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Old 11-06-2016, 14:39   #16
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Re: Installing shore power and wiring

Galvanic Isolators do not work! Period!

If you have galvanic issues with shore power you need a real Galvanic Isolator and the only true Galvanic Isolator I know is called an Isolation Transformer.

A Galvanic Isolator consist of a high current Diode bridge mounted on a huge heat sink. The bridge rectifier provides a threshold voltage of about 1.5 volts on the ground connection. If the shore ground is lifted above that 1.5 volt, and it often is, you still have a galvanic issues. But when a ground current is flowing in, for example a short circuit situation, the diode bridge may burn out despite its heat sink and high current rating. When this happens it provides no safety at all, it has become an insulator. As such is does the exact opposite of what you want and that is to provide electrical safety to the crew.

The problem with those big Diode blocks is that you cannot see it broken. (I refuse to call them Galvanic Isolators because they are not).

What is a good idea in my opinion is to add a differential switch. A differential switch measures the inflow current through the hot wire and it also measures the outflow through the neutral wire. If the difference is more than a set current (say 30 milli Amps) it will trip. This means there can never be more than 30 mA flowing to ground (perhaps through someones body?) The differential switch is then manually reset after the cause of the trip has been removed.

In Europe a differential switch (AKA a ground leak detection switch) is common in almost all installations. One is placed before the usual circuit breakers.
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Old 11-06-2016, 22:49   #17
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Re: Installing shore power and wiring

Quote:
Originally Posted by GordMay View Post
Marinco no longer publishes their excellent:
BOATER’S GUIDE TO ALTERNATING CURRENT (AC) Electrical Systems
But here it is at the C30 site:
http://www.catalina30.com/TechLib/Wi...Electrical.pdf
Many thanks for that guide and here is the complete link.

[url]http://www.catalina30.com/TechLib/Wiring%20Diagrams%20Boat/Marinco%20Boater's%20Guide%20to%20AC%20Electrical. pdf
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Old 12-06-2016, 04:21   #18
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Re: Installing shore power and wiring

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Originally Posted by Bor the Wolf View Post
In Europe a differential switch (AKA a ground leak detection switch) is common in almost all installations. One is placed before the usual circuit breakers.
Aaaahrg, the Anglo-Saxon world seems to call these devices an RCD (Residual Current Device).

So an Isolation Transformer followed by an RCD and then the usual Circuit Breaker(s) is the way to go IMHO.

In such a set-up it is impossible for electrons to travel ashore because there is no copper (or semiconductor) path. Your boat provides its own safety ground, independent from shore power ground.

https://en.wikipedia.org/wiki/Residual-current_device
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Old 12-06-2016, 08:32   #19
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Re: Installing shore power and wiring

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Originally Posted by Bor the Wolf View Post
Aaaahrg, the Anglo-Saxon world seems to call these devices an RCD (Residual Current Device).
Unfortunately in the big colony just South of Canada they do not seem seem to use a single name that covers all residual current devices. They will use different names depending on where the thing is installed.
Rant on
All this seems to be underpinned by a religious belief in that a 30ma 5ms RCD will not save lives, which is backed up by an old experiment (with a long exposure time) that is not relevant now that huge numbers of people have been saved by these devices in Europe and 3rd world countries.

All this helps in creating a halo of confusion and black art that delays the widespread use of RCDs that can save many lives.
Rant off
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Old 12-06-2016, 08:40   #20
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Re: Installing shore power and wiring

Quote:
Originally Posted by Bor the Wolf View Post
Galvanic Isolators do not work! Period!

If you have galvanic issues with shore power you need a real Galvanic Isolator and the only true Galvanic Isolator I know is called an Isolation Transformer.

A Galvanic Isolator consist of a high current Diode bridge mounted on a huge heat sink. The bridge rectifier provides a threshold voltage of about 1.5 volts on the ground connection. If the shore ground is lifted above that 1.5 volt, and it often is, you still have a galvanic issues. But when a ground current is flowing in, for example a short circuit situation, the diode bridge may burn out despite its heat sink and high current rating. When this happens it provides no safety at all, it has become an insulator. As such is does the exact opposite of what you want and that is to provide electrical safety to the crew.

The problem with those big Diode blocks is that you cannot see it broken. (I refuse to call them Galvanic Isolators because they are not).

What is a good idea in my opinion is to add a differential switch. A differential switch measures the inflow current through the hot wire and it also measures the outflow through the neutral wire. If the difference is more than a set current (say 30 milli Amps) it will trip. This means there can never be more than 30 mA flowing to ground (perhaps through someones body?) The differential switch is then manually reset after the cause of the trip has been removed.

In Europe a differential switch (AKA a ground leak detection switch) is common in almost all installations. One is placed before the usual circuit breakers.
+100
A DIN-size standalone RCD in a DIN box just upstream of the main breaker in the boat and/or just upstream of the main breaker in the marina pedestal is the cheapest way to keep people safe from AC (and detect AC leaks that can cause some corrosion) everywhere jn the boat. Total cost under 60 bucks in many countries.

When mixing bits from different origins I just check that the RCD is rated to cut within 5 microseconds with a leak of 30mA, and can withstand same or more A than the rating of the breaker that is upstream or immediately downstream. All the folklore about nuisance trips is irrelevant on boats if the installation has no leaks.

Sent from my SM-G9287 using Cruisers Sailing Forum mobile app
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Old 12-06-2016, 08:42   #21
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Re: Installing shore power and wiring

Wolf - let us know what your native language (or daily language) is. You are clearly speaking "European". Here, in the colony to the north of the colony to the south of us, there are enuff expat Europeans that we can translate for the poor sods to the south ;-)!

TrentePieds
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Old 12-06-2016, 09:01   #22
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Re: Installing shore power and wiring

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Originally Posted by svlamorocha View Post
Unfortunately in the big colony just South of Canada they do not seem seem to use a single name that covers all residual current devices. They will use different names depending on where the thing is installed.
Rant on
All this seems to be underpinned by a religious belief in that a 30ma 5ms RCD will not save lives, which is backed up by an old experiment (with a long exposure time) that is not relevant now that huge numbers of people have been saved by these devices in Europe and 3rd world countries.

All this helps in creating a halo of confusion and black art that delays the widespread use of RCDs that can save many lives.
Rant off
As you know, electroshock drowning remains an issue in North America, while in Europe it's just about unknown, because Europe long ago made such protective devices mandatory on their shorepower connection points. It's better than nothing to have one on the boat, but that doesn't protect swimmers from the neglected boat two slips over. North American electrical code has to mandate these things ASAP so that they get installed as marinas upgrade and expand.

* * *

You guys have me thinking about galvanic isolators. My understanding is that a breaker should have popped long before a damaging current flows through the galvanic isolator's diodes, so the diodes shorting out or opening should in theory be a rare occurrence. I understand that the future plan is to add proper monitoring of the device to raise some indicator or alarm if the device has failed either short or open.

Also, based on a galvanic table, it seems that two diode drops (1.2 v) would provide galvanic isolation in 99% of the encountered situations.

More info appreciated, maybe in another thread?
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Old 12-06-2016, 13:06   #23
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Re: Installing shore power and wiring

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Originally Posted by Lake-Effect View Post
As you know, electroshock drowning remains an issue in North America.......

You guys have me thinking about galvanic isolators. My understanding is that a breaker should have popped long before a damaging current flows through the galvanic isolator's diodes, so the diodes shorting out or opening should in theory be a rare occurrence. I understand that the future plan is to add proper monitoring of the device to raise some indicator or alarm if the device has failed either short or open.

Also, based on a galvanic table, it seems that two diode drops (1.2 v) would provide galvanic isolation in 99% of the encountered situations.
The galvanic isolator has nothing to do with any breaker. It is installed in the AC ground wire and its job is to stop DC current up to 1.2 volts from traveling along the ground wire - in either direction.

Electric shock drowning can happen in fresh water. It never happens in salt water.
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Old 12-06-2016, 13:22   #24
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Re: Installing shore power and wiring

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Originally Posted by mitiempo View Post
The galvanic isolator has nothing to do with any breaker. It is installed in the AC ground wire and its job is to stop DC current up to 1.2 volts from traveling along the ground wire - in either direction.
(I believe you meant to say "stop galvanic current flow caused by a DC voltage difference of up to 1.2 volts", yes?)

Galvanic isolators are rated for like 30 to 50 amps or more. An AC (or DC) source capable of providing that much current is going to have a breaker in it somewhere (if it's at all proper). So my point is - how likely is it that galvanic isolators will experience excessive current of such duration to damage them, without a breaker blowing somewhere beforehand?

(Of course diodes can fail for other reasons - mechanical shock, lightning, etc.)
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Old 12-06-2016, 13:37   #25
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Re: Installing shore power and wiring

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Originally Posted by Lake-Effect View Post
(I believe you meant to say "stop galvanic current flow caused by a DC voltage difference of up to 1.2 volts", yes?)

Galvanic isolators are rated for like 30 to 50 amps or more. An AC (or DC) source capable of providing that much current is going to have a breaker in it somewhere (if it's at all proper). So my point is - how likely is it that galvanic isolators will experience excessive current of such duration to damage them, without a breaker blowing somewhere beforehand?

(Of course diodes can fail for other reasons - mechanical shock, lightning, etc.)
I meant what I posted. Not sure what you mean by "difference" as normally only DC current will travel on the AC ground.

The current crop of approved galvanic isolators are designed to maintain shore ground if the diodes fail.
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Old 12-06-2016, 14:13   #26
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Re: Installing shore power and wiring

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Originally Posted by mitiempo View Post
I meant what I posted. Not sure what you mean by "difference" as normally only DC current will travel on the AC ground.
I believe we're on the same page. Was just splitting a hair - when I went to school, current wasn't measured in volts.

Quote:
The current crop of approved galvanic isolators are designed to maintain shore ground if the diodes fail.
Thanks.

backing up a bit - I asked my question about galvanic isolators in response to bor's assertion that they don't work period... which is something i hadn't heard before. Can anyone shed more light on this? Is it a widespread problem?
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Old 12-06-2016, 14:22   #27
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Re: Installing shore power and wiring

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I asked my question about galvanic isolators in response to bor's assertion that they don't work period... which is something i hadn't heard before. Can anyone shed more light on this? Is it a widespread problem?
No, they do work as advertised.
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Old 12-06-2016, 16:50   #28
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Re: Installing shore power and wiring

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No, they do work as advertised.
But please read the fine print in the advertisement or manual. Galvanic isolation in my mind means electrons have *no* path whatsoever to shore.

I am at the end of a jetty and the power line runs a several hundred yards from the actual ground point. I have measured voltages on the ground wire that far exceed the threshold of a diode bridge. Specially when there is a lot of static in the air. Does the seller of the diode bridge pay for a new propeller if his device fails? I guess not. I'd rather stick to my waterproof, mil-spec transformer and have no worries.

By the way, Isolation Transformers are used on building sites and other hazardous places. That means you don't have to get them from your local Sailing Jeweler. I got a real bargain at a military surplus store. The only thing is, they come in Navy grey only and are designed to survive WW3.
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Old 12-06-2016, 16:55   #29
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Re: Installing shore power and wiring

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Get some extension cords. LOL
Seriously if you don't leave anything on when you leave the boat.
it's an effing 27 cat. KISS even if you install an ac setup!
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Old 12-06-2016, 18:08   #30
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Re: Installing shore power and wiring

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it's an effing 27 cat. KISS even if you install an ac setup!
Thanks. Thought it would be a no,no in the harbor. But after noticing a few other boats on the dock doing the same thing this is what i'll do.

Thanks everyone for the advice and I'll do it the right way after I get all the other bugs worked out first. Got thru hulls and engine to work on first. Safety, comfort, and then back out in the water!!!
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