swimmers who might be in the water near my boat rather than the people on board when it has 240v AC in use, either from a landline or generator, then surely providing an earth leakage into the water in the event of a fault is the last thing I'd want to do? All the time the power is contained on board, swimmers are safe. Once it leaks into the sea, they're not.

The whole thing seems to me to assume two distinct faults. First, one of my appliances, let's say a toaster, has to be faulty so that the chassis becomes live. Then the earth connection via the shoreline has to be faulty so that this live chassis doesn't short to earth and trip the RCD. I'd have to be pretty unlucky for both those faults to coincide but given that they do, I come along and touch the live toaster and I'm standing in the boat on a mat on a GRP floor so I'm insulated anyway.
 
PaulRainbow said:
You find find anyone swimming in your flower bed, your caravan awning or your tent. You might see a swimmer in the water near your boat. Very tiny currents can disable a swimmer and cause drowning.
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Isn't that an argument against directing mains-derived currents through the sea?
 
Catalina36 said:
I've never understood the need to connect AC earth to the sea. The AC circuit already has a dedicated earth wire like any other AC circuit and is also protected by an RCD. The boat is only connected to mains AC when alongside and as such it's connected to AC earth. If I put a battery charger on my car I don't feel the need to drive an earth pole into the adjacent flower bed and connect the AC earth to it. Same applies when on a campsite with a mains power supply. I see no difference just because the boat is floating in water. Perhaps someone who knows could explain.
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In my view it depends on what the hull material is. If its non conductive like GRP its like having a double insulated power tool that ha no earth connection as it is very unlikely for any person to get a shock as all the metal will be insulated from each other.

On my metal boat I do have a earth connected to the hull via a GI because if a the possibility of a short between the mains live and the steel hull.

The connection between mains earth and 12VDC negative is in my view questionable as most waiting on a boat including my steel boat is isolated from the hull and external metalwork. Unless the engine and all metal work underwater is connected together the CD will be isolated in my view
 
Catalina36 said:
It describes a boat as "single insulated" when in fact a non-metallic boat, certainly a GRP boat, is surely double insulated just the same as a plastic-bodied electric drill? If a live wire somehow contacted the inside of a grp hull, how could that electrocute anyone climbing aboard or swimming nearby?
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My point exactly.
 
When it's specified as an essential safety feature by authorities, why argue against it? As Mr Smartgauge said "How many more references do you need?".
 
pvb said:
When it's specified as an essential safety feature by authorities, why argue against it? As Mr Smartgauge said "How many more references do you need?".
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My understand is that the standards say that a mains earth to DC negative is not required i n the case where the DC system is and isolated system.

As I dont earn any income from wiring up boats and just used design electrical and mechanical installations I am not considered a professional installer.
 
pvb said:
When it's specified as an essential safety feature by authorities, why argue against it? As Mr Smartgauge said "How many more references do you need?".
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As far as I can see Mr Smartgauge hasn't updated his article since 2008. Regardless, as others I am sceptical of his analogy between a metal hulled boat and a piece of equipment with a metal casing.

If I remember correctly, in those days the ISO13297 allowed the AC PE not to be grounded aboard the vessel (to the surrounding water) provided that a RCD was installed. This 'loophole' was closed off with the new version in 2012. Obviously the experts who make up regulations saw some potential risk/risks that was not covered. I agree with Antaris, Catalina and others that it would be interesting to know what those risks are.
 
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Rogershaw said:
My understand is that the standards say that a mains earth to DC negative is not required i n the case where the DC system is and isolated system.

As I dont earn any income from wiring up boats and just used design electrical and mechanical installations I am not considered a professional installer.
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So what does "isolated" mean. Does it mean there's no mains charger on board? If there's an autopilot, is it electrically isolated from the rudder post? The authorities which set the standards explore all the possible methods of failure.
 
Rogershaw said:
My understand is that the standards say that a mains earth to DC negative is not required i n the case where the DC system is and isolated system.
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Thats is correct, but the ISO still says the AC PE should be grounded to the sea, by a dedicated external plate (or the hull, if metal).
Connecting it to DC negative would be rather pointless with an isolated DC system.
 
pvb said:
When it's specified as an essential safety feature by authorities, why argue against it? As Mr Smartgauge said "How many more references do you need?".
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I'm not arguing against it, I'm trying to understand the logic behind it. The article itself adopts a patronising tone that all these authorities know best, then inaccurately describes a plastic boat as "single-insulated". I'm still waiting for anyone to give an answer to the question I asked earlier, ie how can allowing electrical power to leak into the sea in the event of a fault as opposed to keeping it isolated on board, possibly make it safer for anyone swimming nearby?
 
pvb said:
So what does "isolated" mean. Does it mean there's no mains charger on board?
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The term used in ISO10133 (which covers DC installations) is 'fully insulated two-wire DC system' and is defined as:
'System in which both positive and negative poles remain isolated from the ground (earth). Example: Systems in which the positive and negative poles are not connected to the water through a metallic hull, the propulsion system or earthed through the AC protective conductor.'
 
Rogershaw said:
In my view it depends on what the hull material is. If its non conductive like GRP its like having a double insulated power tool that ha no earth connection as it is very unlikely for any person to get a shock as all the metal will be insulated from each other.

On my metal boat I do have a earth connected to the hull via a GI because if a the possibility of a short between the mains live and the steel hull.

The connection between mains earth and 12VDC negative is in my view questionable as most waiting on a boat including my steel boat is isolated from the hull and external metalwork. Unless the engine and all metal work underwater is connected together the CD will be isolated in my view
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There is no current requirement for AC ground and DC negative to be bonded. AC ground has to be "earthed" to the sea by some means.

Previous regulations said about connecting them together, presumably on the assumption that the engine/drive train would be connected to the water by the anode circuit. But i guess they forgot about isolated DC systems when they initially added the requirements.

The regs only apply to new builds though.
 
PaulRainbow said:
There is no current requirement for AC ground and DC negative to be bonded. AC ground has to be "earthed" to the sea by some means.

Previous regulations said about connecting them together, presumably on the assumption that the engine/drive train would be connected to the water by the anode circuit. But i guess they forgot about isolated DC systems when they initially added the requirements.

The regs only apply to new builds though.
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Thanks for the reply Paul. Do we agree on this ? :D

In my case (metal hull) th hull ground connecting is very important so my earth will be connected to the sea.

As far as GRP boats its also desirable to provide an alternative path for any leakage current if the main earth shore power connection is compromised.

I do have indicators to show phase reversal and shore power earth continuity using simple neons.
 
Rogershaw said:
Thanks for the reply Paul. Do we agree on this ? :D

In my case (metal hull) th hull ground connecting is very important so my earth will be connected to the sea.

As far as GRP boats its also desirable to provide an alternative path for any leakage current if the main earth shore power connection is compromised.

I do have indicators to show phase reversal and shore power earth continuity using simple neons.
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Heavens Roger, we do agree :)
 
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