AC DC common ground

[s/v Jedi]

Exactly. You will not find a single diagram with the inverter/charger in front of the isolation transformer, it’s complete nonsense and puts your DC right at the shore power pedestal

If you do not want to ground the neutral when the inverter is active, like I have it configured, then you simply flip the configuration setting to OFF.

There is much more to this: for US systems, the 240V is between L1 and L2 which are both hot, i.e. ungrounded. When you would ground L2 you create a dead short. So in order to do this, but still end up with a grounded neutral down the line, the Multiplus has a “ground relay” output signal that goes high when the inverter mode activates. This output connects to the ground relay input on the autotransformer, who makes the new neutral and has a relay to ground it.

I did not connect that either, because I prefer an ungrounded neutral. This means that neutral must be regarded hot and that the distribution breaker panel must have double pole breakers for every circuit. Which is great because it allows easy rewiring between 120V and 240V circuits.

[goboatingnow]

I still don’t see any electrical issue in feeding the invertor into the isolating transformers. After all it’s just another source of AC power your isolating transformer does t care where it’s inputs come from.

Hence I see no reason the whole boat AC transfer switch couldn’t be on the transformer primary feed it would remove the need for multiple RCBOs

Agree re neutral bonding but that’s another days discussion

I certainly don’t see how it compromises anything DC

[s/v Jedi]

Originally Posted by goboatingnow

I still don’t see any electrical issue in feeding the invertor into the isolating transformers. After all it’s just another source of AC power your isolating transformer does t care where it’s inputs come from.

Hence I see no reason the whole boat AC transfer switch couldn’t be on the transformer primary feed it would remove the need for multiple RCBOs

Agree re neutral bonding but that’s another days discussion

I certainly don’t see how it compromises anything DC

I knew you were gonna double down on this silliness. So you install an isolation transformer to isolate your boat from shore power and next you move the electrical installation aboard back to the shore side incl. the DC house batteries. I am sure you are gonna say next that this is okay because you’ll just install a second isolation transformer or maybe a galvanic isolator

Anyway, I am done with this.

[team karst]

GBN: here ya go:

https://www.iqsdirectory.com/article...he%20frequency.

[goboatingnow]

Originally Posted by team karst

GBN: here ya go:

https://www.iqsdirectory.com/article...he%20frequency.

Thanks but nothing new there’s

As I said I see no electrical issue why a invertor cannot feed the isolating unit. Ie the transfer switch fron the inverter is between shore power input and yrbsforner. The Dane bsnk of rcbo provides the Save protection in either cases o know it’s not a common arrangement but I see no circuit issues.

[team karst]

"nothing new there". very true, but folks still don't know some basics.

Lots of ways to bring mains into a vessel that "work". But, some topographies are better (safer or more effective) than others. Not a good idea to put semi's in harms way, when the mitigation path is clear.

Don't get stuck on safety only, when the mission is all of: shock safety, fire safety, flexibility, and reliability. My little boat doesn't have an iso xfrm, but there are clear advantages in using one, and putting it in the best location. Use its characteristics of surge blockage to protect high value stuff, like high power inverters, chargers, etc. The reliability factor is far improved, and I suspect fire safety is improved a bit. A large part of my job is testing and protecting electronics from destruction. One of my tests is a IEC 4kV pulse into switch mode power supplies. A majority of them fail, as designed by the manufacturer. That particular pulse waveshape attempts to simulate lightning into public mains. What they do pass is lower levels, levels that will be exceeded by several causes. How much marina installed surge suppression is upstream, do you suppose? Your boat, your call.

[team karst]

Originally Posted by s/v Jedi

....

I did not connect that either, because I prefer an ungrounded neutral. This means that neutral must be regarded hot and that the distribution breaker panel must have double pole breakers for every circuit. Which is great because it allows easy rewiring between 120V and 240V circuits.

Interestingly, the NEC/building codes forbid greater than 120V to local Earth on any mains conductor. So, that's the basis for split 240/120, earthed N.
But boats aren't buildings, so NEC has no jurisdiction on things that float, and clearly is N America power systems based. Even if its someones home.

I suspect because of this, the ROW (rest of world) has improved touch safety requirements (look at the UK plug/socket vs NA NEMA 5-15). Also, ROW (at least UK) leads in RCD laws on domicile recepts.

[Andrew Lippman]

I am way behind on this thread. On Euro boats, there is a 12v positive and negative wire. The negative is called the return, and it is not connected to protective ground or boat bonding anywhere. I believe this is their solution to galvanic corrosion. Any 12v electrical equipment that requires a connection to ground does so through a capacitor to maintain the DC isolation.

AC connections are through RCDs, and protective ground is not connected to neutral. If you have a source of AC, such as an inverter, it has a switched ground. When it is passing shore power through, ground is not connected to neutral; when it is inverting, ground and neutral are connected as this is then a new source.

The isolation transformer is a new source, so it creates a new protective ground that is connected to neutral at the transformer and is isolated from the shore ground wire. I.e., the primary side of the transformer is part of the shore grounding, and the boat creates a new ground that is not connected to shore at all. This way something wrong on shore cannot send electricity through the ground to my boat.

To the best of my knowledge, nothing in the 12vdc system is connected to ground. It is fully isolated and not connected to AC ground.

Of course, this requires a really special engine installation where the engine is likewise isolated from ground. On my boat, the parts that require the block to be the return are momentarily connected to negative when engaged -- glow plugs, stop relay, etc. All the gauge senders are three-terminal devices. Alternator is likewise isolated.

My question is whether any 12v electronics electronics need to be connected to protective ground or bonding, and if they do, doesn't that imply the bonding is both the AC and DC protective ground?

Certainly the VHF antenna is isolated from the mast. VHF does not need an earth connection or else you couldn't use a handheld.

[Statistical]

Originally Posted by Andrew Lippman

I am way behind on this thread. On Euro boats, there is a 12v positive and negative wire. The negative is called the return, and it is not connected to protective ground or boat bonding anywhere. I believe this is their solution to galvanic corrosion. Any 12v electrical equipment that requires a connection to ground does so through a capacitor to maintain the DC isolation.

AC connections are through RCDs, and protective ground is not connected to neutral. If you have a source of AC, such as an inverter, it has a switched ground. When it is passing shore power through, ground is not connected to neutral; when it is inverting, ground and neutral are connected as this is then a new source.

The isolation transformer is a new source, so it creates a new protective ground that is connected to neutral at the transformer and is isolated from the shore ground wire. I.e., the primary side of the transformer is part of the shore grounding, and the boat creates a new ground that is not connected to shore at all. This way something wrong on shore cannot send electricity through the ground to my boat.

To the best of my knowledge, nothing in the 12vdc system is connected to ground. It is fully isolated and not connected to AC ground.

Of course, this requires a really special engine installation where the engine is likewise isolated from ground. On my boat, the parts that require the block to be the return are momentarily connected to negative when engaged -- glow plugs, stop relay, etc. All the gauge senders are three-terminal devices. Alternator is likewise isolated.

My question is whether any 12v electronics electronics need to be connected to protective ground or bonding, and if they do, doesn't that imply the bonding is both the AC and DC protective ground?

Certainly the VHF antenna is isolated from the mast. VHF does not need an earth connection or else you couldn't use a handheld.

The joining of AC and DC ground is a safety consideration and required by ABYC. Granted ABYC it is a voluntary association not the world police and the ISO has no such requirement.

The general idea is that imagine if you had an AC hot which came in contact with any DC wiring. This could happen through chaffed wiring or in a fault inside a device that uses both like charger or inverter. The DC circuit is now energized and if the connection was high resistance the current flow could be dangerous but low enough to not trip the primary AC breaker.

Now with AC ground and DC negative bus tied together the energy would flow through that low resistance path back to the source (AC transformer the pedestal is connected to). Without AC ground & DC negative bus together the energy is going to find its way back through the DC connection of the engine block through the propshaft into the water and could electrocute someone in the water. At least that is the rationale for the ABYC rule.

My personal opinion is with ABYC now requiring ELCI on the primary shorepanel connection this is not as critical as it once was. If the scenario in question happened the ELCI would detect the current imbalance at the milliamp level and trip. Still ABYC says you need to do it. I feel it is ABYC updating one part of the regs without revisiting how this might change existing requirements but they didn't ask me.

Nigel Calder covers this in the boatowners mechanical guide outlining a setup where you don't use an inverter charger you have a dedicated charger as the only thing connected to shorepower and then a dedicated inverter for powering household loads. There is no direct connection between shorepower and any household AC loads/wiring. If the charger is only grounded to shorepower not the house DC negative then the boat becomes isolated from stray current (galvanic) corrosion. They allow this for isolation transformers but not dedicated chargers. He does point out this violates ABYC requirements although with an ELCI on the shorepower connection and the shore power connect only the a charger and nothing else and that charger connected to the shorepower ground it isn't unsafe just not something the ABYC regs allow.

[Andrew Lippman]

Thanks but that doesn't quite answer my question. If AC hot hits a 12vdc appliance, then on my boat, with a negative return not connected to ground, I am in trouble. I see that. Are you suggesting that the AC protective ground connect to battery negative? That would seem odd and not solve the problem: If 120vac shorted to the +12, how would it get to protective ground?

[Statistical]

Originally Posted by Andrew Lippman

Are you suggesting that the AC protective ground connect to battery negative?

I am not suggesting it ABYC is mandating it for as little or much that matters depending on the jurisdiction and situation. As I indicated later I believe this requirement may be dubious on a boat with ELCI/RCD/GFCI on the shorepower inlet.

That would seem odd and not solve the problem: If 120vac shorted to the +12, how would it get to protective ground?

You wouldn't be protected in that case unless the current traveled through a device and onto the neg and to AC ground. Leaving only the 12+ lines unprotected also removes the electroshock risk. There is on most boats a negative path to the earth through the water via the propshaft and engine ground. It doesn't take much current to drown someone. Any otherwise survivable amount of current can become lethal if you die from the drowning not the shock.

It is all levels of safety but personally (for the absolutely nothing that is worth) I feel the requirement is dated IF a boat has a proper ELCI on the shorepower inlet installed correctly before anything else to ensure it protects the entire boat. I can't see any scenario where tying AC ground to DC neg provides protection where the ELCI wouldn't and a lot of scenarios where ELCI provides additional protection. The AC ground to DC neg tie made a lot of sense when ABYC didn't require ELCI but now they do and when they added that they never went back and changed other regs.

[Pete7]

Originally Posted by Andrew Lippman

I am way behind on this thread. On Euro boats, there is a 12v positive and negative wire. The negative is called the return, and it is not connected to protective ground or boat bonding anywhere. I believe this is their solution to galvanic corrosion. Any 12v electrical equipment that requires a connection to ground does so through a capacitor to maintain the DC isolation.

I am not sure that is correct. My yacht has the 12v DC circuit negative connected to the anode. The 230v AC earth is also connected to the 12 DC circuit negative, wired like this by Moody Yachts the manufacturer.

Originally Posted by Andrew Lippman

AC connections are through RCDs, and protective ground is not connected to neutral. If you have a source of AC, such as an inverter, it has a switched ground. When it is passing shore power through, ground is not connected to neutral; when it is inverting, ground and neutral are connected as this is then a new source.

There are two options for an inverter on the AC side, centre tapped and neutral earth bonded. Most inverters seem to be neutral earth bonded. See attached screen shot of a Sterling Power inverter manual.

A galvanic isolator is normally installed straight after the yacht shore power socket which isolates the yachts earth circuit from the pontoon pedestal. This reduces low voltage leaks creating galvanic corrosion.

Pete

[team karst]

Originally Posted by Andrew Lippman

….
My question is whether any 12v electronics electronics need to be connected to protective ground or bonding, and if they do, doesn't that imply the bonding is both the AC and DC protective ground?

Certainly the VHF antenna is isolated from the mast. VHF does not need an earth connection or else you couldn't use a handheld.

Comm gear may prove to be one exception. Take an ohmmeter from the uhf connector to the black NEG power wire. VHF and SSB radios may enforce a NEG ground only install. Also, an antenna like a metz 5/8wave end fed may connect the metal mounting bracket to the coax shield, thereby earthing NEG via a metal mast. SSB tuners may do the same. btw: I use a .05uF transmitting capacitor in series with my tuner EARTH strap to break that DC path for potential stray dc current. .
RE: euro vs NA boat wiring, surveyors will continue to butt heads on earthing dc NEG. Do US boats fail survey in europe?

[CharlieJ]

@ Statistical #144:

The joining of AC and DC ground is a safety consideration and required by ABYC. Granted ABYC it is a voluntary association not the world police and the ISO has no such requirement.

That may have been true at one time but not now.

ISO 13297 2020-12 states:

6.3 The AC protective conductor(s) shall be provided with a final (single) connection to the hull of a metallic hull craft, or, if the craft has a non-metallic hull, to the main grounding/earthing point of the craft.

And here is the historical perspective of how this subject evolved from Nigel Calder:

https://www.youtube.com/watch?v=iUZwgI7e-vg

And, finally, after the ABYC adopted the ELCI (RCD) requirement, the AC safety ground to DC main ground (B-) requirement was left in place to provide a redundant path back to the source should the ELCI fail and a fault aboard developed.

[s/v Jedi]

Here we go again

Please keep DC isolated from AC. If your boat has those two connected and you are in doubt, hire a professional for help but if your boat has them fully isolated from factory then you have an optimal installation and should not make any changes.

When AC hot touches a DC appliance, nothing bad happens. Imagine what the h@ck must happen to make AC hot touch a DC appliance