AC Grounding

[bill good]

G'day All,

back on the 26th June I raised the question of electrolysis which came up as the result of trying to get to the bottom of the "best practice" to this question & as yet still do not have the answer!! I will beaver on with the AC circuits over the next weeks.

Regards Bill Goodward

[GordMay]

Originally Posted by donradcliffe

Well, I know a lot more about the subject now than when I recommended Casey's article...

I'm certain you’ve learned a lot, over the past 3 days; but I’m less certain that your new-found knowledge trumps that of the ABYC and other experts.

I believe that you’ve learned the wrong lesson(s) from the Hot Marina story; just as you’ve misunderstood the general purpose of a Uffer ground, and the specific requirement for it in your garage.

I think Mark Twain had a couple of apropos remarks:
"What gets us into trouble is not what we don't know. It's what we know for sure, that just ain't so."
“Between believing a thing and thinking you know is only a small step and quickly taken.
"Faith is believing what you know ain't so."

[donradcliffe]

Gord, open your mind to the facts, instead of shooting the messenger.

Here is what I just sent off to the ABYC:

This is an open letter to the ABYC, asking for reconsideration of their Standard E-11, specifically 11.5.4.7.1, or connecting the AC ground to the DC negative bus or engine negative terminal.

In studying the electrocutions and near fatalities in the past 25 years as given in http://www.qualitymarineservices.net/Electric%20Shock%20Drowning%20Incident%20List.doc
it has become apparent to me that this connection has caused as many fatalities as it has avoided. The referenced document contains case studies of more than 40 fatalities, and lists the proximate causes where available. In the following cases, it appears that the ABYC standard 11.4.5.7.1 was followed and the existence of a connection from the AC system ground to the DC system directly contributed to the incidents:

Case 4, 5, 10, 17, 26, and Near Miss Case 5, 7, 19.

On the other hand it appears that the ABYC standard 11.5.4.7.1 was not followed, and the lack of a connection from the AC ground to the DC negative contributed to the following incidents:

Case 8, 20, 25, 44, and Near Miss Case 4.

It is my understanding that 11.5.4.7.1 primarily exists to protect against faults in onboard battery chargers by forcing a trip of the shoreside current protection device. However, the case data shows that (1), the shore ground connection is not reliable, and (2) the existence of the 11.5.4.7.1 connection creates a very dangerous situation for people in the water near the boat when the AC ground is energized as a result of faults in the AC system.

In addition to the documented electrocution problems, the 11.5.4.7.1 connection exposes boats to electrolysis damage which costs considerable money for mitigation and repair.

I light of the above mentioned problems, I urge you to reconsider the 11.5.4.7.1 connection as soon as possible. It is my belief that the preferred alternative would be RCD protection on all shoreside power circuits, but another less-lethal solution would be to isolate the AC ground from the DC bus, but install a fault-warning indicator which would be activated by a minimum potential between them, similar to the reverse polarity indicators.

[GordMay]

I applaud you for attempting to understand and make sense of a difficult issue, and your desire to see improved safety standards. I certainly wouldn’t want to shoot the messenger, in this case.

Notwithstanding, I believe your message is seriously erroneous, and dangerous. During over 40 years in the electrical industry, I’ve never heard/read a convincing argument to dis-bond the AC safety ground (one of your several recommendations).

I, and many others, have no doubt that there are many safety issues that are inadequately covered in the “Standards”.

I look forward to hearing any response you may get from ABYC, to your opinions and recommendations - specifically regarding AC ground bonding.

I doubt that the authors of your linked articles would endorse your interpretation of their articles, nor do their recommendations seem (to me) to entirely match yours.
In that regard, you might also contact:
JIM SHAFER, Harbor Marine Consultants, Inc.
Email: kp2r@bellsouth.net
Tel: 772-284-0855.
And
CAPT. DAVID RIFKIN , Quality Marine Services
Email: qualitymarinesvcs@comcast.net
Tel: 904-379-1101

[s/v Jedi]

The idea in the EU is that an approved battery charger gets it safety ground from the AC feed and any malfunction in the charger is contained within the charger. Just like when you charge batteries at home or in the car/RV... you don't connect a wire between the battery negative and AC ground.

Also: what is the "boat grounding system" ? What about an isolated negative? On a steel boat, this is all clear and simple but does a Cal 28 have a DC grounding system? Just a negative bus bar is not a grounding system.

And another one: what if the charger has an internal connection between AC ground and DC negative terminals?

Lots of if's and they all matter from an electric engineering point of view.

Safest installation is:

1. AC grounding system that interconnects every metal part of the boat plus some grounding plates under water like a dynaplate (but when this doubles as a lightning bonding system, the dynaplates are not good enough). There should be 1 (and only one) central grounding point in this system for making connections with other systems. There should be no loops in this system.

2. An AC isolation transformer that separates shore-ground from this boat's ground. The only parts that are electrically connected to shore power are: the inlet connector, the double pole breaker and the isolation transformer. There should be no electrical connection (check with ohm meter with AC shore-power disconnected) between any of the pins of the shore-power cord and the AC buses at the distribution panel.

3. A connection between the grounding system and the main DC negative bus bar.

4. Zincs on underwater metal parts (which are all connected to the grounding system).

GFCI devices aren't even needed (nor required I think) with this system because it's safe by design.

but if this is feasible on a 28' boat?...

cheers,
Nick.

[scotte]

FWIW, Xantrex has a decent article on this: http://www.xantrex.com/web/id/268/DocServe.aspx

[CharlieJ]

.Just to show that the ABYC experts and their black and white safety prescriptions aren't always 100% right, here is a tragedy where two people would be alive today if the DC and AC grounds were NOT connected

donradcliffe-Loose the us vs. them attitude and negative characterization of the members of the ABYC project technical committees and your position will be better received. There are very, very few "black and white" answers to any difficult issue in the real world...there are, however, many shades of gray.

Regarding RCDs in the USA: ABYC adopted the use of these in the 2008/2009 standards (which become effective July, 2009) where they are called Equipment Leakage Circuit Interrupters and are defined as:

11.4.10 Equipment Leakage Circuit Interrupters (ELCI) - A residual current device which detects equipment ground fault leakage current and disconnects all ungrounded (110 V & 240V) and grounded (110 V neutral) current carrying conductors from the supply source at a preset trip threshold.

11.11 GROUND FAULT PROTECTION – AC SYSTEMS
11.11.1 An Equipment Leakage Circuit Interrupter (ELCI) shall be installed with or in addition to the main shore power disconnect circuit breaker(s) or at the additional overcurrent protection as required by E-11.10.2.8.3 whichever is closer to the shore power connection.
11.11.1.1 This device shall meet the requirements of UL 1053 Standard for Safety for Ground-Fault Sensing and Relaying Equipment and the requirements of UL 943 Ground Fault Circuit Interrupters with the exception of trip level and trip time. Trip level shall be a maximum of 30mA. The trip time shall be a maximum of 100ms.

NOTE: Trip levels of less than 30ma and times of less than 100ms may result in nuisance trips in certain environments.

11.11.1.2 The ELCI shall be readily accessible.

The standard requiring ELCIs on all new construction boats was to go into effect in July, 2009; however, the circuit breaker and panel board manufacturers were having difficulty developing cost effective equipment for the boat owner and asked for an extension to the deadline to July, 2010. The extension request was granted.

As a point of reference, I am currently doing a complete electrical refit on a USA built vessel in a foreign country and attempted to source a 230VAC/32 amp ELCI. A large and reputable panel board manufacture in the US quoted me $1,600US for a 230VAC/single phase/32 amp/30 mA trip/100 msec ELCI (RCD). I was able to get quotes from manufactures in Europe for $300US to $600US but not for a marine rated unit. I am continuing my research because the wide variation in pricing concerns me.

[svtrio]

charlie,

I don't know the price, but this RCD is for marine applications:

Residual Current Rocker Circuit Breaker (RCBO–ELCI, RCBO–GFCI) - Blue Sea Systems

Roger

[goboatingnow]

RCD in boats in Europe are cheap as chips, widely available and use standard domestic rated units, siemens make a whole range of them. They have been standard in boats , in homes and on marina supply posts for years. Its amusing to see ABYC belatedly specifiying them!

The AC DC connection is actually a red herring, In a steel boat you should beusing a isolation transformer and isolated dc returns anyway and in a GRP boat it has little relevance. Use RCD's instead.

BTW

This good article is an eye opener in regard to earthing. It shows that some countries are not able to maintain an effective segregation between AC and DC electrical circuits

Calders article is often referenced in realtion to this his article does not claim countries have such trouble.

[donradcliffe]

I did get a nice response back from the ABYC within hours, which pointed out that they have addressed the issue with their new requirments for an ELCI ( like a RCD) to be required on all boats with shore power by July 31, 2010. They also invited me to comment on the new E-11 standard which is scheduled for review in 2010.

The electrocution data base shows as many people were killed by improper dock wiring as by improper boat wiring, and it would seem to me that the best place to put the RCD would be on the dock. This would not only protect against faults on the boats, but also cases like power cords falling in the water. Jim Shafer, David Rifkin are the creators of the data base, and make a product called Marina Guard, which is a ground fault monitor for marinas (like an RCD but without the trip). Their Marina Guard allows marinas to detect and trace down existing boat and dock wiring problems, but avoid the trips (they envision an installation of both the RCD and the monitor, because of reliablilty problems with the RCD).

The ABYC pointed out that the requirement for the ELCI on the boat is because they do not have influence on the shore based side, but I see a future where there will be an NEC required RCD on the dock duplicating the protection (and cost and spurious trip potential) of the ABYC RCD on your boat.

So where does this lead to the original question of connecting your AC and DC grounds on the boat? The answer is that the experts disagree. In the rest of the world, ISO 13297 4.2 says if you have an RCD, the connection is optional, which probably means that some experts wanted to keep the connection, and some wanted to get rid of it. The ABYC apparently wants you to install an RCD and to keep the connection, but there will probably be heated arguments both ways in 2011. As my final note on the subject, on the commercial side, here is a quote from an advisor to Alaskan fishing boats:

"Although it may contribute to electrolytic
corrosion in the heat exchanger
and other parts, the AC
neutral conductor should be grounded
to the bonding system. To not do so
creates the possibility of dangerous
electrical shock. However, certain
classification societies prohibit
grounding, so if your boat is built to
classification standards, check with

the society to ensure compliance."

[s/v Jedi]

Don,

That quote again refers to the boats bonding system. Most yachts don't have one and I'm pretty sure a Cal28 doesn't have it. You can't connect what you don't have.

ciao!
Nick.

[chala]

Originally Posted by CharlieJ

Chala-And your comment is exactly why there is a requirement to tie the vessel ground and the safety ground together. If AC makes its way into the DC system, AND there is a circuit back to the safety ground, an over current protection device will trip.

An over current protection device will trip if the current exceeds the rating of the over current protection device in most case many Amps. Only few mA are required to electrocute someone. A DC installation could be live and not necessarily trip the over current protection device. Also depending on the fault current loop, during the time an over current protection device take to trip if it trip, the engine could be at a lethal potential level. Electricians, for simple work, prefer to work with insulated shoes, not earthed shoes, prefer insulated ladder to earthed ladder and should when operating earthed switchgear lightly touch with the back of their hand the earthed switchgear to feel for an undesirable voltage before grabbing the handle and, doing so, will make them to live longer.
Working on someone boat engine? I will make sure that the engine is not connected to the AC supply knowing that in many case the marina power supply outlet may have been interfered by the present or previous boating visitors.
Some Standards already require 6 months mandatory checking of RCD operation with resulting cost to the Marina operator. More interfering by boating visitors and more regulation will increase cost to Marina operator with subsequent increase in rental cost.

Originally Posted by CharlieJ

Regarding RCDs: RCDs are sophisticated and somewhat robust GFCIs with a 30 mA/100 mS tripping spec. They trip when the current entering the vessel on the Line exeeds the current leaving the vessel on the Neutral exceeds 100 mA. It provides whole boat protection from lethal levels of leakage current.

An 30mA RCD previously know as ELCB (earth leakage circuit breaker) will disconnect when it detect in the circuit that it is protecting a leakage to earth greater than 30mA. 100mA a think is another now famous Obama Bin Laden?

Originally Posted by donradcliffe

to be required on all boats with shore power by July 31, 2010.

2010 not bad if they get it right.
Some 60 years ago some European nations decided that 220V AC was more efficient than 110V AC (less cost of material, less heat produced) and converted to 220V AC. Now that Global warming is the talk it is to wonder how long it will take for countries still using 110V AC to convert to 220/240V AC?

[CharlieJ]

Chala-

and should when operating earthed switchgear lightly touch with the back of their hand the earthed switchgear to feel for an undesirable voltage before grabbing the handle and, doing so, will make them to live longer.

This practice is foolish and stupid, to say the least; and no, they will not live long at all!

Some Standards already require 6 months mandatory checking of RCD operation with resulting cost to the Marina operator. More interfering by boating visitors and more regulation will increase cost to Marina operator with subsequent increase in rental cost.

So what is your point? Allow substandard electrical systems in the marina so an unsuspecting boat owner can plug in and cause damage to his boat or worse??

100mA a think is another now famous Obama Bin Laden?

Please translate...I do not understand. By the way; the specification is 30 ma/100 milliseconds.

2010 not bad if they get it right.

They is we, folks!

Charlie

[chala]

Originally Posted by CharlieJ

Chala-

This practice is foolish and stupid, to say the least; and no, they will not live long at all!

Charlie

If you ever get a shock from an earthed apparatus you will understand but by then it may be to late.

[GordMay]

It’s quite common for electricians to disconnect the source of supply, test the wires, and then make first contact by brushing the bare wire with the back of the hand/finger. This is a case of belt, suspenders, and “another belt” safety protocal, intended to ensure that we’re not “grabbed” by the conductor (muscle contraction when energised) should it be live, even though ...
The tentative first touch is not a test for live conductors, it’s only added insurance.
I’ve seen many cases where I, or others, “knew” a circuit was de-energised, when it actually wasn’t.
In one case, where a circuit from one source was pulled through a pull box (supposedly) dedicated to another separate source, I was nearly killed.