Importance and Method of Separating Neutrals on Inverter Install?

[boatpoker]

Originally Posted by boatpoker

You'll have to point out to me where it says that. It certainly does not show up in my copy of E-11.

Here's what it says in my copy which also jives with UL1561.

[boatbod]

Failure to separate inverter neutral from incoming shore neutral can compromise galvanic isolation.

Why? Because the shore neutral is typical bonded to shore grounding at some point in the system, and the grounding (green) wire is galvanically isolated between shore and boat. If the inverter decides to bond the ground and neutral (as it can when it is a source of power), your boat ground can become connected to your shore neutral if the two neutrals aren't kept separate. This is bad as the shore neutral is invariably at or close to shore ground dc potential which may be different than boat dc potential.

[Prospective]

Thanks to those who answered the questions I asked. I think I have a reasonable understanding of the need to separate the neutrals on an inverter install as I described. Identifying the neutrals is another matter. When the triplex wire is split far behind the panel, tracing out the hot is not easy. I appreciate the suggestion of creating a jumper that can be used at the outlet and checking continuity at the panel. If anyone has any other methods of identifying the neutrals I'd be curious to hear them.

[Ahmet Erkan]

Originally Posted by Prospective

Thanks to those who answered the questions I asked. I think I have a reasonable understanding of the need to separate the neutrals on an inverter install as I described. Identifying the neutrals is another matter. When the triplex wire is split far behind the panel, tracing out the hot is not easy. I appreciate the suggestion of creating a jumper that can be used at the outlet and checking continuity at the panel. If anyone has any other methods of identifying the neutrals I'd be curious to hear them.

Could you please explain the "reasonable understanding" you have developed so that we (maybe just I) can understand it too?
What problem are you going to solve by separating the neutral of inverter loads from the neutral of non-inverter loads?
Do you have a need to run the inverter continuously when shore power is connected? Or do you need to test the inverter without tripping the shore power CBs and you can't do it now?
Thanks

[Ahmet Erkan]

Originally Posted by boatpoker

Here's what it says in my copy which also jives with UL1561.

Take a good look at diagrams 6 and 7 and then read the applicable text and then tell me where it says the shore ground shall connect to the boat ground either directly or through a galvanic isolator.

[Ahmet Erkan]

Originally Posted by boatbod

Failure to separate inverter neutral from incoming shore neutral can compromise galvanic isolation.

Why? Because the shore neutral is typical bonded to shore grounding at some point in the system, and the grounding (green) wire is galvanically isolated between shore and boat. If the inverter decides to bond the ground and neutral (as it can when it is a source of power), your boat ground can become connected to your shore neutral if the two neutrals aren't kept separate. This is bad as the shore neutral is invariably at or close to shore ground dc potential which may be different than boat dc potential.

You have a valid point sir.
Here is the solution:
One simple common neutral on the boat for all loads just like household wiring.
A low cost simple power relay that has its coil connected across the shore power hot and neutral, and the normally closed contacts of this relay connect the boat neutral to boat ground through a resistor. Inverters and Generators do not have their own inferior circuits that connect the neutral to ground and nuisance trip CBs.
No race conditions on start up because the ELCI or GFCI breakers are compatible with the high resistance grounding (HRG) system.
The galvanic isolator may get shorted for 15mS during the time the relay operates but nothing will corrode in 15 milliseconds.

[hellosailor]

Prospective-
There is something called a "fox and hound" and other similar names. It won't identify the neutral per se, but you hook up (or plug in) a small box at one end of a circuit, that's the fox. Then you take the "hound", which is a little handheld device, and run it along the walls, or wire pairs, etc, and it will pick up a tone that the fox is putting into that wire pair. So you can pretty much identify a specific wire pair very quickly, and then it is just up to you to figure out which of them is the neutral wire.
I think even the big box hardware stores carry them now, if not, a real electrical supply store will. Not very expensive, and they'll know what you mean even if they call it something else.

[Prospective]

Originally Posted by Ahmet Erkan

Could you please explain the "reasonable understanding" you have developed so that we (maybe just I) can understand it too?
What problem are you going to solve by separating the neutral of inverter loads from the neutral of non-inverter loads?
Do you have a need to run the inverter continuously when shore power is connected? Or do you need to test the inverter without tripping the shore power CBs and you can't do it now?
Thanks

Ahmet, to answer your last questions, the device contemplated would be an inverter/charger that would be on all the time, either in invert mode when on the hook or charge/passthrough mode when on shore power.

I do appreciate your responses to my questions. As is obvious, I am no electrical expert. Just a boat owner interested in making sure an inverter install is done (whether by me or a "pro") correctly. So I try to do my research. Usually, install procedures are consistent among knowledgeable sources (electricians, manuals, books) and via applicable ABYC regs. However, sometimes there seems to be disagreement about what is correct and/or necessary. In researching the neutral issue I raised, there seems to be some disagreement so I was hoping for some clarification. This thread points out the disagreement.

But most seem to agree that the neutrals should be separated and my "reasonable understanding" is that if not, it can cause problems with GFCI tripping and galvanic corrosion. I don't really need an understanding beyond that for my purposes. So I'm inclined to separate the neutrals despite it being a LOT more work to identify them.

[Ahmet Erkan]

Originally Posted by Prospective

Ahmet, to answer your last questions, the device contemplated would be an inverter/charger that would be on all the time, either in invert mode when on the hook or charge/passthrough mode when on shore power.

I do appreciate your responses to my questions. As is obvious, I am no electrical expert. Just a boat owner interested in making sure an inverter install is done (whether by me or a "pro") correctly. So I try to do my research. Usually, install procedures are consistent among knowledgeable sources (electricians, manuals, books) and via applicable ABYC regs. However, sometimes there seems to be disagreement about what is correct and/or necessary. In researching the neutral issue I raised, there seems to be some disagreement so I was hoping for some clarification. This thread points out the disagreement.

But most seem to agree that the neutrals should be separated and my "reasonable understanding" is that if not, it can cause problems with GFCI tripping and galvanic corrosion. I don't really need an understanding beyond that for my purposes. So I'm inclined to separate the neutrals despite it being a LOT more work to identify them.

Spoken like a gentleman. You must be a gentleman, I am sure of it.
I also do not claim to be an "expert", just a sailor and an electrical engineer.
You have two options my friend.
Listen to what ABYC and the "experts" dictate how your boat should be wired, tha same way they have been dictating all along, or listen to the guy with the funny name.
If you go with the ABYC and the "experts" you will never know if there is a better way to wire your boat.
One thing you are guaranteed to get if you listen to me is an explanation of everything I recommend. You do not need to be an expert to understand my explanations either. At the end even the experts will agree that what we want is the simplest, safest and most reliable systems for our boats.
1. The chassis (enclosure) of every electrical device on board shall be hard wired to boat ground. (engine block)
2. Shore power green ground conductor shall be hardwired to boat ground through a galvanic isolator.
3. No electrical device on board (this includes all inverters and generators) shall internally connect its neutral terminal to its ground terminal.
4. If multiple shore power cables are used the only common point between the shore power cables shall be the boat ground.
5. The boat shall utilize a military proven high resistance ground (HRG) system when underway.
6. Transition from HRG to grounded neutral systems at the shore power connection shall not spuriously trip any GFCI or ELCI breakers.

Discussion will continue if there is interest.
All the best
Ahmet

[mitiempo]

Originally Posted by Ahmet Erkan

3. No electrical device on board (this includes all inverters and generators) shall internally connect its neutral terminal to its ground terminal.
Ahmet

Except when they are producing power as they are then the source. All marine quality inverter/chargers automatically connect ground and neutral when inverting and separate them when passing through shore power, as do generators.

[Ahmet Erkan]

Originally Posted by mitiempo

Except when they are producing power as they are then the source. All marine quality inverter/chargers automatically connect ground and neutral when inverting and separate them when passing through shore power, as do generators.

Yes sir, you have correctly stated the required functionality of the “marine inverter/charger” and shipboard generators, transformers, frequency converters, UPS etc. However, the problem we are having is the inability of the “marine power sources” to be compatible with existing boat power systems. The nuisance trips of the shore power ELCI breakers occur if we don’t bail out the manufacturers design incompetence by modifying our existing power systems. (ie: tracing neutral wires, adding a separate neutral bus, complicate our wiring etc.)

The benefits of high resistance ground (HRG) system :
1. Increased safety. (ie: No sparks during a ground fault. Low current if operator accidentally touches hot wires, for example while making voltage measurements.)
2. Increased reliability. (ie: No damage to circuit breakers due to opening at high ground fault currents)
3. Mission capability to operate through ground faults while underway.
4. Simple installations due to compatibility with existing boat power systems with common neutral.
5. Increased product quality because all cost competitive “non-marine” electrical products will become
electrically compatible with the marine applications. Some inverter manufacturers that impose twice
the price to boaters will have to really increase the quality of their “marine grade” products rather than
just add a relay to become compatible with ABYC rules.
It is recommended that marine service provider professionals such as yourself request ABYC to review
high resistance grounding systems and depending on their evaluation, revise the applicable ABYC standard to accommodate HRG as a safe and reliable marine grounding system. Natural compatibility with ELCI/GFCI protection devices and elimination of nuisance CB trips will be gravy.
What is in it for me? Nothing other than the satisfaction of having made a value adding recommendation to our fellow sailors.
Cheers
Ahmet

[RONDO]

Hi Ahmet,
i follow this subject with interest can you supply schematic of the HRG system for a typical 240v 50 amp single phase system?
cheers Rondo

[boatbod]

Ahmet,

In a "HRG" system, what happens if a person comes in contact with a hot wire in a wet environment? If we make the presumption that the body of water itself is grounded, current will flow through the person with undesirable results. This is exactly why ELCI/GFCI protection is becoming standardized... too many deaths from electrocution, particularly in fresh water lakes.

[Ahmet Erkan]

Originally Posted by RONDO

Hi Ahmet,
i follow this subject with interest can you supply schematic of the HRG system for a typical 240v 50 amp single phase system?
cheers Rondo

Thank you sir. I had given up on the HRG idea because of the adversarial push back I was getting from the forum but I would be glad to provide more details if there is interest. 120Vac, 240Vac, 120/240 split phase all will work fine with the right HRG system. Three phase larger systems will also work fine. Unfortunately I do not know of a product nor do I have a schematic of a special HRG controller that is operational with both shore power and also with shipboard generators/inverters while underway. I think the first step ought to be writing the requirements for the HRG and more importantly getting the requirements certified by ABYC technical board.
Writing the requirements for the controller is easy.
Preliminary HRG controller requirements can be proposed as follows:
1. Shall connect a neutral to ground resistor (NGR) from neutral to ship’s ground and shall disconnect the NGR when shore power is present.
2. Shall illuminate a green indicator when leakage from line to ship’s ground is less than 5mA.
3. Shall illuminate a yellow indicator when leakage from line to ship’s ground is greater than 15mA.
4. Shall be compatible with operation of any shipboard ELCI protection device if used on board.
5. Shall provide a normally open pair of contacts to activate a circuit breaker voltage trip coil when the leakage from line to ground exceeds 30mA. (ie: A redundant functionality for ELCI protection devices.)
6. Shall sense a ground fault and display a red warning and an audible alarm.
7. While the vessel is operating with a ground fault, shall silence the audible alarm when the operator opens the circuit breaker that is powering the equipment which has caused the ground fault. This action will allow the operator to rapidly isolate the faulty equipment by toggling the circuit breakers OFF and than back to ON.
8. The HRG shall not interfere with the operation of a Galvanic Isolator if present.

Let me know if anybody would like to suggest any other shalls (ie: requirements) to add.
Here is my promise to the boating community:
You get the ABYC technical committee to consider approving the eight requirements above for a high resistance ground (HRG) system and I will do a circuit design, a simulation, printed circuit board design, build a prototype that is fully functional and compliant with safety standards, present/demonstrate the circuit simulation and test results to the ABYC technical committee and share the technical data package with a high quality marine products manufacturers for cost competitive high volume production.

Again, the reason for neutral to ground (NG) bonding is to detect a ground fault by forcing a short circuit current through the circuit breaker which may be thousands of Amps and open the circuit breaker. The HRG system detects a ground fault but limits the short circuit current to less than 1 Ampere and allows an orderly shutdown/repairs when convenient to do so, and it does this without damaging the contacts of circuit breakers opening thousands of Amperes. The other advantages of the HRG system (prevention of sparks, ignition hazard etc.) was explained earlier.

I did request a point of contact from ABYC office but no technical person contacted me as of yet. If anyone else can get their attention please do. If ABYC shows interest we will too, if ABYC tells us to take a hike, I will just take that hike and keep myself busy with my other 1001 projects during retirement.
For example, wine making would be less stressful compared to arguing with engineers :-)
Cheers
Ahmet

[boatbod]

Ed Sherman would be your best bet for ABYC technical contact.

One more question: how do you design the HRG controller to be fail-safe?