DC generator and inverter ground

[exMaggieDrum]

Originally Posted by Maine Sail

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......

Interesting! I have trouble enough just trying to understand good wiring practice in the US and with ABYC, so this is interesting. My motto with AC is better safe than sorry, especially since what we are talking about is something relatively easy to do.

[Maine Sail]

Originally Posted by exMaggieDrum

Interesting! I have trouble enough just trying to understand good wiring practice in the US and with ABYC, so this is interesting. My motto with AC is better safe than sorry, especially since what we are talking about is something relatively easy to do.

The only reason I have those standards is because I work on a lot of EU built boats and wanted to know how they should have been wired or how they may be wired. I was working on a CE-A rated boat two summer ago with about 30 16GA DC positive wires in a single bundle, for the DC system, and I wanted to see how that could possibly meet the ISO standards?

I actually find there are more similarities between the two standards than differences yet on the net the ABYC gets the hip-shoot bash, but not the ISO/RCD??? Course this bashing is usually from those who have never read either set of standards.

[ramblinrod]

Originally Posted by 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.

Sorry to hear you had a bad experience.

Not sure who you talked to, but I can't stress enough when doing something like this to find someone accredited by some respected marine organization.

The salesman in the marine retail shop is not always the most qualified guy (actually rarely, not to demean the ones who are pretty darn sharp.)

Of the many marine retailers staff I deal with, two are good at suggesting electrical product solutions to defined needs, none should really offer electrical product installation advice.

Here's how I believe your (or any similar project) should have gone.

Owner: Contacts a qualified marine electrical equipment installer for advise (either direct or per referral by marine retailer).

Installer: Offers to come see you next time in the area.

Owner: Meets Service Provider and defines needs, wants, budget, etc.

Installer: Offers to prepare a Work Order to produce project plan for fee.

Owner: Accepts or rejects.

Installer: If reject, wish well, else prepare Work Order defining project plan fee, payment terms, and issue to customer.

Owner: Accepts or Rejects.

Installer: If reject, wish well, else prepare the project plan consisting of equipment list, system integration diagram, material list, parts and installation costs. (Preferably with good, better, best options.)

Owner: Pay service provider for plan. Choose option desired (if any), identify any changes desired and return, identify any products to be purchased or installed by self.

Installer: If no further assistance needed, wish owner well. Else, revise Work Order (if acceptable) and resubmit.

Owner: Approve Work Order and forward deposit.

Installer: Order equipment and prepare for installation start day.

Owner: Prepare boat for installation day (clear access to areas required).

Installer: Install equipment according to project plan. If any unforeseen difficulties are encountered, contact owner as early as possible.

Owner: Approve or reject and project plan changes in progress.

Installer: Complete installation, test, commission, instruct owner on proper use and maintenance.

Owner: Pay Service Provider promptly and advise friends the wonderful job completed on time and on budget.

Installer: Honour warranty service offered in writing, should a need arise.

If an owner seeks out a true marine service professional for this kind of project, this is how it will go, pretty much every time.

Ramblin Rod
About Sheen Marine

[PacificGreen]

Rod,

Generally there were all good people and businesses just doing what they do. From a distance standpoint and peoples schedules during this project it is difficult to say the least to coordinate skilled trades from afar.

For instance I had the entire topside, cockpit, rudders and other visable areas showing exposure to wood and even anchor lockers fibreglassed and painted over. The bright work and restoration of locker lids was also included. Some of the work remains to do still as shrink wrap structure sits atop the anchor lockers and of course the ablative is to be applied when it is time to launch. I paid for that dearly but the people were great and took super care of my boat.

Then there was the custom prototype ROV we had designed starting in April of 2013. It arrived today horray!

All in all it is a great experience for me and I do have a very good back up plan at the marina for inspection after the fact. While I don't have any certification in the trade I am more than capable of installing what I have here very quickly, neatly and efficiently according to the best of my ability to follow sound guidelines. The grounding aspect of the project needed consultation on from my safety perspective for myself and others around me.

Having studied it is now time for the practical. The label maker is going to be busy but at least warm by the soothing heat of the infrared heaters.

[smac999]

Originally Posted by sailorchic34

.

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.

no you will end up with weird values like 80 volts leg to ground and 40v leg 2 to ground because both hots are floating with no common reference. (with the inverter powering something)

And you never want to connect one leg of the inverter to ground. Ground is always completely separate from neutral on boats. .

you are incorrect. the ground and netreal are tied together at generater outputs. (otherwise they would be floating hots like your incorrect inverters) also if you have an isolation transformer on board you connect the N to G at the output. if you don't have a isotransformer you are tied together at the dock. so on dock power (with or without an iso transformer), gen power, inverter power you always have a N-G bond (and only one at a time) if wired correctly. that is why you need douple pole transfer switches (for 120v, or triple pole for 240) so you are also selecting which power source provides the N-G bond, and removing the N-G bond from the other sources so you only have one at the time.



you already mentioned inverters were the same as iso transformers.... and iso transformers have this bond. as do marine inverters.

pictures from magnum manual and Charles iso transformer manual. both with N-G bond on the boat.

[exMaggieDrum]

Originally Posted by smac999

no you will end up with weird values like 80 volts leg to ground and 40v leg 2 to ground because both hots are floating with no common reference. (with the inverter powering something)

you are incorrect. the ground and netreal are tied together at generater outputs. (otherwise they would be floating hots like your incorrect inverters) also if you have an isolation transformer on board you connect the N to G at the output. if you don't have a isotransformer you are tied together at the dock. so on dock power (with or without an iso transformer), gen power, inverter power you always have a N-G bond (and only one at a time) if wired correctly. that is why you need douple pole transfer switches (for 120v, or triple pole for 240) so you are also selecting which power source provides the N-G bond, and removing the N-G bond from the other sources so you only have one at the time.



you already mentioned inverters were the same as iso transformers.... and iso transformers have this bond. as do marine inverters.

pictures from magnum manual and Charles iso transformer manual. both with N-G bond on the boat.

This was always my understanding as well FWIW. Thanks for posting the diagrams.

[exMaggieDrum]

Originally Posted by PacificGreen

Rod,

Generally there were all good people and businesses just doing what they do. From a distance standpoint and peoples schedules during this project it is difficult to say the least to coordinate skilled trades from afar.

For instance I had the entire topside, cockpit, rudders and other visable areas showing exposure to wood and even anchor lockers fibreglassed and painted over. The bright work and restoration of locker lids was also included. Some of the work remains to do still as shrink wrap structure sits atop the anchor lockers and of course the ablative is to be applied when it is time to launch. I paid for that dearly but the people were great and took super care of my boat.

Then there was the custom prototype ROV we had designed starting in April of 2013. It arrived today horray!

All in all it is a great experience for me and I do have a very good back up plan at the marina for inspection after the fact. While I don't have any certification in the trade I am more than capable of installing what I have here very quickly, neatly and efficiently according to the best of my ability to follow sound guidelines. The grounding aspect of the project needed consultation on from my safety perspective for myself and others around me.

Having studied it is now time for the practical. The label maker is going to be busy but at least warm by the soothing heat of the infrared heaters.

I'm impressed. Never had a ROV before nor do I know anyone with a personal one. Undersea drone (on a cable I presume).

[PacificGreen]

400' and 100' tethers yes.

[sailorchic34]

Ok there are two different types of small inverters. Cheap inverters like most MSW are sometimes called half wave inverters. That is each leg is at ~60V, one leg plus 60v and one leg minus 60v, giving a total of 120V leg to leg. They alternate with a simply oscillator circuit and have a transformer small as it may be. Most cheap msw inverters are made that way. This is what I have. Ground is not even connected inside the inverter. I took it apart once to change a bad cooling fan.

The more expensive and newer inverters use a switching supply that mimics shore power with a hot leg, neutral and ground. That is completely different, far more complex, from the less expensive MSW inverters. For the larger and newer PSW inverters you do want a ground. You can also connect the neutral and ground as it works just like shore power.

However, you do not want to connect ground to the neutral outlet on a cheaper half wave MSW inverter as both legs are hot, though 180 degrees out of phase. It is important to know, which type of inverter you have.

[ramblinrod]

Originally Posted by sailorchic34

Ok there are two different types of small inverters. Cheap inverters like most MSW are sometimes called half wave inverters. That is each leg is at ~60V, one leg plus 60v and one leg minus 60v, giving a total of 120V leg to leg. They alternate with a simply oscillator circuit and have a transformer small as it may be. Most cheap msw inverters are made that way. This is what I have. Ground is not even connected inside the inverter. I took it apart once to change a bad cooling fan.

The more expensive and newer inverters use a switching supply that mimics shore power with a hot leg, neutral and ground. That is completely different, far more complex, from the less expensive MSW inverters. For the larger and newer PSW inverters you do want a ground. You can also connect the neutral and ground as it works just like shore power.

However, you do not want to connect ground to the neutral outlet on a cheaper half wave MSW inverter as both legs are hot, though 180 degrees out of phase. It is important to know, which type of inverter you have.

Yes there are many different inverter designs. But it matters not, to be ABYC compliant you must connect one leg to ground. When you do this, that leg will be 0Vdc wrt ground, and the other leg will be 120Vac to ground.

If you do not ground one leg, both legs will be floating at some unknown potential wrt ground, but they will still have 120Vac between them. If you touch either leg with one hand and ground with the other, you will pass current through your body based on your resistance (very low if wet with seawater) and the difference in potential between that leg and ground.

You will most certainly receive a shock.

[sailorchic34]

Originally Posted by ramblinrod

Yes there are many different inverter designs. But it matters not, to be ABYC compliant you must connect one leg to ground. When you do this, that leg will be 0Vdc wrt ground, and the other leg will be 120Vac to ground.

If you do not ground one leg, both legs will be floating at some unknown potential wrt ground, but they will still have 120Vac between them. If you touch either leg with one hand and ground with the other, you will pass current through your body based on your resistance (very low if wet with seawater) and the difference in potential between that leg and ground.

You will most certainly receive a shock.

The cheap MSW inverters are using a simple oscillator, power fets and a transformer that coverts DC to AC. For the cheap inverters like my wagan), both legs of the transformer are hot. Just as a 220 EU or 240V USA inverters, both legs are hot. in all those, there is no circuit leg to ground.

If you connect a cheap MSW inverter neutral to ground, then ground will have a ~60v reference. This is why the ground on the cheap inverters is not connected at the outlet. The case ground is only on the 12V side of the circuit.

Unlike the newer PSW inverters that don't use an transformer. They use switching and filtering and they have hot and neutral just like shore power (in the USA ) and you can connect neutral to ground. There you can have a voltage to ground.

While the power looks the same to the device using power. How it's made between cheap inverters with transformers and newer inverters without a transformer are two completely different things. I suspect this is why the Honda 2000 genny's ground floats too.

[exMaggieDrum]

Originally Posted by sailorchic34

The cheap MSW inverters are using a simple oscillator, power fets and a transformer that coverts DC to AC. For the cheap inverters like my wagan), both legs of the transformer are hot. Just as a 220 EU or 240V USA inverters, both legs are hot. in all those, there is no circuit leg to ground.

If you connect a cheap MSW inverter neutral to ground, then ground will have a ~60v reference. This is why the ground on the cheap inverters is not connected at the outlet. The case ground is only on the 12V side of the circuit.

Unlike the newer PSW inverters that don't use an transformer. They use switching and filtering and they have hot and neutral just like shore power (in the USA ) and you can connect neutral to ground. There you can have a voltage to ground.

While the power looks the same to the device using power. How it's made between cheap inverters with transformers and newer inverters without a transformer are two completely different things. I suspect this is why the Honda 2000 genny's ground floats too.

Thanks for the info SC. I learn something every day. Would it be recommended to ground the case on these little MSWs or just leave them be?

[sailorchic34]

Originally Posted by exMaggieDrum

Thanks for the info SC. I learn something every day. Would it be recommended to ground the case on these little MSWs or just leave them be?

Oh boy that's another can O worms. Myself, I do not ground, as a short to negative is not an issue and a short from positive would need a really big ground wire or a small ground wire and fuse, which then negates the ground..

As all the internals are for the most part PC board traces with just a few soldered wires generally from the transformer secondary to outlets and small 26 gauge (?) wires to the fan, I feel that not having a grounded case is almost as safe as a grounded case. The 12V side really isn't a problem anyway.

Others will disagree, but there you go. I don't think the very fine folks at ABYC, really understands the differences in inverter design.

[ramblinrod]

Originally Posted by exMaggieDrum

Thanks for the info SC. I learn something every day. Would it be recommended to ground the case on these little MSWs or just leave them be?

The correct answer is the cheap inverter in question here is not safe, and is not ABYC complaint.

All it would take is an appliance ground fault (happens all the time) to kill you or a loved one.

A "marine" inverter, properly installed to ABYC standards, provides safeguards against this.

I assure everyone here, the ABYC standards committee is completely aware of inverter design, much more so than anyone posting in this thread.

Ramblin Rod
www.sheenmarine.com

[ramblinrod]

Hmmm, in post # 32 you stated...

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.

This was completely wrong and I posted a lengthy correction to this.

Now you post...

Originally Posted by sailorchic34

Ok there are two different types of small inverters. Cheap inverters like most MSW are sometimes called half wave inverters. That is each leg is at ~60V, one leg plus 60v and one leg minus 60v, giving a total of 120V leg to leg.

At least you now acknowledge there is a voltage present with respect to ground. You're getting there.

However, I have to correct you again, as you have introduced yet another error.

AC Volts as read on an AC voltmeter are RMS volts, expressed without polarity. There is no such thing as - 60Vac (rms)

Please stop posting incorrect information.

If you are not familiar with basic fundamentals of electricity, you really should not be giving electrical advice to others.

120 Vac where you very well could be standing in water is nothing to fool with. Even a cheap little 300W floating output inverter could easily electrocute you.

There are many MSW "marine" inverters that are ABYC compliant.

They may be more expensive, but then again, they may save your life.

Here's a 1000W Xantrex MSW inverter that is truly ABYC compliant.

Xantrex Pro Series XM 1000 Power Inverter

Ramblin Rod
About Sheen Marine