DC generator and inverter ground

[ramblinrod]

Originally Posted by roland stockham

There is some argument about this! European regs ask for all grounds to be interconnected. N America is the opposite.

According to NMEA 3.1.1 all independent ground buses (DC ground, DC grounding, AC ground, AC grounding, RF ground, SSB ground, lightning ground, and bonding ground), must be interconnected.

I prefer to go for independent DC, AC and radio grounds. I keep radio separate to reduce the chance of interference. I keep AC and DC separate so that in the event of the ground bolt failing or other machanical failures it is not possible for fault current to flow into the DC neg bus. My DC system is floating i.e. no connection to either shore ground or seawater. AC & radio grounds are to small external bronze plates (made from a foot of scrap flat bar). If using keel bolts check it is not an encapsulated keel! and also be wary if using the keel as the ground plane for radio aerials. Interference again but also a fault current could fry the radio.

Ramblin Rod
About Sheen Marine

[ramblinrod]

Originally Posted by sailorchic34

Might want to study up on isolated power supplies. Then study the schematic of the typical inverters. The typical inverter output is not hot and neutral, but two hot legs. The ONLY circuit path is from leg to leg. Exactly like an isolated power supply.

I have studied "marine" isolated power supplies and inverter schematics. I have installed several of them.

No argument that an inverter AC output wires are floating UNTIL the unit is wired to the boat correctly. Then the hot leg, that will be connected to the vessel AC electrical system white wire (Neutral) must be connected to earth ground.

There isn't a current path from leg to ground, as ground is not a current path in a inverter output.

As soon as the inverter is wired to the boat correctly, there most certainly is.

On inverter away from dock, the only current path is leg to leg.

Incorrect. When the inverter is wired to the boat correctly, the neutral leg of the AC output is connected to earth.

Touch either leg and ground and zero current flows as there is no circuit path.

This could be true if the inverter wasn't wired correctly. If a floating inverter AC output is connected to the vessel AC electrical system, and a device with a ground fault is connected to the vessel AC electrical system, a risk of electrocution would exist. This is why a "marine" inverter output should not be left floating on a boat.

[/QUOTE]Once on shore power there is a ground reference and a ground wire, properly installed will be required.[/QUOTE]

Perhaps the issue here is that you are considering a non "marine" inverter.

Per ABYC 11.5.5.2.4 - The inverter output neutral shall be grounded at the inverter. The inverter output neutral shall be disconnected from ground when the inverter is operating in the charger or the feed-through modes. (As the vessel AC neutral is then connected to the shore power ground).

Ramblin Rod
About Sheen Marine

[PacificGreen]

Perhaps the issue here is that you are considering a non "marine" inverter.

The inverter will never be wired for feed through and can't charge. It will when properly installed have a green wire from the chassis of the inverter to ground bus bar that will then be connected to the DC negative bus bar that is in turn connected to my keel bolt and then finally to the grounding plate. My system resembles figure 9a from e-11 with the exception that I have wired my inverter to the positive, negative and ground bus bars and that the ground won't be attached on the outboard but rather in a similar fashion to figure 18.

This is from the manual for my inverter and it satisfies ABYC 11.5.5.2.4

3-6. AC Safety Grounding：

The AC output ground wire should go to the grounding point for your loads
( for example, a distribution panel ground bus ).

3-6-1. Neutral Grounding (GFCI’S)：

3-6-1-1. 120V models：The neutral conductor of the AC output circuit
of the Inverter is automatically connected to the safety
ground during inverter operation. This conforms to National
Electrical Code requirements that separately derived from AC
sources (such as inverters and generators) which have their
neutral conductors tied to ground in the same way as the
neutral conductors from the utility tied to ground at the AC
breaker panel. For models configured with a transfer relay,
while AC utility power is present and the Inverter is in bypass
mode, this connection (the neutral of the Inverter’s AC output
to input safety ground) is not present so that the utility
neutral is only connected to ground at your breaker panel,
as required.

Ground Fault Circuit Interrupters (GFCI)：

Installations in Recreational Vehicles (for North American approvals) will
require GFCI protection of all branch circuit connected to the AC output of
the hardwire terminal equipped with Inverter. In addition, electrical codes
require GFCI protection of certain receptacles in residential installations.
While the pure sine wave output of the Inverter is equivalent to the
waveform provided by utilities, compliance with UL standards requires us to test and recommend specific GFCI. Cotek has tested the following GFCI – protected 20A receptacles and found that they functioned properly when connected to the output of the Inverter..

a marine rated inverter like a magnum has an internal transfer relay that joins the output N to G while inverting. which is an ABYC requirement to have a N-G bond at a source of power (for gen, shore, and inverter), and opens it up while passing though so the bond goes back to the gen or shore instead. the cheap inverters that float the H and N (and sometimes blow up if you connect the N to G...) do not meat this requirement. those I would not use without GFCI. or at all

So Smac99 would you consider the Cotek 3000 48v 120v to be one of these inverters? I don't want to blow up. These inverters were not cheap and they provided the only function I was after that of inverting not an inverter charger and they provide a 20amp GFCI recepticle for my AC loads.

Also I'm specifically looking for an answer as to how I would ground my 12v system as that will be supplied by a 120vac to 12v converter without a battery inline supplied from inverter that is in turn supplied from the main 48v bank?

Can it be A B or C?

A) Ground the 12v to the 48v negative dc bus bar?
B) Make a separate 12v ground?
C) Leave the 12v from the converter float?

Also I had hoped for simple answers to some of my lingering questions so I don't discover any more unforeseen problems. I realize there is some discussion here but I'm into my last days of reliable internet connectivity to pursue this knowledge

[ramblinrod]

Originally Posted by PacificGreen

Also I'm specifically looking for an answer as to how I would ground my 12v system as that will be supplied by a 120vac to 12v converter without a battery inline supplied from inverter that is in turn supplied from the main 48v bank?

Can it be A B or C?

A) Ground the 12v to the 48v negative dc bus bar?
B) Make a separate 12v ground?
C) Leave the 12v from the converter float?

Use a separate ground buss for each system (AC, 48VDC, and 12V DC) to keep it tidy (labelled), interconnect the ground busses, and then run one cable to a keel bolt and then the Dynaplate.

You should also look into lightning and corrosion protection systems

Ramblin Rod
About Sheen Marine

[sailorchic34]

Originally Posted by ramblinrod

No argument that an inverter AC output wires are floating UNTIL the unit is wired to the boat correctly. Then the hot leg, that will be connected to the vessel AC electrical system white wire (Neutral) must be connected to earth ground.

Ah, no. The inverter ac output is not floating. If not connected leg to leg, there is no current and no voltage. The circuit is only complete if both sides of the transformer is connected to each other. Then there is voltage and current in circuit.

There isn't a neutral wire in an inverter. You have two legs and both are at the same potential, but 180 degrees out of phase, when they are in curcuit. In an open circuit, there is zero voltage. Easily checked by checking voltage of each leg to ground. On shore power there is voltage from hot to ground only (in usa). On inverter there is no voltage from either leg to ground.

And you never want to connect one leg of the inverter to ground. Ground is always completely separate from neutral on boats. This is unlike residential, where neutral and ground are many times connected together at the distribution panel. On a boat that is bad juju. The reason why is that sometimes the shore power outlet is wired with the neutral side hot and sometimes on the boat, someone wires hot to the neutral side of an outlet. Happens all the time.

In fresh water that actually increases the shock hazard if neutral and ground are connected. In marinas, the only common ground to neutral would be at the mains transformer and no where else.

To clarify this consider the following separate cases.

A. I grab a bare wire connected to either inverter leg in my hand and jump in the water.
B I grab both legs, one in each hand, so my body is in circuit.
C I grab a bare section of wire that is in circuit between the two legs.

In case A, there is no shock hazard as a single leg is not in circuit, so there is no voltage and no current path.

In case B, I have placed my body in circuit and there is both voltage and current. That would be shocking.

In case C, while I grab the wire that is in circuit, the circuit path is only between leg and leg. There isn't a current path leg to ground/earth.

That is what it means to have an isolated transformer. There isn't a ground reference. Code still requires a ground, but from a isolation transformer or inverter there is never a ground reference. If there was it would not be a isolation transformer.

Now on shore power, I could grab either neutral or ground and there is no current or shock hazard (Assuming all is wired correctly). Only the hot leg has a current to neutral or to ground. This as USA power distribution does have a ground reference. And if I touch part of the wire in circuit or the hot leg, there is a circuit path between the wire or hot leg and ground. An inverter or isolation transformer does not have a ground reference.

[ramblinrod]

Originally Posted by Frankly

I write this in the hopes to filter out some of the BS and that by understanding the thinking behind modern electrical systems the OP and others can better understand the problem/lingo to help make their own informed decisions.

Thank you for your contribution to this thread.

I think it best to relate the conversation to cruising (recreational) vessels to avoid any unnecessary confusion, as this is the Cruisers Forum target audience.

I completely concur with your information about NEC and grounding electrodes. This usually applies only to the marina electrical service and rarely to a vessel grounding system, other than it's connection to the marina service. This particular case is unusual and unique as the original poster wants to earth ground an AC system when on the hard and not connected to the marina service. In this case, yes, a properly connected grounding rod is appropriate, except for any instance when the vessel is connected to the marina AC electrical service, when it should be disconnected. When not connected to marina service, a properly connected ground electrode, is also required for the vessel lightning protection system effectiveness (if it is so equipped).

Frankly, (sorry ;-) I don't care for the ABYC terminology, as I find way too many people confused between "Ground" and "Grounding". One would think a bunch of intelligent people (ABYC, NMEA, and others) would have considered this and selected different terminology.

In an attempt to avoid confusion, (which may not always be successful) I use the following terminology:

"AC Line" vs ABYC "AC Ungrounded Conductor"
"AC Neutral" vs ABYC "AC Grounded Conductor"
"AC Earth Ground" vs ABYC "AC Grounding"

and

"DC Positive" vs ABYC "DC Ungrounded Conductor"
"DC Negative" vs ABYC "DC Grounded Conductor"
"DC Earth Ground" vs ABYC "DC Grounding Conductor"

Other than this, I believe everything I have stated in this thread complies with ABYC and NMEA standards. No BS whatsoever. ;-)

I absolutely concur that this is SERIOUS STUFF, and the reason I tend to be so vociferous during electrical system discussions. I have seen so many examples where ill-equipped boaters, mucking about with their electrical systems, have inadvertently risked their vessel and lives of themselves, crew, and subsequent owners, it is absolutely SHOCKING! ;-)

For others in this thread...

As I always say, if modifying a marine electrical system, even if you think it is minor, read and understand ABYC E11 and follow it to the letter. If you need to ask questions about what you should do, read it again (and again( until you do understand.

Spending an hour reading, or watching youtube, or polling boaters on a forum, really doesn't cut it. If in doubt, call a professional. If not in doubt, question yourself, because you should be, there is a reason why there are professionals.

Most marine service professionals will offer the first 15 minutes of advice for free (if they are in the area already), after that it will cost hourly rate. Rarely (if ever) will the financial and safety savings as a result of their advice, be less than the cost of the advice.

Speaking of which, I have just spent several billable hours on this thread, so I better get to work making vessel electrical systems safer in practice rather than just in theory.

Ramblin Rod
About Sheen Marine

[PacificGreen]

Mr. Ramblin Rod, and to the other contributors, thank you so much for your time on this very important aspect of this installation that I'm about to undertake. I was not able to fully implement this part of the project on my test bench and not at the boat. That precluded the fact that I did need to find someone knowledgeable on the subject matter and so I thank you for your time.

I had spoken to at least two Marine Electricians on the phone on numerous occasions. At the time I did not as it relates to the project even know the correct questions to ask let alone have any practical experience with Marine Electrical systems.

One was very brief and laughable when I asked for some guidance on electrical schematics as if he was some spiritual guru. The other quoted over twenty hours to install an inverter his way only and repeatedly stated the project would cost more than I could possibly imagine. Needless to say I imported all my own wire, circuit breakers and anything else to get the job done.

Six boxes in all from best boat wire and Greg's Marine. Some early mistakes on wiring on the test bench led to me making simple but really expensive mistakes. That was a cue for me to seek the advice of the good members of this forum. In hindsight I should have asked sooner and I would not have wired up everything on the positive side with yellow connectors as 1/0 and 2awg wire is not cheap.

Looks like I still need a few more bus bars to allocate those different grounding loads and a new brass bolt and some brass stock. I do see a lightning mast in the future and a grounding rod on the dry.

[NorthernIsland]

Originally Posted by ramblinrod

Frankly, (sorry ;-) I don't care for the ABYC terminology, as I find way too many people confused between "Ground" and "Grounding". One would think a bunch of intelligent people (ABYC, NMEA, and others) would have considered this and selected different terminology.

In an attempt to avoid confusion, (which may not always be successful) I use the following terminology:

"AC Line" vs ABYC "AC Ungrounded Conductor"
"AC Neutral" vs ABYC "AC Grounded Conductor"
"AC Earth Ground" vs ABYC "AC Grounding"

and

"DC Positive" vs ABYC "DC Ungrounded Conductor"
"DC Negative" vs ABYC "DC Grounded Conductor"
"DC Earth Ground" vs ABYC "DC Grounding Conductor"

Other than this, I believe everything I have stated in this thread complies with ABYC and NMEA standards. No BS whatsoever. ;-)

I absolutely concur that this is SERIOUS STUFF, and the reason I tend to be so vociferous during electrical system discussions. I have seen so many examples where ill-equipped boaters, mucking about with their electrical systems, have inadvertently risked their vessel and lives of themselves, crew, and subsequent owners, it is absolutely SHOCKING! ;-)

For others in this thread...

As I always say, if modifying a marine electrical system, even if you think it is minor, read and understand ABYC E11 and follow it to the letter.

Ramblin Rod
About Sheen Marine

Please understand that there are different standards for boat AC grounding methods. ABYC is just one and arguably not the best.

Sent from my HTC VLE_U using Cruisers Sailing Forum mobile app

[ramblinrod]

Originally Posted by sailorchic34

Ah, no. The inverter ac output is not floating. If not connected leg to leg, there is no current and no voltage. The circuit is only complete if both sides of the transformer is connected to each other. Then there is voltage and current in circuit. .

I think we are at the point where there is no value in continuing to declare "IS vs IS NOT" positions.

All I can do at this point is:

1. Acknowledge that we differ in opinion.

2. Ask you and others not to connect or operate a marine inverter in the way you have described.

3. Refer you to ABYC E11.5.5.2.4. (I referenced verbatim in a prior post).

4. If you contact a marine electrical professional to work on your boat, please advise them that the inverter installation is not ABYC compliant, so that they don't assume it is wired correctly and the output has a neutral ground. (For the record, I never assume this as most DIY inverter installations are not correct in one way, shape, or form.)

I value your opinion so much I will offer the following:

I have cited the ABYC standard that states that a marine inverter AC output ABSOLUTELY MUST have a Grounded Conductor (neutral) under all conditions.

If you can show me a section of ABYC or NMEA standards that contradicts this, I will recant my declaration that you are in error.

However, if you cannot do so, I believe this confirms my position, supported by the marine electrical standards, prepared by a committee of marine electrical professionals, for this type of device.

Ramblin Rod
About Sheen Marine

[EllisElectric]

[QUOTE=
I have cited the ABYC standard that states that a marine inverter AC output ABSOLUTELY MUST have a Grounded Conductor (neutral) under all conditions.

[/QUOTE]

Could you please re-cite ABYC E11 that states this word for word?

[ramblinrod]

Originally Posted by NorthernIsland

Please understand that there are different standards for boat AC grounding methods. ABYC is just one and arguably not the best.

Sent from my HTC VLE_U using Cruisers Sailing Forum mobile app

I do understand this.

For ABYC, the applicable standard is 11.4.5.5.2.4.

Please cite any applicable marine electrical standard you may have possession of, prepared by a professional body, that states a marine inverter AC output does not require a grounded conductor (neutral).

Ramblin Rod
About Sheen Marine

[EllisElectric]

For ABYC, the applicable standard is 11.4.5.5.2.4.


Can you copy paste those standards for interpretation?

[ramblinrod]

Originally Posted by EllisElectric

Could you please re-cite ABYC E11 that states this word for word?

OK, here it is again....

ABYC 11.5.5.2.4 - The inverter output neutral shall be grounded at the inverter. The inverter output neutral shall be disconnected from ground when the inverter is operating in the charger or the feed-through modes.

As indicated previously, when an inverter is operating in feedthrough mode (if so equipped) or an inverter/charger is operating in charge mode, an internal relay:

1) Disconnects the vessel AC ground connection from the inverter output neutral conductor.

2) Connects the shorepower ground conductor to the vessel AC neutral conductor.

This is to comply with the ABYC requirement, that the neutral conductor must be grounded at the electrical source. In the case of shore power, it is at the marina service distribution panel. On a vessel not connected to shore power, it is at the respective AC generator or inverter (if so equipped).

In any event, the AC electrical source, whether shore power, shore power isolation transformer, generator, or inverter, the AC output neutral must be grounded, at a source only.

If you wish to the see the applicable ABYC standards for all matters relating to vessel grounding, bonding, cathodic, and lightning protection, I recommend you obtain a copy of ABYC "E11 - AC and DC Electrical Systems on Boats".

Ramblin Rod
About Sheen Marine

[exMaggieDrum]

I understand what SailorChick is saying and she is technically correct. House wiring is designed in a different way since one of the "hots" is intentionally grounded to earth. The power grid is also grounded to earth so it essentially is the other conductor.

However, a safety ground is used to cover the instance where a hot (of any flavor) energizes a part of the device (like the case) that should not be hot because it is available to touch. If your body is grounded, such as standing in salt water or touching another grounded material, then you will become part of the circuit and your body will conduct the current, thereby shocking you at best, and killing you at worst. BTW - 48 volts DC can shock the hell out of you.

So while you may have an isolated inverter on board with at least one hot (any way you look at it technically) it is nice to have a safety ground that will conduct electricity better than your body will since electricity will take the path of least resistance. So if you are on the hard, and you are not connected to the (grounded) grid, a safety ground path to the actual earth could be useful.

From a prior question, that could be from the main DC ground bus since we have already discussed the goodness in making that your main ground on the boat for on the water and otherwise.

I am not enough of an expert to discuss the finer merits of ABYC recommendation making but I am aware that not all experts agree with what has been promulgated by ABYC. It is at best a compromise between different thoughts.

Regarding the need and operation of a neutral to ground disconnect/connect relay for marine inverter/chargers, it really only applies to inverters where the AC input from shore (or another source such as a generator) is going to the inverter and passed on as an output. You (OP) should not have to worry about the finer points of what is grounded or not grounded to "neutral" since you are not installing an inverter with either pass-through capabilities or charging capabilities, i.e. you will not be hooking up the inverter to another AC power source, only to DC. But you should still ground your inverter case to earth or water somehow as noted.

Also note that you will have a grounded circuit provided by the three-wire outlet plugs on the inverter. If you do not ground the case of the inverter then anything you plug in to the inverter will not have a safety ground (e.g. power tools, or a microwave, or whatever which require a separate safety ground). SC or EE or Frankly will set me straight I am sure if this is all incorrect. But this is what I would do on my boat if I had your systems.

[Maine Sail]

Originally Posted by exMaggieDrum

I am aware that not all experts agree with what has been promulgated by ABYC. It is at best a compromise between different thoughts.

Interestingly enough many folks are shocked when they learn that the ISO/RCD standards are very, very, very similar to the ABYC in regards to the AC/DC bond as well as generator neutral to ground bond when operating away from shore power etc..

Sadly you only read on the forums that it is the ABYC which is the sole out-liar on the AC grounding to DC grounding bond but the ISO is right there with the ABYC on this point except the ABYC is a voluntary standard and the ISO/RCD is law.

The only point where they vary is that the ISO allows and exception to the AC/DC grounding bond, if a whole boat RCD is fitted and the ABYC requires an ELCI plus the AC/DC bond...

ISO Small craft — Electrical systems — Alternating current installations

"4 General requirements

4.1 The protective conductor insulation shall be green or green with a yellow stripe. Neither colour shall be used for current-carrying conductors.

NOTE The equipotential bonding conductor of the d.c. electrical system (see ISO 10133) also uses green, or green with a yellow stripe, insulation and is connected to various exposed conductive parts of direct-current electrical devices, other extraneous conductive parts and the d.c. negative ground/earth.

4.2 The protective conductor shall be connected to the craft's d.c. negative ground (earth) as close as practicable to the battery (d.c.) negative terminal.

NOTE If an RCD (whole-craft residual current device) or an isolation transformer is installed in the main supply circuit of the a.c. system (see 8.2), the negative ground terminal of the d.c. system need not be connected to the a.c. shore ground (protective conductor)."

As can be seen the AC to DC bond is a requirement under the ISO standards, which are LAW, but they do allow for an "exception" if a whole boat RCD is fitted. Unfortunately I can literally count on one hand the number of EU boats I work on that actually have an RCD fitted....

ABYC is VOLUNTARY, not Federal law, yet does not allow for an exception even if a whole boat ELCI is fitted (very similar to an RCD). This is because the ABYC decided the failure rate of such devices was just too high to allow for such an exception.

So in Europe ISO 13297, and the rest of the ISO standards, are LAW that requires the AC/DC grounding bond, but yet the voluntary standards of the ABYC are always the bad guys on this point. Interesting to say the least......