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Old 09-03-2015, 18:14   #31
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Re: Stray voltage in a marina

Quote:
Originally Posted by DeepFrz View Post
So you have an AC ground plate under water. Guess where the current goes if you have a break in the AC ground wire anywhere in your cct.? I didn't see any mention of an ELCI.
Sorry too many unfamiliar acronyms so I don't understand you. What is cct and ELCI I presume these are US terms?

As far as I am aware if there is a fault in the shorepower cable or inlet box before the onboard RCD the earth route is via the 'green wire' in the shorepower cable to the marina ground.

If there is a short in the A/C side of the charger that could go to ground via the immersed ships ground plate, and yes through the water. BUT only for a fraction of a second until it trips the shorepower RCD (30ma). This is the one on the boat my end of the shorepower lead not anything in the marina wiring. This also means that if there is both hot fault and the ground wire from shorepower has a fault I still have protection because more power is coming onboard that leaving.

If there is a fault in the onboard A/C from the inverter the ground path is back to the Inverter ground via internal earth circuits same as any onboard genorator. The immersed ground plate is connected to the on-board ground circuit but again any current flow above 30ma will be shut off immediatly by the RCD for the onboard circuits.

If you think I have missed something please let me know, improvements are always possible!
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Old 09-03-2015, 18:18   #32
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Re: Stray voltage in a marina

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Originally Posted by svlamorocha View Post
Roland

You seem to take for granted that there is an RCD at every marina power pedestal. At least in the US marinas I am familiar with there are no RCDs in the pedestals. I am not saying that not having RCDs (or not vaccinating children) is a good idea, bit just the way it is in many places.

Also donīt ask me to explain why people get so fussed about hot-neutral polarity instead of making sure the green is at ground potential and there is an RCD.

C
Thanks, I wasn't aware of this. The only US marinas I have been in have been in the Caribbean and did have RCD protection. But also makes me glad I have my own!
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Old 09-03-2015, 18:29   #33
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Re: Stray voltage in a marina

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Originally Posted by Scott Berg View Post
<snip>
Are you saying that there has been a change since then and now they *mandate* GF devices in every pedestal or dock?
<snip>

555 is indeed the controlling code. Some marinas have met it by having whole dock ELCI's, indeed at 100ma (with varying trip timing). I haven't seen a 'whole marina' installation but have seen several whole dock installs. I agree, individual slip systems such as made by Eaton is the right way to go. The codes will catch up; I don't see conspiracy, just bureaucracy.

Several years ago ABYC required whole boat ELCI's but while 30amp units were quick to market
no manufacturer made a 50amp version (and most US Boats I see are 50amp 125/250v) so they kept pushing off the requirement. It took a couple of years for the market to catch up.
I use an industrial IP65 power distribution box which has an RCD and circuit breakers (one for each charger) mounted next to the back of the shorepower inlet. Rating is up to 100a 500v. It is in a locker so does not matter that it looks like it belongs in a shop. Don't like the idea of running A/C wires all the way to an A/C panel at the chart table before going through an RCD, 'whole boat' should mean just that
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Old 09-03-2015, 18:39   #34
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Re: Stray voltage in a marina

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Originally Posted by roland stockham View Post
The problem seems to be so common it must be classed as normal. I have on-board electrics totally isolated from shore side for that reason. Can be done with an isolation transformer but I did it by runing all mains from the inverter so have no shore powered mains on board. Shore power just charges the batteries through good quality chargers with total earth isolation. On-board earth is a separate immersed AC plate. Works for me and means I can draw any voltage/frequency/polarity without worry, just a collection of adapters. The problem goes away if you are not wired into the bank. To set it up you need good knowledge or a pro to design they system but installation is probably no problem
Just one question: If you can pay for the isolation transformer, why do you need to reference the onboard neutral to seawater? Why not just tie boatīs green to neutral coming out of the transformer without bringing the sea into it?
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Old 09-03-2015, 19:36   #35
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Re: Stray voltage in a marina

Quote:
Originally Posted by roland stockham View Post
Sorry too many unfamiliar acronyms so I don't understand you. What is cct and ELCI I presume these are US terms?
I think cct means "circuit". ELCI is one of may words used in the US for RCD.

Quote:
Originally Posted by roland stockham View Post
As far as I am aware if there is a fault in the shorepower cable or inlet box before the onboard RCD the earth route is via the 'green wire' in the shorepower cable to the marina ground.
Agreed

Quote:
Originally Posted by roland stockham View Post
If there is a short in the A/C side of the charger that could go to ground via the immersed ships ground plate, and yes through the water. BUT only for a fraction of a second until it trips the shorepower RCD (30ma). This is the one on the boat my end of the shorepower lead not anything in the marina wiring. This also means that if there is both hot fault and the ground wire from shorepower has a fault I still have protection because more power is coming onboard that leaving.
I am not sure I follow the facts of the situation you describe.

Where is the charger you are referring to? Upstream or downstream of the iso transformer?
Where is your boatīs RCD? Upstream or downstream of the iso transformer?

[QUOTE=roland stockham;1770352]
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Old 09-03-2015, 20:12   #36
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Re: Stray voltage in a marina

Quote:
Originally Posted by svlamorocha View Post
Just one question: If you can pay for the isolation transformer, why do you need to reference the onboard neutral to seawater? Why not just tie boatīs green to neutral coming out of the transformer without bringing the sea into it?
Without it if there is a ground fault in the dock wiring it could potentially bring my onboad ground circuit to Mains potential. Strangely I would not feel any effect but if I then touch something that was grounded to seawater like the engine or seawater tap as well as something earthed on the boat I would get a shock. Not fatal as the RCD would immediately trip but not desirable! (RCD would not initially trip because until the fault current has a ground path there is no imbalance to trip it)
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Old 09-03-2015, 20:33   #37
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Re: Stray voltage in a marina

Quote:
Originally Posted by roland stockham View Post
Without it if there is a ground fault in the dock wiring it could potentially bring my onboad ground circuit to Mains potential. Strangely I would not feel any effect but if I then touch something that was grounded to seawater like the engine or seawater tap as well as something earthed on the boat I would get a shock. Not fatal as the RCD would immediately trip but not desirable! (RCD would not initially trip because until the fault current has a ground path there is no imbalance to trip it)
I disagree.

If you have an iso transformer you should not and do not need to connect boat green to shore green. As far as you are concerned shore green could be at 10 kilovolts from real earth and you would still be safe if you only connect internal boat green to what you call neutral in the secondary of the transformer.

In addition, you are better off installing your RCD after the ISO transformer and connecting green to neutral in between transformer and RCD. That way the RCD will be much more effective and maximize probability of RCD acting before a human conducts the 30mA.

If the shore green may actually be hot because of a broken neutral in a TN/S grounding system ashore (common in USA), or shore green is not connected to anything (say disconencted rod in places with TT earth) then it is a waste of money to have an iso transformer and still connect rely on shore green.
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Old 09-03-2015, 20:38   #38
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Re: Stray voltage in a marina

[QUOTE=svlamorocha;1770420]

I am not sure I follow the facts of the situation you describe.

Where is the charger you are referring to? Upstream or downstream of the iso transformer?
Where is your boatīs RCD? Upstream or downstream of the iso transformer?


This need a circuit diagram but no way of uploading one!

The tread is getting a bit confused. We where talking about isolation transformers as one way of addressing the original posts question. I put forward an alternative solution which I use. Instead of an Isolation transformer which provides A/C onboard and also feeds a charger for the batteries I use an Isolated charger that just feeds DC to the batteries. Think of it as the same as an isolation transformer that produces 12v instead of mains. I also have an RCD at the shorepower input to this charger.
I then have an entirely separate inverter with its own RCD that provides onboard A/C with complete electrical separation from shorepower. In effect I am drawing shorepower but only through a magnetic couple in the charger and via the batteries and inverter not by direct connection

The advantage is that it is cheaper and lighter than fitting an isolation transformer. (also isolation transformer units where not available where I fitted out). Like an isolation transformer it insulate from shorepower faults. Unlike most isolation transformers I have seen it also converts 60Hz input to 50Hz as well at stepping voltages from 120 to 240.

The disadvatage, if you have a larger boat, would be that you are limited to the amount the onboard inverter will supply even when hooked up to shorepower. Not a problem for me as I don't have stuff like air con or other high power consumers
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Old 09-03-2015, 20:40   #39
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Re: Stray voltage in a marina

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Originally Posted by redhead View Post
Is there a test for stray voltage? Our poor rudder cannot take much more....

If this subject has been beat to death elsewhere, just point me in the right direction. Thanks all.
My apologies for taking over this tread somewhat but I hope the discussion helped. It is a somewhat complex subject!
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Old 09-03-2015, 20:55   #40
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Re: Stray voltage in a marina

Quote:
Originally Posted by svlamorocha View Post
I disagree.

If you have an iso transformer you should not and do not need to connect boat green to shore green. As far as you are concerned shore green could be at 10 kilovolts from real earth and you would still be safe if you only connect internal boat green to what you call neutral in the secondary of the transformer.

In addition, you are better off installing your RCD after the ISO transformer and connecting green to neutral in between transformer and RCD. That way the RCD will be much more effective and maximize probability of RCD acting before a human conducts the 30mA.

If the shore green may actually be hot because of a broken neutral in a TN/S grounding system ashore (common in USA), or shore green is not connected to anything (say disconencted rod in places with TT earth) then it is a waste of money to have an iso transformer and still connect rely on shore green.
Agreed, and 'boat green' and 'shore green' are not connected, What I was talking about is if you get a fault in the isolation device which shorts to the case AND the 'shore green is disconnected then, without an immersed plate, there is no earth path at all back to the shore supply. Whether you connect case to shore or boat green makes no difference. Hope my later summary post clarified things
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Old 09-03-2015, 20:57   #41
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Re: Stray voltage in a marina

Sorry instead of later post it is 2 up! If you want to have a really good look at this send me an email address and I can send you the wiring diagram but trying to discribe it just using text is a bit difficult!
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Old 10-03-2015, 16:57   #42
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Re: Stray voltage in a marina

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

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Old 10-03-2015, 18:36   #43
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Re: Stray voltage in a marina

Is an RCD same as a GFI?
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Old 10-03-2015, 19:07   #44
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Re: Stray voltage in a marina

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Originally Posted by US1Fountain View Post
Is an RCD same as a GFI?
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.
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Old 10-03-2015, 19:13   #45
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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

Dave
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.
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