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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 01-19-2011
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Light it up - on same fuse?

Hi,
To light up our engine room we have purchased four LED strips of 20 LEDs each. Each strip uses less than 1/5 amp.
So a total of lees than an amp.

The Wire to the nav station electrical panel will be 16 gauge.

That will be a 1.36 voltage drop at about 20 feet. Which is about the length needed.

So if you fuse 80 percent of the 16 gauge wire what size fuse would we need?
How do you calculate that fuse size?
And would we even need to fuse such a small load on the wire?

Next Question:

If we need to fuse the engine room LED lights then could we have more than one set of lights on the same fuse.

For example:
We have engine room lights at less than and amp

We have a food storage LED light at less than and amp.

Can we have both those wired to the same T fuse block and on the same fuse using differnt 16 gauge wires, one set of wires (- and + )for the food storage and another for the engine room set of lights ?

Both would not likely ever be on at the same time.

Thank you,
Chip

Last edited by SanDiegoChip; 01-19-2011 at 12:51 PM.
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Old 01-19-2011
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You fuse to protect the wire not for the load. The fuse should be sized at less than the ampacity of the wire but larger than the load. I use 15 amp or smaller for 14 awg and 10 amp or less for 16 awg. With such a small load a 5 amp or smaller could be used. The ampacity chart I have seen shows 25 amps for 16 awg and based on this 80% makes no sense. I have included it below - it is from Blue seas.
Remember any distance for DC wiring is measured there and back.
Yes you can have several lights on the same fuse.
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Old 01-19-2011
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fuse the wire

Blue Seas support is where I got the “fuse the wire for 80 percent of the load” I think. So what I am thinking is if the wire is rated to carry the load you have, then fuse it so that if the load gets to 80 percent of the max load you are going to use it for then it will blow. The wire will never see the full load thus never come close to burning up. This seems to make sense to me. But of course a lot of things make sense to me but are nonsense to others.
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Old 01-19-2011
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If you fuse for less than the load there will be a few blown fuses I think.
The fuse should be larger than the load but smaller than the amperage the wire can safely carry. In your case with just LEDs the load is very small. Based on load alone you can use a pretty small wire. Then voltage drop becomes a factor. On a boat I wouldn't use any wire smaller than 16 awg in any case.
So as long as the fuse is larger than the load with all lights on at the same time it won't be a problem.
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Old 01-19-2011
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Just curious why you would accept over a 10% drop in voltage for your lights. That strikes me as counter productive.
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I agree dog - I missed that. I use 3% or less for everything. As a matter of fact I have some interior leds on short runs with 14 awg - overkill but I had the wire handy.
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Old 01-19-2011
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OK thnaks for the help.
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Well what came off the calculator was a 1.04 percent drop. So I thought anything with in 3 percent was acceptable.
Is this not correct?
15 feet
16 awg
12v
1 amp load
Genuinedealz - Technical - Calculators
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No, that is fine... it just sounded like you had a larger voltage drop, since you wrote:

Quote:
That will be a 1.36 voltage drop at about 20 feet.
and didn't say percent anywhere at all.

Personally, I'd go with heavier wire just in case, since you may decided to add a halogen or incandescent light fixture at some point in the future. Running heavier wire is basically cheap insurance towards future upgrades.


Quote:
Originally Posted by SanDiegoChip View Post
Well what came off the calculator was a 1.04 percent drop. So I thought anything with in 3 percent was acceptable.
Is this not correct?
15 feet
16 awg
12v
1 amp load
Genuinedealz - Technical - Calculators
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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