Add an Isolation Transformer Article

[Alaskan Sea-Duction]

Winter project?

https://boattest.com/article/add-is...isw&utm_content=228138172&utm_source=hs_email

 

[twistedtree]

It's a bit surprising that they don't know that Charles got out of that business 5+ years ago.

 

[Circumnavigator]

An isolation transformer is essential for a metal boat, probably a good idea for a wood boat, and can be useful on a glass boat. The reason in the first two cases is that in marinas there is almost always at least one poorly wired boat that has DC riding on the AC line. In a metal boat, that DC can destroy the hull in fairly short order.


They are useful in glass boats because they usually have multiple taps, so you can boost the output voltage. I've never been in a marina that had a solid 240VAC on the line, so the boost is good for motors. On Fintry we have two transformers -- one wired for straight through and one wired for 10% boost. I've never used the straight through.


An added benefit is that most of them have a center tap, so if you run 120/240VAC as in a typical house, you can get the center tap off the transformer and your shore power cord needs only three conductors -- two hot (red and black) and the green ground.


Jim

 

[catalinajack]

The Following is an opinion written by a gentleman who is an active contributor to the ABYC electrical standards.

Amongst the "experts" that comprise the ABYC Electrical PTC, there is significant discussion and debate on this topic. The question being, "why would you INTENTIONALLY cut the ground line between the boat and the shore power pedestal?" That is, after all, what an isolation transformer does.

The answer purports to be, "it opens the path for fault current to return to shore, so eliminates current flowing in the water." Well, it also eliminates the fault clearing path that trips shore power circuit breakers, and it's what happens in fault conditions that codes are intended to address. And the transformer, and the wiring of and around the transformer, can still fail in a way that puts current into the water (the very thing they are supposed to prevent). So in that overall conversation, I'm persuaded that the polarization wiring configuration is a better option than the isolation wiring configuration, if you're gonna have a transformer aboard at all.

Transformers 1) are heavy, 2) need a lot of surrounding open air space (because they) 3) throw off significant amounts of heat, 4) take up a lot of space, 5) are expensive, and 6) can require manual intervention which can damage boat electrical systems in cases of operator error. What could possible go wrong there? The most frequent sales point behind transformers is to eliminate galvanic currents, but there are also Galvanic Isolators to do that. In fact, with the polarization configuration, you are still gonna need a Galvanic Isolator. So "if money is no object," then why not?

Are there any suitable alternatives to transformers? Cheap alternatives, at that? Well yes, as it happens, there are. How about ELCI Technology? ELCIs are ground fault sensors that can detect in an instant (well, 100mS) if there is current leaking out of the electrical system where it's supposed to live and stay. They cost 1/5th or less, installed, what a transformer does, and they work just as well for fault detection. ELCIs (well, called "RCDs" in the rest of the world) weren't common in North America in 2005, but they became "required" by ABYC in 2012 on newly built boats. They are heavily recommended to be retrofit to existing boats these days (but I do acknowledge, they are no where near as "glitzy" as lithium batteries). And, the RCD technology Is also required on docks by the NEC, since 2011, so these devices are going to be part of our futures whether we like it or not, obsoleting shore power transformer technologies on boats.

So, galvanic isolator for galvanic currents and ground fault sensors for current leakage scenarios, is there still a role for isolation transformers?

Not too much in North America. The one legitimate need for transformers is in the case where the shore power provided by the utility is "dirty;" that is, waveform is corrupted past certain tolerance limits for a sine wave because of the distortion caused by power company customer loads in the neighborhood of your marina. This happens primarily in city and industrialized suburban environments, and sometimes in highly rural environments, so if you live in, and keep a boat in, an affected location, a transformer is still the right solution, because it smoothes out noise and distortion from the power incoming on utility company power lines.

Otherwise... And, unless "money is not object..." I recommend you invest in Galvanic Isolators and Ground Fault Sensors on the incoming shore power. The truth is, isolation transformers hide symptoms but DO NOT "fix" anything.

 

[CharlieJ]

@CatalinaJack: What is the citation for this article please?

 

[twistedtree]

The Following is an opinion written by a gentleman who is an active contributor to the ABYC electrical standards.

Amongst the "experts" that comprise the ABYC Electrical PTC, there is significant discussion and debate on this topic. The question being, "why would you INTENTIONALLY cut the ground line between the boat and the shore power pedestal?" That is, after all, what an isolation transformer does.

The answer purports to be, "it opens the path for fault current to return to shore, so eliminates current flowing in the water." Well, it also eliminates the fault clearing path that trips shore power circuit breakers, and it's what happens in fault conditions that codes are intended to address. And the transformer, and the wiring of and around the transformer, can still fail in a way that puts current into the water (the very thing they are supposed to prevent). So in that overall conversation, I'm persuaded that the polarization wiring configuration is a better option than the isolation wiring configuration, if you're gonna have a transformer aboard at all.

Transformers 1) are heavy, 2) need a lot of surrounding open air space (because they) 3) throw off significant amounts of heat, 4) take up a lot of space, 5) are expensive, and 6) can require manual intervention which can damage boat electrical systems in cases of operator error. What could possible go wrong there? The most frequent sales point behind transformers is to eliminate galvanic currents, but there are also Galvanic Isolators to do that. In fact, with the polarization configuration, you are still gonna need a Galvanic Isolator. So "if money is no object," then why not?

Are there any suitable alternatives to transformers? Cheap alternatives, at that? Well yes, as it happens, there are. How about ELCI Technology? ELCIs are ground fault sensors that can detect in an instant (well, 100mS) if there is current leaking out of the electrical system where it's supposed to live and stay. They cost 1/5th or less, installed, what a transformer does, and they work just as well for fault detection. ELCIs (well, called "RCDs" in the rest of the world) weren't common in North America in 2005, but they became "required" by ABYC in 2012 on newly built boats. They are heavily recommended to be retrofit to existing boats these days (but I do acknowledge, they are no where near as "glitzy" as lithium batteries). And, the RCD technology Is also required on docks by the NEC, since 2011, so these devices are going to be part of our futures whether we like it or not, obsoleting shore power transformer technologies on boats.

So, galvanic isolator for galvanic currents and ground fault sensors for current leakage scenarios, is there still a role for isolation transformers?

Not too much in North America. The one legitimate need for transformers is in the case where the shore power provided by the utility is "dirty;" that is, waveform is corrupted past certain tolerance limits for a sine wave because of the distortion caused by power company customer loads in the neighborhood of your marina. This happens primarily in city and industrialized suburban environments, and sometimes in highly rural environments, so if you live in, and keep a boat in, an affected location, a transformer is still the right solution, because it smoothes out noise and distortion from the power incoming on utility company power lines.

Otherwise... And, unless "money is not object..." I recommend you invest in Galvanic Isolators and Ground Fault Sensors on the incoming shore power. The truth is, isolation transformers hide symptoms but DO NOT "fix" anything.

Is all of this from the article you mention, or it it your interpretation? Regardless who, there are quite a few misunderstandings and misinterpretations.

 

[backinblue]

Kind of scary as I have gone into the water at a marina to clear a line that fouled my thruster. Never thought about the danger and even asked permission from the marina first. I guess in the future maybe I'd do this away from the marina or at least unplug neighboring boats? Also had my wife fall over the side while reaching for a line while docking. Scary for several reasons.

My boat has a galvanic isolator. It's not clear to me how this works or performs a similar function as the transformer.

 

[DDW]

Transformers, galvanic isolators, ELCI, all do different things. The things they do overlap, but they are not perfect replacements for each other.

Despite the rhetoric about marina electrocutions, in every marina in my general area (US west coast), divers clean many of the boats on a monthly basis, representing hundreds of dives per week. If it were that dangerous, there would be no divers left - I have yet to hear of one being electrocuted.

 

[backinblue]

Good point DDW. I've never heard of any electrocutions either. I'm sure they happen, but must be pretty rare.

 

[DDW]

BTW, a galvanic isolator just puts a diode drop into the green wire both directions (back-to-back diodes) so that any leakage has to exceed around 0.7 - 1.0v to get across. Since galvanic voltages are normally less than that, it blocks galvanic currents, breaking the circuit, but still allows large ground faults to flow. What makes them so expensive is the ABYC requirement that if they fail, they fail shorted, simulating a solid green wire. That is abnormal behavior for a diode, and adds significant expense.

 

[Jeff F]

Good point DDW. I've never heard of any electrocutions either. I'm sure they happen, but must be pretty rare.

It's rare in salt water, but a genuine concern in fresh water.

https://en.m.wikipedia.org/wiki/Electric_shock_drowning

 

[Delta Riverat]

I'm sure that divers have some way to test for electric fields in the water before they dive in.

 

[tiltrider1]

One issue is that until only a few years ago, fresh water electrocution was miss diagnosed as drowning. It was only 10 years ago that we realized that hundreds of fresh water drowning cases were in fact fresh water electrocution. Turns out this is a much bigger problem than the general public currently understands.

If you see a diver sit on the dock and put his legs in first to see if he feels any current than he is probably educated on the issue. If he just jumps in then maybe he is in need of education on this subject.

 

[sunchaser]

There is a fresh water reservoir near Phoenix called Lake Pleasant. Two years ago a boat owner was doing some electrical work on his dock power. For whatever reason he went into the water and began convulsing. His brother jumped in to save him. They both drowned. Cause of death was electrocution.

 

[heysteve]

Many boats have been retrofitted with a second 30 amp shore power circuit for air conditioning. When I looked into isolation transformers, it wasn't clear how you support this without installing two.

Wrt marina divers, every one we've ever used is clad head to toe in neoprene. That probably helps protect against stray currents. Even down here in the warm waters of Mexico there's almost no bare skin.

 

[backinblue]

I don't know enough about the subject to say whether diving suits help or not. You would think they help but the ones I have worn were called "wet suits" for a reason. They are not watertight. Your skin is still in contact with water and they generally dont completely cover your head, hands, face, etc.

 

[tiltrider1]

Many boats have been retrofitted with a second 30 amp shore power circuit for air conditioning. When I looked into isolation transformers, it wasn't clear how you support this without installing two.

Wrt marina divers, every one we've ever used is clad head to toe in neoprene. That probably helps protect against stray currents. Even down here in the warm waters of Mexico there's almost no bare skin.

Just like there are multiple ways to add power to a boat 30a, 50a 125v, 50a 125/250v, 30a x 2 and so on, there also many ways to do isolation transformers.

In the case of 2 30a circuit, using 2 30a isolation transformers makes the most sense. When you get to 50a 125/250v things can get more complex, are we talking a true 220v boat or are we talking two 110v legs.

It is very unlikely that a diver would suffer electrocution in salt water.