AC/DC grounding and galvanic isolator location

[marchem]

1982 Catalina 27. I want to tie my AC and DC grounds together and install a galvanic isolator in the AC ground line. I'm trying to figure out where to connect the grounds, and where/how to cut into the AC ground for the isolator.

The AC wiring (triplex cable) runs from a coaming mounted receptacle through the port lazarette (where I've got batteries and a DC ground busbar) to a 30A breaker in the cabin. My first thought is to cut the cable, install the isolator, use a terminal block to connect to the other side of the AC cable, and run a wire from the AC ground on the terminal block to the DC ground busbar. I don't know if it's a bad idea to use a terminal block for AC, or how to put a cover on it (I'm not finding any marine terminal blocks with covers, although I have found some with covers: http://www.amazon.com/Amico-Position-Barrier-Covered-Terminal/dp/B005I78U70).

I could also put the isolator just before the AC breaker, but that location is not easy to get into to test the isolator (Yandina, so I need to manually test it) and would require a longer run back to the DC ground busbar.

Thoughts or ideas?

I've got most of the other battery wiring done now and once I finish this I'm going to post some pictures of it. I really appreciate all the help and ideas I've gotten here.

 

[captcoho]

What exactly is your reason for doing this?
Your A/C shore power equipment have a Hot, Neutral ( grounded ) and Equipment Grounding conductors at 120vac.
The D/C system are 12vdc Positive and Negative ( common ).
You would be taking the Equipment Grounding Conductor from the local utillity via your shore power cord to one side of your 12vdc equipment ( ie, stereo, vhf radio, nav electronics lighting, etc. )
Is your thoughts to bond everything together ??? Would you bond the mast and other equipment for lightning protection?
The A/C equipment does not work at sea unless you employ an inverter or generator, and on shore power, your battery charger would be connected to the batteries. This may introduce noise to sensitive electronic equipment.

 

[marchem]

What exactly is your reason for doing this?
Your A/C shore power equipment have a Hot, Neutral ( grounded ) and Equipment Grounding conductors at 120vac.
The D/C system are 12vdc Positive and Negative ( common ).
You would be taking the Equipment Grounding Conductor from the local utillity via your shore power cord to one side of your 12vdc equipment ( ie, stereo, vhf radio, nav electronics lighting, etc. )
Is your thoughts to bond everything together ??? Would you bond the mast and other equipment for lightning protection?
The A/C equipment does not work at sea unless you employ an inverter or generator, and on shore power, your battery charger would be connected to the batteries. This may introduce noise to sensitive electronic equipment.

It's my understanding that the AC and DC ground should be connected, for safety. My AC use is only at the dock.

 

[TENACITY CS36T]

It's my understanding that the AC and DC ground should be connected, for safety. My AC use is only at the dock.

That is correct, ABYC covers this extensively, safety first.

 

[captcoho]

http://search.yahoo.com/r/_ylt=A0oG...lator%20Article%20-%20D.Rifkin%2010-25-06.pdf

 

[captcoho]

 

[marchem]

That diagram shows the AC grounding (green) connected to the engine negative terminal (boat ground), i.e., DC gound. What seems odd is that the boat AC ground (green) is not connected to anything besides itself. That seems wrong.

 

[marchem]

http://search.yahoo.com/r/_ylt=A0oG...lator%20Article%20-%20D.Rifkin%2010-25-06.pdf

The need to monitor/test the galvanic isolator is why I want to locate it in an easily accessed area.

Not having a galvanic isolator allows any stray current on the AC ground to exit through my boat, causing more rapid loss of zinc anode than normal.

Another article on the same web site talks about why the AC and DC grounds should be connected, for safety: http://www.qualitymarineservices.net/Metal Boat Quarterly Article, DC-AC Ground Connection.pdf

 

[Stu Jackson]

Yes, you're right. The diagram is correct except for the fact that tyhere should be either a DOT whrre the green to engine crosses the grounds to the AC outlets and devices, or simply another green ground connecting the incoming ground to the AC wiring on the boat and a separate green to the engine. Otherwise, the diagram is correct and shows the kind of information you're looking for.

 

[marchem]

Yes, you're right. The diagram is correct except for the fact that tyhere should be either a DOT whrre the green to engine crosses the grounds to the AC outlets and devices, or simply another green ground connecting the incoming ground to the AC wiring on the boat and a separate green to the engine. Otherwise, the diagram is correct and shows the kind of information you're looking for.

That makes sense. Part of my question is if using terminal strips for the AC is bad form. I need to find a place to insert the galvanic isolator, and doing it with a terminal strip (for the hot and neutral AC wires) works, but may not be best practice.

 

[Stu Jackson]

I've used terminal strips (for installing our combined inverter/charger) but made sure they're in a place where absolutely nothing could connect to them. Terminal blocks are easy to use. Consider sticking them in a Rubbermaid container, simple solution to avoiding having something arc the connections, unless you can find one with a cover, although I don't recall seeing them except for fuseholders.

 

[Sailvayu]

The galvanic isolator goes in line in the AC shore ground between the panel and the shore power inlet. The isolator blocks DC current from the shore side entering your boat. DC happens when your boat acts like a cell in a battery, other boats around you being the other cells and the dock ground wire being the conductor between cells just like a giant battery. The isolators will have large bolt type lugs on them. you can cut the ground wire and insert the isolator in-line or remove the ground from the buss bar at the panel and connect it to the isolator and then run a short wire back to the ground buss. Make sure your isolator is rated for your power load IE if 30 amp service get a unit rated for 30 amps. I use a strip of Formica to cover terminal strips if needed, just cut to some length and width and use a couple of screws to secure over the top. Also in the wiring diagram it says the reverse polarity light is optional. It is now required on 30 AMP 120 volt service optional on 50 AMP 240 volt service

Capt. Wayne Canning, AMS
www.projectboatzen.com

 

[Stu Jackson]

The correction to the diagram in #6 noted in my reply #9 can be found here, just for the record:

http://www.westmarine.com/webapp/wc...01&page=Marine-Grounding-Systems#.UUJmcFdXr-I

 

[Maine Sail]

That makes sense. Part of my question is if using terminal strips for the AC is bad form. I need to find a place to insert the galvanic isolator, and doing it with a terminal strip (for the hot and neutral AC wires) works, but may not be best practice.

There should be no need to cut the black & white AC wires to install a GI.. Just peel back the jacket on the triplex wire and tap into the green. That said the Yandina GI does not meet current safety standards. As long as you are comfortable with that then you're all set..

Also keep in mid that GI's only rely limit galvanic corrosion. The best prevention for marina based issues is to either unplug or install an isolation transformer.

 

[marchem]

There should be no need to cut the black & white AC wires to install a GI.. Just peel back the jacket on the triplex wire and tap into the green. That said the Yandina GI does not meet current safety standards. As long as you are comfortable with that then you're all set..

Also keep in mid that GI's only rely limit galvanic corrosion. The best prevention for marina based issues is to either unplug or install an isolation transformer.

Thanks. One problem with just cutting into the triplex wire is it doesn't give me a place to connect to the DC ground, which the terminal strip does.

I understand the limitations of the Yandina GI. I figure it's better than the current wiring, with no AC-DC ground connection. I've also tested my marina wiring and it seems ok, but I will continue to monitor it.

 

[mitiempo]

Thanks. One problem with just cutting into the triplex wire is it doesn't give me a place to connect to the DC ground, which the terminal strip does.

There is no need to connect the DC ground to the galvanic isolator. The DC ground and AC ground (green) should be connected behind the panels where you can use a 10 gauge wire from the AC ground bus to the DC negative bus.

I have the same Yandina galvanic isolator and installed it directly to the shorepower inlet so there wasn't a need to cut into the AC incoming wire.

 

[marchem]

There is no need to connect the DC ground to the galvanic isolator. The DC ground and AC ground (green) should be connected behind the panels where you can use a 10 gauge wire from the AC ground bus to the DC negative bus.

I have the same Yandina galvanic isolator and installed it directly to the shorepower inlet so there wasn't a need to cut into the AC incoming wire.

Can you get at the Yandina easily to test it? If I put mine at the shorepower inlet I can't get at it easily to check the diodes.

 

[mitiempo]

Yes it is easy to get to - it is just in behind the shorepower inlet.