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Old 18-06-2020, 05:41   #1
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Isolating Inverter Neutrals

Hi folks, I am the proud new owner of a 2003 Heritage East Sundeck Trawler. I am working thru an issue with my inverter. I have read that according to current ABYC standards that the inverter supplied circuit’s neutrals need to be on their own buss. Our inverter has an AC supply with internal transfer switch. We have run into a problem connecting to shore power with the new pedestals equipped with the GFCIs.
My questions are this:
1. What neutral do I use to feed the isolated buss?
2. What neutrals do I include on that buss? Inverter supplied branch circuits, Inverter AC input, Inverter output, etc..
Any help would be greatly appreciated.
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Old 18-06-2020, 05:50   #2
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Re: Isolating Inverter Neutrals

Never heard of that, only thing I have heard of is a neutral / ground disconnect relay whenever AC power is supplied by a source other than the inverter.
Your inverter does have a relay that disconnects the neural and ground whenever it’s not operating doesn’t it?
If not then that may be your problem, maybe.

I have never heard of a separate bus for inverter neutral, as there aren’t any inverter only neutrals in a normal installation, the inverter just becomes a secondary AC power supply.
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Old 18-06-2020, 13:13   #3
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Re: Isolating Inverter Neutrals

It's just way to broad a statement. Plenty of inverters have a common input and output neutral, so impossible to isolate, even if thee were som motivation to do so.



To solve the problem you will need to really dig into the exact wiring setup that you have, make and model of inverter, how neutral to ground bonding is handled, and probably a host of other things.
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Old 18-06-2020, 13:24   #4
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Re: Isolatieng Inverter Neutrals

All my Freedom inverters/ chargers required the input and output neutrals be separated. For a typicalI inverter feeding receptacle circuits I just cut the neutral bus bar (IP has a pretty well organized electrical system) to isolate the two receptacle circuit neutrals. Have since changed to a Renogy IC and just continued the same arrangement. Not a big deal if you can identify the neutrals.


Often the new ground fault interrupted shore power pedestals will be tripped off line by a ground to neutral connection on the yacht.


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Old 19-06-2020, 05:46   #5
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Re: Isolating Inverter Neutrals

From my understanding is that most if not all current Marine Inverters by code bond neutral to ground when inverting. If the unit is equipped to pass AC shore power thru is it will release the neutral to ground bond via the internal transfer switch. The problem is that by time the inverter sees the 120v signal the GFCI will likely trip. My further understanding is that the requirement to isolate the inverter supplied circuit neutrals came about the same time as the requirement for the new 30 mA GFCI protected pedestals. I have also read that if you have two 30A inputs that each leg’s neutrals should be isolated from one another. In full disclosure my knowledge in the ABYC world is fairly shallow.
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Old 19-06-2020, 06:38   #6
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Re: Isolating Inverter Neutrals

Quote:
Originally Posted by VB Mike View Post
We have run into a problem connecting to shore power with the new pedestals equipped with the GFCIs.

You may find that installing an isolation transformer is a more straightforward way to solve the presenting problem, depending on the extent of the wiring and equipment changes you would have to make to isolate the neutral buses on your boat.



Quote:
What neutral do I use to feed the isolated buss?
The general idea if you go this route is that you switch and feed the neutral buses the same way you switch and feed the hot. You would use the neutral output from your inverter/charger to feed the bus with all the circuits that the hot output from your inverter/charger feeds.


The shore power neutral would feed a separate bus that feeds loads that aren't supplied by the inverter, including the inverter input and (depending on how your boat is wired) possibly a water heater or air conditioner.


Similarly if you have two shore power inputs you would divide the neutrals just as you do the hot, so that the branch circuits connected to shore #1 have their neutrals on shore #1 and the branch circuits on shore #2 have their neutrals on shore #2.
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Old 19-06-2020, 08:00   #7
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Re: Isolatieng Inverter Neutrals

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Often the new ground fault interrupted shore power pedestals will be tripped off line by a ground to neutral connection on the yacht.


Frankly

That is one reason why you should have a relay that ties the inverter neutral to ground whenever the Inverter is on, and breaks that connection when it’s off.
If an inverter doesn’t come wired that way already, which a good marine one should, it wouldn’t be hard at all to add a relay.
You can’t isolate Inverter neutrals any other way, excepting of course unless the inverter has its own separate electric system, which you could do if you only wanted one or maybe two receptacles.

The other reason you want the neutral tied to ground is safety, in case there is current on the neutral.
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Old 19-06-2020, 08:06   #8
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Re: Isolating Inverter Neutrals

To continue just a little, there should be no neutral to ground connection, excepting the source of the power, a generator for instance should have the neutral and ground bonded, and an inverter, but those should be temporary bonds that are broken whenever the shorepower is connected as there should only be one neutral to ground connection, and that should be at the source of power. Hence the need for a relay on the inverter, and the generator power switch should also switch neutral also.


You guys are trying to make it way more complicated than it is, an inverter is just a supply of electricity, just like the shorepower cord or a generator. There in no need for separate busses or other complex wiring, just a make / break neutral to ground bond is all that’s needed.
I bet if there is a transfer switch in the inverter, it already has one, my Magnum it’s a simple green wire with connectors, plug them into each other and the bond occurs, leave them unplugged, and there is no bond.
That’s all there is to it.

This screen shot explains it.
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Old 19-06-2020, 09:28   #9
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Re: Isolating Inverter Neutrals

The inverter nuetrals need to be seperate. They need their own bus bar.

The output netreal from the inverter goes to that bus. The. Then the neutrals from inverter loads get moved to that bus. Ie outlets, etc.

A boat will trip gfi / elci breakers without seperating them.

If the inverter has a common input and output neutral. You’ll need to replace the inverter.
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Old 19-06-2020, 09:33   #10
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Re: Isolating Inverter Neutrals

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You guys are trying to make it way more complicated than it is, an inverter is just a supply of electricity, just like the shorepower cord or a generator. There in no need for separate busses or other complex wiring, just a make / break neutral to ground bond is all that’s neededl

When you plug your boat in. The magnum (and every other inveryer chsrher) takes ~30 secs to test the power. Before It starts charging and ac pass through. That inverter g-n bond is kept during that 30 secs. The Gfi trips instantly due to the n-g bond on the boat. It does not wait 31 secs before it checks.

The sepeterate neutral bar is needed on a dock gfi breaker or a boat main elci breaker. It means the dock never sees the inverter g-n bond.
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Old 20-06-2020, 06:06   #11
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Re: Isolating Inverter Neutrals

I agree with you completely Smac999. I think I have my answer. I am going to install a separate buss and connect the inverter output neutral to it along with the branch circuit neutrals. The AC input from shore neutral will remain on the common AC neutral buss. In that manner the GFCI will not see the neutral to ground bond at any point. When the internal transfer switch closes to allow AC shore power pass thru to the inverter branch circuits it will supply the neutral connection to the same.
Am I missing anything?
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Old 20-06-2020, 06:47   #12
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Re: Isolating Inverter Neutrals

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When you plug your boat in. The magnum (and every other inveryer chsrher) takes ~30 secs to test the power. Before It starts charging and ac pass through. That inverter g-n bond is kept during that 30 secs. The Gfi trips instantly due to the n-g bond on the boat. It does not wait 31 secs before it checks.

The sepeterate neutral bar is needed on a dock gfi breaker or a boat main elci breaker. It means the dock never sees the inverter g-n bond.
Mine doesn’t, the inverter only closes and bonds the neutral and ground together when the inverter, is inverting, not when it’s laying idle.
1. So every single Magnum inverter / Charger will trip a GFI breaker when wired according to Magnums instructions?
2. No Magnum inverter / Charger can be used to power the whole AC side of the boat, but must have separate devices / plugs specific just for inverter use?

Wire your inverter according to the instructions, if it doesn’t work, call the manufacturers product support.
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Old 20-06-2020, 07:00   #13
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Re: Isolating Inverter Neutrals

Oh, and there is no 30 sec “test” interval either, shore power is passed on immediately, and the spec transfer interval for the inverter if shorepower is lost is 16 milliseconds.
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Old 20-06-2020, 07:54   #14
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Re: Isolating Inverter Neutrals

Wow... there is so much confusion in this thread! And a lot just plain wrong. On the need for a separate neutral bus, the answer is IT DEPENDS! So every answer so far that includes the word “always” or “never” is wrong.

Let’s be clear, there are a number of different cases, and they are NOT all handled the same way. There are Inverters, and there are inverter/chargers. There are inverters that are used in parallel with shore power, and those that are used to replace shore power to the entire boat. Things get more complex on boat’s with more than one shore power connection and more than one inverter, so let’s leave those out for now...

In answer to the OP’s question: If you have SOME circuits on the boat that are powered by shore power, and others that are powered by an inverter, then a separate neutral is indeed required for the two sets of circuits. This SHOULD be obvious to anybody who understands electricity. Connect two separate sources of power to the same neutral would result in ALL kinds of bad things happening. This is the ABYC requirement that you heard about.

If you have an inverter that is used to replace shore power, you must have a selection switch to ensure than both can NEVER be connected to the same circuit(s). This can be an automated transfer switch, or a manual one. It might be built into the inverter, or a separate device.

The selection switch MUST be a three pole switch that switches hot, neutral and ground. Once the switch is used to select “Inverter” then the boat’s neutral wiring is all isolated from shore power and is essentially an “inverter only” neutral bus. No separate bus is needed. Again, this situation should be obvious to anyone who understands how electric power works.

This is exactly how an inverter/charger with a transfer switch works. When the inverter power is selected, either manually or automatically, the neutral (Along with hot and (in most cases) ground) is separated from shore power for all the circuits connected to that inverter/charger. This might be less obvious, because it happens automatically and internally.
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Old 20-06-2020, 08:07   #15
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Re: Isolating Inverter Neutrals

You don’t need a separate neutral bus for an inverter that only powers it’s own separate circuits.
You will however need a relay or switch that prevents having both the neutrals connected at the same time.
It’s just too easy a problem to fix without installing a separate bus, and not that my opinion means anything, but why would you want a separate inverter electrical system? You can do that, but it’s illegocial.

Switching the neutral is not just an inverter “thing” the neutral should be switched with an onboard generator too.
We don’t with portables because we use the shorepower plug there, and you can’t be connected to the shorepower neutral because the cord isn’t connected.
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