Isolating Transformers, The Earth wire connection conundrum

[goboatingnow]

Originally Posted by pbiJim

On the subject of electro-shock drowning, I assume that would require a swimmer to be a better conductor than the water around him. Does anyone know of a study that has documented the difference in resistance between these two?

It seems strange to me intuitively that a swimmer 10 feet away from a poorly wired boat would have a problem. I can certainly see that a person in the water touching a boat with bad wiring could have a problem though.

Does anyone have more info on this sort of thing?

There are several papers. The problem is more acute in freshwater. But there is voltage gradient that develops across the swimmers body when swimming through a electric current flowing through water

Dave

[goboatingnow]

Originally Posted by pbiJim

After much googling, it appears as though ABYC is starting to get on board with Europe when it comes to ground faults.

THE AMERICAN BOAT AND YACHT COUNCIL RESPONDS TO ELECTRIC ... PDF - Pdfsdb.com

Heaven forbid, the public should be informed.

If you have an hour & a half to kill, this might be an interesting webinar -

Old news ,well last years news , that's why I included RCDs in my drawings , there is common agreement now on whole boat RCD protection

About time for ABYC though .

Dave

[pbiJim]

The webinar was about 90% bleeding heart documentary on how electricity is dangerous & only about 10% useful information on how to handle the issue. The guy speaking was the father of a child that had been killed in an electrocution by a boat with faulty wiring, rather than someone with a strong electrical background, so I guess that is to be expected.

Some interesting info that was in there:

A voltage gradient in the water of 2vac/foot is considered lethal.

You only get that kind of gradient in fresh water

The human body conducts better than fresh water, but not so much better than salt water.

In salt water, you pretty much need to almost touch the boat with the bad wiring in order to get into trouble.

Using a clamp-on ammeter around a whole power feed cord (hot & neutral both in the clamp at the same time) is a quick & easy way to estimate leakage current.

A dock with 100ma indicated leakage should be remunerated immediately. Lower leakages should be investigated. 30ma is considered problematic.

A lot of boats they measured were leaking around 6 amps. That is huge.

Rednecks with electrical skills below that of Larry the Cable Guy, should not wire their own boat lifts.

The useful tech info could have easily been covered in 10 minutes. The rest of it tried to be a human interest story &/or tear jerker.

Apparently, watching that video is considered by some to qualify as a credential of some sort.

Of course these guys think that ABYC electricians are the only guys the world over that are capable of doing anything correctly. This guy seemed to think that all ABYC electricians are electrical engineers, or at least that's what it sounded like he said @ 52:46.

They are just now starting to catch on to the advantages of ground fault sensing equipment (ELCI).

[RaymondR]

Originally Posted by CarinaPDX

I picked up a ways back that your boat is steel. IIRC S/Y Jedi is aluminum. If I had a metal hull I would almost certainly isolate all AC and DC electrical systems from the hull, and particularly if it is aluminum. But I would also take great care that it stays isolated through the wear and tear of years. My fiberglass hull isn't likely to see damage as a result of stray corrosion, but metal boats can be damaged badly by it. And a metal hull would make a great conductor for any potential electro-shock drowning. So insulate, and make sure it stays that way.

Greg

I am pondering how to put in a monitoring system that will set off an alarm when anything goes to ground through the hull. You can buy them but they are expensive. Raymond.

[RaymondR]

I seem to recall that our blood is not far from the salinity of sea water. If this is true and one was immersed in fresh water and reached up and touched a current source the current would probably preferentially pass to earth through the lower resistance, salty blood than the relatively resistant fresh water. Since our arteries and veins are full of the salty blood these would also probably be the thickest conductors and with a connection through the heart, an organ very sensitive to current flows. This may also be the explanation for the required voltage gradient in fresh water to make it fatal.

Just guessing really but sounds feasible?

[goboatingnow]

Originally Posted by RaymondR

I am pondering how to put in a monitoring system that will set off an alarm when anything goes to ground through the hull. You can buy them but they are expensive. Raymond.

RCD?? ( with an aux contact)

Dave

[pbiJim]

The ABYC guys that are now saying ground fault equipment should be used are caught in a bit of a conundrum. They want to add ground fault sensors to protect people, but here in the US, anything that protects a person needs to trip at 5ma max. As Dave has noted in previous threads, something that sensitive will trip from stray leakage currents when you don't want it to. The ABYC guys want to go to the 30ma devices that are used on boats in Europe, but since they are considered equipment protection here in the US, it is not acceptable to use them for the protection of people here. The standards in the US may need to evolve a little.

(...waiting to hear Dave say - I told you so)

[goboatingnow]

All that happened is that 5ma trips simply will not work on a whole electrical system. The 30ma has been the experience in Europe for decades as a practical level of protection. IN Europe 30ma is regarded as sufficient for human protection ( we build em stronger over here!) The 5ma figure was invented because its practical on a single outlet.

even in Europe, where we use single outlet RCD we do not go below 30ma as a rule see Selectric Seal Range for info

at 30ma and 230VAC were all still alive here too.

Ive being saying for years that ABYC has arrived at really the worst of both worlds, due to leaving RCDs out of consideration. An over focus on requiring fuses to blow has lead to the DC AC interconnection , too much thinking has lead to all bonded underwater and connected to AC earth, all of which has led to impressed corrosion issues , whereas incorporating RCDs would have restored the balance between personal safety and corrosion ( there always is a balance)

dave

[CarinaPDX]

Been MIA, back now.

The guy in the video is our local ABYC rep, but didn't realize that he covered the Pacific coast. Understandably he has been very active at pushing the ABYC standards, as he sees them as the prevention for accidents like his son's death. I have to agree that there is more selling than contemplating of the ABYC standards.

The 5ma trip current for GFCIs has always been problematic. When the NEC (National Electrical Code) first required them for damp areas (e.g. bathrooms) they tripped far too often and many homeowners pulled them out, thus defeating the purpose. Of course many bathrooms get steamy when someone is showering, resulting in condensation which can cause leakage at the socket and an unnecessary trip. It is a bit silly, as we know it takes several times as much current to kill.

I think part of the problem is that the ABYC standards have evolved from a non-RCD world rather than rethinking things with the new technology. The standards also largely equate galvanic isolators with isolation transformers and seem to ignore the safety possibilities as Dave suggests. Fresh thinking with a blank slate wouldn't come up with the ABYC standards IMHO.

As for marine "electricians" being electrical engineers, that is a good one. I have met some competent ones, but I have also met a lot of incompetent ones or at least encountered their work (here and in Europe). In the US there is no licensing requirement for working on yachts. Some of the best have chosen to get ABYC certification, which assures knowledge of their standards but not the larger design issues discussed here. I have not heard of a similar certification in Europe, so suspect that at least there is no requirement for certification.

I have a problem with using the term "electricians" for this field. I grew up in a family-owned electrical construction company and know what it takes to be an electrician; applying the same name to tinkerers without any of the same training/testing/apprenticeship requirements does a disservice to journeymen electricians.

Greg

[transmitterdan]

I refer to would be "electricians" as "sparky" to avoid giving real electricians a bad name.

I think this discussion pretty much exposes the dilemma that ABYC faces. They have to recognize the many boats and wiring standards that are still in service and the practical problems that ground fault detection and prevention have. When everyone ends up with spoiled food because the GF device tripped is that really improving safety? Electrocution around boats is rare by any measure.

A multi level approach might be worth considering. If one were to have a GF device that tripped instantly above a relatively high threshold (e.g. 30mA) but also tripped if a lower threshold existed for a longer time then nuisance trips would be reduced. Also, an automatic reclosure after say 30 minutes would go a long way toward eliminating common complaints about GF devices.

[goboatingnow]

Originally Posted by transmitterdan

I refer to would be "electricians" as "sparky" to avoid giving real electricians a bad name.

I think this discussion pretty much exposes the dilemma that ABYC faces. They have to recognize the many boats and wiring standards that are still in service and the practical problems that ground fault detection and prevention have. When everyone ends up with spoiled food because the GF device tripped is that really improving safety? Electrocution around boats is rare by any measure.

A multi level approach might be worth considering. If one were to have a GF device that tripped instantly above a relatively high threshold (e.g. 30mA) but also tripped if a lower threshold existed for a longer time then nuisance trips would be reduced. Also, an automatic reclosure after say 30 minutes would go a long way toward eliminating common complaints about GF devices.

Don't think you could ever have automatic RCD reconnect.

30ma seems very safe from nuisance trips in my experience on boats. Rare to see a trip unless something is genuinely wrong.

Dave

[RaymondR]

Pondering on the incidence of RCD trips whilst they have been fairly common I cannot recall that any were due to an appliance on my boat. All the ones I can recall were due to damaged AC cords falling into the water and being found to have faulty insulation or other boats on the same circuit not having plugs with the correct IP rating and rain getting into them.

[Colin A]

Couple of quick points.
The ELCI (RCD) requirement in ABYC was supposed to go into effect in 2010 but it was delayed several years do to technical issues see the story below from Ed Sherman who is one of the leaders of the ELCI movement at ABYC.
Introducing the ELCI
They had some trouble with false trips at first. The company I work for has been assembling panels with ELCI modules for a coupe of years now for several large power boat builders and we haven't had any trouble with them recently.

As I understand it the US Navy actually floats their grounds. At least the equipment we build is set up to.

On inverters here is what ABYC reads "The generator or inverter neutral is grounded at the generator or inverter" combine that with the AC earth to DC ground connection and essentially they are all tied together when making your own AC power.

[Capn Morgan]

Sorry for barging into this thread with a question but I'm a bit baffled.

I installed a Victron 7000w IT. Just out of interest and to check that the connections were correct I checked for continuity between the two earth (yellow/green) wires. I have not jumpered L2 to the boat earth so it is a floating system. I expected to find an open circuit, but found continuity instead, around 400 ohms. I disconnected the shore terminals and tested again, finding an open circuit. I checked the cable from the shore power receptacle to the IT and found not to be compromised. I replaced the shore power connector only to find that the continuity was back.

So, there is no continuity if the cable is out of the receptacle but there is as soon as I replace it. Where is the connection from the boat safety wire to the shore earth?

[transmitterdan]

I don't really understand what you are trying to measure. Do you have a galvanic isolator?