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Old 04-18-2019, 03:24 PM   #1
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Galvanic isolator with an Inverter

I'm wanting to know the correct place for my galvanic isolator when using an inverter. Very straight forward setup:

Shore powers going to the inverter with built in transfer relay and breakers. From there it goes out to the main panels 30 amp breaker. Currently the galvanic isolator is on the ground/green wire at the main panel bypassing the 30 amp main panel breaker and going out right to the ground bar.

I'm wondering if its better to have it closer to the inverters out or leave it at the main panel where its at. There's a 8' run between the shore power connection and the inverter then another 8' from inverter to the main panel. I don't believe it should be before the inverter, but I could be wrong (that's happened before .

I don't see this in the codes or in the galvanic isolator's manual, or in the inverters manual. Its easy enough to move, but I don't want to if it makes no difference. I also don't want to fry it as it was not cheap..
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Old 04-18-2019, 03:46 PM   #2
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I think you want the galvanic isolator as close to the shore power inlet as is reasonably possible given the need to keep it dry, etc.

In some sense, it doesn't matter where it is, as long as it isolates the boat's ground from the earth ground(*), thereby preventing your boat's zincs (or less noble metals in useful components!!!) from getting consumed protecting your neighbors' boats that share the same earth ground.

There may be other reasons that aren't coming to my mind, but i think the big reason one wants it close to the shore inlet is just to prevent it from accidentally getting bypassed. If any ground bypasses it, by intention or accident, since they are all tied together, everything has bypassed it.

(*) One does want the boat's ground to be tied to the shore ground for safety reasons, which is why the galvanic isolators only isolate up to ~1.4V -- allowing the ground to function normally for safety beyond that. In this way, they provide isolation for the low voltages stray currents that cause corrosion -- but a ground path for the high voltage electrical problems that could otherwise kill someone.
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Old 04-18-2019, 10:10 PM   #3
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Hello CEC,
If it was my boat, I (a residential / commercial electrician with 20 years + experience) would try get the best professional answer to your galvanic isolator question. One person i would ask would be, Steve D' Antonio asksteve@stevedmarineconsulting.com.
Great wealth of marine knowledge can be found on Steve's website
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Old 04-19-2019, 08:22 AM   #4
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Quote:
Originally Posted by CEC View Post
I'm wanting to know the correct place for my galvanic isolator when using an inverter. Very straight forward setup:

Shore powers going to the inverter with built in transfer relay and breakers. From there it goes out to the main panels 30 amp breaker. Currently the galvanic isolator is on the ground/green wire at the main panel bypassing the 30 amp main panel breaker and going out right to the ground bar.

I'm wondering if its better to have it closer to the inverters out or leave it at the main panel where its at. There's a 8' run between the shore power connection and the inverter then another 8' from inverter to the main panel. I don't believe it should be before the inverter, but I could be wrong (that's happened before .

I don't see this in the codes or in the galvanic isolator's manual, or in the inverters manual. Its easy enough to move, but I don't want to if it makes no difference. I also don't want to fry it as it was not cheap..

Unlike a fuse or circuit breaker which should be as close to the source of power as possible, a Galvanic Isolator can be anywhere in the ground wire between the shore power ground and the first ground connection to the boat. It MUST be installed before any ground connection to the boat or you defeat how it works.


Ken
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Old 04-19-2019, 09:21 AM   #5
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Ken explained it correctly. I will add only one thing. The purpose of the isolator is to prevent low voltage induced DC currents existing on the shore power ground connection. It has nothing to do with any inverter or any other power source on the boat.
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Old 04-19-2019, 11:09 AM   #6
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Thank you all for the answers. Iím going to leave it where itís at. Itís great to have confirming feedback to help with reinforcing even a professionals opinion. Thereís no other boat connection to the inverter, so the isolator will remain before the boat panels connection.

Moving it closer to the out of the isolator gets me nothing.

Putting it before the inverter would just open me up to no isolation when the inverter is in use so thatís not correct.

Thanks again.
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Old 04-19-2019, 12:09 PM   #7
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CEC,

Just to make sure...

Metals have different electrode potentials. Some of them are more reactive (less noble), others less reactive (more noble). When dissimilar metals are in an electrolyte like salt water, more active metals form positively charged anodes, less active metals form negatively charged anodes. The electrolyte carries the ions from the anode to the cathode, destroying the anode. This current flow between metals through an electrolyte is basically how a battery works.

Our boats basically suffer from the same thing. They are a bunch of dissimilar metals floating in salt water. As a result the salt water conducts ion flow among the metals, corroding the more active (less noble) ones. This is why we attach zincs to our boat. zinc is very active, so it'll supply ions to the other metals, so the metals we care about aren't donors, and don't corrode.

Since our boats are tied to earth ground via the ground wire on shore power, we can get these currents flowing among boats. That means that one boat's zincs can end up protecting another boat. Or, worse, one boat's bronze can get dezincified, becoming less dense and spongy, slowing the corrosion of another boat.

Galvanic isolators work by disconnecting our boats from the earth ground. Thus, our boat only needs to protect our boat. One could do this just by leaving the ground wire "open" -- but that would be dangerous for the humans it protects. So, what these galvanic isolators do is use a couple of diodes, or something like that, to allow the ground to be open for low voltage DC currents -- so we aren't protecting other boats -- but to switch closed for high voltages, so we are protected from electrical hazards.

The reason I mention this is that, when your boat is running on the inverter it is most likely completely disconnected from shore power, e.g. while underway. Because it is disconnected from shore power, it is protected from this type of corrosion, anyway. The ground wire isn't attached to shore. The exception would be if you have the shore power breaker turned off and are running off the inverter, but the cable is still connected -- the breaker only interrupts the hot wire, not the ground wire.

When I mention running off the inverter, I don't mean the inverter's transfer relay is activated to power the boat from shore power. Insead what I mean is that the inverter is supplying AC power from DC power, because there is no shore power (and further, that shore power is completely disconnected).

The only important thing about the galvanic isolator is that it break that connection between the boat's ground and shore ground (for low voltages). It can be anywhere that lets it do that and work effectively. The only thing is, the deeper it gets installed into the system, the easier it is for someone to accidentally or unknowningly install something that bypasses it.
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Old 04-19-2019, 12:30 PM   #8
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One point, a galvanic isolator does not disconnect the ground wire from shorepower, it puts one or 2 diodes in the line to provide up to about 1.5V of isolation between the boat's ground and shorepower ground. This voltage level is more than tyical galvanic voltages, hence the "galvanic isolation". Even with a galvanic isolator installed, a true power to ground fault will still allow the ground fault current to be able to be conducted to ground.


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Old 04-19-2019, 12:34 PM   #9
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Hi Ken,

If that was directed to me, I think I had it burried in there. I probably should use fewer words for clearer meaning :-)

"So, what these galvanic isolators do is use a couple of diodes, or something like that, to allow the ground to be open for low voltage DC currents -- so we aren't protecting other boats -- but to switch closed for high voltages, so we are protected from electrical hazards. "

Cheers!
-Greg
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Old 04-19-2019, 12:42 PM   #10
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I just realized in reading back through the thread that in my original reply in one place I wrote "stray current" when I was talking about galvanic action. That was a bit of a finger slip.

Stray current is when current, usually intended to be part of an electrical circuit, is returning via the boat's metal fittings and the water. The classic example is that the wiring for a bilge pump falls into the bilge and, although some current runs through the intended circuit -- some leaks through a wet connection into the water in the bilge, and then completes the circuit via the boat's metal fittings and the water. These currents can cross boats -- but most often don't. "The one who smelt it dealt it".

Because these tend to be 12V circuits (or 24V circuits) their voltages are way higher than the millivolts of galvanic action and they tend to be dramatically more damaging dramatically faster than the much smaller galvanic currents of galvanic action. They can burn right through whatever metal allows them to leave the vessel, e.g. turn a thru-hull into a hole.

Galvanic isolators are of no protection. Zinc anodes are of very little protection. A good bonding system can slow the damage only by spreading it out over much more metal so all of the metal corrodes more slowly instead of a little super fast.

Sorry if I caused any confusion.
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Old 04-19-2019, 12:55 PM   #11
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Hi Ken,

If that was directed to me, I think I had it burried in there. I probably should use fewer words for clearer meaning :-)

"So, what these galvanic isolators do is use a couple of diodes, or something like that, to allow the ground to be open for low voltage DC currents -- so we aren't protecting other boats -- but to switch closed for high voltages, so we are protected from electrical hazards. "

Cheers!
-Greg

I didn't mean any disrespect, but I wanted to make sure it was clear that even with a galvanic isolator installed, there still was a path to safety ground for fault currents.


Ken
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Old 04-20-2019, 11:06 AM   #12
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My main concern was the inverter and itís transfer relay. When reading the manual it indicates three wires into its block from shore power and two only hot and neutral coming out. You then connect the ground to a different screw on the inverter that then goes to the boats ground.

What was worrying me was that ground but further reading explains thereís a ground relay that flips between shore power and inverter power. Itís a separate relay from the transfer relay but I think itís tripped by the transfer relays position.

It moves the ground connection between closed for shore power when connected to open when on inverter power.

This is why I was considering the location of the isolator before or after the inverter. Leaving it weíre its at in the main panel is best I think because itís a visual reminder./indicator. My fear is the inverter might hurt the isolator somehow but I think Iím overthinking it. Seems itís really not doing anything when on inverter power.

Thanks thereís a lot of great explanations in this thread.
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Old 04-20-2019, 11:20 AM   #13
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Do you have an inverter bypass switch installed?
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Old 04-22-2019, 12:49 PM   #14
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Do you have an inverter bypass switch installed?
No I do not but considering putting one in place.
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Old 04-24-2019, 07:45 PM   #15
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Do you have an inverter bypass switch installed?
Is there a bypass switch you can recommend?
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Old 04-24-2019, 09:11 PM   #16
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CEC,

Someone earlier in the week (Maybe Sunchaser?), I think on a different thread, mentioned using the Blue Sea Systems rotary switch for an inverter bypass switch.

I took a look at the Blue Sea Systems 9009 (1481 with panel) to see what it switched and how:
-- https://www.bluesea.com/products/900...ns_120V_AC_30A

Since the wiring wasn't posted in that thread, I started to quickly throw together a potential wiring schematic to post. But, I never got around to double checking it and I lost the thread and had to erase my whiteboard before I got back to it. So, I'll post it here.

But, please, let's take it for what it is: A 4 minute fast sketch that might have errors. A scribble I started to do over lunch one day. Please no one use it without careful thought and checking.

The good news is, I suspect it won't take long for folks here to correct any mistakes! :-)

Edit: Looking at my post, I realized I drew the isolation transformer's output-side ground wrong internal to the transformer. I just photoshopped it and fixed it.
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Old 04-24-2019, 09:49 PM   #17
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Originally Posted by gkesden View Post
CEC,

Someone earlier in the week (Maybe Sunchaser?), I think on a different thread, mentioned using the Blue Sea Systems rotary switch for an inverter bypass switch.

I took a look at the Blue Sea Systems 9009 (1481 with panel) to see what it switched and how:
-- https://www.bluesea.com/products/900...ns_120V_AC_30A

.
Yup, that is the style I mentioned. Very common and advertised by Blue Seas and vendors as an inverter bypass switch. The marine tech I frequently use said he has installed dozens of rotary bypass switches over the years. Mine is mounted adjacent to the Magnum 2800.
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Old 04-25-2019, 12:05 AM   #18
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Hi all,

Actually, I *really* want to revise my prior post. As I look more at it, I don't like it at all. I wouldn't wire my boat that way. I was originally concerned that a cut-off switch was an unnecessary complexity and tried to avoid it. But, I now think it is essential.

One thing about the first sketch is that I have the 30A main breaker feeding the bypass switch. This has me double-tapping that breaker, which isn't good in general. Specifically, in this case, it would mean that a problem on the feed leading to the inverter-charger or with the bypass switch could disable the main AC panel, even on shore power. Less important, it would mean that the wiring would need to be rated for the full 30A, all the way along the path to the inverter panel. Basically, drawing it this was was a mistake. I didn't think it through.

I'd rather wire it as attached. This does require an extra cut-off switch, but so be it. And, it requires the inverter's input and output wiring be rated for at least the same current as the inverter-charger's breaker, but that is okay.

Looking at the sketch, we see that the same rotary switch is going to power the inverted-load panel and bus from either the inverter's input circuit or the inverter's output circuit, thus it acts as a bypass. This put it on a nice 15A or 20A breaker (or whatever is required) in the circuit, either way. The rotary switch acts as a cut-off for the inverter's output, by disconnecting it when the switch is OFF or selecting shore power as the source.

I've drawn a cut-off switch on the input of the inverter/charger. This is essential for the case where the charger is popping the breaker or boiling the batteries, or otherwise misbehaving.

This drawing provide proper circuit protection for everything, avoids having the same breaker protect two different things at the same time, and enables the charger-inverter to be completely removed from the system.

I'm also now imaging a situation where I wanted to run the inverted-load panel off of the house main in order to let the house batteries charge faster. In this case, I would want the rotary switch to select the shore power as the input without opening the inverter-charger's input cut-off. This would mean that the combined load of the inverter-charger charging and the inverted load panel couldn't exceed the breaker. That might work out okay if the device load was load enough on the panel.

Otherwise, the way to adjust things would be to run another AC circuit, with its own breaker, to use for the bypass instead of allowing it to be shared between the inverted-charger-load and the inverter input. This would then mean that the extra cut-off switch wouldn't be needed -- the inverter-charger's input breaker would serve that purpose, as it always has. I actually like this approach better and I would prefer it, a slot for a breaker available.

Again, my own boat doesn't have a bypass and I've never installed one. So, I'm just thinking this all through for the first time in between a bunch of other things. But, having read these conversations recently, I think I'll put adding one "on the list". :-)

I just worked on this for a very few minutes in between doing some other things. So, I could have goofed up again. None-the-less, I trust the crowd to let me know!

Cheers!
-Greg
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Old 04-25-2019, 01:08 PM   #19
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Thanks for the info on the switch. All I really desire is the ability to bypass the inverter in the event it breaks down or I need to replace it ext. Currently Iíd be doing a lot of wire work to retain shore power if the inverters transfer relay was not working. The simple 3 way rotary will do the trick it looks a bit awkward so finding a spot for it will be the next hurdle.
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Old 04-29-2019, 09:19 PM   #20
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If I'm understanding you correctly, your galvanic isolator is connected AFTER your inverter. I'm assuming your inverter was not original equipment, and sounds like a Victron. It actually doesn't matter the brand or type of inverter, but your GI needs to be just after the shore power inlet, before ANY device. If it's connected at your panel, after the inverter, it needs to be moved or it is useless.
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