Marine AC - Why Tie Neutral and Earth?

[Baronkrak]

Originally Posted by Wotname

Well then you haven't made your case very clear.

Let me make is easy for you.

Is it -

1. Fully floating is safer
or
2. A tied N&E with a AC ground is safer
or
3. Wottie doesn't have sufficient electrical knowledge to understand.

4. Wottie is kidding us.

5. A tied Neutral to Earth Wire at the source if more than one outlet is provided.

6. A tied Neutral to Earth Wire with ELCB at the source if more than one outlet is provided.

So

1…1. Fully floating is safer if only one outlet is provided.
2…6
3…5
4…4
5…3. With reservations.

[s/v Jedi]

Originally Posted by Lake-Effect

The joys of a public forum...

One of the most important criteria for the "safest possible system" is how likely it is that it will be understood and duplicated successfully by the most people. Your technical rationales and explanations are top-shelf... but unless people are prepared to approach your level of knowledge, and/or follow your recipe to the letter, and fight with surveyors, insurers and techs who won't deviate from the existing standards... would they not be better off overall by following the current standards, which are more widely understood by more users and marine techs, and better-supported in the technical literature ("boat books" and websites), and by the available panels, breakers, and and supplies?

Absolutely not. If someone does not understand how an isolation transformer works then that person is not qualified to make any decision on how to wire a boat. Isolation transformers are common, fully understood and every EE (that’s not “installers”, talking about engineers here) knows exactly how to design this.

I so don’t care... go ahead and replicate shore based electrical code on a boat. Just don’t complain when your prop falls off or someone swimming next to your boat receives electric shock

Nobody did yet explain to us how earth ground works in land mobile use. Maybe drag a dynaplate behind the car?

[Lake-Effect]

Originally Posted by s/v Jedi

If someone does not understand how an isolation transformer works then that person is not qualified to make any decision on how to wire a boat. Isolation transformers are common, fully understood and every EE (that’s not “installers”, talking about engineers here) knows exactly how to design this.

Well, that's my point.

I'm not saying you're wrong, or that you haven't made a convincing case. I am saying that in the absense of broader understanding and acceptance, and corresponding standards and guidelines that specify the correct way to do a floating marine AC system (and panels etc built to that spec)... how many will successfully implement a truly safer AC system? CF is full of examples of people who scoff at or willfully ignore guidelines for current standards (eg ABYC)

[Thumbs Up]

Originally Posted by s/v Jedi

It’s hopeless right? Hunt for Red October, making a floating power distribution work like one with grounded neutral, absolute cluelessness about earth not being a return path behind an IT... it doesn’t stop. The most basic principles are not understood or even worse, ignored.

The problem is that there are people here who want to install the safest possible system but, not being EE’s, get confused by ignorant and even trolling remarks. As I’m just here trying to help people, I’ll only post for them from here on.

So take the diagram I posted and remove the 50A shore power part of it. This is as safe, reliable and as efficient as it gets. You can change it to just one inverter/charger, just one distribution group etc. If not US power, you can delete the auto transformers all together.

What is not in the diagram is the wiring from distribution breakers to outlets etc. Everything wired to the double pole breakers must also have a ground wire which connects to the boat ground busbar.

With all the naysayers attacking the diagram, remember that in all the years this has been posted about, nobody ever could describe a single thing that is not better than a non floating power distribution. Everything brought up was proven incorrect or just too silly to even discuss.

Ask me anything about that diagram

Since you are inviting a debate, I will bite.

Here is the diagram.

I once again am going to argue in favor of Goboatingnow's approach.

I connect the existing boat side protective “ Earth “ wire to the neutral at the output of the transformer and fit a standard type AC ( speed S) rated RCBO into that circuit. This provides the hot fault disconnect feature I mentioned .https://www.cruisersforum.com/forums...er-242781.html

Which is also the recommended installation method of marine isolation transformer's vendors.
It is also being recommended here by Jammer.
A fully floating distribution system still has some caveats on a boat.

Imperfect Isolating
In the previous examples, we assumed a perfect system. Unfortunately, a perfect system is impossible
to attain.
Returning to the example of the isolating transformer, we can convert the isolated system back to a
grounded system easily, by connecting one secondary conductor of the transformer to ground. This
would create the potential for current to flow from the opposite conductor to ground, as it would in any
grounded electrical distribution system.
An isolated system can be unintentionally grounded. For example, if the drill is plugged into the system
with the ground intact and there is a fault in the drill to the grounded enclosure, that single fault
converts the entire system into a grounded system.
Keep in mind no perfect insulators exist either. What we commonly call “insulators,” such as rubber or
plastic coverings on wire, are actually just poor conductors. All materials conduct electricity to some
degree. Thus, everything attached to the secondary conductors of an isolating transformer will partially
ground the system. Examples of items that partially ground the system, without making direct
connection to ground, include the following:
• Insulated wires enclosed in grounded metal conduit
• Electrical components within permanently installed electrical equipment
• Electrical components within portable devices housed in grounded enclosures (commonly referred
to as the capacitance of the system)
Because an isolated system can easily become grounded without giving any indication to the user, a
way must be found to monitor the integrity of the isolation in the system. With this monitoring, there
must be some warning when the system becomes grounded. When the system becomes partially
grounded, the warning is still necessary, but a limit must be set for the warning to be soundedhttps://stevenengineering.com/Tech_S...DFs/45HIPS.pdf

Because you can never achieve perfect isolation you need a warning system!
I still believe that you would have a safer and better system if you designate a neutral and tie your boat ground buss bar to it. Now that I understand your system better, the tie in point is clear. Your isolation transformer's (unused) secondary neutral (center tap) should be tied to your boat ground buss bar!
I realize that this does not create a truly isolated distribution system. But as I said before, the source of it is still isolated from shore power, shore ground, local ground (the water), and the boat hull and it's underwater fittings! Mission accomplished!
Here is what Victron isolation transformer manual has to say:

Figure 5: Output neutral grounding
A Residual Current Device (RCD) or Ground Fault Circuit
Interrupter (GFCI) must be installed in the output cable of
the isolation transformer. For this RCD to operate
correctly, the output neutral must be connected to ground
(= all the metal parts in the boat). This is achieved by
placing a jumper on male push-on connectors J21, J33
(see fig 5), and by grounding the enclosure of the isolation
transformer.https://www.victronenergy.com/upload...r1800-3600.pdf

The burden of showing that a new approach is safer is on those who propose it. Jammer

[s/v Jedi]

Originally Posted by Thumbs Up

Since you are inviting a debate, I will bite.

Here is the diagram.

I once again am going to argue in favor of Goboatingnow's approach.

Which is also the recommended installation method of marine isolation transformer's vendors.
It is also being recommended here by Jammer.
A fully floating distribution system still has some caveats on a boat.

Because you can never achieve perfect isolation you need a warning system!
I still believe that you would have a safer and better system if you designate a neutral and tie your boat ground buss bar to it. Now that I understand your system better, the tie in point is clear. Your isolation transformer's (unused) secondary neutral (center tap) should be tied to your boat ground buss bar!
I realize that this does not create a truly isolated distribution system. But as I said before, the source of it is still isolated from shore power, shore ground, local ground (the water), and the boat hull and it's underwater fittings! Mission accomplished!
Here is what Victron isolation transformer manual has to say:

The isolation transformer in my diagram has no neutral so it’s impossible to ground it. It only has L1 and L2, i.e. it is 240V only. The whole diagram has no neutral beyond the primary winding of the isolation transformer.

I know it feels weird to not have a neutral, but there’s plenty of appliances that only take L1 and L2. My A/C, circulation pumps, the 1.5hp motor of the watermaker high pressure pump, the heating element of my water heater, they all connect to just L1 and L2 240V. There’s even outlets that don’t have the neutral... it’s the NEMA 6-x range.

If I wanted to make a neutral, then it would be all the way at the end where the auto transformers are. They have a center tap that I use to create 120V. If you ground that, then it would become a neutral. But if you do,you can only have one transformer.

Let’s say we have only one auto transformer and we connect it’s center tap to boat ground. What do we win? .... nothing. Nothing is gained by that action. Does it get easier to understand? Nope. On the negative side,it does limit us to one auto transformer and in my case, I can’t switch to a regular grounded shore power like I do with the 50A shore power connection.

[Thumbs Up]

Originally Posted by s/v Jedi

Let’s say we have only one auto transformer and we connect it’s center tap to boat ground. What do we win? .... nothing. Nothing is gained by that action. Does it get easier to understand? Nope. On the negative side,it does limit us to one auto transformer and in my case, I can’t switch to a regular grounded shore power like I do with the 50A shore power connection.

Not true. You gain the functionality of the double RCD breaker that could be protecting the panel. (or single circuit RCDs if you went that route). The safety ground acts as a sensing wire for the RCD. Otherwise no type of fault would activate the RCD. For this to work in your current system, you would need to have each group of 110v outlet's safety grounds (as well as any 110v hardwired cases) wired back to their respective autotransformer neutrals. The remaining chassis grounds from the devices running off of 240v (autotransformers, inverters, A/C, circulation pumps, water maker high pressure pump, water heater) should all be connected to L2 output of your isolation transformer. Then any current in these sensing wires will cause The transformer output (or autotransformers) RCDs to trip. The way you have it now, there is no way to even know if you have faults.

I am no engineer but do consider myself a decent electrician. Electricians normally don't need to delve into complex almost esoteric aspects of electricity. So stuff like transient voltage spikes, electromagnetic interference, harmonic distortion, static electricity, impedance, capacitance of the environment don't normally clog up our thought process. But I have read that these types of forces can be an issue with full floating AC power distribution.

If I was asked to install an isolation transformer (in isolation configuration), I would be referencing all of my safety grounds back to neutral (or L2 if no center tap), so they can act as a sense wire for the RCD exactly as the installation manuals recommend.

You have not explained why you think it better to be full floating with no fault detection. A boat is not an operating room. An operating room needs uninterruptable power. Some functions on a ship do too but they pay for it with expensive monitoring equipment that you do not have. All of the important functions on a sailboat use low voltage DC. Unless I have made some error of reasoning, it appears that you still have not explained the advantage of your system. By changing around a few connections you could bring it line with the prescribed method, I think that it would improve your system.

[Wotname]

Originally Posted by SailRN

What is a kelvin watt?

Originally Posted by SailRN

No, K is kelvin, a measure of thermodynamic temperature, so KW is kelvin watt.



If they meant kilowatt, they would have used the correct term kW, as k is the prefix kilo.


It's more than just "grammar police" another poster mentioned. You have to know enough of the basics to not only understand yourself, but to be able to communicate correctly to others. I guess going to work for Rickover and then later becoming a critical care/trauma nurse one knows the importance of this. Which do you want, a 5 mg infusion of potassium chloride, or does it matter to you, your family, and your heirs if it's 5 Mg?


You just have to be wary of all of this advice when the poster doesn't know (as demonstrated) what they're writing.


Watch for my soon to be published book, The Care and Feeding of My Pet Peeves, due out in 2055. It has a chapter on incorrect usage of terms and symbols.

Crikey, I hope I don't have you caring for me in a critical care/trauma situation. I would expect my carer to know there is no scientific term 'kelvin watt' and thus realise KW is either a typo or given the subject matter and thread focus, more likely a simple sailor's error. I would like my carer to focus on the bigger picture and make a reasonable assumption that he/she meant kilowatt.

Then again, maybe the originator of "KW" was referring to Kelvin Watt although I would not be sure of which Kelvin Watt; there are many scores of them on social media sites.

[Wotname]

Originally Posted by SailRN

My point in an earlier post, if they don't know the difference between 5 mV and 5 mA, how can you believe what they write?


I've always like soldering personally, but for mission-critical applications crimping is required. NASA for instance does not permit soldered connections. A gas-tight mechanical crimp is required.

Are you sure NASA does not permit soldered connections? If you are sure, do you have any external reference to support this view.

Now it is true I haven't worked for NASA but nevertheless I am fairly certain that NASA equipment includes many printed circuit boards which contain many soldered connections.

Of course it is possible you didn't mean those pesky PCB soldered connections even though you wrote "does not permit soldered connections"

[SailRN]

Originally Posted by Wotname

Crikey, I hope I don't have you caring for me in a critical care/trauma situation. I would expect my carer to know there is no scientific term 'kelvin watt' and thus realise KW is either a typo or given the subject matter and thread focus, more likely a simple sailor's error. I would like my carer to focus on the bigger picture and make a reasonable assumption that he/she meant kilowatt.

Then again, maybe the originator of "KW" was referring to Kelvin Watt although I would not be sure of which Kelvin Watt; there are many scores of them on social media sites.

Perhaps, if you read my posting again, and think about my question "What is a kelvin watt" you might suddenly realize I asked "What is a kelvin watt" because that was a term that I thought was incorrect as it didn't make sense. Duh. I did not consider it a typo because it was repeated a few times, therefore the poster didn't appear to be familiar with the correct unit symbols. Another poster wrote 5 mV when it should have been 5 mA. So what "bigger picture" and reasonable assumption should someone reading that, especially those unfamiliar with the subject and trying to learn from this forum, assume the writer meant?


There are units of K/W, but I'm probably confusing you more.



And perhaps you also might rethink whether you want your nurse to be detail oriented or just see the "bigger picture" and just administer whatever looks like it might do, or guess the doctor's orders "probably" meant something other than what the doctor wrote. Duh.

[SailRN]

Originally Posted by Wotname

Are you sure NASA does not permit soldered connections? If you are sure, do you have any external reference to support this view.

Now it is true I haven't worked for NASA but nevertheless I am fairly certain that NASA equipment includes many printed circuit boards which contain many soldered connections.

Of course it is possible you didn't mean those pesky PCB soldered connections even though you wrote "does not permit soldered connections"

Disregard, I read it in a NASA technical specifications manual, but I'm not wasting the time to look it up again. And I've also read in other technical journals and articles of the superiority of a properly crimped connection over soldered, but again I'm not taking the time to look it up again.


And I was talking about interconnections using wiring or cables, not PCBs. My apologies for not being more specific in the original posting.

[s/v Jedi]

Originally Posted by Thumbs Up

Not true. You gain the functionality of the double RCD breaker that could be protecting the panel. (or single circuit RCDs if you went that route). The safety ground acts as a sensing wire for the RCD. Otherwise no type of fault would activate the RCD. For this to work in your current system, you would need to have each group of 110v outlet's safety grounds (as well as any 110v hardwired cases) wired back to their respective autotransformer neutrals. The remaining chassis grounds from the devices running off of 240v (autotransformers, inverters, A/C, circulation pumps, water maker high pressure pump, water heater) should all be connected to L2 output of your isolation transformer. Then any current in these sensing wires will cause The transformer output (or autotransformers) RCDs to trip. The way you have it now, there is no way to even know if you have faults.

I am no engineer but do consider myself a decent electrician. Electricians normally don't need to delve into complex almost esoteric aspects of electricity. So stuff like transient voltage spikes, electromagnetic interference, harmonic distortion, static electricity, impedance, capacitance of the environment don't normally clog up our thought process. But I have read that these types of forces can be an issue with full floating AC power distribution.

If I was asked to install an isolation transformer (in isolation configuration), I would be referencing all of my safety grounds back to neutral (or L2 if no center tap), so they can act as a sense wire for the RCD exactly as the installation manuals recommend.

You have not explained why you think it better to be full floating with no fault detection. A boat is not an operating room. An operating room needs uninterruptable power. Some functions on a ship do too but they pay for it with expensive monitoring equipment that you do not have. All of the important functions on a sailboat use low voltage DC. Unless I have made some error of reasoning, it appears that you still have not explained the advantage of your system. By changing around a few connections you could bring it line with the prescribed method, I think that it would improve your system.

Well, you’re wrong and your proposed installation would be rejected by engineering.

You talk about a RCD breaker that works for grounded neutral but not for a floating system. This is 100% false and has been debunked many years ago. It also shows that you just don’t get it. I will demonstrate both observations:

1. The RCD trips when it detects a difference in current between the two current bearing conductors. It has nothing to do with ground and nothing to do with a grounded neutral or not. I have attached a diagram that further shows this but many here are able to confirm.

2. You don’t get it: the reason for having an RCD breaker is the danger of a grounded neutral. It is dangerous because it makes ground (earth) a return path. Current can flow through the phase, into your hand, through your body to the wet bilge, to ground, to neutral and you are electrocuted. The RCD breaker is supposed to detect that current took a different return path and break the circuit to save your life.
With a floating system, ground/earth is not a return path. This means you can grab the phase while wrapping bare copper ground wires around your heart and nothing happens. The reason for not having the RCD breaker is that it serves no function because of the inherent safety provided by the isolation transformer. This is the core of the matter and all isolation transformer documents explain this.

[Wotname]

Originally Posted by SailRN

Perhaps, if you read my posting again, and think about my question "What is a kelvin watt" you might suddenly realize I asked "What is a kelvin watt" because that was a term that I thought was incorrect as it didn't make sense. Duh. I did not consider it a typo because it was repeated a few times, therefore the poster didn't appear to be familiar with the correct unit symbols. Another poster wrote 5 mV when it should have been 5 mA. So what "bigger picture" and reasonable assumption should someone reading that, especially those unfamiliar with the subject and trying to learn from this forum, assume the writer meant?


There are units of K/W, but I'm probably confusing you more.



And perhaps you also might rethink whether you want your nurse to be detail oriented or just see the "bigger picture" and just administer whatever looks like it might do, or guess the doctor's orders "probably" meant something other than what the doctor wrote. Duh.

Err... you haven't confused even once so far. I get it, you asked about the 'kelvin watt' (and about voltage levels). You may have be been serious, you may have been a smart aleck or you may have had other reasons - it didn't matter. However after others answered your queries, you double down about the accuracy and trust etc.

Of course there are units of K/W; along with myself, I think most readers of this thread would know that. We would understand that XX isn't X/X so I am left wondering why you would mention K/W. I won't elaborate on my guesses.

And yes, I would like my nurse to be detailed oriented along with having enough nous to understand the bigger picture. Both is best.

[Wotname]

Originally Posted by SailRN

Disregard, I read it in a NASA technical specifications manual, but I'm not wasting the time to look it up again. And I've also read in other technical journals and articles of the superiority of a properly crimped connection over soldered, but again I'm not taking the time to look it up again.


And I was talking about interconnections using wiring or cables, not PCBs. My apologies for not being more specific in the original posting.

Disregarded as requested.
Apologies accepted with grace.


Time to share beer or beverage of your choice

[Wotname]

Originally Posted by s/v Jedi

........ the reason for having an RCD breaker is the danger of a grounded neutral. It is dangerous because it makes ground (earth) a return path. Current can flow through the phase, into your hand, through your body to the wet bilge, to ground, to neutral and you are electrocuted. The RCD breaker is supposed to detect that current took a different return path and break the circuit to save your life.
With a floating system, ground/earth is not a return path. This means you can grab the phase while wrapping bare copper ground wires around your heart and nothing happens. The reason for not having the RCD breaker is that it serves no function because of the inherent safety provided by the isolation transformer. This is the core of the matter and all isolation transformer documents explain this.

Agreed and repeat there are some small advantages in having all outlets with internal RCDs as we have discussed upthread.

[Wotname]

To all those presenting good electrical knowledge to this thread and in particular to s/v Jedi and Jammer for detailing their respective arguments in great detail.

However it is the sum of all the posters that makes the thread worthwhile so the thank you applies to all.