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Old 26-10-2013, 01:34   #196
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Re: Isolating Transformers, The Earth wire connection conundrum

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Originally Posted by sailorchic34 View Post
Actually ISO is a standard organization like ABYC or ASTM or any one of 100's out there. It's recommendations, not actually an enforced code. Not in the US anyway. Nice to have but not the only game in town. Nor is it a "CODE" as in enforcement, permits, etc. The NEC is the electrical CODE of the land. But it stops at the dock.

Really Jedi's an engineer, You don't think he knows what he's doing???
And did we forget the UL factor?

lloyd
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Old 26-10-2013, 02:11   #197
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pirate Re: Isolating Transformers, The Earth wire connection conundrum

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Originally Posted by sailorchic34 View Post
Actually ISO is a standard organization like ABYC or ASTM or any one of 100's out there. It's recommendations, not actually an enforced code. Not in the US anyway. Nice to have but not the only game in town. Nor is it a "CODE" as in enforcement, permits, etc. The NEC is the electrical CODE of the land. But it stops at the dock.

Really Jedi's an engineer, You don't think he knows what he's doing???
Standards Orgs, as quoted by CFR, including ABYC, UL,



CFRTitle 46Chapter ISubchapter TPart 175 › Section 175.600



46 CFR 175.600 - Incorporation by reference.


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§ 175.600
Incorporation by reference.
(a) Certain material is incorporated by reference into this subchapter with the approval of the Director of the Federal Register under 5 U.S.C. 552(a) and 1 CFR part 51. To enforce any edition other than that specified in this section, the Coast Guard must publish notice of change in the Federal Register and the material must be available to the public. All approved material is available for inspection at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030 or go to Code of Federal Regulations Incorporation by Reference. The material is also available for inspection at the U.S. Coast Guard, Office of Design and Engineering Standards (CG-521), 2100 2nd St., SW., Stop 7126, Washington, DC 20593-7126, and is available from the sources listed below.
(b) The material approved for incorporation by reference in this subchapter and the sections affected are shown in Table 175.600:
Table 175.600: Subchapter T Incorporations by Reference Standards organization and name of standard Section(s) incorporating the standard American Boat and Yacht Council (ABYC), 613 Third Street, Suite 10, Annapolis, MD 21403 A-1-93—Marine Liquefied Petroleum Gas (LPG) Systems (“ABYC A-1”) 184.240. A-3-93—Galley Stoves (“ABYC A-3”) 184.200. A-7-70—Boat Heating Systems (“ABYC A-7”) 184.200. A-16-89—Electric Navigation Lights (“ABYC A-16”) 183.130. A-22-93—Marine Compressed Natural Gas (CNG) Systems (“ABYC A-22”) 184.240. E-8 Alternating Current (AC) Electrical Systems on Boats (July 2001) (“ABYC E-8”) 183.130; 183.340. E-9 Direct Current (DC) Electrical Systems on Boats (May 28, 1990) (“ABYC E-9”) 183.130; 183.340. H-2-89—Ventilation of Boats Using Gasoline (“ABYC H-2”) 183.130; 182.460. H-22-86—DC Electric Bilge Pumps Operating Under 50 Volts (“ABYC H-22”) 182.130; 182.500. H-24-93—Gasoline Fuel Systems (“ABYC H-24”) 182.130; 182.440; 182.445; 182.450; 182.455. H-25-94—Portable Gasoline Fuel Systems for Flammable Liquids (“ABYC H-25”) 182.130; 182.458. H-32-87—Ventilation of Boats Using Diesel Fuel (“ABYC H-32”) 182.130; 182.465; 182.470. H-33-89—Diesel Fuel Systems (“ABYC H-33”) 182.130; 182.440; 182.445; 182.450; 182.455. P-1-93—Installation of Exhaust Systems for Propulsion and Auxiliary Engines (“ABYC P-1”) 177.405; 177.410; 182.130; 182.425; 182.430. P-4-89—Marine Inboard Engines (“ABYC P-4”) 182.130; 182.420. American Bureau of Shipping (ABS), ABS Plaza, 16855 Northchase Drive, Houston, TX 77060 Guide for High Speed Craft, 1997 (“ABS High Speed Craft”) 177.300. Rules for Building and Classing Aluminum Vessels, 1975 (“ABS Aluminum Vessel Rules”) 177.300. Rules for Building and Classing Reinforced Plastic Vessels, 1978 (“ABS Plastic Vessel Rules”) 177.300. Rules for Building and Classing Steel Vessels, 1995 (“ABS Steel Vessel Rules”) 183.360. Rules for Building and Classing Steel Vessels Under 61 Meters (200 feet) in Length, 1983 (“ABS Steel Vessel Rules (< 61 Meters)”) 177.300. Rules for Building and Classing Steel Vessels for Service on Rivers and Intracoastal Waterways, 1995 (“ABS Steel Vessel Rules (Rivers/Intracoastal)”) 177.300. American National Standards Institute (ANSI), 11 West 42nd Street, New York, NY 10036 A 17.1-1984, including supplements A 17.1a and B-1985—Safety Code for Elevators and Escalators (“ANSI A 17.1”) 183.540. B 31.1-1986—Code for Pressure Piping, Power Piping (“ANSI B 31.1”) 182.710. Motor Vehicles Operating on Land Highways (“ANSI Z 26.1”) 177.1030. ASTM International (formerly American Society for Testing and Materials) (ASTM), 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959. ASTM B 96-93, Standard Specification for Copper-Silicon Alloy Plate, Sheet, Strip, and Rolled Bar for General Purposes and Pressure Vessels (“ASTM B 96”) 182.440. ASTM B 117-97, Standard Practice for Operating Salt Spray (Fog) Apparatus (“ASTM B 117”) 175.400. ASTM B 122/B 122M-95, Standard Specification for Copper-Nickel-Tin Alloy, Copper-Nickel-Zinc Alloy (Nickel Silver), and Copper-Nickel Alloy Plate, Sheet, Strip and Rolled Bar (“ASTM B 122”) 182.440. ASTM B 127-98, Standard Specification for Nickel-Copper Alloy (UNS NO4400) Plate, Sheet, and Strip (“ASTM B 127”) 182.440. ASTM B 152-97a, Standard Specification for Copper Sheet, Strip, Plate, and Rolled Bar (“ASTM B 152”) 182.440. ASTM B 209-96, Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate (“ASTM B 209”) 182.440. ASTM D 93-97, Standard Test Methods for Flash Point by Pensky-Martens Closed Cup Tester (“ASTM D 93”) 175.400. ASTM D 635-97, Standard test Method for Rate of Burning and or Extent and Time of Burning of Self-Supporting Plastics in a Horizontal Position (“ASTM D 635”) 182.440. ASTM D 2863-95, Standard Method for Measuring the Minimum Oxygen Concentration to Support Candle-Like Combustion of Plastics (Oxygen Index) (“ASTM D 2863”) 182.440. ASTM E 84-98, Standard Test Method for Surface Burning Characteristics of Building Materials (“ASTM E 84”) 177.410.
Institute of Electrical and Electronics Engineers, Inc. (IEEE), IEEE Service Center, 445 Hoes Lane, Piscataway, NJ 08854 Standard 45-1977—Recommended Practice for Electrical Installations on Shipboard (“IEEE 45-1977”) 183.340. International Organization for Standardization (ISO), Case postale 56, CH-1211 Geneva 20, Switzerland ISO 8846, Small Craft-Electrical Devices-Protection Against Ignition of Surrounding Flammable Gases (Dec. 1990) (“ISO 8846”) 182.500. ISO 8849, Small Craft-Electrically Operated Bilge Pumps (Dec. 15, 1990) (“ISO 8849”) 182.500. International Maritime Organization (IMO), International Maritime Organization, Publications Section, 4 Albert Embankment, London SE1 7SR, United Kingdom Code of Practice for the Evaluation, Testing and Acceptance of Prototype Novel Life-Saving Appliances and Arrangements-Resolution A.520(13), dated 17 November 1983 (“IMO Resolution A.520(13)”) 175.540. Use and Fitting of Retro-Reflective Materials on Life-Saving Appliances-Resolution A.658(16), dated 20 November 1989 (“IMO Resolution A.658(16)”) 185.604. Fire Test Procedures For Ignitability of Bedding Components, Resolution A.688(17), dated 06 November 1991 (“IMO Resolution A.688(17)”) 177.405. Symbols Related to Life-Saving Appliances and Arrangements, Resolution A.760(18), dated 17 November 1993 (“IMO Resolution A.760(18)” 185.604. Lloyd's Register of Shipping, 71 Fenchurch Street, London EC3M 4BS Rules and Regulations for the Classification of Yachts and Small Craft, as amended through 1983 (“Lloyd's Yachts and Small Craft”) 177.300. National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02269-9101. NFPA 10-1994—Portable Fire Extinguishers (“NFPA 10”) 176.810. NFPA 17-1994—Dry Chemical Extinguishing Systems (“NFPA 17”) 181.425. NFPA 17A-1994—Wet Chemical Extinguishing Systems (“NFPA 17A”) 181.425. NFPA 70-1996—National Electrical Code (NEC) (“NFPA 70”) 183.320; 183.340; 183.372. NFPA 302-1994—Pleasure and Commercial Motor Craft, Chapter 6 (“NFPA 302”) 184.200; 184.240. NFPA 306-1993—Control of Gas Hazards on Vessels (“NFPA 306”) 176.710. NFPA 1963-1989—Fire Hose Connections (“NFPA 1963”) 181.320. Naval Publications and Forms Center, Customer Service Code 1052, 5801 Tabor Ave., Philadelphia, PA 19120 Military Specification MIL-P-21929C (1991)—Plastic Material, Cellular Polyurethane, Foam-in-Place, Rigid (2 and 4 pounds per cubic foot) (“NPFC MIL-P-21929C”) 179.240. Military Specification MIL-R-21607E(SH) (1990)—Resins, Polyester, Low Pressure Laminating, Fire Retardant (“NPFC MIL-R-21607E(SH)”) 177.410. Society of Automotive Engineers (SAE), 400 Commonwealth Drive, Warrendale, PA 15096-0001 SAE J-1475—Hydraulic Hose Fittings For Marine Applications, 1984 (“SAE J-1475”) 182.720. SAE J-1928—Devices Providing Backfire Flame Control for Gasoline Engines in Marine Applications, August 1989 (“SAE J-1928”) 182.415. SAE J-1942—Hose and Hose Assemblies for Marine Applications, 1992 (“SAE J-1942”) 182.720. Underwriters Laboratories Inc. (UL), 12 Laboratory Drive, Research Triangle Park, NC 27709 UL 19-1992—Lined Fire Hose and Hose Assemblies (“UL 19”) 181.320. UL 174-1989, as amended through June 23, 1994—Household Electric Storage Tank Heaters (“UL 174”) 182.320. UL 217-1993—Single and Multiple Station Smoke Detectors (“UL 217”) 181.450. UL 486A-1992—Wire Connectors and Soldering Lugs For Use With Copper Conductors (“UL 486A”) 183.340. UL 489-1995—Molded-Case Circuit Breakers and Circuit Breaker Enclosures (“UL 489”) 183.380. UL 595-1991—Marine Type Electric Lighting Fixtures (“UL 595”) 183.410. UL 710-1990, as amended through September 16, 1993—Exhaust Hoods For Commercial Cooking Equipment (“UL 710”) 181.425. UL 1058-1989, as amended through April 19, 1994—Halogenated Agent Extinguishing System Units (“UL 1058”) 181.410.
UL 1102-1992—Non integral Marine Fuel Tanks (“UL 1102”) 182.440. UL 1110-1988, as amended through May 16, 1994—Marine Combustible Gas Indicators (“UL 1110”) 182.480. UL 1111-1988—Marine Carburetor Flame Arresters (“UL 1111”) 182.415. UL 1113, Electrically Operated Pumps for Nonflammable Liquids, Marine, Third Edition (Sep. 4, 1997) (“UL 1113”) 182.520. UL 1453-1988, as amended through June 7, 1994—Electric Booster and Commercial Storage Tank Water Heaters (“UL 1453”) 182.320. UL 1570-1995—Fluorescent Lighting Fixtures (“UL 1570”) 183.410. UL 1571-1995—Incandescent Lighting Fixtures (“UL 1571”) 183.410. UL 1572-1995—High Intensity Discharge Lighting Fixtures (“UL 1572”) 183.410. UL 1573-1995—Stage and Studio Lighting Units (“UL 1573”) 183.410. UL 1574-1995—Track Lighting Systems (“UL 1574”) 183.410.
[USCG-2003-16630, 73 FR 65203, Oct. 31, 2008, as amended at USCG-2009-0702, 74 FR 49240, Sept. 25, 2009]

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Old 26-10-2013, 02:13   #198
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It's important to realise , that the ISO 13297 in Europe , in itself is not a regulation ,or " code" , however it is excepted that compliance with the ISO standards is " one" of the excepted ways of demonstrating compliance with the Recreational Craft Directive.

In Europe a dockside shore power system typically has several , ( at least three) RCDs in a feed to a boat ( and in the boat ) it's very unlikely that all will fail.

Arguing about RCD failure in isolation is ridiculous , because you really need to examine the whole system fault probability including all devices and appliances so connected to the AC system. Never mind the European insistence that 30mA is a sufficient low enough trip level to prevent fibrillation.

Secondly ISO 13297 does not specifically address IT installations ( which is what we are talking about in this thread ) which is what we are dealing with here. Hence in an IT based boat , essentially the code applies to the shore power to IT section , after that things get fuzzy.

Until we have a specific code ( like ABYC ) for IT installations, we have this conundrum.

What slightly annoys me , is that this thread is a specific technical thread arguing the technical merits of different systems. Instead we have people with a confused understanding of electrical circuitry arguing " code" and fault logic

I called it a conundrum for a reason.

I think nicks setup is very safe , I be yet to see a cogent argument that shows it isn't

Dave
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Old 26-10-2013, 03:12   #199
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I think Lloyd's post above nicely summarises where this thread is currently at!

It would be nice (but probably not possible) if we could now have a short summary of the acceptable scenarios.
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Old 26-10-2013, 03:30   #200
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Re: Isolating Transformers, The Earth wire connection conundrum

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Originally Posted by sailorchic34 View Post
Actually ISO is a standard organization like ABYC or ASTM or any one of 100's out there. It's recommendations, not actually an enforced code. Not in the US anyway. Nice to have but not the only game in town. Nor is it a "CODE" as in enforcement, permits, etc. The NEC is the electrical CODE of the land. But it stops at the dock.

Really Jedi's an engineer, You don't think he knows what he's doing???

Here is my issue from Nicks own post/schematic. Now it seems that we have earth/ground on the shore side isolated.

But his very own diagram shows "Ships Ground" now if this ships ground comes in contact with sea water, then we have an earths reference aboard, that not only includes the AC side, but the DC side as well.

So now we have an A Real Earth Potential, by passing everything that the IT is to protect against.

Now if we are relying on a 30mA RCD, and it only takes =5 mA to create a hazard then what.

Also note the Euro Directive, only requires a 10 mA GFCI in machine spaces and galleys/heads, as well as weather decks.

Which exceed our US required 5 mA.

Now factor in that if RCD's/GFCI's are tested/exercised they may be a fault. And this is both from US/EURO studies where the failure rate can be as high as 10 in 100.



Lloyd
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Old 26-10-2013, 03:45   #201
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Re: Isolating Transformers, The Earth wire connection conundrum

Now I want to post in deference to Nick/Jedi I think his schema works on paper, but not in the real world. I don't believe he would under-wite it.

I seriously doubt any credited College EE Professor, would allow his lab, or it's students to hook up an O-Scope to his system that wasn't properly earthed.

Lloyd
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Old 26-10-2013, 04:07   #202
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Re: Isolating Transformers, The Earth wire connection conundrum

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Lloyd honey, We're talking boats here and NFPA 70/NEC does not actually cover boats. Its a building code and oddly enough, a boat is not a building. Do try to keep up.
Actually any boat tied to a dock in the good old USA, will fall under that Direction.

I was on the Mayor's committee City of Seattle, for the current Covered Marina Fire Code

Quote:
But it will still work as a GFI on a 2 wire IT (under the right improbable conditions) on a boat, which is outside US building codes.

Plus there are many many older homes, where owners have installed GFI on 2 wire systems. Not code no. But it still protects and really that's the important part now, isn't it.
Until there is a fault in a wet basement.



Quote:
As an aside, steam power plants, the boilers and piping bits are not covered by building codes either. Just an odd titbit.
Here's an odd tidbit, I happen to manage a 4 mil BTU Steam Boiler in an old 1914 building....it's called a Brick Yard Boiler

Lloyd
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Old 26-10-2013, 04:49   #203
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Re: Isolating Transformers, The Earth wire connection conundrum

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Me I'm just this blonde chic who doesn't know anything and never spent a day in collage in my life. I have however, in the past sat and passed the professional engineers PE exam as well as a few others. Oh I'm not an EE, though I've read the books, and have had lovely discussions with and worked with some of the best in the country.

I do have some small ability with mechanical, plumbing, hydronics and utility plant design though, having been senior project engineer or lead engineer on a number of interesting projects in the $500 million to billion dollar price range, plus software design, Digital electronics and a handful of other boring things.

So your quite right that I know practically nothing and am just this Bimbo

So, whats your background.
Oh I don't know,

Whats your real background

Do you have a BS?...i think you do.

But are you BS'ing in Engineering.

Lloyd
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Old 26-10-2013, 05:20   #204
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Re: Isolating Transformers, The Earth wire connection conundrum

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Originally Posted by FlyingCloud1937 View Post
Here is my issue from Nicks own post/schematic. Now it seems that we have earth/ground on the shore side isolated.

But his very own diagram shows "Ships Ground" now if this ships ground comes in contact with sea water, then we have an earths reference aboard, that not only includes the AC side, but the DC side as well.

So now we have an A Real Earth Potential, by passing everything that the IT is to protect against.

Now if we are relying on a 30mA RCD, and it only takes =5 mA to create a hazard then what.

Also note the Euro Directive, only requires a 10 mA GFCI in machine spaces and galleys/heads, as well as weather decks.

Which exceed our US required 5 mA.

Now factor in that if RCD's/GFCI's are tested/exercised they may be a fault. And this is both from US/EURO studies where the failure rate can be as high as 10 in 100.



Lloyd
Respectfully, you have a complete misunderstanding of how shore-side ground connected to a boat works.

In addition, if you re-examine the diagram, there is no connection between shore ground and boat ground. So, it's not "by passing everything that the IT is to protect against."

Quote:
But it will still work as a GFI on a 2 wire IT (under the right improbable conditions) on a boat, which is outside US building codes.

Plus there are many many older homes, where owners have installed GFI on 2 wire systems. Not code no. But it still protects and really that's the important part now, isn't it.

Quote:
Originally Posted by FlyingCloud1937 View Post
Until there is a fault in a wet basement
Huh? Please explain how different return paths, like a wet basement, affect the operation of a GFI??

The fact is, as explained many times in previous posts, if >5ma current 'escapes' that circuit, no matter the return path, the GFI will open the circuit. The return path could be a wet basement, a wet towel, a wet dog, or anything other medium capable of carrying electrical current.
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Old 26-10-2013, 05:50   #205
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Re: Isolating Transformers, The Earth wire connection conundrum

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Respectfully, you have a complete misunderstanding of how shore-side ground connected to a boat works.

In addition, if you re-examine the diagram, there is no connection between shore ground and boat ground. So, it's not "by passing everything that the IT is to protect against."
Just so this doesn't get far out of hand.

Earth Ground is the potential.

Ships Ground, includes sea water, by definition, so I can only assume that Ships ground by the schematic posted would link Sea to Earth, ie: earths potential.








Quote:
Huh? Please explain how different return paths, like a wet basement, affect the operation of a GFI??
Chick,

said many older homes have used 2 wires Line/Neutral connected to three prong outlets and they saved lifes.

If someone in a wet basement plugged in a non-double insulated devise and expected to be protected from an appliance fault, they would be wrong.

That's precisely, why we have properly wired GFCI's and double insulated appliances.

Quote:
The fact is, as explained many times in previous posts, if >5ma current 'escapes' that circuit, no matter the return path, the GFI will open the circuit. The return path could be a wet basement, a wet towel, a wet dog, or anything other medium capable of carrying electrical current.
The fact remains that 10 in 100 RCD/GFCI's fail on testing.
Fact remains that if the said RCD/GFCI's are not exercised they may fail.
The fact is just like on boats, basements are a high probability to corrosion, that exaserbates the failure mode of said RCD/GFCI's.

So what was your point?
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Old 26-10-2013, 06:20   #206
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Re: Isolating Transformers, The Earth wire connection conundrum

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Now I want to post in deference to Nick/Jedi I think his schema works on paper, but not in the real world. I don't believe he would under-wite it.

I seriously doubt any credited College EE Professor, would allow his lab, or it's students to hook up an O-Scope to his system that wasn't properly earthed.

Lloyd
If the scope is powered by the IT its fine. Not to mention the number scopes that get the earth wire disconnected , because they are too stingy to buy a differential input or probe.

The problem with scopes and ITs is the wiring in the scope , not the IT.


Again its important to stop quoting building regs and approaches or arguing this from a "code" basis. i.e. its wrong, cause the codes says its wrong, yet the code may not in reality have no ( or limited) applicability in this case.

( for example, a amateur built boat in Europe does not have to comply with any regulations at all, nor is there a requirement that an owner maintain a boat in "CE" class, post purchase , with th exception of a commercial major craft modification) )


Lets example the floating IT issue technically , IN industrial/domestic environments its typical ( but not mandatory) to ensure the secondary AC is earth referenced ( Ground or GND is a different thing) . This ensure that common mode voltages or short circuit paths to ground do not get generated where multiple devices each with a IT, get interconnected ( This is a real issue for medical IT systems and is where there is a lot of code) .

However an IT based boat can be regarded as "one appliance" there is NO other source of AC power that is live at the same time, there are not parallel AC shore power feeds to the boat ( and this should never be allowed in a floating system).

Hence the common mode voltage or mixed floating and earth referenced does not apply.

Lets look at the equipotential earth bonding system so beloved by ABYC and extended to bonding the DC system and bonded underwater fittings. Funnily the code ( I believe) does not ensure that large items like engines and props are actually connected to the DC system, they could be isolated.

Furthermore, The ABYC equipotential takes no account of the issues of METAL boats ( which I believe S/V Jedi is) , and was one of the reasons why in Europe the DC AC link was left out. If you read the experts on boat electrical systems and especially aluminium, they will all recommend floating AC and DC systems with the hull electrically dead.

The issue with RCD failure rates is a somewhat red herring, firstly they are not in common use on boats in the US in the first place, Secondly in Europe there is likely to be several RCDs in the feeds. The tests done in France and Italy on RCD reliability , suggest that most failures are due to lack of testing and the buildup of dust and foreign bodies in RCDs ( which are often outside in consumer units) Regular use of the test button ( once a month or so) drops the failure rate to statistically insignificant rates. This is no different to circuit breaker failure issues, i.e. the mechanical gumming up of the mechanism leading to failure. Faults in the control circuits are extremely rare.


LET me be very clear, in a non IT environment, you DO need to run an earth wire throughout the boat, but I fully support the RCD methodology and no AC DC connection and no bonded fittings on GRP boats. This is why impressed current corrosion is not an issue in European 230VAC boats and why it is a problem in US ones.

However the fact remains, that there are significant safety benefits , in a IT based fully floating AC system, even though in a marine environment nothing is every truly floating and the secondary common mode voltage will in fact usually converge towards earth potential or a small way from it.

Removing earth from the equation, also removes what some people see as a unreliable RCD protection. as a whole boat RCD on the secondary , does little ( and yes maybe nothing). Its does little cause there are fault scenarios where it can act, but these are rare.

Postulating more elaborate faults , like dual live to case appliances faults is really ridiculous, any system including equipotential earth bonded systems have fault scenarios that can still harm you. Treating the boat like a single appliance fed by a single source of power, is exactly like double insulated tools. Furthermore there are several additional protections that can be added to floating systems to add protection to cover these scenarios.

It worth pointing out as I did at the very start with the diagrams, that the ABYC IT solution offers no additional safety to either onboard or swimmer based electrocution and in fact can circumvent the whole boat ELCI approach that has now been adopted because the ELCI is in the wrong place, in a ABYC compliant IT solution

Again a quick summary

Non IT = whole boat RCD+double pole breakers, plus equipotential earth wire ( AC/DC connections and bonding at your own "code" discretion)

IT senario A
RCD on shore lead to IT, double pole CB on secondary, optional RCD on secondary. Local earth established and connected to one live side of the IT to earth reference the IT. No through earth from shore power. ( a galvanic isolator is NOT needed in this case)

IT senario B

RCD on shore lead to IT, double pole CB on secondary, optional RCD on secondary, optional either insulation testing or earth lamps or socket RCDs, or even just using case connections and connecting them to protect against unknown high side faults. no swimmer electrocution, no earth path in fault currents, ideal for metal boats etc,


in both cases the removal of impressed shore power currents and the polarising nature of IT transformers are benefits in all cases. ( note running a earth wire from shore to appliances in an IT situation destroys the corrosion protection and results in polarisation benefits only.)

your takes you pick, there is no perfect system

PS as an aside , European works on 30mA RCD systems because under the reveleant ISO code, <5mA allows you to release the wire, whereas 30mA does not , but will not cause fibrillation to the extent of harm. Hence <30mA is seen as a lower limit for nuisance trips. ( lower limit and higher limit RCDs are also commonly available in any electrical supply store.) its a common trick for electricians to turn of a supply by triggering the RCD with their body ( do not try this at home )

dave
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Old 26-10-2013, 06:25   #207
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Re: Isolating Transformers, The Earth wire connection conundrum

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Now I want to post in deference to Nick/Jedi I think his schema works on paper, but not in the real world. I don't believe he would under-wite it.

I seriously doubt any credited College EE Professor, would allow his lab, or it's students to hook up an O-Scope to his system that wasn't properly earthed.

Lloyd
Lloyd,

This is done all the time in labs supervised by EE professors. Some measurements must be made with the 0-Scope floating above ground. It is perfectly safe to do so long as the safe voltage limits of the isolation transformer are not violated. The main issue here is that the "case ground" of the O-Scope is going to be "hot" by the potential of the reference plane of the measured system. If this plane can conduct to earth ground then a hazard exists if someone is connected to earth ground and touches the case of the O-Scope.

But we are not talking about anything like that here. The voltage between the boat's reference plane and earth is zero. Thus no similar hazard exists.

I wish we could stick to analyzing the circuits proposed rather than bringing up unrelated and dissimilar scenarios and standards.

Jedi's system works on paper and in the real world. I would doubt that anyone ever gets a shock from his boat. It would take multiple failures for that to happen making the probability into the tiniest fraction of a percent. Circuits don't know anything about standards or practices around the world. Let's leave that out of this discussion please.

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Old 26-10-2013, 06:41   #208
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Re: Isolating Transformers, The Earth wire connection conundrum

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Originally Posted by FlyingCloud1937 View Post
Just so this doesn't get far out of hand.

Earth Ground is the potential.

Ships Ground, includes sea water, by definition, so I can only assume that Ships ground by the schematic posted would link Sea to Earth, ie: earths potential.
Towards the effort to keep this from getting out of hand. Please don't assume, a ships ground includes sea water only when connected deliberately. Also, don't assume, but please review and understand that electric current flow requires a 'circuit', a complete path from the source and back to the source. Current will not flow through a broken circuit. In the drawing you referenced, the shore ground is broken at the IT. Hence, current cannot flow to/from the shore ground to/from the ship/earth ground therefore you have no circuit, and that is the galvanic corrosion/isolation feature of an IT.

And, more to the point of this discussion, the IT provides a completely new power source that isn't aware of ship/earth ground unless deliberately connected. Earth ground is not some magical entity, commercial power sources are connected to earth deliberately. Therefore earth ground can be a return path back to the commercial power source. This in no way implies that earth ground is a return path for a different power source like an IT. This whole discussion is about the merits of connecting that IT source to ship ground/earth ground/sea water ground.


Quote:
Originally Posted by FlyingCloud1937 View Post
Chick,

said many older homes have used 2 wires Line/Neutral connected to three prong outlets and they saved lifes.

If someone in a wet basement plugged in a non-double insulated devise and expected to be protected from an appliance fault, they would be wrong.

That's precisely, why we have properly wired GFCI's and double insulated appliances.

The fact remains that 10 in 100 RCD/GFCI's fail on testing.
Fact remains that if the said RCD/GFCI's are not exercised they may fail.
The fact is just like on boats, basements are a high probability to corrosion, that exaserbates the failure mode of said RCD/GFCI's.

So what was your point?
Ah, so now we're back to GFCI/RCD device failures. Good way to divert the discussion. Failure modes of GFCI's has been linked to power surges, not corrosion. Yes, they need be tested and replaced if necessary.

But, again, the point of this discussion is that without the ground return path to the source, with or without a GFCI, how is the circuit completed???
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Old 26-10-2013, 09:13   #209
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Re: Isolating Transformers, The Earth wire connection conundrum

Lloyd, I'm not going to talk "code" with you. It distracts from the question at hand. I've read way too many codes and standards in my lifetime, including a goodly part of the complete NFPA codes of which NFPA 70/ NEC is a small part, to ever want to do that now. Once again I agree completely with GBN, Jedi and Dotdum.

ABYC has a few requirements, AC ground tied to DC for one, that while I can see it working in a perfect world, actually creates potential ground loop issues which creates additional hazards, not less.

BTW, As I've said in the past, I've not spent even an hour in collage. I have zero (0) degrees in any subject. I do have a professional engineers license, which is not all that easy to get, even if you have a engineering degree.
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Old 26-10-2013, 10:42   #210
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Re: Isolating Transformers, The Earth wire connection conundrum

Well, For recreational boating, the below is a listing of federal code standards.

This from the USCG site btw.

The pertinent parts of the Code of Federal Regulations to Recreational Boating Safety are:

Vessel Numbering and Casualty and Accident Reporting: 33 CFR 173
State Numbering and Casualty Reporting Systems: 33 CFR 174
Manufacturer certification: 33 CFR 181.5-19
Identification of boats: 33 CFR 181.21
Display of capacity information: 33 CFR 183.21-27
Safe loading: 33 CFR 183.31-43
Safe powering: 33 CFR 183.51-53
Flotation: 33 CFR 183.101-335
Electrical systems: 33 CFR 183.401-460
Fuel systems: 33 CFR 183.501-590
Ventilation: 33 CFR 183.601-630
Start-in-gear protection: 33 CFR 183.701-715
Navigation lights: 33 CFR 183.801-810
Backfire flame control: 46 CFR 25.35

And for those that like to read a lot here is a link to GAO site where you can download your very own copy of the the second section of 33 CFR which includes recreational boating. 33 CFR 183.401-460 the electrical bits, start on page 1004 for the 2012 code,and page 1024 of the 2013 code of the second section. Enjoy!

FDsys - Browse Code of Federal Regulations (Annual Edition)

33CFR 401-460 does reference NEC/ NFPA70. But only in regard to conductor size in systems over 50 volts. Oddly enough GFI is not even listed, just basic over current protection. So its not quite perfect. But that my friends is the law of the land when it comes to Recreational boats. Commercial boats/ ships are covered in 46 CFR and that does reference ABYC.
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