Galvanic Isolator or Isolation Transformer Question

[sail sfbay]

New to me 1984 Symbol 44 Sundeck has two (2) 30 and one (1) 50 amp shore connections. I am guessing the boat will need one galvanic isolator (or isolation transformer) for each shore connection. Is that correct?

[dkenny64]

I would think you only need one galvanic isolator..
you have one connection between your AC system and you DC system


-dkenny64

[BillKny]

Originally Posted by dkenny64

I would think you only need one galvanic isolator..
you have one connection between your AC system and you DC system


-dkenny64

Actually.... you think wrong.

There will be THREE connections between the boat and the marina ground system, and EACH needs an isolator or isolation transformer.

A galvanic isolator does not break the connection between the DC system and the AC ground, rather it "breaks" the connection between the boat's ground and the marina's ground. Every place that a safety ground (green wire) enters the boat needs isolation as the FIRST thing that is in line.

I just really wonder, do you use SO much power that you need 150 amp service? I have had houses that had 100 Amp service, and my 52 foot boat does everything I ask it to do with 30 Amps.

[manitu]

First, if you need to ask this , there is reason to suspect that you should contact a electrician for any modification of the ac system , 120v can kill you , and if you ever venture into brakkish or fresh water , it can kill kids in the water near your boat.

Yes, you will need a galvanic isolator on every ground connection to shore.
If you have one direct ground connection , the galvanic isolators on the other shore power connections are of no use.

Likewise, if you have a galvanic isolator on one shorepower connection , isolation transformers on the other connections are of no use, the ground plane in your boat is still connected to shore through the diodes in the galvanic isolator.

You really just need one ground connection , and when you use a isolation transformer , it stops in the transformer's casing anyway.

So it could be possible to get away with connecting only one ground , or all grounds to a common isolator. But because of different distribution systems and regulations, I can't give you a definitive answer. Your local electrician will know!

If you go for isolation transformers, they do a lot more than isolate earth , and you will need one for each connection. Together with the correct GFCI's This is by far the best solution both for safety and galvanic corrosion.

.manitu

[dkenny64]

Originally Posted by BillKny

Actually.... you think wrong.

There will be THREE connections between the boat and the marina ground system, and EACH needs an isolator or isolation transformer.

A galvanic isolator does not break the connection between the DC system and the AC ground, rather it "breaks" the connection between the boat's ground and the marina's ground. Every place that a safety ground (green wire) enters the boat needs isolation as the FIRST thing that is in line.

I just really wonder, do you use SO much power that you need 150 amp service? I have had houses that had 100 Amp service, and my 52 foot boat does everything I ask it to do with 30 Amps.

no...if the boat isn't plugged in then the question dosen't matter..
no the boat AC ground is still the same as the marina ground is the same.. but this isn't the boat ground..am I missing something..
not in a physical connection..but galvanic... 1.4v difference that the galvanic isolator provides??
-dlkenny64


sorry but I lost 1.5lbs of zine in 3 months because I didn't have a galvanic isolator...in the same marina where my zincs lasted for 2 yrs...hum.. other that stray currents from other boats what changed? now they last...

[dkenny64]

Billkny,
just really wonder, do you use SO much power that you need 150 amp service? I have had houses that had 100 Amp service, and my 52 foot boat does everything I ask it to do with 30 Amps.

I hear yea...
my last house had a 200amp service..but our max KW was 15...not Kwh..but KW..
most was less than 4KW... just measured by the power company..not me..
-dkenny64

[dkenny64]

Originally Posted by BillKny

Actually.... you think wrong.

There will be THREE connections between the boat and the marina ground system, and EACH needs an isolator or isolation transformer.

A galvanic isolator does not break the connection between the DC system and the AC ground, rather it "breaks" the connection between the boat's ground and the marina's ground. Every place that a safety ground (green wire) enters the boat needs isolation as the FIRST thing that is in line.

I just really wonder, do you use SO much power that you need 150 amp service? I have had houses that had 100 Amp service, and my 52 foot boat does everything I ask it to do with 30 Amps.

well no..
my boat only have has 3 AC connections.
hot, neutral, ground...
so the galvanic isolator breaks the AC ground( green wire) and the DC Ground system..


even on a boat that is fed with 240v ac.... 2 hots, neutral and Gnd..
its the same.. one ac gnd connected to dc ground...with an isolator between.



how am I wrong? please explain...
-dkenny64

[BillKny]

Originally Posted by dkenny64

well no..
my boat only have has 3 AC connections.
hot, neutral, ground...
so the galvanic isolator breaks the AC ground( green wire) and the DC Ground system..


even on a boat that is fed with 240v ac.... 2 hots, neutral and Gnd..
its the same.. one ac gnd connected to dc ground...with an isolator between.



how am I wrong? please explain...
-dkenny64

You really need to do what manitu suggests and call an electrician who can answer questions based on a detailed understanding of what you have and what you want to accomplish.

There are a lot of variables and subtleties around grounding and isolation and it really sounds like your level of understanding of how an AC system works is rudimentary.

A short answer is just unlikely to actually take all the issues into account, including if your boat is actually wired correctly in the first place.

[manitu]

A galvanic isolator does not isolate the boat AC from the boat DC.
It isolates the shore AC ground from the boat AC/DC ground.

Actually, it does not completely isolate the grounds , but it puts in a 1.4 volts "step" that stops ground currents at lesser voltages. This voltage is usually enough, as the metals used in your boat will never create that much voltage potential.

While a galvanic isolator will stop galvanic currents created by the metal potential in your boat , it will not do anything with problems like hot shore ground , ground fault in neighbouring boats , etc.
This can eat up the metal in your boat at astonishing speeds.

If you spend a lot of time on shorepower, I would not consider anything but a proper isolation transformer. It wil allso isolate the phases themselves, + add 120/230 transformation capabilities.

.manitu

[smac999]

are all 3 used at once or is there a switch to choose?...

if there is a switch you may get away with one. but it depends how it's wired.

IE a single 50a galvanic isolator would protect against either the 50a or 30a plug being used at once.

but if all 3 are used you'd either need a single 110a isolator (which likly doesn't exist) or 3 smaller ones.

[Dsanduril]

I’m a bit curious how the boat is wired. If the AC grounds are connected to the DC negative at some point then at some point they are also all common. In which case a single isolator at that common point could possibly be acceptable. As long as the ground wires run direct from the shore power connection to the common point it would be electrically identical.

[boatpoker]

Originally Posted by sail sfbay

New to me 1984 Symbol 44 Sundeck has two (2) 30 and one (1) 50 amp shore connections. I am guessing the boat will need one galvanic isolator (or isolation transformer) for each shore connection. Is that correct?

A lot of misinformation here.

Yes you can run multiple shore grounds through one Galvanic isolator as long as it is appropriately sized.

One 60amp isolator for the two 30amp lines
+
One 50amp isolator for the single 50amp line.

Best you talk to an ABYC Certified Marine Electrician or Certified Marine Corrosion tech.

Check ABYCinc.org , they've been running free on-line mini seminars lately

[Dsanduril]

Technically ABYC requires the isolator to be sized based on the rating of the main breaker(s) on the AC panel(s) rather than the shore power connector size.

Which is why how the boat is wired comes into play. Some boats have dual 30A/single 50A feeding into a single panel and you use one but not both.

All depends on how the boat is actually configured.

[smac999]

Originally Posted by Dsanduril

I’m a bit curious how the boat is wired. If the AC grounds are connected to the DC negative at some point then at some point they are also all common. In which case a single isolator at that common point could possibly be acceptable. As long as the ground wires run direct from the shore power connection to the common point it would be electrically identical.

If you found one rated for 110a then yes....

[GordMay]

Originally Posted by boatpoker

A lot of misinformation here.

Yes you can run multiple shore grounds through one Galvanic isolator as long as it is appropriately sized.

One 60amp isolator for the two 30amp lines
+
One 50amp isolator for the single 50amp line.

Best you talk to an ABYC Certified Marine Electrician or Certified Marine Corrosion tech.

Check ABYCinc.org , they've been running free on-line mini seminars lately

Originally Posted by Dsanduril

Technically ABYC requires the isolator to be sized based on the rating of the main breaker(s) on the AC panel(s) rather than the shore power connector size.
Which is why how the boat is wired comes into play. Some boats have dual 30A/single 50A feeding into a single panel and you use one but not both.
All depends on how the boat is actually configured.

Indeed.

I think you'll need a Galvanic Isolator for each Main Breaker.
If all your shore power inlets supply (through some sort of selector sw) a single main breaker, you'll only need one isolator.
Otherwise, you'll need an isolator for each Shore Power "Service".