passage makers canaries in coal mines article...

I dont normally give a hoot about an article but this one has me baffled.
https://www.passagemaker.com/technical/-through-hull-fittings-and-canaries-in-coal-mines

Read it (lots of good stuff) and consider the following statement,

To minimize this risk, boatbuilders and boatyards provide an alternative path by connecting the green wire to all of your seacocks and through-hulls. If the shorepower safety circuit is compromised, the current has an alternative path to the water via the through-hulls. The good electrical connection through the green bonding wire provides a preferred path for the current, favoring the low-resistance electrical circuit to the meager choice your body offers (swimmers are still at risk). This safety circuit works so well you probably won’t even know that you have a killer aboard, unless your through-hulls tell you.

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I find that almost impossible to believe. There is no way they (boatbuilders and boatyards) bond thru hulls to prevent onboard electrocution. I have never read anything other than "tying all metals to the same electrical potential is to prevent galvanic corrosion".

Add to that, the statement flies in the face of galvanic isolators. They intentionally disrupt the "shorepower safety circuit" by adding diodes in the path to prevent current from flowing.

Any comments?

The galvanic isolator prevents low voltage DC current from traveling boat to boat on the marina ground wire, so that they don't all form one big battery. It doesn't stop AC in the event of a on board short to ground. However, if that ground connection isn't good, current would go to ground through the hull fittings. All this assumes the AC appliance is properly connected to ship's ground and the bonding system.

mike66 said:

. All this assumes the AC appliance is properly connected to ship's ground and the bonding system.

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Mike, are you saying the AC ground systems should be connected to ship's green wire bonding system?

We just departed from a marina on the Great Lakes that has a newly installed electrical system, which monitors boats that hook up to the power posts at the slips. The marina attendant commented that a surprising number of boats are rejected by the monitoring system, which prohibits power from flowing to such boats. A big red light illuminates on the main power distribution box when a boat with a faulty system is detected. I'm not smart enough in the electrical department to know how it knows...but it's a great safety feature, particularly at fresh water sites. The docks also have large "No Swimming, Electrocution Hazard" signs prominently posted. Many of the older marinas need to play catch up.

No, the appliances and other AC devices have their cases grounded to ship's ground, which is also the point that the dc ground and bonding wires come together.

I don't think any of you are actually addressing the original question asked.

[edit: Mike just did as I was posting]

well sort of, but not quite yet.

My question is how can the author state that the ac grounds are tied to the thru hulls in order to provide an alternate current path to the water so you dont get electrocuted.

Surely that cant be true.

Well, I would not want to grab the handle of a hot appliance while on the boat.

Like mike66 pointed out...

The green grounds on appliances wind up connected to the bonding system dumping hot appliance currents directly to the water via metal through hulls, ground plates, zincs and prop shaft.

Rather than through you to some alternative gounding path.

All appliance greens come together. All DC negatives come together and are connected to the engine block usually. The bonding system connects all metal and is also often commected to the block. These 3 systems are also tied together so there is a path or multiple paths to ground. ABYC suggests the best interconnection points, but often these systems are tied together at several points...not the best but evolve that way anoard.

Of course most of the time you arent grounded, but for the times you might be.

Article makes sense to me.

Rufus said:

We just departed from a marina on the Great Lakes that has a newly installed electrical system, which monitors boats that hook up to the power posts at the slips. The marina attendant commented that a surprising number of boats are rejected by the monitoring system, which prohibits power from flowing to such boats. A big red light illuminates on the main power distribution box when a boat with a faulty system is detected. I'm not smart enough in the electrical department to know how it knows...but it's a great safety feature, particularly at fresh water sites. The docks also have large "No Swimming, Electrocution Hazard" signs prominently posted. Many of the older marinas need to play catch up.

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The overly simple version....

The big red light just means all the current going to the boats via the hot wire(s) isnt coming back through the neutral like it is supposed to. It might be entering the water and is a hazard to swimmers or people on boats.

Basically a GFCI on a larger scale and usually trips at a few milliamps higher.

Thanks. From the description given by the marina guy it seemed each power post was monitored individually and the power wouldn't flow to that particular post when an offending boat plugged in. Probably more likely it's one overall system monitor. That said it would seem difficult to detect such a small leak (percentage wise) within the overall power grid. Good that they're locking out the bad boats in either case. And I got a courtesy check on the boat. Was planning to have it done by an electrician after reading that thread about those kids.

Rufus said:

Thanks. From the description given by the marina guy it seemed each power post was monitored individually and the power wouldn't flow to that particular post when an offending boat plugged in. Probably more likely it's one overall system monitor. That said it would seem difficult to detect such a small leak (percentage wise) within the overall power grid. Good that they're locking out the bad boats in either case. And I got a courtesy check on the boat. Was planning to have it done by an electrician after reading that thread about those kids.

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It sounds like they just installed ECL breakers at all the posts. They trip when there is more than a 30ma imbalance between the two power conductors. "Monitoring" makes it sounds like there is central control station with 24x7 monitoring of every electron. That's very, very unlikely.

Could be, but something turns on the large red light at the main distribution box...perhaps a small feedback wire from each pedestal?

Rufus said:

Could be, but something turns on the large red light at the main distribution box...perhaps a small feedback wire from each pedestal?

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Yes, that would make sense. Was there a single indicator light for any fault, or were there individual lights, one of each outlet? Sounds like a nice system, especially considering how often things probably trip and they transition ECL breakers.

Don't know if it's only for ground fault. There's one big green light and one big red light prominently displayed at central distribution box, so any passer by can alert the marina staff. Nothing at the pedestals. I believe this new system is the "current" standard for Michigan, at least. Might be for across the Lakes....should be. Going to be quite a few surprised and PO'd boaters when they arrive and can't get shore power.. If anchorage is available, I'll bet boats with dirty systems will be on the hook just outside the marina with gensets running. Or gensets running in slips after the staff leaves for the night.

Sounds like some one did not pay for a technical editor.