Separating Inverter and Shore Circuits

[dsteinfeld]

Originally Posted by DotDun

Since this can only happen when the shore neutral/hot are disconnected, what problem would this cause?

No, it happens when the shore power cord is connected but the AC system is taking it's input from the inverter (with an output switched as discussed earlier in the thread). Inverter neutral is to chassis ground (green wire), which is tied to shore power ground, which is tied to shore neutral.

In my case my inverter (Morningstar Sure Sine) does not connect ground to neutral only when running, it's a permanent connection external to the inverter. So if I didn't switch the grounds when switching between shore and inverter I'd have ground and neutral tied together on the boat when running on shore-- a no-no.

[DotDun]

Originally Posted by dsteinfeld

No, it happens when the shore power cord is connected but the AC system is taking it's input from the inverter (with an output switched as discussed earlier in the thread). Inverter neutral is to chassis ground (green wire), which is tied to shore power ground, which is tied to shore neutral.

In my case my inverter (Morningstar Sure Sine) does not connect ground to neutral only when running, it's a permanent connection external to the inverter. So if I didn't switch the grounds when switching between shore and inverter I'd have ground and neutral tied together on the boat when running on shore-- a no-no.

Your inverter is designed to feed a dedicated receptacle, it's not designed to feed a distribution box or string of receps that are switched between inverter and shorepower. Hence, your inverter does not have an internal transfer switch.

If you are switching between inverter and shorepower external from your Morningstar, you need to use a 3 pole switch so you can switch the ground along with the neutral and line.

[dsteinfeld]

Originally Posted by DotDun

Your inverter is designed to feed a dedicated receptacle, it's not designed to feed a distribution box or string of receps that are switched between inverter and shorepower. Hence, your inverter does not have an internal transfer switch.

If you are switching between inverter and shorepower external from your Morningstar, you need to use a 3 pole switch so you can switch the ground along with the neutral and line.

Which is exactly what I said back in post #21.

[DotDun]

Originally Posted by dsteinfeld

Which is exactly what I said back in post #21.

Originally Posted by dsteinfeld

...and this was my point going back to the OP system. By not following ramblinrod's point (opening the shore power "grounding" connection when using the inverter) you wind up with the shore power grounded connection connected to the generator/inverter grounded connection via their grounding connections. At the very least this presents a surprise shock hazard at the inverter output when the inverter is unpowered and shore power is in use.

So to switch the grounding connection as well I decided a 3 pole relay was needed as a transfer switch.

I think (?) the point you are missing......even though the generator neutral is connected to ground/chassis at the generator when using shorepower, the generator neutral is disconnected from the distribution panel, hence the generator neutral/ground bond is of no consequence (i.e., no current can flow thru that connection).

An inverter that includes a transfer switch only connects neutral to ground when shorepower is disconnected. Again, the shorepower neutral/ground bond is of no consequence since the shorepower neutral is not connected when the inverter is powered on.

[Colin A]

Originally Posted by DotDun

I think (?) the point you are missing......even though the generator neutral is connected to ground/chassis at the generator when using shorepower, the generator neutral is disconnected from the distribution panel, hence the generator neutral/ground bond is of no consequence (i.e., no current can flow thru that connection).

An inverter that includes a transfer switch only connects neutral to ground when shorepower is disconnected. Again, the shorepower neutral/ground bond is of no consequence since the shorepower neutral is not connected when the inverter is powered on.

This^

Also if your using a subpanel or section of breakers their neutrals should be segregated from the rest of the panel.

[accomplice]

Originally Posted by ramblinrod

I am not sure if you are getting my point.

Per ABYC definitions and colour codes, the black wire is the "ungrounded" current carrying conductor, the white wire is the "grounded" current carrying conductor and the green wire is the "grounding", non current carrying conductor.

If we all use these definitions we should be able to keep it straight.

The "grounding" green conductor in the AC power system, must be connected to the source.

For shore power, the "grounding" connection is through a prong in the shore power cord, that connects back to the marina AC distribution panel, and somewhere, a rod driven into the earth.

I think we're getting our wires crossed here.

Modern inverter/chargers are designed exactly for this application and maintain separate power buses while conforming to ABYC.

When connected to shore power the grounding and ground are connected on shore (and hopefully the electrician who installed the electrical system at the marina did so correctly). The ground and grounding are run to separate bus bars on the boat. The ungrounded (hot) is run to the inverter/charger.

The inverter/charger is grounded to the boat's AC ground. In the event that the AC coming from shore is of sufficient quality, it is passed through to the boat's high-load breaker-bar where it is distributed to large loads such as watermakers, A/C and washer/dryer. The ungrounded source is also passed, through the inverter, to the boat's second, low-load breaker-bar where it is distributed to smaller loads such as outlets, microwave and icemaker. In the event that the current drawn from the shore power exceeds some adjustable value, the inverter supplements the output with power from the DC system. In the event that the shore power goes away, or does not meet the minimum quality requirements, the inverter/charger draws power only from the DC system to distrubute to the low-load AC system.

As a picture may be worth another thousand words, here is the diagram of the inverter/charger from the manual for the Victron Multiplus 24/5000/120

Thus there is a single point of ground connection (on shore), yet two AC distribution systems -- conforming to ABYC.

[...]
Per ABYC, 2 sources of AC power (even two shore power cords) cannot be connected to the same AC distribution system at the same time.

That is why two AC distribution systems are used -- one for low-load and one for high-load.

Because AC receptacles and GFCIs have only one "grounding" connection, even if a duplex receptacle has each socket isolated, and one connected to the shore power and the other to an inverter, thereby being two separate AC distribution systems, because they share the "grounding" connection, which by the standard must be connected to "the" (one and only) source, there is no way to make this ABYC compliant.

I am not advocating connecting two different AC systems to the same receptacle, but there is no reason why two systems cannot share the same ground, connected at the source (back on shore).

Personally, I would never do this. Even if someone proceeds like this, and makes the system non ABYC compliant, there should be a label at every receptacle socket, indicating the source. IMHO, painting a specific colour is not acceptable. This is not a standard, and means nothing to anyone else.

IMHO the best solution is a marine grade inverter, that :

1. Automatically feeds shore power / generator AC and corresponding "grounding" connection to the AC distribution panel when available, and feeds inverter produced AC and "grounding" connection when not.

Agreed.

2. Automatically disables the charger when the inverter is operating.

While I agree in general, there are specific cases -- such as when the shore/generator power is deemed too dirty for passing on to appliances, but is considered good enough for charging -- the AC tolerance of good chargers is remarkable.

3. Automatically starts the generator (if applicable) and switches the "grounding" connection, at the minimum battery cycle voltage desired (e.g. 50% DOD)

I don't want my generator starting when I didn't ask it to. There are many cases where I wouldn't want it to, but a simple and frequent one is that no raw water is available for cooling (and thus we carry many impeller spares!)

4. Automatically disables the inverter, if the battery voltage drops below 70% DOD).

Perhaps, but I prefer a programmable value with the ability to override.

[...]
If one does not understand electrical systems well enough to install one, they really shouldn't be mucking about with the vessel electrical system.

Agreed. There is more than one compliant way to crack that nut though.

[ramblinrod]

Originally Posted by accomplice

I think we're getting our wires crossed here.

Modern inverter/chargers are designed exactly for this application and maintain separate power buses while conforming to ABYC.

When connected to shore power the grounding and ground are connected on shore (and hopefully the electrician who installed the electrical system at the marina did so correctly). The ground and grounding are run to separate bus bars on the boat. The ungrounded (hot) is run to the inverter/charger.

The inverter/charger is grounded to the boat's AC ground. In the event that the AC coming from shore is of sufficient quality, it is passed through to the boat's high-load breaker-bar where it is distributed to large loads such as watermakers, A/C and washer/dryer. The ungrounded source is also passed, through the inverter, to the boat's second, low-load breaker-bar where it is distributed to smaller loads such as outlets, microwave and icemaker. In the event that the current drawn from the shore power exceeds some adjustable value, the inverter supplements the output with power from the DC system. In the event that the shore power goes away, or does not meet the minimum quality requirements, the inverter/charger draws power only from the DC system to distrubute to the low-load AC system.

As a picture may be worth another thousand words, here is the diagram of the inverter/charger from the manual for the Victron Multiplus 24/5000/120

Thus there is a single point of ground connection (on shore), yet two AC distribution systems -- conforming to ABYC.

That is why two AC distribution systems are used -- one for low-load and one for high-load.

I am not advocating connecting two different AC systems to the same receptacle, but there is no reason why two systems cannot share the same ground, connected at the source (back on shore).

Agreed.

While I agree in general, there are specific cases -- such as when the shore/generator power is deemed too dirty for passing on to appliances, but is considered good enough for charging -- the AC tolerance of good chargers is remarkable.

I don't want my generator starting when I didn't ask it to. There are many cases where I wouldn't want it to, but a simple and frequent one is that no raw water is available for cooling (and thus we carry many impeller spares!)

Perhaps, but I prefer a programmable value with the ability to override.

Agreed. There is more than one compliant way to crack that nut though.

Nope, no wires crossed on my part.

There is nothing wrong with having two isolated AC distribution systems, one for inverter source, and another (or combined) for shore power source, where either can feed common loads.

Related to this thread, there are two issues that I don't recommend:

Issue 1: You can't have shore power and an inverter or generator ground connected to a receptacle ground screw. This lacks the isolation stated above.

Issue 2: Separate, isolated receptacles for different AC sources. This achieves the isolation above, but is a lot of effort for little benefit and possible detriment.

[exMaggieDrum]

Originally Posted by ramblinrod

I am not sure if you are getting my point.

Per ABYC definitions and colour codes, the black wire is the "ungrounded" current carrying conductor, the white wire is the "grounded" current carrying conductor and the green wire is the "grounding", non current carrying conductor.

If we all use these definitions we should be able to keep it straight.

The "grounding" green conductor in the AC power system, must be connected to the source.

For shore power, the "grounding" connection is through a prong in the shore power cord, that connects back to the marina AC distribution panel, and somewhere, a rod driven into the earth.

For a generator or inverter produced AC on-board, the shore power "grounding" connection must be opened, and the "grounding" conductors connected to the "grounding" connection on the inverter or generator. Some inverters do not have a "grounding" connection (isolated output) and therefore cannot be connected to the vessel AC system and be compliant.

Per ABYC, 2 sources of AC power (even two shore power cords) cannot be connected to the same AC distribution system at the same time.

Because AC receptacles and GFCIs have only one "grounding" connection, even if a duplex receptacle has each socket isolated, and one connected to the shore power and the other to an inverter, thereby being two separate AC distribution systems, because they share the "grounding" connection, which by the standard must be connected to "the" (one and only) source, there is no way to make this ABYC compliant.

Personally, I would never do this. Even if someone proceeds like this, and makes the system non ABYC compliant, there should be a label at every receptacle socket, indicating the source. IMHO, painting a specific colour is not acceptable. This is not a standard, and means nothing to anyone else.

IMHO the best solution is a marine grade inverter, that :

1. Automatically feeds shore power / generator AC and corresponding "grounding" connection to the AC distribution panel when available, and feeds inverter produced AC and "grounding" connection when not.

2. Automatically disables the charger when the inverter is operating.

3. Automatically starts the generator (if applicable) and switches the "grounding" connection, at the minimum battery cycle voltage desired (e.g. 50% DOD)

4. Automatically disables the inverter, if the battery voltage drops below 70% DOD).

This is how my personal vessel is set up (though no generator) and I set up customer electrical systems with inverters.

I have removed and replaced an inverter on a customer vessel (not installed by me) that a surveyor correctly declared "non-compliant to ABYC standards" because it did not have a source "grounding" connection and transfer method when the inverter was in use.

I have also seen vessels where the owner made DIY modifications to have some isolated inverter powered AC receptacles, and other shore power / generator dedicated AC receptacles.

In my opinion, this needlessly cuts up the boat, and makes it less safe.

I disagree that this is a KISS approach. There is little more simple than an auto "grounding" transfer connection relay. It basically removes all operator error possibilities, (like an auto battery combiner compared to an A, B, A/B, Off manual battery switch).

If one does not understand electrical systems well enough to install one, they really shouldn't be mucking about with the vessel electrical system.

What he said!!!

[accomplice]

Originally Posted by ramblinrod

Nope, no wires crossed on my part.

There is nothing wrong with having two isolated AC distribution systems, one for inverter source, and another (or combined) for shore power source, where either can feed common loads.

Related to this thread, there are two issues that I don't recommend:

Issue 1: You can't have shore power and an inverter or generator ground connected to a receptacle ground screw. This lacks the isolation stated above.

Issue 2: Separate, isolated receptacles for different AC sources. This achieves the isolation above, but is a lot of effort for little benefit and possible detriment.

I disagree. Two AC systems on a boat not only may share the same ground, but *must* share the same ground.

From ABYC E11, 11.4.2 -- the definition of an AC grounding conductor -- "A conductor, not normally carrying current, used to connect the metallic non-current carrying parts of AC electrical equipment to the AC grounding bus, engine negative terminal or its bus, and to the source ground."

As repeated multiple times in E11.17, "APPLICATION OF TYPES OF SHORE POWER CIRCUITS" (E11.17.2, E11.17.3, E11.17.4, E11.17.5, E11.17.6), "The shore grounding (green) conductor is connected, [...] from the shore power inlet to [...] to all non-current carrying parts of the boat’s AC electrical system, including the engine negative terminal or its bus."

In 11.5.5.3, "The main AC system grounding bus shall be connected to the engine negative terminal or the DC main negative bus on grounded DC systems, or the boat’s DC grounding bus in installations using ungrounded DC electrical systems."


My reading of that is that there must be a single AC ground. I see no way to satisfy the requirement that the ground must be connected to the engine negative terminal or its bus while simultaneously isolating two separate grounds. In other words, there must be a single ground, not two isolated grounds.

The matter of multiple sources is addressed in 11.5.5.6.2, "Multiple Shore Power Inlets - Where more than one shore power inlet is used, the shore power neutrals shall not be connected together on board the boat." It does not say that grounds should be isolated -- only that neutrals should.

Can you please refer me, and other readers, to the section of E-11 which you believe requires isolated grounds, galvanic isolation notwithstanding?

[DotDun]

Originally Posted by accomplice

I disagree. Two AC systems on a boat not only may share the same ground, but *must* share the same ground.

From ABYC E11, 11.4.2 -- the definition of an AC grounding conductor -- "A conductor, not normally carrying current, used to connect the metallic non-current carrying parts of AC electrical equipment to the AC grounding bus, engine negative terminal or its bus, and to the source ground."

As repeated multiple times in E11.17, "APPLICATION OF TYPES OF SHORE POWER CIRCUITS" (E11.17.2, E11.17.3, E11.17.4, E11.17.5, E11.17.6), "The shore grounding (green) conductor is connected, [...] from the shore power inlet to [...] to all non-current carrying parts of the boat’s AC electrical system, including the engine negative terminal or its bus."

In 11.5.5.3, "The main AC system grounding bus shall be connected to the engine negative terminal or the DC main negative bus on grounded DC systems, or the boat’s DC grounding bus in installations using ungrounded DC electrical systems."


My reading of that is that there must be a single AC ground. I see no way to satisfy the requirement that the ground must be connected to the engine negative terminal or its bus while simultaneously isolating two separate grounds. In other words, there must be a single ground, not two isolated grounds.

The matter of multiple sources is addressed in 11.5.5.6.2, "Multiple Shore Power Inlets - Where more than one shore power inlet is used, the shore power neutrals shall not be connected together on board the boat." It does not say that grounds should be isolated -- only that neutrals should.

Can you please refer me, and other readers, to the section of E-11 which you believe requires isolated grounds, galvanic isolation notwithstanding?

I agree! (And disagree with Rod)

The important issue is that each source has neutral and ground bonded at the source. To understand this, follow the current flow! Multiple sources sharing a common ground IS the goal. In the above example of splitting a duplex recep with 2 sources, having a common ground on that recep is proper. Remember, the ground is simply a return path the neutral/ground bond at the source.

[ramblinrod]

Originally Posted by DotDun

I agree! (And disagree with Rod)

The important issue is that each source has neutral and ground bonded at the source. To understand this, follow the current flow! Multiple sources sharing a common ground IS the goal. In the above example of splitting a duplex recep with 2 sources, having a common ground on that recep is proper. Remember, the ground is simply a return path the neutral/ground bond at the source.

Yes, as indicated the neutral must be connected to ground at source, ONE ONLY.

So if a split receptacle (AC from inverter at one socket and AC from
Shorepower at the other socket, the single ground on that socket would have to be connected to neutral at the inverter and marina distribution panel at the same time. Not compliant, based on the E11 sections you cited.

[DotDun]

Originally Posted by ramblinrod

Yes, as indicated the neutral must be connected to ground at source, ONE ONLY.

So if a split receptacle (AC from inverter at one socket and AC from
Shorepower at the other socket, the single ground on that socket would have to be connected to neutral at the inverter and marina distribution panel at the same time. Not compliant, based on the E11 sections you cited.

You are looking at it from the wrong wire. Ground is ground, it is connected to everything. It's no different if there were 2 receptacles next to each other, one fed from shorepower and the other from the inverter. The grounds would be tied together at the DC bus bar, i.e., same potential.

[john61ct]

Actually, the engine negative buss or terminal is the "one ground". Both DC negative (batteries and distribution panels) and AC green, from its distribution panel, get connected there.

[john61ct]

http://www.projectboatzen.com/wp-con...-simplejpg.jpg

[ramblinrod]

Originally Posted by DotDun

You are looking at it from the wrong wire. Ground is ground, it is connected to everything. It's no different if there were 2 receptacles next to each other, one fed from shorepower and the other from the inverter. The grounds would be tied together at the DC bus bar, i.e., same potential.

Whoops, brain fart. I stand corrected. All metals connected to vessel ground. Circuits cannot be fed by a neutral connected to ground at different sources.