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Old 05-10-2011, 14:44   #1
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First Post - Electrical Help !

Hi all,

I have recently purchased a 1969 Gulf Island 29. I am currently going through the electrical system . It was in serious chaos at the time we purchased the boat and without shore power.

My question - I cant seem to locate the ships ground. All of the old electrical has been pulled, and I am beginning to put in the new 12v system, as well as a simple 110v shore power system.

There was previously a ferrymen diesel inboard, and I am wondering if everything was grounded to that before it was pulled? I'll attach a photo of the only spot I am thinking could be the ground. This is a post coming through the hull. It has wires coming off it and going to the salt water cooling valve for the old motor.

If not what are my options in terms of grounding?

As I understand it, both my AC and DC system should be grounded to the same spot.

Thank you kindly.
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Old 05-10-2011, 14:51   #2
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Re: First Post - Electrical help!

Usually the engine block is the DC ground. AC should also return via the shore power connection.
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Old 05-10-2011, 15:36   #3
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Re: First Post - Electrical help!

Seduction is correct. AC panal/ ground green wire is grounding out the boat through the marinas system. On my boat all DC grounds led to the engine block.
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Old 05-10-2011, 16:11   #4
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You might not have had a safety ground. My 1969 Roamer doesn't have any 120v safety grounds on the inboard side of the isolation transformer.

As an electrical engineer, i assure you that AC ground and dc negative are not electrically equivalent when the 120v system is connected *directly* to shore power. If you tie the safety ground and dc negative together at the engine block or other grounded thru hull, you will turn it into a sink for ac ground.

Google 'earth potential rise' and 'ground potential rise' if you want further reading on the matter.


Later,
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Old 05-10-2011, 16:28   #5
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Re: First Post - Electrical help!

Check the ABYC electrical guide. It is no longer recommended that the DC system have a common ground at the engine block. All DC returns should go to a bus bar and then a single cable to the DC Shunt and a single cable from there to negative on the house battery system. The starter DC return should also lead back to that single bus bar as should the negative from the starter battery. Don't make the mistake of running the negative from the starter battery to the house battery side of the Shunt. DC and AC grounds should connect (according to ABYC) at one point only, and that should be at the DC return bus bar. The green wire system that you are looking at is the bonding system and is a separate system from the DC return system. I'm not sure if they should be connected at the bus bar or not.

Blue Sea systems has some drawings of proper DC electrical systems and some excerpts from the ABYC specs.
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Old 05-10-2011, 19:10   #6
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Re: First Post - Electrical Help !

Quote:
Originally Posted by neptunesjester View Post
As an electrical engineer, i assure you that AC ground and dc negative are not electrically equivalent when the 120v system is connected *directly* to shore power. If you tie the safety ground and dc negative together at the engine block or other grounded thru hull, you will turn it into a sink for ac ground.
It is common practice and a requirement of AYBC rules to connect the AC safety ground to DC negative. From AYBC rules:

11.17.1.4

The shore-grounding (green) conductor is connected, without interposing switches or overcurrent protection devices (See E-11.5.5.5), from the shore power inlet to
11.17.1.4.1 an optional galvanic isolator, and then to
11.17.1.4.2 all non-current carrying parts of the boat’s AC electrical system, including
11.17.1.4.3 the engine negative terminal or its bus.

Eric
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Old 05-10-2011, 20:57   #7
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Re: First Post - Electrical Help !

Welcome Aboard Cruisers Forum
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Old 06-10-2011, 08:08   #8
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Of course, you could always follow European practice and fit a RCB. Then Ac and Dc ground interconnection is not necessary. Electrically speaking it's much better that they are not.

Dave
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Old 06-10-2011, 08:34   #9
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Re: First Post - Electrical Help !

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Originally Posted by goboatingnow View Post
Of course, you could always follow European practice and fit a RCB. Then Ac and Dc ground interconnection is not necessary. Electrically speaking it's much better that they are not.

Dave

ELCI's/RCD's are already part of the current ABYC standards, have been since July 31, 2010. E-11 still requires AC Green and DC ground to be tied together on-board even with an RCD/ELCI.

As has been said the engine is still the most common ground point on most vessels.

With an inboard engine it is pretty hard not to have the engine as ground. To do this would require the alternator, starter, alarm systems, and in some cases the fuel pumps, to be converted to isolated ground not case ground.
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Old 06-10-2011, 09:55   #10
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Re: First Post - Electrical Help !

Hey islandfellow...welcome to the forum.
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Old 06-10-2011, 13:38   #11
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Re: First Post - Electrical Help !

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Originally Posted by Maine Sail View Post
ELCI's/RCD's are already part of the current ABYC standards, have been since July 31, 2010. E-11 still requires AC Green and DC ground to be tied together on-board even with an RCD/ELCI.

As has been said the engine is still the most common ground point on most vessels.

With an inboard engine it is pretty hard not to have the engine as ground. To do this would require the alternator, starter, alarm systems, and in some cases the fuel pumps, to be converted to isolated ground not case ground.
Wasnt suggested that the engined wasn't connected to DC ground. What I was suggesting is that DC ground ( ie -negative) shouldn't really be connected to AC protective earth. Firstly DC ground is a current carrier and AC earth is not, secondly AC earth is notorious for carrying spurious DC and AC currents and RF and general electrical noise and the connection couples this into the DC negative. not to mention impressed current corrosion.

The fact is that the original ABYC idea was to to effectively extend the safety of protective earth to items on board that were not part of the AC protective earth circuitry, things like the engine and tanks etc. However an RCB/ELCI provides that additional safety and allows in the case of CE certification that link to be avoided. All safety systems are a compromise between levels of safety and actual usage issues.

Dave
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