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Old 04-01-2022, 05:40   #46
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Re: Recommended advanced AC power for EU boats

Note that there is a downside to fully isolated power distribution. It needs to be "monitored" to insure that each leg, is, in fact, isolated from earth. If you have a device fault that allows some leakage, or worse, contact with either isolated conductor to a touchable, conductive case, you are setting up a hazard. But, not yet a positive shock hazard. The next fault, may now involve the OTHER leg, again a leakage to an exposed piece of machinery. So, you have two pieces of machinery, with each exposed piece conducting to alternate sides of the line. No overcurrent yet exists. However, touching both devices now exposes one to full, or near full line voltage potential.

So, with multiple devices being supplied power from a fully isolated power system, you need to monitor each leg, REF earth, to insure that the legs, are, in fact, isolated.

In actual practice, fully isolated HV (Hazardous Voltage) systems are typically done for a single device feed, or, if you are a Navy ship, involve a monitored system. btw, Navy does this to increase power reliability after battle damage. Any single conductor (single instance) can contact earth without an over current fault, even with high power three phase feeds.
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Old 04-01-2022, 08:29   #47
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Re: Recommended advanced AC power for EU boats

Jedi and/or anyone with a Victron Multiplus can you confirm how the Muliplus operates with the "conn L case ground" (green wire) from dc negative battery? Is it internally wired to a relay that opens when shore AC is closed? I have read in their literature that there are some ground relays that can be programmed within the Multiplus but I was not sure if they were referring to this one. Is that conn L wire only the case ground while inverting?
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Old 04-01-2022, 12:17   #48
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Re: Recommended advanced AC power for EU boats

@Lyric #47
The case ground (Conn-L Case Ground in the referenced drawing) is a heavy gage case ground that is the same size or one size smaller than the B+ conductor. Typically, it will be > AWG 2/0.

The G>N relay internal to the unit bonds when the inverter/charger is inverting and is open when mains power is available. It is programmable.

Hope this helps.
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Old 04-01-2022, 21:50   #49
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Re: Recommended advanced AC power for EU boats

Quote:
Originally Posted by team karst View Post
Note that there is a downside to fully isolated power distribution. It needs to be "monitored" to insure that each leg, is, in fact, isolated from earth. If you have a device fault that allows some leakage, or worse, contact with either isolated conductor to a touchable, conductive case, you are setting up a hazard. But, not yet a positive shock hazard. The next fault, may now involve the OTHER leg, again a leakage to an exposed piece of machinery. So, you have two pieces of machinery, with each exposed piece conducting to alternate sides of the line. No overcurrent yet exists. However, touching both devices now exposes one to full, or near full line voltage potential.

So, with multiple devices being supplied power from a fully isolated power system, you need to monitor each leg, REF earth, to insure that the legs, are, in fact, isolated.

In actual practice, fully isolated HV (Hazardous Voltage) systems are typically done for a single device feed, or, if you are a Navy ship, involve a monitored system. btw, Navy does this to increase power reliability after battle damage. Any single conductor (single instance) can contact earth without an over current fault, even with high power three phase feeds.
The monitoring requirement is only for IMO registered ships, not for yachts. Also, by wiring the ground conductor like in my diagram, the double fault scenario is prevented because it would lead to a short that triggers the breakers.

My problem is that you call this a downside while it is superior to a grounded neutral system, where a dangerous voltage becomes touchable after just the first faults in that scenario. For an isolated system, the first fault is actually the same as what is done on purpose with a grounded system (where one power carrying conductor is connected to ground).
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Old 05-01-2022, 05:45   #50
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Re: Recommended advanced AC power for EU boats

RE: post 1 diagram. I can't tell what is going on inside the xfrmer. Really need a true schematic, not a block diagram/wiring diagram...

But, universally; touching either leg on an ungrounded sourced system will not cause any current to flow. That is indeed safe. The problem statement becomes when one or both legs has less than a very high R to EARTH.
Yes, your very last paragraph is true, its the second fault that produces the hazard. The system starts safely, but there are downstream faults that CAN make the system more dangerous than an EARTH ref system.

Also consider the second order effects. For instance, unbalanced capacitive loads on the legs. While passing even a DC hi-pot test, capacitive currents can be dangerous as well.

Lastly, consider a large, iso system on a large ship. If lightning involves a power buss, there is no low Z path to earth. There will then be a common mode surge waveform, where the voltage will rise to discharge at any number of undefined points, compromising insulation. ie: the CM surge Voltage will be higher than a grounded system. We see this a lot in power substations, where the 125/250V dc battery feed system is ungrounded, to insure reliability in the face of a single, short to earth. CM voltages on these busses tend to be quite high, relative a grounded feed.

No system is foolproof. I think the scenario you are painting, is an ungrounded device sustains a fault to a conductor. Yes, that scenario is safer than a grounded feed system, where the L side touches a floating frame, and does not trip a breaker. That is for sure a good case. The Earth ref system does depend on likewise earthing of touchable, conductive chassis, anytime it encloses line voltage. This same argument can also be carried to portable generators. Should those be ground referenced? My vote is actually to isolate a small system, since now direct contact with either conductor to earth will not result in a lethal current. But, as the systems become larger, the precautions to insure that isolation become more onerous, and again, the lightning issue. Or, the primary power line falls on a previously isolated conductor. That would be very exciting...
That scenario also brings us to the ship example. Where you may have 13kV feeds into step down transformers. If you are intending to have an isolated secondary from EARTH, this presents a difficult demand on the safety isolation of that transformer. A safety/isolation transformer is built differently than a run of the mill transformer hanging on your power pole. If that transformer develops a primary to secondary fault, and the secondary is floating, very bad things will happen. Like, the kitchen toaster case may rise to near 13kV...
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Old 05-01-2022, 06:23   #51
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Re: Recommended advanced AC power for EU boats

"My problem is that you call this a downside while it is superior to a grounded neutral system, where a dangerous voltage becomes touchable after just the first faults in that scenario. "
actually, that requires TWO faults;
first is lack of chassis earthing (thats a violation), second is Line to chassis touching
For an isolated system, the first fault is actually the same as what is done on purpose with a grounded system (where one power carrying conductor is connected to ground).
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Old 05-01-2022, 20:34   #52
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Re: Recommended advanced AC power for EU boats

Quote:
Originally Posted by team karst View Post
RE: post 1 diagram. I can't tell what is going on inside the xfrmer. Really need a true schematic, not a block diagram/wiring diagram...

But, universally; touching either leg on an ungrounded sourced system will not cause any current to flow. That is indeed safe. The problem statement becomes when one or both legs has less than a very high R to EARTH.
Yes, your very last paragraph is true, its the second fault that produces the hazard. The system starts safely, but there are downstream faults that CAN make the system more dangerous than an EARTH ref system.

Also consider the second order effects. For instance, unbalanced capacitive loads on the legs. While passing even a DC hi-pot test, capacitive currents can be dangerous as well.

Lastly, consider a large, iso system on a large ship. If lightning involves a power buss, there is no low Z path to earth. There will then be a common mode surge waveform, where the voltage will rise to discharge at any number of undefined points, compromising insulation. ie: the CM surge Voltage will be higher than a grounded system. We see this a lot in power substations, where the 125/250V dc battery feed system is ungrounded, to insure reliability in the face of a single, short to earth. CM voltages on these busses tend to be quite high, relative a grounded feed.

No system is foolproof. I think the scenario you are painting, is an ungrounded device sustains a fault to a conductor. Yes, that scenario is safer than a grounded feed system, where the L side touches a floating frame, and does not trip a breaker. That is for sure a good case. The Earth ref system does depend on likewise earthing of touchable, conductive chassis, anytime it encloses line voltage. This same argument can also be carried to portable generators. Should those be ground referenced? My vote is actually to isolate a small system, since now direct contact with either conductor to earth will not result in a lethal current. But, as the systems become larger, the precautions to insure that isolation become more onerous, and again, the lightning issue. Or, the primary power line falls on a previously isolated conductor. That would be very exciting...
That scenario also brings us to the ship example. Where you may have 13kV feeds into step down transformers. If you are intending to have an isolated secondary from EARTH, this presents a difficult demand on the safety isolation of that transformer. A safety/isolation transformer is built differently than a run of the mill transformer hanging on your power pole. If that transformer develops a primary to secondary fault, and the secondary is floating, very bad things will happen. Like, the kitchen toaster case may rise to near 13kV...
I’msure we miscommunicate: an isolated system has per definition no connection to ground whatsoever. This is what happens inside the isolation transformer: the shore power is used to create a magnetic field to which our secondary windings couple and the shore ground is terminated without any conductivity further into the boat electrical system.

The first fault in your scenario is safe and everything keeps working; with the second fault the breakers trip (the ground conductor shorts the power) so it’s safe as well or at least safer and higher availability than a grounded system.

Bonding and lightning damage control are separate systems (grounding masts and rigging)
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Old 05-01-2022, 20:40   #53
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Re: Recommended advanced AC power for EU boats

Quote:
Originally Posted by team karst View Post
"My problem is that you call this a downside while it is superior to a grounded neutral system, where a dangerous voltage becomes touchable after just the first faults in that scenario. "
actually, that requires TWO faults;
first is lack of chassis earthing (thats a violation), second is Line to chassis touching
For an isolated system, the first fault is actually the same as what is done on purpose with a grounded system (where one power carrying conductor is connected to ground).
No, there is no ground (as in earthing) in an isolated system. Touching earth never contributes to electrocution. This is why EE’s always use an isolation transformer on their workstation.
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Old 05-01-2022, 21:37   #54
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Re: Recommended advanced AC power for EU boats

I would agree with Jedi , removing earth/ boats metallic components/ etc from the fault path is the best safety compromise
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Old 06-01-2022, 06:07   #55
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Re: Recommended advanced AC power for EU boats

I believe my point was lost in clutter.

The fully isolated feeder L1 makes contact with a steel object. Lets say its "floating",OR earthed.

Feeder L2 makes contact with a second, but non-earthed metallic object. No OC device trips.
Homer makes contact with both metal objects. Homer receives a full V shock.

bottom line; neither isolated or non-isolated feeder systems work with two faults. They both work with one fault.
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Old 06-01-2022, 06:14   #56
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Re: Recommended advanced AC power for EU boats

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I believe my point was lost in clutter.

The fully isolated feeder L1 makes contact with a steel object. Lets say its "floating",OR earthed.

Feeder L2 makes contact with a second, but non-earthed metallic object. No OC device trips.
Homer makes contact with both metal objects. Homer receives a full V shock.

bottom line; neither isolated or non-isolated feeder systems work with two faults. They both work with one fault.
No, you overlook the short created by the ground wiring. Even though this wiring is not connected to earth, it does interconnected the metal surfaces of appliances and thus in the highly unlikely scenario you describe, L1 and L2 are shorted through the ground conductor and the breaker(s) trip.
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Old 06-01-2022, 06:22   #57
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Re: Recommended advanced AC power for EU boats

only if you bond the appliances together.
What about a toaster, or a lamp, or a .... Many appliances, even fixed devices not bonded.
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Old 06-01-2022, 06:38   #58
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Re: Recommended advanced AC power for EU boats

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only if you bond the appliances together.
What about a toaster, or a lamp, or a .... Many appliances, even fixed devices not bonded.
All approved appliances are either double insulated or grounded. All proper installations have ground conductors installed. If any of those are faulty then not only is the problem with those faults but also the isolated system is still much safer than the earthed system.

The isolated system is much, much safer than an earthed system. The reason we don’t use it en masse is the cost. Houses don’t have it, but operating rooms do. Offices don’t have it but electronics labs do. Production boats don’t have it, but your boat can
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Old 06-01-2022, 06:50   #59
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Re: Recommended advanced AC power for EU boats

hmmm, If my (or your) boat had an isolation system, would it not fail ABYC; those pesky rules about bonding N to E on the output of the iso xfrm? so much for isolation, its now back to E ref wiring.... iso just moved E from shore to sea..

reread your first line above. You are saying if there are no faults then it is safe. Agree 100% ! but, we are talking fault scenarios.

I'm not knocking iso xfrms. And yes, i do use those at work. Especially doing work on copper sheets used for RF ground planes. ALL I'm saying is each system is good, up until two carefully faults are applied. Then, folks get bit.

btw, interesting example. Many homes still use 3 wire feeds to their dryers. This is a case of only needing ONE OPEN connection to cause a fatal shock. That's just ONE fault, and not even a short at that. Old lady leaning on the washer while opening the dryer door. hmmm
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Old 06-01-2022, 08:13   #60
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Re: Recommended advanced AC power for EU boats

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hmmm, If my (or your) boat had an isolation system, would it not fail ABYC; those pesky rules about bonding N to E on the output of the iso xfrm? so much for isolation, its now back to E ref wiring.... iso just moved E from shore to sea..

reread your first line above. You are saying if there are no faults then it is safe. Agree 100% ! but, we are talking fault scenarios.

I'm not knocking iso xfrms. And yes, i do use those at work. Especially doing work on copper sheets used for RF ground planes. ALL I'm saying is each system is good, up until two carefully faults are applied. Then, folks get bit.

btw, interesting example. Many homes still use 3 wire feeds to their dryers. This is a case of only needing ONE OPEN connection to cause a fatal shock. That's just ONE fault, and not even a short at that. Old lady leaning on the washer while opening the dryer door. hmmm
In the diagram I posted, things are completely safe even within the unlikely scenario that you described. This is why I posted it as a “reference diagram” for those who don’t mind spending a little extra to create a better and safer system and why the ground conductor is there, which was your question, right?

Also, an isolated system has no earthing per definition. That ABYC does not describe this, does not mean it doesn’t exist or that it isn’t much safer than what they describe. What they do is take the most common setup for yachts and give guidelines for than (they are not rules, just recommendations). OR’s don’t follow ABYC; commercial fishing vessels don’t follow ABYC, yet these are all better, safer than what ABYC recommends. They are also more expensive.

There is no question/debate than an isolation transformer is the gold standard for protection of underwater metals as well as persons aboard boats: it’s a well accepted fact.

Putting a jumper between N and E is normal, but in this case there is no N: we have L1 and L2 and eliminated N. This is why all breakers are double pole.

In my diagram for US installations, I create a new pseudo N all the way at the end with the distribution breakers. The rest of the system incl. inverter/chargers are just L1 and L2 and N as well as E are dropped at the shore power inlet.

Yes, shoreside installations are more dangerous. They are also cheap
This leads to another reason for the isolated, floating power distribution systems: availability. When you get a single short between L and the metal housing in an appliance, the breaker triggers and power is out. The same scenario with the isolated setup and no power is lost. It makes a big difference when that happens in an operating room or clean room, even when a UPS takes over (alarms, different lighting etc.)
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