Be careful! When you are using shore power, neutral and ground are not connected to each other. When using an inverter, they must be connected for safety. Marine inverter systems take care of this automatically. If you plan to use a non-marine inverter, make sure it is installed properly.
I finally found Calder's book and read the fine print that was not in other sources. Nancy is right, and I revised my post # 37.
Pete, what has occurred to me is that you may need a lot more understanding of boating system electrical info that you seem to have at hand. In addition to learning about that, you could also download some of the inverter installation manuals and start looking at the wiring diagrams.Thanks; good advice. I do, however, think the hard-wiring of standalone inverter into existing AC outlets will be well worth the effort and expense via a 3PDT switch.
Thanks. Actually, I've already read several user/installation manuals. I'm now very familiar with their recommendations. Actually, another thread introduced me to the issue of shore vs ship's ground when switching back and forth between shore and inverter. That was new to me and not mentioned here or in the aforementioned manuals. I'm glad to receive multiple sources of information and sort through them. It's a process which is not complete, but I'm certainly gaining on it. As mentioned, I now believe a 3PDT switch is the way to go to ensure that we always have a proper safety ground and never permit the shore ground to be tied to ship's ground which can lead to electrolysis. As an aside, also from another forum, an isolation transformer inserted into the shore power connection, will allow one to revert back to the DPDT switch and use ship's ground as the AC safety ground whether connected to shore or inverter. That's a far superior solution especially with respect to electrolysis, but again those isolation transformers are not cheap. While these forums are great, one does need to sort through all the sometimes conflicting inputs. That of course does require a technical background and a willingness to learn. Rest assured that I will not order anything until I am fully confident of what I'm doing. In the meantime, I continue to learn and hopefully will be in a position to share my results, whether good or bad, with others.Pete, what has occurred to me is that you may need a lot more understanding of boating system electrical info that you seem to have at hand. In addition to learning about that, you could also download some of the inverter installation manuals and start looking at the wiring diagrams.
Every time we discuss these kinds of issues with folks, especially if they come up with "...I've learned on another forum..." comments, I personally begin to care very much about the SAFETY of that person.
I think you're trying to cut corners, and would do well to do some more homework before you buy and start wiring.
Your safety is our primary concern.
Good luck.
Thanks. The first West Marine link confirms what I have learned on another forum. To summarize it's best to isolate the shore ground from ship's ground to prevent electrolysis. The best (and most expensive) way is via an isolation transformer and the second best way is via a relatively inexpensive galvanic isolator. Here is a quote from that link that explains it better than I can:You WANT the ships ground and the AC shore power ground to be connected. This is an important safety connection.There is a device called galvanic isolator that connects to the shore power ground right after it enters the boat shore power plug. It allows current to pass but only if it is over 2-3 volts. Since the corrosion voltages are less than that --> no corrosion.
As Stu said, we value you safety and it is what you do not know that can result in unfortunate events.
West marine has a great primer on grounding in boats, AC, DC, radio, corrosion and lightning... yes Martha it can be done but you have to see the big picture.
http://www.westmarine.com/webapp/wc...catalogId=10001&page=Marine-Grounding-Systems
and some pitfalls to avoid
http://www.westmarine.com/webapp/wc...51&catalogId=10001&page=Ten-Deadly-Conditions
I have already priced out a recommended isolation transformer, the Charles IsoG2 3.8 kVA. Here is a link to one:The best solution is a heavy and expensive isolation transformer. The acceptable solution (for the rest of us) is to install a light and inexpensive Galvanic Isolator in the green wire, between the shorepower cord socket on your boat, and the connection to the boat's AC panel. Then, connect the grounding conductor (green) of the AC panel directly to the engine negative terminal or its bus.
Thanks. That article does an excellent job of explaining the neutral ground connection issue. And, yes it would seem that a 3PDT switch is preferred so that when in the shore position, neutral and ground are connected on shore and when in the inverter position neutral and ground are connected at the inverter. As noted, they should be tied together at the source. If the ground were not switched (along with hot and neutral), one could have the situation where neutral was tied to ground both on shore and at inverter. Fortunately 3PDT switches are readily available at reasonable cost.Be careful! When you are using shore power, neutral and ground are not connected to each other. When using an inverter, they must be connected for safety. Marine inverter systems take care of this automatically. If you plan to use a non-marine inverter, make sure it is installed properly. See http://www.google.com/url?sa=t&rct=...sg=AFQjCNEq84QR4KlS0lAjpMsxLL_IPDA0uA&cad=rja
Thanks. Based upon my study to date, we should use a 3 gang switch which will switch hot, neutral, and ground to ensure that shore ground is isolated from ship's ground when not using shore power. Also, when using shore power, shore ground should not be connected directly to ship's ground; rather it should be isolated with either an isolation transformer or galvanic isolator. You are right, if safety was the only concern, however, we intend to be safe and eliminate electrolysis. When you think about it, electrolysis is also a safety concern since the ultimate result, if unchecked, is the loss of a thru-hull fitting. My philosopy is that if I'm going to all this work, might as well do the job rightYou NEVER switch the ground wire.
Check the diagram again. You only switch the hots and neutrals. The ground wire connects everything all the time no matter what position the transfer switch may be in.
Also, I'm thinking you are getting a little target locked on the electrolysis issue. most of us do not have galvanic isolators or transformers and we manage to survive. I'd only add one if I had a problem.
Thanks for the warnings. Unfortunately, you address the pitfalls without presenting solutions that provide for both safety and freedom from electrolysis. I am now looking into the use of a DPDT switch in combination with galvanic isolator installed in the shore ground wire. This may be a cost effective solution that avoids the possibility of switch failing. By the way, I consider electrolysis a safety issue. Please be aware that I'm not messing with AC; rather I'm climbing the learning curve; there is a difference. Sometimes experts forget that at some point in the perhaps distant past they weren't expertsLets try this tack
The reason you never want to switch the grounds is if the switch breaks you will not have safety circuit and could electrocute yourself or others.
Having the inverter and shore power grounds connected will not effect the electrolysis issues in any way what so ever. The problem with shore power is not it's ground connection to the inverter. It is with being connected to all the other boats in the marina via the ground. Having the inverter ground tied into that circuit will not matter in the lease as far as electrolysis is concerned.
Course if you do switch the grounds and forget and leave the inverter on then switch the transfer switch to shore power you wil have a floating ground on the inverter side which will allow the hot and neutral to have some voltage not associated with 120 volts AC referenced to a common ground. ie you could have 480-500 volts ac (net 120 volts AC) on the inverter which will no doubt cause some interesting effects. Now ask yourself, is the transfer switch rated for that kind of voltage or will it blow/arc and release $200 worth of the magic blue smoke?
If you don't get this you really should not be messing with AC.
Pete,Thanks for the warnings. Unfortunately, you address the pitfalls without presenting solutions that provide for both safety and freedom from electrolysis. I am now looking into the use of a DPDT switch in combination with galvanic isolator installed in the shore ground wire. This may be a cost effective solution that avoids the possibility of switch failing. By the way, I consider electrolysis a safety issue. Please be aware that I'm not messing with AC; rather I'm climbing the learning curve; there is a difference. Sometimes experts forget that at some point in the perhaps distant past they weren't expertsSince others read these forums, I hope to be able to describe, in the not too distant future, a solution that satisfies both requirements.
Pete
Pete, #1 simply isn't true. You have three choices: do nothing and don't stay plugged in, get a galvanic isolator or get an isolation transformer.Thanks for the warnings.
1. Unfortunately, you address the pitfalls without presenting solutions that provide for both safety and freedom from electrolysis.
2....I hope to be able to describe, in the not too distant future, a solution that satisfies both requirements.
Thanks. That Sterling is a great find. On our boat it's difficult to route wires around, so I still think it will be easier to switch inverter to the existing AC outlets. Also, given the location of microwave plug it will be difficult to switch it back and forth, but I'll keep that in mind as we progress.Pete,
Please don't try to cut corners on shore/inverter isolation. Sterling sells a VERY REASONABLY priced transfer switch. They do the same as the Newmar or Blue Sea switches only for a lot less money.
Sterling AC Transfer Switch $29.00
For they type of inverter you want to buy it is often easier to simply wire it to two or three dedicated "inverter outlets" and be done with it. This is what I've done on our boat. I only ever use it for running tools and charging tool & camera batteries (pure sine as I ruined a number of power tool batteries running of a modified sine inverter). Wiring in two outlets was less money than wiring in a transfer switch and re-wiring my system so the inverter was isolated from battery charger and hot water heater etc..
I generally do not recommend Xantrex but their ProWatt SW sine wave inverters are very reasonably priced. I've installed a few and not YET had an issue. If I do have an issue I consider them almost disposable at the price so no big loss.