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Catalina/Capri 25/250 Sailor's Forums

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DC Wiring - wire size?

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Daniel
1st Mate

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78 Posts

Initially Posted - 03/15/2004 : 10:09:23

I am re-doing the wiring in my 1989 C25. The wiring diagram in the new (1988) manual specifies "#4" wire for most of it (which I assume to be 4 ga.) from batteries to switch, batteries to ground and between the two batteries (I am using group 24). This seems overkill - would 6 ga or smaller be acceptable? For the subpanel wiring (to fuse or circuit breaker panel for interior lights, navigation equip, etc.) 10 ga. is specified.

I have a 10 amp charging coil on the Honda outboard and no power-hungry electronics anywhere in the boat. No shore power.

What did the original 1989's REALLY ship with? The wiring I have seen on other C25s did not appear to be 4 ga. but rather something much lighter.

Edited by - on

frog0911
Master Marine Consultant

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1349 Posts

Response Posted - 03/15/2004 : 10:24:34

Our 04 C250 came with 10 gauge from battery to panel and 14 gauge everywhere else. The only time I would go bigger than 10 is if joining to golf cart batteries in series for house keeping batteries. I would use 4 gauge for the series joining only and 10 gauge to the panel.

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Douglas
Master Marine Consultant

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1595 Posts

Response Posted - 03/15/2004 : 23:05:07

Yep you can get away with 14 gage wire but there is a catch. The wire length itself eats up current. If your going to power items on the mast like a deck light or spreader light , nave light etc on the mast and you run a 14 gage wire dont expect your lights to be as bright as they should be. If you want to be able to push current over a length of wire it needs to be of correct size. Hope this link helps

http://www.powerstream.com/Wire_Size.htm

Edited by - Douglas on 03/16/2004 19:27:19

OJ
Master Marine Consultant

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4382 Posts

Response Posted - 03/15/2004 : 23:39:22

And Dan, you are using the tinned stranded wire?

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Daniel
1st Mate

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Response Posted - 03/17/2004 : 17:04:06

Yes, indeed: I am using tinned (Ancor) wiring with heat-shrink connectors or tubing where needed. I am including a 25 or 30A circuit breaker in the main, which was not in the original design. The PO has installed an off-the-shelf panel with non-tinned wire and there was some ominous fraying and corrosion inside, so it has to be redone.

Why would Catalina specify "#4" wire in the owner's manual if that is really excessive?

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OJ
Master Marine Consultant

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Response Posted - 03/17/2004 : 17:17:23

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Daniel
 with heat-shrink connectors or tubing where needed.

For what it's worth, there's a brand (the name doesn't come to mind) of heat shrink tubing that has adhesive on the interior surface - making it more moisture resistant.

Why would Catalina specify "#4" wire in the owner's manual if that is really excessive?

As most of us are using 14 gauge, maybe the "#4" is just a typo . . . 
<hr height="1" noshade id="quote"></blockquote id="quote">

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dgabel
1st Mate

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75 Posts

Response Posted - 03/17/2004 : 17:59:22

When you use 14 gauge wire for lamps and so forth, check that chart link that was in one of those messages. I think the chart says that the current limit for 14-ga wire is 5.9 amps. If you're using 14-ga wire, you want your circuit protection to open up well before current reaches 30 or 35 amps. If you try to push that much current down that small gauge wire, the wire will heat, and it could cause a fire. So make sure that you size the circuit breaker to the wire that you're using. Using too large a breaker for the wire size is like putting a penny into a fuze socket: You can carry the current, but it could be dangerous.

Dave Gabel
Walkure
1979 Tall rig, fin keel
Sail 1484

Edited by - on

oldsalt
Admiral

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USA
578 Posts

Response Posted - 03/17/2004 : 21:01:27

Daniel the reason that the #4 AWG wire is specified in the areas you mentioned isn't because it's needed to carry the amperage in a properly functioning system.

#4 AWG is recommended in order to handle the current your batteries will produce in a short circuit condition in those non fuse protected portions of your main wiring system, without immediately glowing red hot and causing a fire. A shorted battery system will turn inadequately sized wiring red hot as quickly as an old flashbulb. Using #10 wire for your main system will create a serious safety hazzard.

For the branch circuitry I would use #10 in order to avoid any voltage drop. Voltage drop is a function of the current in the circuit, the size of the wire and the length of the wiring run.

I hope this helps.

Edited by - on

Waterboy
Navigator

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204 Posts

Response Posted - 03/17/2004 : 22:22:15

ditto what Old Salt said ... I'll add that, knowing some degree of corrosion is almost inevitabe, larger gauge will keep the current carrying capacity of the wire well in the safe zone even with some corrosion induced degradation. Also, regarding smaller gauge wire eating up current, the bottom line here is that you batteries will last longer with larger wire, and it's likely to be cheaper in the long run (http://www.copper.org/applications/electrical/energy/onesizeup.html)
Casey's "Sailboat Electrics Simplified" provides a formula for determining current loss with any load/gauge combination, but as an example, using #14 wire with a 10 amp charging load, you start losing a siginificant amount of current after about 10 feet ... that's 5 each way ... with brand new, dry, unflexed, unpinched, uncorroded bright shiny new wire with perfect connections.

I hate having to walk up the same hill twice, and I'll using #2 or larger for the battery wires. I've yet to calculate the loads and distances for the various circuits so I can't say what sizes elswhere ... 'course I'm a 'lectro toy junkie, too (FeEeL tHe PowWwErR!!!)

You may not need #4, but I'd sure go larger than #14.

'just my two clams ...

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Leon Sisson
Master Marine Consultant

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1893 Posts

Response Posted - 03/17/2004 : 23:16:12

Daniel,

I agree with Mark, in a wire run without over-current protection, the wire needs to be sized for the battery's nonimal voltage, divided by its internal resistance (when new). That calculation will indeed suggest a heavy wire guage.

Another way to greatly reduce the risk of a short circuit in the battery leads causing a fire, is to install a fuse or circuit breaker in each battery positive lead within the shortest practical lead length from the battery. This over-current protection would need to be larger than your highest anticipated current, in or out of the battery. An example of worst case peak current would be an electric starter draw plus the rating of the main DC circuit breaker or fuse. (Maybe 100A or so, total.) Then you can size the wire for the rating of over-current protection installed.

When in doubt about which wire guage to choose, refer to the standard Current/Volt Drop/Run Length charts. West Marine provides copies in their catalog (page 660 of the 2004 big book). Remember to add the lengths of both the positive and negative wires together. I would suggest using the 3% chart for everything with the possible exceptions of: electric starter, cabin lights, fans, pressure water. If you use cigarette lighter style utility outlets, be sure they are all wired and over-current protected for the most power hungry accessory you might ever plug in. A 1,000,000cp hand-held spotlight, for example, draws maybe 10A.

-- Leon Sisson

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OJ
Master Marine Consultant

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4382 Posts

Response Posted - 03/18/2004 : 09:58:21

Dan and others,

This site should provide some clarity.

http://www.ancorproducts.com/

Go to the Wire Calculator under Technical Information

Edited by - on

Daniel
1st Mate

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78 Posts

Response Posted - 03/18/2004 : 16:54:42

Thanks, everyone. I had gone thru the WM and the Ancor guidelines pretty closely and done all the calculations (with device amperages, wire lengths and gauges,etc., branch and main circuits), but hadn't figured (or read anything) on heavy wiring for possible short circuit in the main. I was planning to put circuit breakers near each battery as well to address that, so perhaps I can safely use 6 ga. wire in the main circuit.

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Waterboy
Navigator

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204 Posts

Response Posted - 03/18/2004 : 19:21:51

OJ - EXCELLENT link ... definately gets added to favorites

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