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**Ex-Calif** · 01-07-2007, 18:57

Quote:

Originally Posted by Crak

Thank you for the reply's .

Should I connect the AC protective earth to the DC -ve ground ? (Should I connect the AC protective earth to the engine block ?)
There is a safety advantage in doing this, as it will provide protection in the case of AC coming in contact with the DC system due to chafing of wires etc.

Just my opinion but I would keep the systems 100% separate. Depending on where you are in the project, disciplined wire routing will keep AC bundles from DC bundles eliminating the AC/DC chafing question.

The AC system is grounded (neutral) to shore and the earth is also routed to shore. If I bond all my AC equipment to green & follow good build practice on the AC wiring I shouldn't have an issue.

Rodz · 01-07-2007, 19:03

Quote:

Originally Posted by Ex-Calif

Just my opinion but I would keep the systems 100% separate. Depending on where you are in the project, disciplined wire routing will keep AC bundles from DC bundles eliminating the AC/DC chafing question.

The AC system is grounded (neutral) to shore and the earth is also routed to shore. If I bond all my AC equipment to green & follow good build practice on the AC wiring I shouldn't have an issue.

Everything is fine if you do not have a battery charger or inverter where both systems meet, if there is no moisture or condensation.

DeepFrz · 01-07-2007, 20:35

Quote:

Everything is fine if you do not have a battery charger or inverter where both systems meet,

This is exactly where the problem lies. If you have a piece of equipment that shorts the AC to the DC you have a very real safety hazard if you go with seperate grounds. The articles referenced give you the answer. What is worth more, a galvanic isolator or a life?

**EngNate** · 03-07-2007, 11:06

Boy, this is quite a topic, and I will try to post more on it. YES, connect the AC safety ground and DC ground together - if you are a boat manufacturer, it's the law. (I'll find it on this $250 CD sooner or later) NO, it is not the cause of electrolysis or stray or galvanic currents.

NO, do not connect AC safety ground and neutral anywhere on a boat, EXCEPT 1. at a transformer secondary; 2. at a generator; THIS is a common cause of stray AC currents, and this, in conjunction with other defects (poor integrity of the dock neutral conductor), is a cause of "hot docks". In particular, check 220V appliances like ranges for a factory installed ground link and remove it. 110/220V appliances on boats must be wired with 4-wire cords. The ground/neutral connection for the entire dock system is made at the transformer feeding the dock, and may be connected at the distribution panel, but nowhere else in the system, including the connected boats.

Connect AC and DC grounds together at one point only, between the main busses of each.

Galvanic isolators prevent sharing your zinc with your neighbors. If you like buying and replacing zincs and want to be a good neighbor, don't have one.

Nate
tech@midatlanticseatech.com

Rodz · 03-07-2007, 18:01

Quote:

Originally Posted by EngNate

.... YES, connect the AC safety ground and DC ground together - if you are a boat manufacturer, it's the law. ....

do you refer to the US law? If so, I would like to point out that the thread was started by Crak who's location is PERTH ... I believe it is Perth, Australia. Does the same regulation apply in Australia and EU??

Chris

**Ex-Calif** · 03-07-2007, 19:20

In the great article posted by DeepFrz it does state that Europe allows the circuits to be separated and Ground Fault Isolators used. He does pointout he drawbacks with this method.

I don't know if Oz follows European practice or not.

Crak · 03-07-2007, 20:19

Thank you for all those people who took the time to reply.

In summing up,

In Australia & New Zealand the green protective earth wire (in the 240vac shore power cable) HAS to be connected to the DC earth buss by law.
This WILL increase the chance of galvanic corrosion, so it is recommended a galvanic isolator be placed in series with the green protective earth wire at the input of the boat connection. An isolation transformer will also offer added safety and also help reduce galvanic corrosion.
Removing the shore power connection and relying on solar / wind power will remove the galvanic corrosion circuit and will drastically eliminate galvanic corrosion.

Crak

**EngNate** · 04-07-2007, 11:24

Quote:

Originally Posted by Rodz

do you refer to the US law? If so, I would like to point out that the thread was started by Crak who's location is PERTH ... I believe it is Perth, Australia. Does the same regulation apply in Australia and EU??

Chris

Yes, sorry about the confusion, that's ABYC Standards and USCG/CFR. Yes, the thread was started from Perth, but it's been viewed 298 times now.

Thousands and thousands of US built boats work for dozens of years wired according to these standards, with no corrossion problems at all, and the same is true for EU boats. To corrode or not to corrode is a question that is not dependent on those particulars.

There is some point of difference in the systems in that EU is a single-ended configuration and North America is a balanced (double ended) configuration. However, except for the voltage level, the half-side of the US system is the same as the EU system. In the US, we power 220V devices by connecting across two 110V lines that are opposite in phase, one side is at peak voltage in the + direction when the other is peak in the - direction, and the device connected between these gets the sum of the two. With the grounded conductor in the "middle", the shock potential touching any one live conductor is 110V. The EU system presents a shock potential of 220V to ground, and I'll tell you from experience it's a good whack, hence the GFI requirements and the nuisance that frequently comes with them. We favor using GFI's on individual branch circuits where the risk of contact is high and conditions exist that increase the hazzard. In most cases, a 110V shock is not more than a nuisance itself, injuries like bruises and scrapes result from the surprised reaction when it happens.

I seems to be agreed by most here that the shore power ground and neutral are not to be connected aboard the boat. If the DC and AC grounds are connected, circuit protection will trip if a live AC circuit contacts a DC circuit. With GFI protection, the AC side will trip without this connection, thus it is not necessary.

A galvanic isolator is the first device inside the boat from the shore inlet, that's where it goes, before the ground wire connects to anything else. Refer to my posts in the thread "Zincs and the hot marina" for more about that.

Rodz · 04-07-2007, 16:26

EngNate, I think we going into a wrong debate that is for professionals. It is enough to say that that:
1. AC neutral and ground (earth) are separate on the boat.
2. galvanic isolator is to be connected right next to power inlet on ground wire.
3. galvanic isolator method can be replaced with isolating transformer but the connections are different.
4. grounding (earthing) wire and dc ground are to be connected together except where is GFI is installed and such connection is not required by regulations.

By the way, I believe in the EU the household voltage has been standardized to 240/415V system. The NA and European distribution systems are slightly different and we should not confuse our fellow sailors by telling them what is a split phase transformer. As for shock - either 110V or 240V is dangerous for a human being. Either of them can kill instantly. This is why there is a protection required on every electrical circuit or the voltage is reduced to a very low level.
As for corrosion, it is not how a boat is wired only but also includes other boats and land circuits as a part of a system.