electrolysis

[Trojan]

Jim, I think you buy them by the pound. There a product of their function. The more current they can carry the bigger the copper wire size and core size. You know the price of copper per pound today. A/Cs were options back when. It wasn't until a few years ago that they became a standard.

BILL

 

[Trojan]

A galvanic isolator is not the cure-all. They can be very dangerous. They operate by using the inverse threshold voltage of the diode to make them conduct. Which in turn raises the ground up from actual ground. So there is the potential for the boat side voltage of the isolator to be a lot higher in voltage than the actual shore ground itself. By raising the ground potential you prevent the stray DC voltage. The diode will not conduct DC only AC. What it means is that it takes a minimum reverse voltage before the diode will trigger or pass AC voltage. If this diode gets tired or opens the ground voltage can rises to the point of no ground. NOT good.

BILL

 

[jim rosenthal]

By the pound....oh, well. Blue Note is going to be about 500 lbs lighter with Cummins engines than the Caterpillars...except that now she will have mufflers, which adds a little. Maybe a new set of diodes...I hate to start throwing weight back into her when we're doing well with the diet. Maybe I should just seal all the holes and fill the boat with Heliox. Then we'll all sound funny...

 

[Genesis]

I'd add a second isolation transformer for the AC, personally.

Yes, if you don't look at the diagram CAREFULLY you might think the CASE is grounded on both sides. Its NOT.

I don't like ground isolators. Were I tempted to do something like that I'd put GFIs on all the inlets and not ground the boat AT ALL! That satisfies the safety requirements for shock prevention and avoids the issue. However, it would likely drive a surveyor NUTS, 90% of whom only know what ABYC writes and not how things actually work.

Isolation transformers are heavy and big because you need enough core in the transformer to dissipate the heat and prevent saturation for the load in question. No way around this but lots of copper and iron.....

 

[Trojan]

Jim I don't know what they cost. But being mostly made of copper they must be costly. There was a big unit on e-bay. I think it was quite large 3ft X 3ft and the weight was 500lbs and the first bid was $5OO.. It was 15 kw I think. A little on the big size. I'm going to shop around for one and see what I can find. I want to do some electrical up grades on my boat this summer. I saw a real neat touch panel on Boat fix Tv. You just touched the screen to turn on any system you wanted. All of the functions had manual backups. It had to cost a bundle

BILL

 

[Nick]

I have been following this thread and trying to understand how the isolation transformer is wired according to the electrical drawings for our 37 in relation to Maynard's boat. The Hatt drawings I looked at show that the ships service is wired to a Jefferson Electric Cat No. 211-111-120 5KVA shoreline transformer. The AC service is NOTwired through the isolation transformer.

The Hatt drawings specify "This is a 120 V 2 wire (plus grounding wire) distribution system. The ships service and generator sections are polarized by neutral grounds at the secondary of the shoreline transformer and the generator respectively. By use of the shoreline transformer, the ships service is not shoreline polarity sensitive. The AC system utilizes 2 pole circuit breakers throughout and therefore is not shoreline polarity sensitive".

The drawings also clearly show that the Shore side ground is connected to the Case Ground of the transformer. The hot and neutral shore service to the transformer windings. The secondary (outlet) of the transformer hot and neutral are wired to the two pole ships service breaker 30 A. The neutral on the transformer secondary windings is grounded at the transformer case. The ground from the transformer case is connected to the ground bus of the service 120 panel. The neutral and ground at the generator are also connected together at the generator.ie Neutral grounds.

I am not second guessing any previous posts; just looks like our Hat is wired like Maynard's and probably others. I will check on the specific transformer that is installed and see if it sheds more like on why it is wired the way it is by Hatteras. Probably will lead to more confusion??

Have you checked for a leaky 12 v circuit in a wet or damp area as a cause of the short lived zincs. Years ago I traced a problem to a 12v bilge wire chaffed at a bulkhead and leaking current to the bilge. Ate my zincs in less than 2 months.

 

[Maynard Rupp]

I have two comments on this. One is that Calder's books are the best. I got one as a gift over the holidays and it really goes into great detail. The second comment is that the VC-17 that Maynard has on his boat has a very high copper content. I understand that you do have a stray current problem, but the dissimilar metals in the bottom paint and running gear may be making the zinc degradation even worse.

If I had the wiring that you have, Maynard, I would add a second isolation transformer to that A/C line. With only one transformer, you are really defeating the purpose of having them all together. I just don't understand why Hatteras would have only protected one incoming line like that.

Sky, In the owners manual it states that there is no need for an isolation transformer on the AC line as it is devoted to that use only and has double pole breakers for that entire system. I just can't figure out why I cannot get the ground lines isolated from the bonding even for a test. I hear what everybody is saying, but I have a hard time believing that Hatteras would make a mistake like that. They sure didn't think it was a mistake as they show the whole thing on my blueprints. I will call them tommorrow and try to pick a brain or two.

 

[Maynard Rupp]

I agree; if you are going to have an isolation Xformer on the incoming ship's service line, there should be one on the AC incoming line as well if it is separate. Some of our boats are wired so that AC comes on from shore as 220vac, and then splits into two 110vac lines, one of which runs AC units which are 110vac. Maynard, do you have two shore cords of 110vac or one of 220vac? Just curious.

Karl, you may have already covered this, but have the recommendations on how to wire a boat for incoming shore current changed a lot over the last ten or fifteen years, or are the practices the same? I have no idea.

The Calder diagram is very good, with the exception that when you look at it, you could easily think the shore green conductor is connected to the case, not the internal shield. As a matter of fact, if you had not made a point of it, I would not know it just from the diagram.

While we're on this subject, do all isolation Xformers weigh dozens of pounds, or are there any lighter ones available? Not only are they expensive, they weigh a lot.

No Jim, they are both 120vac 30 amp connectors. They also have those stupid fuses on both the black and white wires of each connector.

 

[Beckytek]

I just checked the wiring diagram for my 88 40" DC after reading all these posts and my shore side grounds are connected the same as Maynards. Grounds from the 240ac 120ac and generator are all tied to case ground buss.
The neutral of the iso is also tied to the same buss. If this is wrong then a lot of our boats are unsafe! Ron

 

[Maynard Rupp]

I have been following this thread and trying to understand how the isolation transformer is wired according to the electrical drawings for our 37 in relation to Maynard's boat. The Hatt drawings I looked at show that the ships service is wired to a Jefferson Electric Cat No. 211-111-120 5KVA shoreline transformer. The AC service is NOTwired through the isolation transformer.

The Hatt drawings specify "This is a 120 V 2 wire (plus grounding wire) distribution system. The ships service and generator sections are polarized by neutral grounds at the secondary of the shoreline transformer and the generator respectively. By use of the shoreline transformer, the ships service is not shoreline polarity sensitive. The AC system utilizes 2 pole circuit breakers throughout and therefore is not shoreline polarity sensitive".

The drawings also clearly show that the Shore side ground is connected to the Case Ground of the transformer. The hot and neutral shore service to the transformer windings. The secondary (outlet) of the transformer hot and neutral are wired to the two pole ships service breaker 30 A. The neutral on the transformer secondary windings is grounded at the transformer case. The ground from the transformer case is connected to the ground bus of the service 120 panel. The neutral and ground at the generator are also connected together at the generator.ie Neutral grounds.

I am not second guessing any previous posts; just looks like our Hat is wired like Maynard's and probably others. I will check on the specific transformer that is installed and see if it sheds more like on why it is wired the way it is by Hatteras. Probably will lead to more confusion??

Have you checked for a leaky 12 v circuit in a wet or damp area as a cause of the short lived zincs. Years ago I traced a problem to a 12v bilge wire chaffed at a bulkhead and leaking current to the bilge. Ate my zincs in less than 2 months.

Thanks Nick. Those words and that wiring are exactly the same as ours. I will workon checking the 12v. stuff tommorrow. Thanks. I hope Nick reads this as your quote of the manual is exactly like ours.

 

[Nick]

Got it Maynard!

 

[SKYCHENEY]

No Jim, they are both 120vac 30 amp connectors. They also have those stupid fuses on both the black and white wires of each connector.

Maybe those fuses wouldn't blow so often if you weren't sending so much current in to the "battery". And by "battery" I mean the salt water electrolyte under your boat.

 

[Genesis]

Then Hatteras wired it wrong.

See the diagram guys, and correct it to be that way. If there is no shield on the transformer put a GFI on the inlet lines to the transformer as close to the shore inlet as you can (this obviates the need for a safety ground on that line as any ground fault that results in a short at the transformer case will trip the GFI)

 

[Maynard Rupp]

Maybe those fuses wouldn't blow so often if you weren't sending so much current in to the "battery". And by "battery" I mean the salt water electrolyte under your boat.

I hope you are right Sky. I also gave some thought to that VC-17 issue. I don't really think that stuff has as much copper as a lot of other paints. I only use 2 quarts for a re-coat. Most folks with that thick crap have to mop on about 2 or 3 times that amount. I do need to stop charging the water. If it gets any worse I may be able to find my boat at night by looking for the glowing water.

 

[TedZ]

Just getting back to a computer.

Calder's diagram shows everything bonded, i.e. grounds to neutrals on the boat. That's the way any boats i've worked on do it.

If the isolation transformer is a balanced - that is a type - unit, diagram is fine as long as the coffee maker is not failing to ground and you are on the dock and grab a bonded piece of metal on the boat. If unbalanced, huge electrolysis as there is voltage ground to ground. If anyone has ever wired a transformer, they are clear on that.

I don't want to state the obvious but when all of this continuity checking is going on i assume there is no light in the circuit and you are not reading through the filament. Hot to ground/neutral resistance measurements are very difficult to do as little neon lights, of course any incandescent, some ballasts etc. will conduct. I understood all breakers were off. Watch out for GFI breakers and any other out of the way warning light as they will conduct in the circuit you are trying to test. No sense making the transformer folks rich if there is no problem, but i do like iso transformers if wired right!! :--)

Ted

PS It would be helpful if you shared the resistance reading, and measure the resistance in a light bulb just to make sure you are in the right ballpark.

PPS Bottom paint?? Seems like a real stretch...talk to the manufacturer. Got to be a real downside if the paint selection melts zincs.

 

[REBrueckner]

Nick posts:
"This is a 120 V 2 wire (plus grounding wire) distribution system. The ships service and generator sections are polarized by neutral grounds at the secondary of the shoreline transformer and the generator respectively. By use of the shoreline transformer, the ships service is not shoreline polarity sensitive. The AC system utilizes 2 pole circuit breakers throughout and therefore is not shoreline polarity sensitive".

(There are so many incorrect or non specific statements earlier in this thread as to be VERY confusing to anyone. Genesis is 100% correct for an ISOLATION TRANSFORMER.)

However, the quote here is NOT the description of a traditional isolation transformer. This quote appears to describe a POLARIZATION TRANSFORMER in which shoreside ground IS connected to both sides of the transformer. It does NOT provide galvanic isolation as does an isolation transformer. See Calder, Page 103 for a deescription.

 

[SKYCHENEY]

Good point. Is this really an isolation transformer or is its only purpose to prevent reverse polarity? Maynard, what does the plate on the transformer say?

 

[Maynard Rupp]

Hi Sky...The unit is made by Jefferson Electric. They call it a "power transformer". Catalog # 211-101-120. It also says 120/240 volts ac in and out. 3kva. This unit is about 6" square and about 10" high
I lifted the bond strap from the main ground bus and measured 1.8mvac and 1.1mvdc between the ground bus and the removed bonding strap. I also removed the wire that the print says is the ground wire from the air cond. inlet from the ground bus in the main elec. panel. Same very low millivolt readings between this wire and the ground bus. I did this with and without the air units running.
Here is a link to a site I used as guidence for these tests. They also manufacture a galvonic isolator.

http://www.yandina.com/electrolysis.htm

 

[Genesis]

The difference between an isolation and polarization transformer is the presence of a shield that is isolated from the two cores and is between them such that a primary-to-secondary electrical fault is IMPOSSIBLE without contacting the shield.

This prevents an internal transformer short from energizing the water (or the ship's ground) and presenting a shock risk.

There is a "fight" going on in the ABYC over this, and in fact the ABYC is now apparently trying to enforce wiring isolation transformers as polarization ones!

Of course its not THEIR boat that gets eaten by the stray current - its YOURS.

The risk they are trying to protect against (electrifying the water around the boat if there is a fault IN THE TRANSFORMER) can be eliminated through the use of GFI breakers. These will prevent ANY leakage to ground (no matter which ground reference we're talking about) and thus eliminate the shock risk.

IMHO the BEST solution lies there - lift the grounds, use your transformer as an isolation transformer (even if its not technically one as the shield doesn't meet the specs for one) and ADD GFIs to both the inlet and outlet side of the transformer so that faults that shunt current to local ground (on either side of the system) cause an immediate trip of the GFIs.

High-current GFIs are inexpensive and so are NEMA-3R (outdoor rainproof) enclosures. Such an enclosure installed in a place where it is not subject to direct innudation (but might get sprayed with water mist as it would if rained on) is perfectly fine. That solution is not only recommended for high voltage use in wet locations, its REQUIRED under the NEC for shore-based use. The same sort of safety implications apply to waterborne use and have the same solutions. In fact, the NEC specifically allows the use of GFI protection in place of a ground, because it is in fact superior protection.

This is tremendously more safe than a "bonded" or straight isolation transformer system. Without the GFIs were you to intentionally (or accidentally) grab a "hot" and ground yourself (to the water or a piece of metal in the boat that is immersed) you would be electrocuted - isolation transformer or no. WITH the GFIs the secondary side GFI would instantly trip, and no electrocution would take place.

The GFI on the primary side protects against a fault in the transformer (or the inlet wiring from the inlet itself to the transformer) that allows current flow to the water (which is at shoreside ground protection.) This is a FAR less likely scenario but it can happen and for the inexpensive cost of protecting against it is worth doing.

You won't find the ABYC advocating this - but its not their boat or underwater metals. They're yours.

Ironically, the risk to PEOPLE in the water near your boat if there is such a fault is almost nil in salt water due to its high conductivity and thus low voltage gradient. In FRESH water the risk is VERY HIGH if you manage to sink AC voltage to the water, because the conductivity is quite LOW and thus the voltage gradient between two points in the water is high enough to electrocute a swimmer near your boat.

Of course the risk to your boat's METALS in fresh water is much lower than in salt! The risks to property and life are almost completely reversed.....

 

[Maynard Rupp]

My thanks to everyone. You all put lots of thought into solving my perceived problem. I do have a call in for the Hatteras electrical guru. I think all of your ideas make a lot of sense. i just don't understand why Hatteras did the whole thing the way they did. I looked at the prints and no shield is shown on the wiring for the isolation amp. so i guess its total job is to correct reverse polarity. With voltage readings so low,(I hope I set up correctly to get them), I guess I don't really have a problem. I was glad to hear that I am not crazy and many of you have exactly the same wiring arrangement.