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Ground wire

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RichardG
Admiral

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USA
990 Posts

Initially Posted - 08/18/2003 : 13:19:10

I mistakenly posted this question in the "Feedback" section. Let's try it here...

Another post reminded me of the state of the wiring in my boat. The two positive wires from the batteries to the main A/B/Both Switch(only one of which is in current use since replacing the two 12v batteries with two 6v golf cart batteries hooked up in series) are relatively thick red wires (2.0 guage?). However, the single negative wire is relatively thin black wire (8 guage?).

Is this original? Do others have this?

It seems original to me because the hole through the battery compartment wall for the black wire is barely large enough to fit the current wire.

Understanding the electric system is definitely my weak side. Nevertheless, it doesn't seem logical to me that a thinner wire would be used for the ground wire since electricity has to go through both pos. and neg. wires, regardless of the extent of loads. In this regard, is the voltage drop between the battery and the main switch dictated by the thinnest wire (either pos. or neg.)?

RichardG 81 C25 SR/FK "Sanity"

Edited by - on

Stu Jackson C34
Admiral

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844 Posts

Response Posted - 08/18/2003 : 15:34:16

Richard

The voltage drop is determined by the combination of the wires, not just the thickest or thinnest. It's like a garden hose. If you have a thick, say 3/4 inch hose, and you attached a smaller 3/8 inch hose to it's end, the pressure drop would be the addition of the drops in each section.

What this means for your boat is that the voltage drop is the sum of the larger red wire and the smaller black wire, since you're right that for the circuit to be completed the electrons have to go through both the positive and negative.

In order to find out what's going on, check any catalog in the electrical section for voltage drop tables in the wiring section. You'll find that depending on the length of your small black wire, you are most likely exceeding the recommended 3 or 10% voltage drops.

What this means is that first you'll have excessive voltage drop, and second the wire could, I say could, get hot.

A lot of it also depends on what amerage you are running through your wire, which you will also need to know when using the tables. If you hardly run anything on your boat, it may, I say may, not matter. If you use a few DC things at the same time, and depending on how your boat is wired (i.e., does the VHF go through the switch or had it been wired directly to the battery bank?), you may want to consider a larger negative wire.

In any event, I'd go larger and at least match the positive, but do the research on amps, wire length, i.e., distance and voltage drop and prove it to yourself.

Stu

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 08/18/2003 : 15:49:02

At the battery, electrons out must equal electrons in... so yes, the negative lead gets just as much current as the positive lead.

Go here... http://www.bluesea.com/index.htm

Click on the the 'technical' page and the 'Circuit Protection' topic... I think you will find that it is well written and very clear. (very well done in fact)

They also have a nice section on ABYC standards and other papers that give lots of very good information on boat wiring !

Currently maintaining two holes in the water...'77 Venture 23 and new to the family,
'78 Catalina 25

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Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 08/18/2003 : 21:56:26

Hey Stu,
Great explaination
Sounds like you know your way around a multimeter

Frank Gloss
89WK/TR

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Stu Jackson C34
Admiral

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844 Posts

Response Posted - 08/18/2003 : 22:23:14

Frank

Just glad to help. Had a C25 for 11 years before getting our C34 in 1998. I KNOW thhe difference between "what I knew now I wish I didn't know then!" or something like that.

Stu

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Bill Holcomb
Admiral

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USA
769 Posts

Response Posted - 08/19/2003 : 09:12:46

Hi Richard,

As to your "is it original" question. Probably not. My memory is that the original wiring used the same gauge wire for both + and - sides of the circuit.

Bill Holcomb - C25 Snickerdoodle #4839

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RichardG
Admiral

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USA
990 Posts

Response Posted - 08/22/2003 : 14:10:12

Stu & Bill:

Thanks a lot for the great explanation!

Maybe the boat was originally wired for just one battery using the same guage wire for pos. and neg., and a previous owner added the second battery by switching the original neg. wire to the new pos. wire and adding a smaller guage wire for the combined neg. wire?

On family trips I'm often running several things at once (kids watching TV/VCR down below and me running cd player and autopilot above) for several days at a time, hence the reason I put in the golf cart batteries. I've checked the wires for heat and have not felt any. Regardless, I didn't think it was set up right and will do the research, math, et al and put in a heavier guage ground wire.

RichardG 81 C25 SR/FK "Sanity"

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Arlyn Stewart
Master Marine Consultant

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USA
2984 Posts

Response Posted - 08/23/2003 : 09:58:24

Richard...

Were missing something here... The two heavy red wires were likely used for positive leads during the previous installation of two 12v batteries to seperate them on each pole of the two battery switch.

However, using the two six volt golf cart batteries will allow you to take advantage of the unused heavy wire. Unhook the unused red wire from the battery switch and wrap the end with black tape marking it now a ground wire. Do the same for the unused end at the battery box. Now, swap it for the smaller black ground wire or add it in parallel to the black ground wire and in doing you will have a full electron super highway circuit instead of the restrictive far smaller black wire that greatly limits the amperage capacity of your system. This would be espcecially important if having an electric start.

Arlyn C-250 W/B #224
<img src="http://www.stewartfam.net/arlyn/rr.jpg" border=0>
N/E Texas and Great Lakes

[url="http://www.cox-internet.com/arlynstewart/"]Arlyn's C250 Mods n Cruisin Stories[/url]

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deastburn
Captain

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USA
334 Posts

Response Posted - 08/23/2003 : 11:22:35

This thread reminds me that the great thing about this forum is that someone always can provide a detailed, easy-to-follow answer. Reading this thread reminded me, however, of an article in this month's sail magazine (p.22):

"Wiring problems account for 55% of fires aboard boats, according to a two-year study by BoatUS Marine Insurance..."

The short article points to the importance of a main on/off switch and an AC breaker, since electrical fires can reignite even after they have been put out with an extinguisher.

It reminded me to check the wiring on Wood Duck (which I have never done, except for the times I have added to it or worked on it). Those places where battery wires pass through sharp-edged holes in the fiberglass are perfect sites for chafe, and consequent problems.

I don't mean to panic anyone, but it is one more item I have added to my periodic check list...

Dave on "Wood Duck" (#2616)

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Arlyn Stewart
Master Marine Consultant

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USA
2984 Posts

Response Posted - 08/23/2003 : 16:18:18

Good thoughts Dave,

Without exception... there should be a fuse as close as possible to all positve leads off a battery. Any installation not fused is playing the odds.

Incidentally... I bought my c250 new... the battery was ten feet from the breaker panel... and had no fuse at the battery... there is now.

Arlyn C-250 W/B #224
<img src="http://www.stewartfam.net/arlyn/rr.jpg" border=0>
N/E Texas and Great Lakes

[url="http://www.cox-internet.com/arlynstewart/"]Arlyn's C250 Mods n Cruisin Stories[/url]

Edited by - on

RichardG
Admiral

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USA
990 Posts

Response Posted - 08/27/2003 : 01:15:37

Thanks, Arlyn, for that very helpful suggestion in switching the unused pos. cable to a ground cable. However, two things may prevent it. First, whoever originally wired it left no excess wire which may make it difficult to reach the left corner of the battery compartment on one end and the ground bus on the other. Second, the ground bus is better described as a connector block with a wire/latice jumper attachment between all the terminals -- its #8 screws will probably not accept large battery cable lugs.

Looks like I've opened a nice can of worms...

RichardG 81 C25 SR/FK "Sanity"

Edited by - on

Arlyn Stewart
Master Marine Consultant

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USA
2984 Posts

Response Posted - 08/27/2003 : 02:07:02

Both problems could be solved. If there is not a lot of wire ties bundling the wire... shift its length toward the battery. If there are... splice a section on the end. If the ground bus is long enough, unwrap the cable stands and seperate them out to the size that will work on several lugs, otherwise splice several wires to it.

Arlyn C-250 W/B #224
<img src="http://www.stewartfam.net/arlyn/rr.jpg" border=0>
N/E Texas and Great Lakes

[url="http://www.cox-internet.com/arlynstewart/"]Arlyn's C250 Mods n Cruisin Stories[/url]

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 08/27/2003 : 09:19:44

Richard... Remember that Arlyn is in fresh water. Take special care adding splices in a salt-air environment. I'd run new wires (and did so) to get the length and gauge I need--making it tinned as well.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

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Stu Jackson C34
Admiral

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844 Posts

Response Posted - 08/27/2003 : 13:50:56

Richard

Another Solution to Your Issue

If the "reused red wire with the black ends" is a tad too short, buy a Power Post Plus to fit the lug at the ground bus end. The PP+ has a large bolt to hold the lug from the wire, and the + part is that it has #8 or #10 screws around the base for you to make that last connection(s) to the ground bus right from the same piece. Easy to find in either West or BoatUS catalogs. It also avoids having to undo the lug, strand wire, etc. regardless of whether it's salt or fresh water, it's still electricity and connections are always a bear. They make different sized posts, so make sure you know what your lug size (hole) is.

Stu

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RichardG
Admiral

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USA
990 Posts

Response Posted - 08/28/2003 : 14:46:42

Thanks again, Arlyn. I like your style of thinking.

But while I originally had hoped to avoid it, I'm now leaning towards putting in a proper bus bar. And if I'm putting one in anyway, I might as well take the old one out to keep things cleaner back there (it just means having to reconnect about 10 terminal rings). But this will also require a new ground wire of the proper length and guage, if I'm to avoid splitting/splices/etc.

RichardG 81 C25 SR/FK "Sanity"

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RichardG
Admiral

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USA
990 Posts

Response Posted - 08/28/2003 : 15:08:43

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>had no fuse at the battery... there is now.
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

What size fuse did you use? How is it hooked up?

Thanks.

RichardG 81 C25 SR/FK "Sanity"

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