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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

What gauge wire for 12 volt stuff

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sodonnell
1st Mate

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76 Posts

Initially Posted - 08/22/2005 : 13:53:03

I'm going to wire a couple 12 volt fans in my C25.
Maybe move around some of the cabin lighting.

What gauge wire is appropriate for this kind of stuff?

Edited by - on

Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 08/22/2005 : 13:59:40

wire gague depends on three things:
Amperage of the device you are powering
Length of wire, in the case of 12 volt it is the total length of the positive and ground wire
The voltage drop you find acceptable, either 1% or 3 %
From that you can get your wire gague from a table
Check out the Ancor website, they have tables. I think the west marine catalog has tables. The Don Casey book "Sailboat electrics simplified" has tables.

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Buzz Maring
Master Marine Consultant

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1775 Posts

Response Posted - 08/22/2005 : 14:47:47

Hi Scott,

The original C-25 manual has a schematic of the wiring ... a note on the schematic says that "all wires shown are 14 gauge, except for the grounds which are 10 gauge" ... here is a link to that page:

[url="http://www.catalina25-250.org/manbro/pictures/owners11.gif"]Lighting Wiring Schematic[/url]

'Hope that helps ... I can barely spell electricity ... now that I've given you the link, I'm out of airspeed and ideas

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Oscar
Master Marine Consultant

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2030 Posts

Response Posted - 08/22/2005 : 15:49:57

Page 662 of the West Marine Catalog (you do have one don't you?

....not to order from mind you, but to figure out what you need and then you go surfing for deals...)...anyway, page 662 has wire specs....14 gauge is good up to 35 amps (*12=420 watts) at 10% voltage drop you're good up to 160 feet........since your longest run will be 20 feet and nothing you are installing will be an interstate flood light or swamp boat thrust fan you are good with 14 gauge.....

I personally find it harder to work with very light gauge wire....crimp connectors become uncooperative...14 gauge is nice.

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jlguthri
1st Mate

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USA
93 Posts

Response Posted - 08/22/2005 : 16:14:59

perhaps off topic...

when you are talking AC amps, you are almost always talking a RMS (root mean square) average. This is an attempt to come up with a DC heating equilivilant. For example, your 20Amp AC circuit is actually 20 times the square root of 2 peak voltage. The 20 amp is aprox what the heating effects would be if it were DC. It is heating you are worried about. Voltage has nothing to do with heating. (i^2)*t

What i'm getting at is that I would expect to find the values for max ampreage DC to be real close to the same as the values given in places like the National Electrical Code for a given thickness wire and insulaiton type. but by all means, look that the manufacture's tables. also note the differences between solid and stranded (solid is usually a pretty bad idea on boats -- it likes to break).

just food for thought for next time you are on jeporady.

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sodonnell
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Response Posted - 08/22/2005 : 21:31:15

Thanks to everyone for the input.

I'll keep the swamp boat thrust fan in mind for next season.

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Oscar
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2030 Posts

Response Posted - 08/22/2005 : 21:53:59

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">solid is usually a pretty bad idea on boats<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

And squarely against ABYC/CG guidelines/regulations. Your insurance man might have issue with it too.....

Marine Grade is a good idea in all things electrical/flammable.

Edited by - Oscar on 08/22/2005 21:55:10

britinusa
Web Editor

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5404 Posts

Response Posted - 08/22/2005 : 23:33:25

Don't skimp on wiring!
If this was a helicopter you would be weighing the cable and finding the shortest route for the wire to travel. But it's a boat, the weight of the cable is really not an issue, so use tinned copper multistrand and don't skimp on the guage!

There's some great tables for calculating the wire size in casey's book.

See Chap 4 of 'Sailboat Electrics Simplified' by Don Casey (Available from West Marine (go via the [url="http://www.catalina25-250.org/links.html#westmarine"]link on the links[/url] page so you earn the Assoc a few pennies (actually about a $1.00))

Hmmmm, 1,500+ members * 1 book or thingy per year = oodles of dinero!

Edited by - britinusa on 08/22/2005 23:40:27

sodonnell
1st Mate

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Response Posted - 08/23/2005 : 00:22:12

Yep.
I'm going to pick up the Don Casey Book.

One really stupid question in the mean time.

Looking at the 12 volt fan I bought, there is no negative wire.
Just positive and ground.
Why?

I know there is a green ground wire connected to all the components in the boat but where is it wired to?

Edited by - on

britinusa
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5404 Posts

Response Posted - 08/23/2005 : 07:20:20

The majority of 12v DC devices use the ground as Negative.
eg. We purchased two of the 12V DC fans from west marine, just +ve & -ve cables from the fan.

NOTE: It is imperitive that the connections are not reversed! It doesn't matter much with filemant lamps, but many devices have capacitors (especially motors as in fans) which will literally explode if the connections are reversed. It is essential that all new wire runs and equipment are correctly connected.

I really recommend that you Read The Fine Manual (Casey's book) first.

You are unlikely to get hurt from a 12v shock, but your equipment will suffer irepairable damage if it gets reversed connections. (crossing wires = Expensive!)

Good luck with your upgrades, it is easy once you understand the basics. And the fans make a heck of a difference (especially here in SoFla)

Paul

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sodonnell
1st Mate

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76 Posts

Response Posted - 08/23/2005 : 09:32:53

So can I or do I wire the ground back to the negative terminal or to the green ground wire on the boat the runs to somewhere ????

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frog0911
Master Marine Consultant

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1349 Posts

Response Posted - 08/23/2005 : 10:40:48

Just remember that in DC system + = positive and - = negative/ground. As Paul said, make sure on DC motors you hook the wires up properly. Also green wire on all boats is not necessarily negative/ground. Sometimes they are black and sometimes other colors. For instance on my 04 C250 the mast wiring harness in the boat has white as negative/ground wire while the actual wiring in the mast has green for the negative/ground wire. So you can see all boats do not conform to any standard wiring setup no matter what there age.

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Happy D
Admiral

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921 Posts

Response Posted - 08/24/2005 : 17:31:28

Here is a little [url="http://www.ancorproducts.com/"]wire sizer[/url] program I found. Click on Technical Information and then click on wire. Remember that the length of wire is round trip, not one way.
Dan

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DanM
Captain

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USA
256 Posts

Response Posted - 08/25/2005 : 08:06:18

That little Ancor calculator program is cool! Could someone please add Happy D's link to the tech tips page for easy future retrieval?

While looking over that site, check out this wire color idea:

UL 1426 Tinned Boat Cable
ANCOR recommends the use of yellow conductors onboard boats to replace DC black conductors. The reason is to avoid confusion between AC black conductors (hot lead) and DC black conductors (negative lead).
Yellow conductors should be used as the DC negative lead and black will remain as part of the three conductor AC circuits.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.