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 Electrical Ground		  New Topic  Topic Locked
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Bladeswell
Captain

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USA
490 Posts
Initially Posted - 02/18/2016 :  21:15:56  Show Profile  Visit Bladeswell's Homepage
Hello All,
Sense our boats,(most anyway), don't have inboard motors, What serves as our primary electrical ground ? Thanks.

Bladeswell
C25 TR FK Hull #973 1979 L-Dinette. So.Cal.

slim
Navigator

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USA
113 Posts
Response Posted - 02/19/2016 :  05:42:29  Show Profile
Hi Bladeswell

I am no expert on electrical however i can say that on your boat you will be dealing with both DC and AC and there will be a difference in the way each is handled by you. I think your best bet in understanding your electrical systems will be in reading the book Sailboat Electrics Simplified by Don Casey. It’s available on amazon, used now for about $10 for the hardback and worth every penny of it. I too am rewiring my boat at this time and this book has been a real lifesaver for me.

Slim
1978 - C25 - standard rig - Fixed keel #1040
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RickR
1st Mate

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USA
25 Posts
Response Posted - 02/19/2016 :  08:08:01  Show Profile
On my 81 I've just rewired, CD supplies a ground buss bar with that switch panel kit they offer. I ran two 10GA from each battery to that buss bar and it has additional space for a dozen or so returns. Running lights, anchor and steaming lights on the mast, all have a common ground/return to that buss along with cabin lights, stereo, etc. Hope that helps.
RickR
Jamestown, NY
81 C25/SK/SR/Trad #2668
"Vind Dansor"
Edited by - RickR on 02/19/2016 12:10:18
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slim
Navigator

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USA
113 Posts
Response Posted - 02/19/2016 :  08:23:41  Show Profile
Also you might want to take a look at the Pre-1988 Catalina 25 Owner's Manual, Lighting wiring schematic and Circuit Schedule. It is aviable on line in a pdf at http://www.catalina-capri-25s.org/manbro/Cat25manpre88.pdf or at your left under manuals and brochures.

Gives you everything you might need to rewire with.

Slim
1978 - C25 - standard rig - Fixed keel #1040
Edited by - slim on 02/19/2016 08:26:22
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Bladeswell
Captain

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USA
490 Posts
Response Posted - 02/19/2016 :  11:26:12  Show Profile  Visit Bladeswell's Homepage
Good Morning All,

And thanks for your replies. As it happens Slim, I do own the Don Casey book and yes, it is great. Some how I think my question must be unclear. I know what a buss bar is and have one. However a buss bar is just a common ground for all of the circuits and then it would have one larger gauge wire leading to a primary ground source. Maybe an enclosed 12 volt system doesn't need a primary ground. but thats what I'm trying to find out.
I also own the Cat 25 manual and the CD Cat 25 manual. Both wonderful. But allof them just show the schematic and show the symbol for ground at the primary end. They just don't say what source that is. On a car, it would be your engine block. Same with a boat that has an inboard engine. See what I mean ? Thanks.

Bladeswell
C25 TR FK Hull #973 1979 L-Dinette. So.Cal.
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capted
1st Mate

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39 Posts
Response Posted - 02/19/2016 :  12:03:47  Show Profile
In a sense, the final ground for your 12V system is the return to the negative post of the battery. There is no need for another ground for the 12V system. Now if you were talking about lightning protection, a primary ground is important and complicated. Similarly, if you have 120 VAC on the boat there are issues with electrolytic corrosion which require care with grounding. Your reference book should discuss these other issues. I don't know if connecting the buss bar to a lightning ground is good or not.
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Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts
Response Posted - 02/20/2016 :  09:48:22  Show Profile
quote:
Originally posted by capted

...I don't know if connecting the buss bar to a lightning ground is good or not.
It's great if you want your insurance company to buy you a whole new electrical system and electronic gear. All it would take is a strike to the water within maybe 100 yards.

Here's a good discussion from a marine surveyor:

quote:
Grounds and Grounding
One of the least understood aspects of a boats electrical system, and the most troublesome, is the proper method of grounding. That we often get questions of whether AC or DC electrical equipment should be grounded to the boat's bonding system is illustrative of this point. AC and DC grounding systems are two separate systems, for distinctly different reasons. If you don't understand these systems, you run the distinct risk of creating a disaster. Actually, there are four separate ground systems: DC ground, AC ground, AC grounding (or bond), and the vessel's bonding system. You can add to this lightning and HF radio grounds as well. Do you know the principles of each? Are you sufficiently confused to discourage you from doing your own wiring? I hope so. For unless you understand each thoroughly, you're headed for trouble.

The AC ground and grounding systems are "free floating," meaning that they do not ground on the vessel, but only to shore. The ground, or neutral, is a current carrying conductor, and is the source of many troubles because people do not regard it as such. The grounding, bond or green wire is the "safety" intended to channel current safely to ground in the event of a short circuit. Both of these circuits are capable of conducting current and can be the source of electrolysis when there are system faults with the dock or marina wiring. This is very easy to test for.

There is only one point where the DC side is grounded, and that is at the battery. It, too, is a "free floating" system in which nothing is ever grounded to any metallic part of the vessel, most especially not the bonding system. Just like a car sitting on rubber tires, completely insulated from earth potential, the battery itself provides the negative potential.

The bonding system, also green wire, has nothing to do with electrical systems. Underwater metals are simply wired together to equalize differences in potential of different kinds of metal. Nothing should ever be grounded to the bonding system. Unfortunately, some people don't understand this and use it to ground electrical equipment, occasionally with disastrous results.


(Most C-25s won't have and don't need bonding systems.)

I never liked the term "ground" for the negative side of a DC system--including the engine block in a car. It's the negative side--not ground. Same in a boat.
Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge
Edited by - Stinkpotter on 02/20/2016 09:52:27
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Voyager
Master Marine Consultant

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USA
5231 Posts
Response Posted - 02/20/2016 :  10:00:06  Show Profile
I largely agree with CapTed. A lot of people confuse 12VDC systems: a car uses 12V and can generally be thought of as being a "grounded" system because traditionally cars were made from metal and automakers routinely connected all negative terminals to the frame ground. Tail-lights, battery negative, starter, alternator, windshield wiper motors, radio, dashboard lights and indicators, solenoids and relays all were grounded to the chassis. In that case it had nothing to do with ground, since cars run on rubber tires - an insulator from earth. The frame is just a common "return".

Our boats have a different kind of 12VDC system. There's no metal chassis like a car, so a frame ground is not an option. Each appliance: light, radio, gps, meter, sounder, audio component, fan, alternator - whatever has two wires on it, has a positive 12VDC input and a negative 12VDC input. Each of these must ultimately be connected to battery + and battery -.

Tradition says that you should put an on/off switch and fuse on the plus side and you can connect all the negative cables together at the battery negative. Again, tradition dictates don't switch or fuse the negative side. To make wiring easier, most people add a negative buss bar with multiple connections to attach all the negative cables at a convenient point, then run a high ampacity cable back to the battery negative to handle the load.

On the plus side, you could add a positive buss bar, however, the switch panel on our boats does that job. The common positive from the battery is switched to the panel, then each circuit is individually switched to its device(s). Most people don't switch the engine/starter/alternator or the AC battery charger as this can lead to problems, but it is critical to fuse them.

On boats there are three things that seem like grounds, but IMHO should never be electrically connected together:
1. 12VDC negative - as described above
2. 120VAC - either green ground (earth) or white (neutral)
3. Lightning protection grounding plate on the outside of the hull

If you connect 1&2, you're potentially allowing lethal voltages onto your harmless 12VDC circuit when your shore power is connected. If you connect 1&3 you're ensuring that almost any lightning activity nearby your boat will fry your VHF, chartplotter and audio gear. If you connect 2&3, it's possible that you're connecting 120VAC to the water around your boat. If a nearby boat on the slip did the same but used the opposite leg, the consequences are deadly.

Moral of the story: for best results, keep them all separate.
Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain — Milford, CT
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Bladeswell
Captain

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USA
490 Posts
Response Posted - 02/20/2016 :  11:56:58  Show Profile  Visit Bladeswell's Homepage
Thanks so much Dave and Bruce.

That was exactly the answer to my questions and very understandable. Again, my thanks.

Bladeswell
C25 TR FK Hull #973 1979 L-Dinette. So.Cal.
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