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Author Topic:   Choosing the Proper Wire Size for the Current Load
eportfolio posted 03-24-2006 11:56 AM ET (US)   Profile for eportfolio   Send Email to eportfolio  
I want to add a 12 [volt] power plug to my 13-foot whaler. What size wire do I use?
Jerry Townsend posted 03-24-2006 01:34 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
eport* - I assume that by "a 12 power plug" you mean 12-volt. What is the "power plug"? A cigarette lighter receptacle?

But the big question - and one necessary to answer your question - what are you planning on plugging into this plug? What is the current requirements of this thing you are going to plug into the plug? --- Jerry/Idaho

HAPPYJIM posted 03-24-2006 02:00 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
If you plan to light a cigar from it run a 12-AWG wire with a 20 ampere in-line fuse. Just about anything can run from the receptacle after that.
eportfolio posted 03-24-2006 04:09 PM ET (US)     Profile for eportfolio  Send Email to eportfolio     
Yes, you're right, 12 volt. My fingers don't always listen to my brain.

The only thing I can think to plug in would be a spotlight. My 13-foot Boston Whaler boat isn't exactly big enough to serve blended drinks.

deepwater posted 03-24-2006 04:46 PM ET (US)     Profile for deepwater  Send Email to deepwater     
What is the current drawn by the spot lite?
eportfolio posted 03-24-2006 04:57 PM ET (US)     Profile for eportfolio  Send Email to eportfolio     
I didn't make myself clear. Sorry. Future spotlight. I haven't bought one yet, but if I buy one and don't like it, I don't want to re-wire. Should I just be safe and use 12-AWG wire? or 10-AWG?
Buckda posted 03-24-2006 05:10 PM ET (US)     Profile for Buckda  Send Email to Buckda     
I used 12-AWG wire on mine. I use a spotlight from time to time, but I don't LEAVE it on, like some people do. When using a spotlight, it's typical for me to beam an unlighted buoy or other marker and extinguish the light. After traveling some distance closer, I may beam it again to make sure it's still where I think it is and then quickly extinguish it again before beaming the next nav aid.

Leaving the spotlight on for long periods is a significant current draw, in my opinion. It's not that I think I'll overwhelm the wiring or anything, but it can't hurt! And that's just how I was taught to use spotlights.

I normally also use a Mag-Lite flashlight which is used when I need my night vision even more, or if there is other boat traffic in the area. Nothing worse than being lit up by some yahoo's Q-Beam just when you're checking his position. Talk about destroying night vision! I want those other boaters to have as much night vision as possible so they can avoid hitting me!


Chuck Tribolet posted 03-24-2006 06:12 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I agree with Happy Jim: 12 ga wire, 20 A fuse. And will add:
All Ancor marine-grade stuff.

And BTW, get the good Marinco locking socket. They are an
order of magnitude better than anything else I've seen. The
original whaler socket corroded in short order. The
replacement Marinco has been on board at least 7 years and
is going strong.


jimh posted 03-25-2006 02:18 AM ET (US)     Profile for jimh  Send Email to jimh     
The size of the wire depends on several factors:

--current to be carried
--length of the wire
--desired minimum voltage drop

For most electrical accessories that plug in to a receptacle 12-AWG should be adequate. The circuit can be fused at 20-Ampere, as suggested above.

Backlash posted 03-25-2006 08:35 AM ET (US)     Profile for Backlash  Send Email to Backlash     
I agree with the others to use 12 gauge wire with a 20 amp fuse to wire the 12 volt receptacle. Also use the Marinco receptacle, as Chuck suggests, as it is all plastic/nylon and will not corrode. You will find the receptacle handy for plugging in cell phones, hand held GPS, etc.

If the future spotlight is the ONLY thing you plan to plug in, why not just get a rechargeable one?

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