Fail-Safe Galvanic Isolator vs. Isolation Transformer

[Saltyhog]

Originally Posted by Andina Marie

We passed all ABYC specifications when we first started manufacturing our Galvanic Isolator. We have not updated the design to meet the latest revisions regarding a capacitor or remote monitoring (and can sell for $100 less). With over 20,000 sold on unconditional warranty and zero returns, our track record indicates their reliability. They were tested independently by West Marine and sold under their brand name for about 10 years.

We do have fail safe functions in our GI but I'm not going to say it is 100% fail safe because NONE of the GIs are fail safe. I can cause any GI, including ours, to fail "unsafe" however in normal installations with a circuit breaker on the shore power, we are fail safe.

The CAPACITOR is rarely needed. You quoted AC leakage on docks up to 1 volt but leakage ON THE DOCK has nothing to do with the Galvanic Isolator on a boat. It is AC leakage ON THE BOAT that flows down the ground cable and attempts to flow through the GI. The AC voltage from the leakage is added on every half cycle to the DC voltage from electrolytic sources and if the total of the two exceeds 1.2 volts then some DC current flows through the diodes on the GI. As the AC voltage gets higher, a higher percentage of the time DC will sneak through on top of it, decreasing the GI performance up to a maximum of 50%. You can easily determine if this is a problem by measuring the AC voltage across your GI. We've only sold about 50 capacitors in 15? years so it is rare that they are needed. I've not checked lately but the capacitor used to be an option in the ABYC specifications.

If you have 3 amps of AC leakage you have a serious problem with some of the equipment on the boat. You should be eliminating the cause of the leakage rather than trying to bypass it across the GI. However if you can't, our Capacitor can carry 5 amps and maintain AC voltage below 0.5 volts, a 66% increase over the ABYC specification. I'm not going to submit it for independent evaluation, selling only 2 or 3 a year would not pay for the testing.

We are currently in production of a Double Galvanic Isolator. It is the equivalent of two GIs in series to give 2.4 volts isolation. This not only helps protect aluminum boats and boats using magnesium anodes but doubles the rejection of AC leakage.

You've mentioned the 0.5 volts at 5 amps twice. That's a pretty BIG capacitor, over 25,000 uF if I remember my AC circuits class at all. Maybe I'm missing something basic?

[goboatingnow]

Originally Posted by GatorDontPlay

Thanks for the thoughts, Saltyhog.

It does look like Yandina claims ABYC compliance for their Galvanic Isolator:

Galvanic Isolator Data Sheet

"Meets ABYC standards. (When fitted with a remote monitor, not included)"

DEI looks like a good product, from what I can tell roughly equivalent to the ProSafe but perhaps a bit more expensive.

Calder mentions the RCD (equating it to GFCB, GCFI, and RCCB terms; doesn't use the ELCI term but sounds like the same thing also) but specifically writes (in bold all caps italics):

"it is a BAD IDEA to break the AC-to-DC ground connection" just because you have a RCD/GFCB/GFCI/RCCB/(ELCI?) installed -- as you
are then dependent on said electrical device working (and they apparently have a failure rate in the teens, mostly due to vulnerability to lightning strikes) in order to be safe for swimmers (the trip point, whether 5 mA per US requirement or 30 mA for Europe, is also a safety question). Also says attempting whole-boat protection (as opposed to at each particular AC outlet/device) is likely to cause a lot of nuisance tripping.

Then Calder is wrong and the 10 s of thousands of whole boat RCD on Europe are full of tripping RCD. I love this theorising when the real life practice is staring you in the face.

The dc AC negative connection. Is the whole cause of impressed current corrosion issues in uS boats along with bonded. Together underwater fittings.

The fact is that dc to AC connection is protecting you against a rather esoteric fault. Firstly there has to be a stray hot to dc appliance and secondly the RCD then has to fail to operate. I mean millions and millions of homes in Europe are protected by RCDs under mandatory codes.

Arguing they might fail is not in itself an argument to act differently ( loads of things could fail )

Furthermore with the lack of whole boat RCDs , the AC dc bond can create a situation, especially on freshwater that allows leakage currents below the value of the fuse or breaker but well on the lethal range to flow via faulty earth through the bond and into the water

RCD failure rates are between 0.5 % to 2.5% and are lowest when the device is regularly tripped by the test button. Since most failures are caused by dust buildup. The trip test should be done every 3 months.



GI may or may not give you protection from stray AC earth wire currents. Of course you won't really know if its working or not on most cases anyway.

They are fine for what the are but only a iT really solves the problem.


The trouble is people buy these products GIs without really understanding what's going on , how to detect it and how to correct it.

Dave
Dave

[goboatingnow]

Originally Posted by Saltyhog

You've mentioned the 0.5 volts at 5 amps twice. That's a pretty BIG capacitor, over 25,000 uF if I remember my AC circuits class at all. Maybe I'm missing something basic?

Which is why on reality the capacitor is a placebo. The trouble is in an environment where GIs are installed because suspicion is on the earth wire. The likelihood is that the GI is conducting anyway and not doing anything useful. The whole idea was to protect against small dc impressed currents but that's not often the issue.

Dave

[Saltyhog]

Originally Posted by goboatingnow

<snip>

They are fine for what the are but only a iT really solves the problem.


The trouble is people buy these products GIs without really understanding what's going on , how to detect it and how to correct it.

Dave
Dave

Wait... if you have no connection from green wire to DC ground what protection does an IT provide towards impressed current corrosion? For electrical safety, I see the value of an IT, but no value for impressed current corrosion since the connection is not there to begin with.

[Saltyhog]

Originally Posted by goboatingnow

Which is why on reality the capacitor is a placebo. The trouble is in an environment where GIs are installed because suspicion is on the earth wire. The likelihood is that the GI is conducting anyway and not doing anything useful. The whole idea was to protect against small dc impressed currents but that's not often the issue.

Dave

I guess I was actually questioning how they were stuffing a non-polarized 25,000 uF capacitor with a ripple current ratting of over 5 amps into that little box. Assuming that it *is* a 25,000 uF cap, if you can manage to keep your AC leakage currents below 5 amp, the cap will do it's job and the diodes won't conduct and will do their job.

[goboatingnow]

Originally Posted by Saltyhog

Wait... if you have no connection from green wire to DC ground what protection does an IT provide towards impressed current corrosion? For electrical safety, I see the value of an IT, but no value for impressed current corrosion since the connection is not there to begin with.

It protects you against inadvertent leakage paths
Even of the AC dc bond isn't there

Dave

[Saltyhog]

Originally Posted by goboatingnow

It protects you against inadvertent leakage paths
Even of the AC dc bond isn't there

Dave

Yes, I guess your right about that, as the secondary of the IT isn't referenced against earth (seawater).

[GatorDontPlay]

Originally Posted by Andina Marie

We passed all ABYC specifications when we first started manufacturing our Galvanic Isolator. We have not updated the design to meet the latest revisions regarding a capacitor or remote monitoring (and can sell for $100 less). With over 20,000 sold on unconditional warranty and zero returns, our track record indicates their reliability. They were tested independently by West Marine and sold under their brand name for about 10 years.

Perhaps you should update your web page to indicate that your GI has not been updated since before the 2001 revision, so is does not actually meet current ABYC standards.

Originally Posted by Andina Marie

We do have fail safe functions in our GI but I'm not going to say it is 100% fail safe because NONE of the GIs are fail safe. I can cause any GI, including ours, to fail "unsafe" however in normal installations with a circuit breaker on the shore power, we are fail safe.

Fail-safe in this context is defined by the ABYC standard, and there is a clear testing methodology.

Originally Posted by Andina Marie

The CAPACITOR is rarely needed. You quoted AC leakage on docks up to 1 volt but leakage ON THE DOCK has nothing to do with the Galvanic Isolator on a boat. It is AC leakage ON THE BOAT that flows down the ground cable and attempts to flow through the GI.

Then why have diodes going both directions???

Originally Posted by Andina Marie

I've not checked lately but the capacitor used to be an option in the ABYC specifications.

Optional perhaps if you can satisfy the corresponding test requirement without a capacitor... but independent test lab is not optional.

Originally Posted by Andina Marie

If you have 3 amps of AC leakage you have a serious problem with some of the equipment on the boat. You should be eliminating the cause of the leakage rather than trying to bypass it across the GI. However if you can't, our Capacitor can carry 5 amps and maintain AC voltage below 0.5 volts, a 66% increase over the ABYC specification.

The numbers you are citing have nothing to do with the ABYC specification because you aren't applying them to the same test setup (theirs adds in a specific simulated galvanic DC bias), and not testing to the same endpoint -- your target is maintaining AC voltage on the ground conductor below 0.5 Volts; their target is reducing the DC current on the ground conductor (which causes galvanic corrosion) below 5 mA.

Originally Posted by Andina Marie

I'm not going to submit it for independent evaluation, selling only 2 or 3 a year would not pay for the testing.

Fair enough, I just think you should be clear to your 2 or 3 customers/year that it isn't designed to meet (and hasn't been certified as meeting) the current ABYC spec.

[CharlieJ]

The virtues of 30mA have been highlighted in this thread. It probably is worthwhile to understand that, at least according to OSHA (and others),

the following table demonstrates this general relationship for a 60-cycle, hand-to-foot shock of one second's duration:

The table http://is.gd/b4MQpO then shows that for current > 17mA;

Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible.

So the virtues of a 30mA RCD are...?

[GatorDontPlay]

Originally Posted by CharlieJ

The virtues of 30mA have been highlighted in this thread. It probably is worthwhile to understand that, at least according to OSHA (and others),



The table http://is.gd/b4MQpO then shows that for current > 17mA;


So the virtues of a 30mA RCD are...?

Not sure that 30 mA leakage/ground fault on the boat translates to 30 mA in a swimmer's body. Calder describes a voltage gradient around the boat that is potentially lethal if it's above 6 volts/meter where the swimmer is. That being said, a swimmer doesn't necessarily need to get shocked as bad as they do on land in order to die -- just enough that they can't swim anymore and sink. Curious how commercial divers protect against or avoid these conditions.

[goboatingnow]

Originally Posted by CharlieJ

The virtues of 30mA have been highlighted in this thread. It probably is worthwhile to understand that, at least according to OSHA (and others),

The table http://is.gd/b4MQpO then shows that for current > 17mA;

So the virtues of a 30mA RCD are...?

iEC 60479 states that for 230vac systems , 7ma is the " let go " threshold. , greater then 50 ma is where fibrillation occurs hence it says that 30ms is suitable for personal shock protection.

Here a summary from Ireland's codes http://www.etci.ie/docs/ET214.pdf ( as its European 230 but in English ) see the section on shock protection.

So 30 ma is adequate for shock protection.

Dave

[transmitterdan]

Originally Posted by GatorDontPlay

Curious how commercial divers protect against or avoid these conditions.

The conditions generally do not exist in salt water where most commercial divers work. In fresh water marinas few divers will work near boats where they don't know the power installation is done right. Even then, they should insist that boats nearby are disconnected from dock power before working below.

[Andina Marie]

Originally Posted by Saltyhog

You've mentioned the 0.5 volts at 5 amps twice. That's a pretty BIG capacitor, over 25,000 uF if I remember my AC circuits class at all. Maybe I'm missing something basic?

Correct, that is why it is an option that costs about 1/2 as much as the Galvanic Isolator to do it correctly.
However we are only concerned with one half of the AC voltage. On one 1/2 cycle the voltage is ADDED to the DC voltage and can cause DC to flow through with it, on the other 1/2 cycle the DC is subtracted and less likely to reach 1.2 volts.

[Andina Marie]

Originally Posted by GatorDontPlay

Perhaps you should update your web page to indicate that your GI has not been updated since before the 2001 revision, so is does not actually meet current ABYC standards.

I contend that the AYBC specifications are heavily influenced by paranoia in their legal department and fear of litigation if something went wrong that resulted in injury and they had not covered it in the specifications.

Experience has shown that all galvanic isolators are an order of magnitude more reliable than the shore power cables to which they are connected. If you are going to spend money on safety and monitoring there are much better candidates that a Galvanic Isolator.

Fail-safe in this context is defined by the ABYC standard, and there is a clear testing methodology.

Then why have diodes going both directions???

When a fault or miswiring causes current in the ground lead, the GI has to be able to carry 120% of rated AC current continuously. This is AC current so diodes need to go in both directions to handle both polarities of the AC current. It is not reasonable to think that the capacitor is going to be, or needs to be, any significant help under these conditions.

Optional perhaps if you can satisfy the corresponding test requirement without a capacitor... but independent test lab is not optional.

So far the ABYC police have not been carting me off. If you want bells and whistles and certifications, go spend twice as much. For the practical sailor with a limited budget we offer a low cost solution with UNCONDITIONAL warranty, and so far not a single warranty claim.

The numbers you are citing have nothing to do with the ABYC specification because you aren't applying them to the same test setup (theirs adds in a specific simulated galvanic DC bias), and not testing to the same endpoint -- your target is maintaining AC voltage on the ground conductor below 0.5 Volts; their target is reducing the DC current on the ground conductor (which causes galvanic corrosion) below 5 mA.

Perhaps different numbers but same result. If you keep the VOLTAGE below the 1.2 diode conduction voltage then DC current will not flow at all, whether you are measuring it or not.

Fair enough, I just think you should be clear to your 2 or 3 customers/year that it isn't designed to meet (and hasn't been certified as meeting) the current ABYC spec.

I really don't care for something we hardly sell. It exceeds the ABYC requirements if you wish to test it.

[CharlieJ]

If you are going to spend money on safety and monitoring there are much better candidates that a Galvanic Isolator.

Unless the boat owner is trying to mitigate protective galvanic current from leaving his vessel via the safety ground wire that now has a set of semi-conductors inserted in it.

in their legal department

ABYC does not have such a department.

So far the ABYC police have not been carting me off. If you want bells and whistles and certifications, go spend twice as much.

There is also no ABYC police department.