Electrolysis Bonding Question

[GordMay]

Originally Posted by allene222

You absolutely do not want the marina AC ground and the boat DC ground connected for small currents. Just a little terminology first...
Allen

Allen: Are you confusing the AC "safety" Ground (green), with the Grounded AC Neutral Conductor (white)?
If not, I'm confused (entirely likely, these days).

[allene222]

Originally Posted by GordMay

Allen: Are you confusing the AC "safety" Ground (green), with the Grounded AC Neutral Conductor (white)?
If not, I'm confused (entirely likely, these days).

I am not confusing neutral,which is one of the two AC circuit wires, with green ground, which only carries current if a fault has occurred. Let me clarify.

You have boat DC ground and boat AC ground. These should be connected together under most circumstances. You also have marina AC ground, the green wire on the power cord from the dock. These should not be connected directly together but rather most likely through a galvanic isolator.

If you can afford an isolation transformer, it will completely isolate the marina AC ground and the boat AC ground. This is used instead of the galvanic isolator and are superior.

I think the confusion is that there are 3 grounds, not two. There are 2 AC grounds, both green wires.

Defender.com Search Results: galvanic isolators
Defender.com Search Results: isolation transformer

Isolation transformers are in the $1,000 range, galvanic isolators in the $200 range.

Allen

[s/v Jedi]

Actually, an isolation transformer galvanically isolates your boat from all shore power conductors.. ground, neutral and hot(s). It not only provides protection against galvanic corrosion, but is also a safety device unmatched by anything else.

cheers,
Nick.

[allene222]

Originally Posted by s/v Jedi

Actually, an isolation transformer galvanically isolates your boat from all shore power conductors.. ground, neutral and hot(s). It not only provides protection against galvanic corrosion, but is also a safety device unmatched by anything else.

cheers,
Nick.

Good point!

A isolation transformer removes you from the need to have the dock ground connected correctly so I would agree that it improves the safety it should be pointed out that the AC out of an isolation transformer can still kill you. The idea of neutral and ground in AC is worth a comment. AC comes off a power distribution transformer with two leads. One of them is connected to ground at a single point and we call it neutral. These two leads still carry the AC current it is just that one of them is eventually tied to ground. With an isolation transformer, you establish this safety ground connection on your boat so (assuming everything is working) you know it is good. It also stands a lot better chance of being good than a galvanic isolator stands of being good. I should probably add so that there is no confusion that you never want to connect dock neutral to boat ground. What a GFI does is insure that all the current going out the hot comes back the neutral and none is going through some poor swimmer instead.

Allen

[foggysail]

You obviously do not understand the mechanics of galvanic corrosion and seem to not understand why the grounding conductor in AC circuits should be grounded, not debated. There is nothing more for me to say on this topic.

Foggy

[allene222]

Foggy,

Wow, what brought that on? I understand perfectly.

I must say that your statement that "AC circuits should be grounded" leaves open the question what part of an AC circuit should be grounded to what ground. Let me just repeat what I have said in case someone else is confused. If your boat has an AC system, then the boat AC Ground (green wire on the boat) needs to be grounded to your DC system ground as there are just too many ways things can go wrong if it isn't and people can die. This is for safety reasons and is extremely important. You then need to establish a connection for that green boat AC ground. If you tie that to marina ground, the green wire in your power cord to the dock box, you are putting your boat and every other boat in the marina that has a similar mis-wiring at risk for serious corrosion as I explained in my article. The boat AC ground needs to be connected but galvanically isolated from marina AC Ground. There are two ways to do that, a galvanic isolator and an isolation transformer.

Is that clear now?

As this is a new thread, the article I am referring to is this one:
Bonding and Corrosion

Allen

[s/v Jedi]

Hmm yes, I think it's just not clear to all reading this thread. Let me try to explain:

AC ground (the green or green/yellow wire) is not needed for AC powered devices to operate; it is purely a safety to prevent electric shock and fire. The basic idea is that this wire provides a direct path to ground and it is connected to metal parts on the outside of AC powered devices. If a short occurs, a lot of current flow flow through this wire to ground which trips the breaker.

Now the "2 grounds" we have to deal with aboard boats:

1. shore ground. This is the ground conductor in the shore power cable. Somewhere ashore, it is connected to a grounding rod driven deep into the ground (literally, the soil).

2. boat ground. And this is where differences pop up. How is this ground "made" ?! We need ground to work while on shore-power, while on genset away from the dock and also while using inverter power. Clearly, we can't run a cable back to shore all the time, so establishing our own ground aboard is the best option.. one that works for every situation.

The easiest way to create a boat ground afaik is using some grounding plate under the hull. This creates electrical contact with the water around us which provides the path to ground.

Let's assume we have this, our own boat ground. This works just great when away from the dock, both for genset and for inverter. But when we dock and roll out the shore power cord... the two grounds are gonna meet each other.

This is what is to be prevented. Do NOT connect them. If you really don't want to spend $$ for an isolation transformer, at least buy one of those galvanic isolator thinghies. If you value the life of you and your family above $$ then select an isolation transformer.

cheers,
Nick.

[allene222]

Originally Posted by s/v Jedi

Hmm yes, I think it's just not clear to all reading this thread. Let me try to explain:

AC ground (the green or green/yellow wire) is not needed for AC powered devices to operate; it is purely a safety to prevent electric shock and fire. The basic idea is that this wire provides a direct path to ground and it is connected to metal parts on the outside of AC powered devices. If a short occurs, a lot of current flow flow through this wire to ground which trips the breaker.

Now the "2 grounds" we have to deal with aboard boats:

1. shore ground. This is the ground conductor in the shore power cable. Somewhere ashore, it is connected to a grounding rod driven deep into the ground (literally, the soil).

2. boat ground. And this is where differences pop up. How is this ground "made" ?! We need ground to work while on shore-power, while on genset away from the dock and also while using inverter power. Clearly, we can't run a cable back to shore all the time, so establishing our own ground aboard is the best option.. one that works for every situation.

The easiest way to create a boat ground afaik is using some grounding plate under the hull. This creates electrical contact with the water around us which provides the path to ground.

Let's assume we have this, our own boat ground. This works just great when away from the dock, both for genset and for inverter. But when we dock and roll out the shore power cord... the two grounds are gonna meet each other.

This is what is to be prevented. Do NOT connect them. If you really don't want to spend $$ for an isolation transformer, at least buy one of those galvanic isolator thinghies. If you value the life of you and your family above $$ then select an isolation transformer.

cheers,
Nick.

@Nick. That should help. But I am not sure why you want to connect boat ground to the ocean. Are you worried that an AC hot might hit the water and if you have a ground near you might be protected? Not sure with the high resistance of the water than even helps that case. Some people talk about having a plate to give lightning a path to ground and there might be logic in that, not sure as lightning is kind of a mystery in that it has so much power it really does what it wants. Anyway, what is the logic of having the boat ground so well referenced to the ocean?

Your final point about not connecting boat ground and shore ground except through a device made for that job is the point some readers seem to be missing.

Allen

[Beausoleil]

I just want to pipe in here and let you know what I eventually did do. This post is over two years old, and in subsequent reading I decided to not bond the thru-hulls when re-doing the electrical system. They are all isolated.

I'm not yet ready to agree with Allen that AC systems don't belong on a boat - when speaking in general terms of "boat". An AC system on a Folkboat or a Dana 24 - no, that's probably not a good idea. But a liveaboard and actively cruised boat like our Formosa 51? 12V or 24V appliances are extremely expensive and not nearly as rugged, in my experience. The market for them just isn't big enough for economies of scale to kick in...

[chala]

Originally Posted by s/v Jedi

AC ground (the green or green/yellow wire) is not needed for AC powered devices to operate; it is purely a safety to prevent electric shock and fire
cheers,
Nick.

It is undeniable that electrical appliances that require to be earthed shall be earthed. Most countries have Electrical Standards. Some Standards will demand that a boat be earthed (be connected to the shore supply earth) when connected to shore, some will demand that a boat is not earthed (be NOT connected to the shore supply earth) when connected to shore. My boat is made of steel so it is inevitable that all parts of this boat are more or less at the same potential (in reference to bonding or not bonding). When the appliances and wiring on board are connected to the shore supply the boat itself is not connected to the shore supply earth this in accordance with the Standard what is fine by me. Why should the boat become the earth stake for the rest of the marina?

Originally Posted by s/v Jedi

1. shore ground. This is the ground conductor in the shore power cable. Somewhere ashore, it is connected to a grounding rod driven deep into the ground (literally, the soil).
cheers,
Nick.

In fact to a multitude of rods or plates in such a way that this earth wire does not gain any potential above earth.

See

Stray Current Corrosion . . . - Page 2 - Cruisers & Sailing Forums

Isolation Transformers - Page 6 - Cruisers & Sailing Forums

AC Grounding - Page 3 - Cruisers & Sailing Forums

Bonded vs Unbonded Boats - Page 10 - Cruisers & Sailing Forums

Shorepower and dc Wiring Runs - Cruisers & Sailing Forums

[allene222]

At the risk of beating a dead horse this issue is very clear.
1) You must have a setup that will trip the shore power circuit breaker if you connect your boat AC hot to your boat AC ground (the case of your microwave for example).
2) You must have your boat AC ground isolated from the marina AC ground.

Sounds impossible? They make two devices that accomplish the above.
1) Isolation transformers
2) Galvanic isolators.

Bonding or not bonding is a question of connecting things to the boat DC ground. Completely different topic. With a metal boat, you basically must connect your boat AC ground and DC ground. You have no choice. But if you don't isolate that from shore AC ground, you are asking for lots of trouble.

Allen

[s/v Jedi]

Originally Posted by allene222

@Nick. That should help. But I am not sure why you want to connect boat ground to the ocean.

because if you don't do this, you have no ground. It would be the equivalent of not connecting shore-ground to any grounding rods.. just a wire connected to nothing. This would not flip the breaker when the metal parts of AC powered devices short to a hot wire.

In other words: a boat ground that isn't connected to anything else than your outlets is useless. I agree that the ground might not be needed when there's GFCI outlets etc. in place.

cheers,
Nick.

[chala]

Forgot to mention this thread

Originally Posted by EngNate

They can detect AC stray current because their eyelids twitch rapidly as they approach an affected part.

[goboatingnow]

This thread is crazy few people understand the first principles and are mixing up country codes with electrics , incorrect GFCI understanding ( which have all been replaced by RCDs)

I'll give you the near universal European practice ( arguably an area with more safety rules then anywhere on the planet)

all Marina feeds have a RCD, all boats have a RCD , no bonding oh underwater fittings. No connection between protective AC ground and DC ground. ( you never connect the AC neutral to the DC system and it's never described as a ground).

The result , we all still alive overhere, our skin fittings are still intact and actual instances of excessive zinc or underwater corrosion are rare. All this at 230VAC

Dave

[allene222]

@Dave Sounds like an excellent approach. Do you have a standard that lays this all out? I would like to reference it in my article. By the way, I don't think anyone suggests connecting neutral (white) to DC ground. That is universally considered a fault in my understanding. The connection that gets confused is connecting AC Ground (green) to DC ground which should only be done through an isolator. That last word is what some people miss. As I have said, my boat has no AC system, and what AC I use is protected by a GFI breaker at the dock box.

What is the advantage of RCD over a GFI breaker?