Amp draw on DC lights

[DeepCMark58A]

I am running new wiring on my old tin Deep C, up front I have a bow light, spot light, and a 12v power point. I decided to run 1 heavy set of jacketed wires up front and put together a power distribution strip up there so to only run 1 set of wires under the floor. I was thinking of 12 gauge, is that right on the edge? I do have access to 10 gauge but that seems like overkill.

 

[Alumarine]

Without knowing the draw I'll guess and say the 12 gauge is ample unless you have a super duper spot light.

Here's a link that might help.
http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

 

[gm280]

I have to completely agree with marc c. We have no idea what all those accessories draw in current. Usually 12 gauge would work nicely. But without knowing the current you will be pulling, and the length from the battery, it is merely a guess. JMHO

 

[Silvertip]

16 gauge is very adequate to feed any navigation light, instrument panel lights and gauges, and other low amperage devices. Power outlets have a maximum current rating normally printed on the package. Size the wiring and fuse according to the outlet capability, not what you might plug into it. A "feeder" circuit (the topic of your inquiry) needs to be a wire size capable of handling the demands of all accessories fed from it. Based on the lack of detail regarding accessories, it would appear 12 gauge is fine in your application. The current draw of the spot light will likely be the highest current draw.

 

[NYBo]

I think you need to rethink your plan. With just one set of feeds, everything is switched together unless you also put your switches for the individual devices up there. Not very convenient.

 

[DeepCMark58A]

I ran the wire to the front of the boat to a 6 point terminal strip mounted on a din rail. Two wires in contacts for 3 inputs out.

 

[DeepCMark58A]

No Title

 

[DeepCMark58A]

I think you need to rethink your plan. With just one set of feeds, everything is switched together unless you also put your switches for the individual devices up there. Not very convenient.

I am rewiring back to the original switches.

 

[gm280]

DeepC, I would use separate switches AND individual fuses/circuit breakers for each circuit. Otherwise if one feed shorts out, you loose everything. So separate all the different circuits, and install fuses/breakers and switches. Then you have total control over everything. I realize you have a fuse at the main run at the battery (or I hope so), but you also need fuses/breakers at the break out junctions as well. So before rewiring everything. Draw up a plan and post it back on here for us to see. If it looks correct and safe, we will tell you so. JMHO!

And one issue I would like to say. But mine you , this is just MY opinion. Some talk about fusing to the limit of the wiring run. But I disagree with that assumption and here is why. If I run 12 gauge wire, and I read that 12 gauge wire can handle 15 amps for a 10 foot run. I don't use a 15 amp fuse or breaker in that circuit. I use a 10 or 12 amp fuse instead. Because yes it can handle 15 amps when everything is fresh and all the connections are bright and shiny and new. But over time degradation takes hold and now 15 amps may cause the wires to heat up. And the worst it gets the hotter the wire gets. So in time it could start a fire if 15 amps were drawn across it now. So I usually fuse for a little over what I will draw on that wire. So add up what you will use on that circuit and then figure in just a little over that and fuse for that amount. I doesn't matter if the wire can handle more or not. It is a safety factor. Example, if your depth locator uses 4 amps max, I would use a 5 amp fuse, not a 15 amp fuse. Bu that is just my opinion. Not everybody likes that idea. So whatever you do, just don't exceed the wire capability.

 

[DeepCMark58A]

I am looking to convert the bow and stern rights to LED. My main reason for the power run to the terminal strip is because I wanted to run just 1 set of wires under the floor so it is simply a power distribution strip, I am fusing from the strip to the existing 1958 switches. The only real amp draw will be on the spot light and it will be operational but seldom used. I don't see well at night so I am off the water before dark.

 

[Grandad]

I agree with gm's assessment. It's an electrical industry standard to not continuously load a fuse or circuit breaker to more than 80%. They tend to cook and fail early when loaded at 100%. So a 4 amp load should have a minimum 5 amp fuse for a load that might be on for several hours. I think too many people feel that if they use a large wire, they can use a large fuse. That works for wire protection, but if the wire is proportionately oversized to the actual load, the device itself may have insufficient protection. All of that said, I still tend to slightly increase the size of fuses for critical loads such as a bilge pump, but never beyond the wire's capacity. I would likely size a "main" fuse at 100% of the wire's current rating, assuming that it feeds proportionately sized branch circuits, each having individual fuse protection. And always carry a range of spares. - Grandad

 

[DeepCMark58A]

I understand fuse protection and amp draws not certain I get the insistence about fusing for lights, unlike most loads when lights fail the circuit opens because the filament accost the contacts is gone not possible to short out. Have you ever had a household light trip a breaker or blow a fuse?

 

[gm280]

I understand fuse protection and amp draws not certain I get the insistence about fusing for lights, unlike most loads when lights fail the circuit opens because the filament accost the contacts is gone not possible to short out. Have you ever had a household light trip a breaker or blow a fuse?

DeepC, yes that is a fair question. However, if you ever decide to go LEDs instead of incandescent, LEDs are actually diodes, and there for can short. So I would certainly have every circuit prepared for whatever could happen. Fuses and breakers are cheap and can be the difference from burnt wires and a possible fire, to a blown fuse or popped breaker. Your call there. JMHO!

 

[DeepCMark58A]

That was a rhetorical question, I already have the inline fuses purchased. But in all honesty if you consider the possibilities we tend to go way overboard I mean if you were that concerned about all the what if's that could happen why would you ever put the boat in the water?

 

[gm280]

That was a rhetorical question, I already have the inline fuses purchased. But in all honesty if you consider the possibilities we tend to go way overboard I mean if you were that concerned about all the what if's that could happen why would you ever put the boat in the water?

Again DeepC, a very fair question. My answer is this. If you ever have a fire on a boat, and are out in the lake someplace, you can't run away from the fire. You are stuck there with the boat fire. Not a pretty scenario. It isn't being paranoid. It is wiring for safety. That's all. And honestly, every suggestion on these forums are just that...suggestions. It is your boat and your decisions. Just pointing out the proper way to wire things. Certainly not trying to upset you or contradict you in any way or fashion. Merely making suggestions. eace:

 

[DeepCMark58A]

No not at all like I said it is rhetorical. People would freak out about how the old wiring was done. The old fabric jacketed wire with the negative "grounded" to the boat and the live positive going straight to the battery. The boat made it 59 years without an incident. Modern electronics and circuit boards sure complicate things.

 

[NYBo]

Fuses protect the wiring, not the device connected to them. If you end up with a dead short before the device and there is no fuse, the wires can become dandy fire starters.

 

[bruceb58]

Fusing a wire has nothing to do with the length of the run. The length of the run only determines the voltage drop in the wire and has nothing to do with how much current a wire can safely handle.