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Old 11-03-2015, 12:23   #46
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Re: Stray voltage in a marina

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Originally Posted by goboatingnow View Post
Never understand the purpose of an AC ground plate. I've always been taught that the boat should be treated as an appliance and ground faults are returned via the protective earth line.

Most international codes do not recommend creating local grounds
That assumes that the protective earth line works. I don't see why having a local ground would be a serious issue. After all creating a local ground without intending to do so must be quite common.
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Old 11-03-2015, 12:37   #47
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Re: Stray voltage in a marina

Thanks all - right now we have a good weather window so we unplugged entirely from the dodgy shore power and are mast climbing - our priority list shifts as does the wind. As soon as I get back to the OP problem, I will give more detail.
The thread is way above my head, probably husband can explain. My OP was how to establish whether it's my 30 year old neglected boat leaking juice or the shore power delivered by what look like a household power cord. We're way out on a dock in a yard not designed for in-water storage. I'll get back to this very shortly, but thanks all for your input.
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Old 11-03-2015, 16:24   #48
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Re: Stray voltage in a marina

Quote:
Originally Posted by goboatingnow View Post
Never understand the purpose of an AC ground plate. I've always been taught that the boat should be treated as an appliance and ground faults are returned via the protective earth line.

Most international codes do not recommend creating local grounds

Dave
If your boat follows ABYC code it has a local ground. Because the code asks for interconection between A/C, D/C, Radio earth plus corrosion protection circuit it crates a ground fault route either via the engine block and prop and/or bonded underwater fittings. Most other codes recommend against this and require separate grounds. A/C is then ideally a separate immersed plate. You could use an un-bonded skin fitting but it could lead to corrosion problems.
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Old 11-03-2015, 18:57   #49
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Stray voltage in a marina

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Originally Posted by K_V_B View Post
That assumes that the protective earth line works. I don't see why having a local ground would be a serious issue. After all creating a local ground without intending to do so must be quite common.

Most house wiring seeks not to establish any good unintended local grounds. Of course unintended grounds can occur from time to time, but are typically higher resistance then a properly established protective earth path

The aim to control the path of leakage of fault currents.

I see no purpose to an AC ground plate. All this stuff of course never sees the light of day on a 220 vac boat


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Old 11-03-2015, 18:58   #50
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Re: Stray voltage in a marina

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Originally Posted by mitiempo View Post
In a perfect world the fault would return through the ground (green) wire. ABYC requires the AC ground to be connected to the DC negative bus (and from there to the engine block usually) as there is not a guarantee that the marina's ground connection always exists. By creating this extra path for a fault it eliminates the chance of the entire DC system from being energized by AC current in the event of a fault in a dual current device - charger or inverter typically.

With whole boat ELCI , there is no justification for AC and DC interconnects. IMHO


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Old 11-03-2015, 19:02   #51
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Stray voltage in a marina

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Originally Posted by mitiempo View Post
An RCD as it is known in the EU and an ELCI as it is known in North America is a 30 millivolt "whole boat" GFCI. A GFCI is a 5 millivolt single circuit device.

RCB, ELCI , GLCI are all the same family of devices. Typically available in a range of trip currents from 5mA to around 60 mA. Their use and trip currents ( not millivolts ) are typically mandated by code. They all sense an imbalance of currents in the live an neutral and on doing so open a breaker

In Europe they are often combined with an overload breaker ( a MCB ) to form a combined unit called a RCBO


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Old 11-03-2015, 19:18   #52
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Re: Stray voltage in a marina

[QUOTE=goboatingnow;1772357]With whole boat ELCI , there is no justification for AC and DC interconnects. IMHO
/QUOTE]

Personally I see no justification in any circumstances, I think it is dangerous and the code gets it wrong. Most countries advise against any interconnected grounds on safety grounds. I believe the justification was to do with the potential for stray current corrosion affecting fittings if there was no single ground reference point rather than fault safety.
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Old 11-03-2015, 19:31   #53
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Re: Stray voltage in a marina

Quote:
Originally Posted by goboatingnow View Post
Most house wiring seeks not to establish any good unintended local grounds. Of course unintended grounds can occur from time to time, but are typically higher resistance then a properly established protective earth path

The aim to control the path of leakage of fault currents.

Perfectly true and very similar to the boat situation. A house normally has a long copper stake driven into the ground as the local grand reference point, Isn't this the same as the immersed plate? My view is they both serve exactly the same purpose, to provide a safe, controlled earth path in the event of a supply line fault.

I see no purpose to an AC ground plate. All this stuff of course never sees the light of day on a 220 vac boat

??? You explain very clearly what it is there for above and it is the recommended best practice in European codes for 220v A/C systems, although not always done.

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Old 11-03-2015, 19:52   #54
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Re: Stray voltage in a marina

In fact these days the tendency to use local ground stakes has almost disappeared and most tie the protective earth to neutral and the meter box.

There are codes for all these configurations but let's try and avoid it

In my view ABYC is seriously deficient in its on board mains AC protocols. Combined with the requirement for bonded together underwater fittings , all tied together is simply creating a massive impressed current corrosion issue.

There is a sensible compromise based on RCD ( ELCI) protection and eliminating interconnected electrical system


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Old 11-03-2015, 20:05   #55
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Re: Stray voltage in a marina

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Originally Posted by goboatingnow View Post
I see no purpose to an AC ground plate. All this stuff of course never sees the light of day on a 220 vac boat

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What is a 220 VAC boat? North America has a 120/240 VAC standard. Is that what you are referencing? If so, what do you understand the ABYC applicable standard to be?
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Old 11-03-2015, 20:10   #56
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Re: Stray voltage in a marina

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Originally Posted by St. Elsewhere View Post
What is a 220 VAC boat? North America has a 120/240 VAC standard. Is that what you are referencing? If so, what do you understand the ABYC applicable standard to be?

I'm well aware of the ABYC codes of practice I hesitate to call them rules since they are voluntary for leisure vessels.

Again I see significant issues with ABYC codes of practice for US leisure vessels in relation to bonding on GRP vessels a d the use of interconnected grounds and bonding etc.




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Old 15-03-2015, 21:46   #57
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Re: Stray voltage in a marina

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Originally Posted by goboatingnow View Post
In fact these days the tendency to use local ground stakes has almost disappeared and most tie the protective earth to neutral and the meter box.
That statement is misleading. Many countries (and the UK standard for marinas) keep using TT earthing in which the green wire is not tied to neutral at consumer end, only to a copper rod. This system has advantages (green does not get hot if there is a broken neutral) and disadvantages (impedance too high to be sure that hot-to-green fault will trip an overcurrent breaker, hence RCDs are necessary).

By the way, it is an awful idea to tie the green of the internal installation to a metal meter box. If the hot from the utility (without RCD protection) touches then box then all the green wire gets hot and people can die by touching the washing machine or microwave or a lamp.

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Old 16-03-2015, 01:54   #58
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Re: Stray voltage in a marina

Quote:
Originally Posted by goboatingnow View Post
RCB, ELCI , GLCI are all the same family of devices. Typically available in a range of trip currents from 5mA to around 60 mA. Their use and trip currents ( not millivolts ) are typically mandated by code. They all sense an imbalance of currents in the live an neutral and on doing so open a breaker

In Europe they are often combined with an overload breaker ( a MCB ) to form a combined unit called a RCBO
Yes, mA. Too tired when I posted.

In North America they can be combined as well with a breaker.

I agree that with a whole boat ELCI there is no real reason for the AC and DC interconnect. But very few boats in North America have an ELCI and most are unlikely to ever have one. It is an ABYC standard only for new construction and has no effect on existing installations. While a few will add one the majority will not ever have an ELCI.
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Old 16-03-2015, 04:46   #59
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Re: Stray voltage in a marina

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Originally Posted by svlamorocha View Post
That statement is misleading. Many countries (and the UK standard for marinas) keep using TT earthing in which the green wire is not tied to neutral at consumer end, only to a copper rod. This system has advantages (green does not get hot if there is a broken neutral) and disadvantages (impedance too high to be sure that hot-to-green fault will trip an overcurrent breaker, hence RCDs are necessary).

By the way, it is an awful idea to tie the green of the internal installation to a metal meter box. If the hot from the utility (without RCD protection) touches then box then all the green wire gets hot and people can die by touching the washing machine or microwave or a lamp.

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Indeed I was more referring to domestic installation. I understand the issues around TT or TN systems


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