Inverters, correct wiring without shocking results!

[hollywood8118]

I am reviewing the wiring system on my boat. I know that the system has several short comings that I am in the process of correcting, but want feedback from the readers..
The basics of the system are, shore power at the dock coming in to the boat through a homemade isolation transformer that has been humming away under the bridge dash for forever, ( the builder of my boat was a very resourceful guy... hand made almost everything.... most stuff very well ), a 4kw cruise generator belted to the main engine, a 3kw diesel genset, a proper inverter/charger.
My questions are......

1- Shore power runs through the iso. trans., do the 2- gens and inverter. also need to?
2- the system bonds are all grounded to the prop shaft, I keep the prop and shaft painted. Will this transfer adequately if called upon?

I have read Calders book many times and I don't find adequate info on this
LD

 

[Marin]

Those are the kind of questions I would ask of a professional and experienced marine electric company. I don't know where you are located but we use Rasmussen Electric in Bellingham, WA for all our boat's electrical requirements. The owner is Brian Rasmussen, the shop was started by his father. Brian spent years commercial fishing in Alaska and is very familiar with the realities of marine electrical system. We just had him install a completely new battery setup in our GB.

There are plenty of other equally qualified shops in the area. But as RickB described in his posts on the diver electrocution discussion, marine electrical systems aren't the sort of thing you want to be getting wrong.* So I would get professional advice on this one where there are warranties, years of experience, and professional reputations to back the advice up.


-- Edited by Marin on Thursday 15th of April 2010 11:52:15 AM

 

[sunchaser]

I'm with Marin - get a pro. Having said that, your isolation transformer should be used for incoming shore power. Your bonding system should tie to a big zinc plate mounted on the stern just below the water line. My 2 centavos worth.

 

[Peter B]

I'm sure Rick can confirm or otherwise, but to my simple mind, the point of an isolating transformer is to break all connection between shore power and the boat power, especially via the ground, so there is no direct connection allowing a current to flow causing galvanic corrosion. On the other hand, 120 or 240 volts AC is still lethal, if the wiring is such that one can come in contact with a live surface and ground that live surface through ones body, unless there is an earth current leakage safety trip switch also in circuit. Therefore, theoretically there should be no need for the inverter or on board generator to go though the isolating transformer. I think that's right - now stand ready to be corrected.

 

[RickB]

Peter B wrote:

but to my simple mind, the point of an isolating transformer is to break all connection between shore power and the boat power, especially via the ground, so there is no direct connection allowing a current to flow causing galvanic corrosion.

That is my take on the subject but*with one qualification, galvanic isolation is a separate but related issue. There is no need to run inverter or generator output*through an isolation transformer, they are already as isolated from shore as*anything can be.*

Isolation of incoming AC power is to enhance safety, galvanic isolation is to reduce the problems associated with DC current leakage between boats carried on the AC safety ground.

When a galvanic isolator is inserted in the shore safety ground wire, some of the security of complete isolation is sacrificed. The potential for a failure of the GI to create a dangerous condition is very very slight but it exists. The potential*for a wiring*problem or error within the case of the transformer is probably higher than a GI failure but since we are discussing possibilities and potential for failures or problems it is fair to show where they may be created*when trying to*reduce another risk elsewhere.

The bottom line is what Marin and others have suggested, don't take an anonymous poster's advice when it comes to something that may take someone's life. If you are not positive about what you are doing, hire a pro, at least he has libability insurance.*

Here a*couple of links to*isolation transformer manuals which show connection options and*discuss some of the issues that have been mentioned. Another link is to a GI manufacturer's document which*provides some very easy to understand discussion of the potential problems.*

http://www.smartgauge.co.uk/galv_tran.html
http://www.charlesindustries.com/marine_manual/isogrd3.8.pdf
http://www.pmariner.com/download.php?file=ProSafe%20Transformer%20Owners%20Manual.pdf


-- Edited by RickB on Friday 16th of April 2010 08:41:51 AM

-- Edited by RickB on Friday 16th of April 2010 08:42:34 AM

 

[Delfin]

Hollywood, as others have noted, you do not need to run the gensets through the isolation xfrmer.* It is isolating shore from ship's ground to avoid current leakage from a common ship/shore ground on the boat to a current leak in the water.* One of the most common sources for such leaks is cheap automotive battery chargers on a vessel nearby that has a common ship/shore ground.* Bad news.

Regarding bonding, if everything is bonded to the prop shaft you have a couple of areas of exposure.* First, some shafts may not have adequate continuity between the shaft and the engine.* Put a continuity/ohm meter between metal that is bonded to the shaft and the shaft itself.* There should be no resistance.* Second, you should have zincs on the shaft.* Presumably these are not painted, but if you are depending on the shaft for a ground point and it and the prop are painted, you are depending on clean contact between the zinc on the shaft, and the zinc and the water.* If the zinc is painted, you lose.* If the connection between the zinc and the shaft has resistance, you lose.* So, you can paint the shaft and prop is you like, but you should not paint the zinc or the metal below the zinc.* And you should ensure that there is no resistance between the metals you are bonding and the shaft to which you are bonding them.

I hope that helps.