Importance and Method of Separating Neutrals on Inverter Install?

[Ahmet Erkan]

Originally Posted by 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.

Very good point boatbod.
The HRG system at the marina is in exactly the same configuration as our existing ABYC approved grounded neutral shore power systems with ELCI/GFCI protection devices. Furthermore, the inverter/charger products can have their Neutral to Ground (NG) jumpers removed so that they will never trip the ELCI devices while transitioning from charger to inverter mode. Once the shore power cord is unplugged the swimmer around the boat is safe, because what kills the swimmers is a reversed ground and hot terminals which makes the boat hull hot with respect to other boats and sea floor and the voltage gradient kills the unfortunate swimmer. As you have pointed out the swimmers body becomes a better conductor in a fresh water Voltage gradient and the situation becomes much more lethal. HRG system while underway is safer because when the wet sailor comes into contact with the live 120V the neutral ground resistor (NGR) limits the initial peak current through his body to less than 300 milli Amperes (0.3A) before the 30mA ELCI (0.03A) trips. The HRG can provide redundancy in leakage protection to the existing ELCI devices if the circuit breakers have trip coils that can be activated by the HRG controller. The ELCI detects difference in current while the HRG detects voltage across the NGR and they both trip the CB.
Cheers mate
Ahmet

[Ahmet Erkan]

Originally Posted by 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?

Another excellent point boatbod. Thank you again.
We need to add one more requirement.
How about this :
The HRG controller shall have a test button that verifies the neutral to ground resistor (NGR) is connected from the ship's ground to common neutral when shore power is disconnected and the ship's inverter or generator is operating.
Let me think for a day about how to implement this circuit but it seems pretty easy. (Oooops I forgot, nothing in engineering is as easy as it looks :-)

Now I have a question:
Is the "marine inverter charger" required to have a test button that verifies it has internally connected the neutral to ground when in the inverter mode?

About the fail-safe question.
Resistors are just as reliable as a jumper when they are used at a de-rated power dissipation with respect to their rating. (Typically 50%) In the HRG not only proper de-rating but multiple resistors ought to be used in parallel so that if one fails the other two or three can get the job done. Also remember that the NGR is powered only if there is a ground fault. In MIL grade design this requirement is called eliminating the single point failures. The test function we have just introduced should also test if all resistors are connected and operating properly.
Ahmet

[boatbod]

Originally Posted by Ahmet

Now I have a question:
Is the "marine inverter charger" required to have a test button that verifies it has internally connected the neutral to ground when in the inverter mode?

No, there is no test button. Older inverters having user-selectable bonding typically implement it through the addition of a bolt during installation. Many newer marine inverters implement the bond internally within the transfer switch wiring.

[Ahmet Erkan]

Originally Posted by boatbod

No, there is no test button. Older inverters having user-selectable bonding typically implement it through the addition of a bolt during installation. Many newer marine inverters implement the bond internally within the transfer switch wiring.

Not having a test button for verification of neutral to ground connection while underway is a deficiency. The HRG controller will have self test capability.

By the way, status on the HRG paper design :
So far the simulation is indicating a robust and straight forward leakage detection sensor and circuit design is possible.

Plans forward :
Submit the HRG requirements (see below) for approval from the forum and ABYC technical committee. Please propose additional requirements and/or make comments as you like.
Cheers
Ahmet



High Resistance Grounding (HRG) controller requirements:

SCOPE : Shipboard power systems with up to 140Vac Line to Neutral voltages and GFCI/ELCI devices with up to 30mA leakage protection limits.

HRG controller requirements while the vessel is underway. (ie: Shore power cable disconnected)
Shall (1) have a neutral grounding resistor (NGR) that has greater than 300 Ohms and less than 360 Ohms resistance.
Shall (2) have an NGR with 150 Watts or greater power rating at 25°C ambient air temperature.
Shall (3) connect the NGR from ship’s ground to ship’s common neutral
Shall (4) illuminate a green indicator when leakage from line to ship’s ground is less than 5mA.
Shall (5) illuminate a yellow indicator when leakage from line to ship’s ground is greater than 15mA.
Shall (6) provide a normally open pair of dry contacts to activate a circuit breaker trip coil when the leakage from line to ground exceeds 30mA. (ie: A redundant functionality for ELCI protection devices.)
Shall (7) sense a ground fault and display a red warning and an audible alarm.
Shall (8) de-activate the alarms when the ground fault is removed. The operator may open/reclose circuit breakers one at a time and/or unplug/re-plug equipment one at a time to isolate the fault.
Shall (9) have self test functionality.

HRG controller requirements while the vessel is connected to shore power.
Shall (10) disconnect the NGR within 15mS after shore power is energized.

HRG controller environmental requirements.
Shall (11) be capable of operating under all TBD shipboard environments. (ie: Temperature, humidity, shock, vibration, EMI etc.)

[Ahmet Erkan]

Hello All,
Had no idea how busy one can be during retirement. I heard a friend say retirement has three stages. Go go stage, go slow stage and finally the dreaded no go stage. I think one should try to extend the go go stage as long as possible.
Getting back to the HRG subject. Here is another long winded post. Sorry, I did not have the time to write shorter. (where did I hear that?)
OK I was thinking about what Mr. Boatbod said regarding the "fail safe" capability of a HRG controller. The worse case scenario might be a load failing with a ground fault and the HRG controller has failed and unable to sound an alarm and turn on a red LED to warn the sailor. Firstly (by the way, this word comes from the same dictionary that "bigly" came) the HRG controller self test should detect the failure, however if that also fails, the chassis of the equipment is grounded to the ships ground so the ships company would not be in risk. Lastly, a 1A or 2A circuit breaker could simulate the grounding of the shore power cable Neutral to Ground and verify the loads on board do not have ground faults prior to connecting to shore power. The low Ampacity test circuit breaker can also be wired to test the galvanic isolator if desired. If the captain ignores all warnings and does nothing prior to connecting to shore power cable while the boat has a ground faulted load, the shore power circuit breaker will trip when he tries to connect to shore power. So the bottom line is HRG controller can have two levels of automatic fail safe functionality and two levels of manual test capability and if all goes wrong, the system is still safe.
By the way, I just checked my Honda 2000 and the Neutral is not hardwired to ground. Started the Honda measured 62.4Vac Neutral to Ground, 63.1Vac Hot to Ground, connected a 362 ohm resistor neutral to ground and the neutral to ground stray voltage dropped to 0.2Vac. This test indicates the HRG controller will make all Honda2000 or similar generators used on board boats safe. All "non marine" inverters will also become safe. The marine inverters can reduce their cost by getting rid of the NG shorting contactors etc, isolated neutrals and related complications will no longer be necessary.
So now I am asking Boatbod to contact ABYC technical committee via Mr. Ed Sherman and we the "Cruisers" can start making proposals for updates in ABYC standards regarding our own safety on board.
Fair winds.
Ahmet

[michaelroberts]

Hello Ahmed - it's now 2024 - are you still giving advice?

A few years ago I installed a Chinese hybrid inverter on my boat. It was a very tidy installation with separate circuit breakers for galley, port, stb etc.

The inverter promptly blew up - smell and smoke

I think it was caused because I had wired the neutral bus bar (where all the boat's appliances connect to the inverter's neutral) to the ground bus bar (where all the battery negatives and engine metal etc are connected)

I'm guessing that these inexpensive Chinese inverters drive the load with a centre tapped transformer with the centre grounded and both line and neutral live and in opposite phase. So grounding the neutral would short one leg of the transformer and kill the inverter.

Anyway they promptly sent a replacement, I disconnected the wire linking the boat's neutral busbar from the ground busbar and everything worked fine for a couple of years.

Until yesterday when I plugged in the boatyard's power. Smell of burning transistors. Inverter blown again. Obviously the boatyard has a grounded neutral. And somehow the boat's inverter neutral remained connected to the boat yard neutral.

So I am about to buy another hybrid inverter.

BUT WHAT TO DO ABOUT THE BOAT'S GROUND AND THE INVERTER'S NEUTRAL

Any help is very much appreciated - thanks
Michael

[Ahmet Erkan]

Originally Posted by michaelroberts

Hello Ahmed - it's now 2024 - are you still giving advice?

A few years ago I installed a Chinese hybrid inverter on my boat. It was a very tidy installation with separate circuit breakers for galley, port, stb etc.

The inverter promptly blew up - smell and smoke

I think it was caused because I had wired the neutral bus bar (where all the boat's appliances connect to the inverter's neutral) to the ground bus bar (where all the battery negatives and engine metal etc are connected)

I'm guessing that these inexpensive Chinese inverters drive the load with a centre tapped transformer with the centre grounded and both line and neutral live and in opposite phase. So grounding the neutral would short one leg of the transformer and kill the inverter.

Anyway they promptly sent a replacement, I disconnected the wire linking the boat's neutral busbar from the ground busbar and everything worked fine for a couple of years.

Until yesterday when I plugged in the boatyard's power. Smell of burning transistors. Inverter blown again. Obviously the boatyard has a grounded neutral. And somehow the boat's inverter neutral remained connected to the boat yard neutral.

So I am about to buy another hybrid inverter.

BUT WHAT TO DO ABOUT THE BOAT'S GROUND AND THE INVERTER'S NEUTRAL

Any help is very much appreciated - thanks
Michael

Yes Michael it is 2024 indeed. I can't believe 7 years has gone by since we all had this rather heated discussion.
I will type up a recommended checklist tonight (or tomorrow morning) for your new inverter before installing it and power up.
Hope all is well with you.
Ahmet