ABYC/ISO AC-DC grounding requirements

[boatpoker]

Originally Posted by s/v Jedi

Nah, it’s just that you only managed to quote that part of my post

Whadidya expect

[s/v Jedi]

Originally Posted by boatpoker

For about 30 years my entire social circle has been built on people in the marine business, a number of small shops, a couple dozen of independent contractors and SAMS Accredited surveyors. I can't think of any of them that that don't have qualifications or certifications in their field. A pro continually invests in education. It's the cost of doing business.

I've been taking courses and building an expensive library of standards for almost 30 years. I consider it like a carpenter or mechanic buying tools for his trade.

There are about 250 marine surveyors in Ontario so I find it curious that I see the same 25-30 surveyors, marine electricians, mechanics, corrosion techs at every course I've taken. I think I'd prefer to hire someone from that group for my own boat.

There are likely five or six times the number of contractors and 10 times the number of surveyors that have no education or certification in the field of endeavour but call themselves "experts". None of these people are in my circle.

Oh I agree with that, most so called professionals deliver horrible work with horrible service. Not just electric. And yes, most of that is because they are completely ignorant in the field they work.

Other than for hauling out, pressure washing and sanding the bottom, we haven’t hired anyone for decades. Sometimes we tried but couldn’t find anyone qualified to do the job.

I am not a mechanical engineer, but I have to learn more and more for servicing diesels, acquiring specialist tools as I go just because professional mechanics can’t be bothered to offer their services and those who do aren’t qualified. They don’t even have the tools that I now have.

But that doesn’t mean there’s people here on the forum with knowledge about diesel engines that goes beyond that of any diesel mechanic. And when boat owners post pictures of engines that look like balls of rust, that doesn’t mean there’s owners who do all maintenance themselves and have immaculate engines!

Also, there is a big difference between techs and engineers. I guess techs dislike engineers and engineers roll their eyes too much when they engage on this forum, which is the friction often seen in these threads.
These courses and expensive documents are meant for techs; they provide a solid basis that enables them to deliver safe installations. The problem is that often these courses and documents teach outdated methods, lag behind new products (sometimes by decades!) and have a conflict of interest with boat owners because the courses and documents are created by the industry rather than owners. Owners may want the best product rather than the one you are selling etc.

[Lake-Effect]

Originally Posted by s/v Jedi

To all who advocate that “ground” is something tied to earth: explain “chassis ground”.

God what a p1ssing match...

"Ground" and "earth" came into early common usage because of radios, which did need a connection to The Actual Earth for optimum performance. Many radios still do, though it's also possible to fake it through the use of a constructed or de-facto counterpoise. or balanced antennae. In other circuits, ground is used interchangeably with "common". Though for optimum management of shielding and interference,as well as for safety when mixed with AC power, a connection to The Actual Earth is often used.

Anyway, there's your explanation.

Is the -DC supply connected to the metal chassis or case of most marine electronics? Yes it is. Do DC-powered marine electronics REQUIRE some connection to seawater in order to function? No, they do not.

Homework:
1) If only the positive side of DC power is fused, and there is a risk that a positive conductor could touch boat metal, should that metal be bonded to the negative DC so that DC protection devices will trip?

2) If there's a chance that shorepower 120vAC could come into contact with boat metal and/or 12v common (particularly when there's no isolation transformer), should boat metal and the 12v common be bonded - with galvanic isolation - to the AC ground, so that AC protective devices (breaker, RCD, GFCI) will operate?

I have no fear of jedis and GBNs having unsafely wired boats. I worry about the more common and less knowledgeable owners of 4KSBs without isolation transformers reading threads like these and coming away confused, or persuaded not to bond their in-water metal, which is exactly half the ingredients needed for creating an ESD situation.

[Matt Johnson]

Annual ABYC membership for an individual is $190. Towards the end of my membership I bought the standards book for 21-22 for around $100.

ABYC's website also has access to the ISO library. It wasn't a free add-on, but it was pretty inexpensive for a years access. It seems like it was an additional $200 for members (it shows $809 for non-members currently)

[team karst]

Ground doesn't mean anything in particular. It sorta means a "local" reference point that is not supposed to kill you if you contact it.

But, that word is carried into PCB design, where you might have a bunch of truly isolated ground references. So, back to it doesn't mean anything in particular.

I suspect a lot of folks have heartburn with this "isolated ground" concept.

[s/v Jedi]

Originally Posted by Lake-Effect

God what a p1ssing match...

"Ground" and "earth" came into early common usage because of radios, which did need a connection to The Actual Earth for optimum performance. Many radios still do, though it's also possible to fake it through the use of a constructed or de-facto counterpoise. or balanced antennae. In other circuits, ground is used interchangeably with "common". Though for optimum management of shielding and interference,as well as for safety when mixed with AC power, a connection to The Actual Earth is often used.

Anyway, there's your explanation.

Is the -DC supply connected to the metal chassis or case of most marine electronics? Yes it is. Do DC-powered marine electronics REQUIRE some connection to seawater in order to function? No, they do not.

Homework:
1) If only the positive side of DC power is fused, and there is a risk that a positive conductor could touch boat metal, should that metal be bonded to the negative DC so that DC protection devices will trip?

2) If there's a chance that shorepower 120vAC could come into contact with boat metal and/or 12v common (particularly when there's no isolation transformer), should boat metal and the 12v common be bonded - with galvanic isolation - to the AC ground, so that AC protective devices (breaker, RCD, GFCI) will operate?

I have no fear of jedis and GBNs having unsafely wired boats. I worry about the more common and less knowledgeable owners of 4KSBs without isolation transformers reading threads like these and coming away confused, or persuaded not to bond their in-water metal, which is exactly half the ingredients needed for creating an ESD situation.

Actually, ground was first being used for telegraph… as the return path so that only 1 conductor was needed.

Homework #1. So a typical boat 12V DC circuits have 1-pole breakers on only the positive conductor and the negative conductor is not grounded nor bonded. When the positive touches a metal that is not bonded either and one wants this to trigger a breaker to flip… yes duh then you are forced to connect that metal to DC negative.

Similarly, when you want the breaker to flip when DC positive touches the metal frame of your glasses, then you need to walk around with a wire attached to your glasses at all times.

The question to ask is why; why do you want to touch metal with DC positive and why do you want to see the breaker to flip when you do that?

Homework #2. Same thing. With dangerous voltage from shore power how can one face the risk of it touching your metal wrist watch, not even thinking of your jeans zipper!

For both cases, here is the eye opener from an engineering perspective: instead of dealing with the risk of shore power touching your galley stove, how about eliminating that risk?! Why persist in protective measures when the risk that they protect against can be eliminated?!

It’s like burning a wood fire on the wooden floor of the attic because you have a sprinkler system. Or installing a sprinkler system in the attic after removing all combustion sources first.

[Lake-Effect]

Originally Posted by s/v Jedi

For both cases, here is the eye opener from an engineering perspective: instead of dealing with the risk of shore power touching your galley stove, how about eliminating that risk?! Why persist in protective measures when the risk that they protect against can be eliminated?!

Well, as I mentioned, you jedis have this stuff nailed. For the other 99.9% of boaters...

[team karst]

Most standards allow much looser law when dealing with voltages below a certain value. Wet area makes a diff.
If 12V pos hits a isolated piece of metal, so what it doesnt trip a OCP. Safer to make an arc and blow a fuse??

[Dieseldude]

Originally Posted by boatpoker

For about 30 years my entire social circle has been built on people in the marine business, a number of small shops, a couple dozen of independent contractors and SAMS Accredited surveyors. I can't think of any of them that that don't have qualifications or certifications in their field. A pro continually invests in education. It's the cost of doing business.

I've been taking courses and building an expensive library of standards for almost 30 years. I consider it like a carpenter or mechanic buying tools for his trade.

There are about 250 marine surveyors in Ontario so I find it curious that I see the same 25-30 surveyors, marine electricians, mechanics, corrosion techs at every course I've taken. I think I'd prefer to hire someone from that group for my own boat.

There are likely five or six times the number of contractors and 10 times the number of surveyors that have no education or certification in the field of endeavour but call themselves "experts". None of these people are in my circle.

Good for those people who upgrade. Not disputing he value of knowledge and credentials. But when just having a copy of the latest standards costs thousand$, it tends to favor the established larger operators. Smaller operators and new entrants get forced out. The smaller pool makes it bad for clients who have fewer choices.

[Dieseldude]

Originally Posted by team karst

Most standards allow much looser law when dealing with voltages below a certain value. Wet area makes a diff.
If 12V pos hits a isolated piece of metal, so what it doesnt trip a OCP. Safer to make an arc and blow a fuse??

Isolated systems have their benefit. Shorts to "ground" become less common. I always doubted the building standard for the AC wiring that ties the "neutral" to the third wire "ground". If the "neutral" were not "grounded", the "neutral" and the "hot" would be the two sides of a balanced transmission line. And keeping it this way has safety advantages. A damp floor can become one electrode of a death trap with the "grounded" "neutral" arrangement.

[Lake-Effect]

Originally Posted by team karst

If 12V pos hits a isolated piece of metal, so what it doesnt trip a OCP. Safer to make an arc and blow a fuse??

Well, it's about where and when you want to have an arc... do you want it at the fault when the protective device blows, or later when you accidently bridge a 12v energized part of the boat with an electronic device's chassis... or no arc but some smoke when there's a thin wire bridge that takes just enough current to overheat, without popping the OCP?

Hey, anyone mention static or electrostatic fields in the vicinity of t-storms, and unbonded metal?

[hjohnson]

Originally Posted by Dieseldude

Isolated systems have their benefit. Shorts to "ground" become less common. I always doubted the building standard for the AC wiring that ties the "neutral" to the third wire "ground". If the "neutral" were not "grounded", the "neutral" and the "hot" would be the two sides of a balanced transmission line. And keeping it this way has safety advantages. A damp floor can become one electrode of a death trap with the "grounded" "neutral" arrangement.

The problem with balanced/isolated power is that (baring somewhat sophisticated test equipment) while your first fault is free, your second one is deadly. You can have a silent fault somewhere in your system and never know about it until it happens a second time. This is why, largely, AC systems have one leg tied to earth. This was especially important when, in the past, it was relatively easy to come into contact with one of the conductors (think screw base lamp sockets). It’s also why in situations where isolated/balanced power is permitted (think operating rooms) there is increased ongoing inspection and testing requirements.

[Dieseldude]

Originally Posted by team karst

Ground doesn't mean anything in particular. It sorta means a "local" reference point that is not supposed to kill you if you contact it.

But, that word is carried into PCB design, where you might have a bunch of truly isolated ground references. So, back to it doesn't mean anything in particular.

I suspect a lot of folks have heartburn with this "isolated ground" concept.

Chassis ground simply means that for an electrical device that has a metal housing, the negative terminal of the power supply is connected to the housing. This offers the convenience and cost savings of single wire distribution. There is the safety advantage that if the positive of the supply touches the metal chassis, it will immediately trip the breaker or blow the fuse. So the hazard of a "live" chassis is eliminated. Also, any induced interference that might be intercepted by the chassis gets shorted to the negative terminal, and in theory is eliminated.



Systems that do not connect the negative terminal of the supply to the metal housing are called isolated systems. They use two wires for distribution, which are isolated from the chassis.

[hjohnson]

So question to the wise ones on this thread: As I talked about in my own thread, I’m doing a significant upgrade to the electrical system on my E27. Part of this is bringing the electrical system into compliance with modern standards (where it makes sense). As part if this, I’m installing a 2000w victron inverter/charger. There is a bonding screw on the chassis that I will be bonding to my DC negative. The question is: do I base the bonding wire size on my AC conductors (10AWG, so a 12 AWG bonding wire), or on the DC conductor (2/0 conductors so 0AWG bonding).

[Dieseldude]

Originally Posted by hjohnson

The problem with balanced/isolated power is that (baring somewhat sophisticated test equipment) while your first fault is free, your second one is deadly. You can have a silent fault somewhere in your system and never know about it until it happens a second time. This is why, largely, AC systems have one leg tied to earth. This was especially important when, in the past, it was relatively easy to come into contact with one of the conductors (think screw base lamp sockets). It’s also why in situations where isolated/balanced power is permitted (think operating rooms) there is increased ongoing inspection and testing requirements.

Isolated versus "earthed" distribution systems have been debated since the "earthed" standard began. Each has its advantages and each has its faults. As stated earlier, in an earthed system, a damp floor or a steel deck in combination with conductive shoe soles becomes the negative electrode of a death trap, should a person touch the "hot" side. Certainly not an advantage. Commercial vessels, which are generally constructed of steel, do not have "earthed" "neutrals". Perhaps this is because of the possibility of a steel deck or bulkhead becoming one side of an electrocution hazard. And also there is the problem of "ground paths" to shore power.