Trojan Boat Forum

well, now I know how fires start... that's been on my list of things to discover for a while now

I added two add'l engine room lights about two weeks ago. I wired them in series, tapping off the two existing lights. I installed a 12v/60w bulb in each and have been using them ever since. I noticed that the original two weren't as bright as they used to be but figured that probably made sense since I divided the circuit futher by adding the two additional lights.

I happened to reach into the storage area behind the helm (storage for me, I hinged the panel which is screwed in place) and accidentally touched the wires going to the switch. They were HOT and one of the connectors had turned black. Yikes....

The wire looks like it's 16/2 which should be able handle the roughly 20amps (240 watts/12) but doesn't account for the distance run which might be the difference. If it's 18/2 then I'm definitely over the limit.

Does anyone know what else is on the engine room lights circuit? I really don't want to add another circuit/switch so fluorescents might be the way to go.

Tip 'o the day... check your wiring!

Bob

You wired them in series ? I hope not .if you did the would be very dim if they worked at all . I am betting you did not , easy way to check is unscrew one bulb and if the all go out you did .


16 gage wire maybe to light if any length to the wire

I've replaced my 60w engine room lifts with LED strips, and added two more. Nice and bright and draws less than the original set-up.

You are fortunate you identified he issue before it became a real problem.

prowlersfish wrote:You wired them in series ? I hope not .if you did the would be very dim if they worked at all . I am betting you did not , easy way to check is unscrew one bulb and if the all go out you did .


16 gage wire maybe to light if any length to the wire

+1

when I added mine wthey were popping the breaker.

By the way, THAT'S how I realized in 2005 that those panel switches were not switches at all, but actual individual breakers.

(I know I've mentioned that tip here as nauseum, but it's a real important safety issue that everyone needs to be aware of.)

My solution was to replace the higher wattage bulbs with the smallest 12volt I could find, still plenty of light and no issues. I just can's recall what wattage I ended up with.

RWS

Since I already have the lights, I'm going to replace the bulbs with 25w fluorescents which should drop the consumption from 20 to around 8 amps. No issue at thar draw.

I "jumped" each new light off an existing light so I guess those two are in series, the original two are not.

Speaking of breakers, I wish one have tripped right away. I had no idea what was going on and only found out accidentally.


Bob

If it was me I would want a minimum 14ga wire if not 12 ga to be safe. That long of a run in wire you may consider the 12ga and a heavier duty switch. Like a 50amp switch. But thats me.

The best rule of thumb for electrical wire size is #14 15 amps #12 20 amps #10 30 amps and #8 40 amps. When I wired my house this was the code. It would take a really big boat to exceed the recommended length of run for these wire sizes.

hey, current determines wire size. insulation determines voltage carring ability. 12 gauge will handle 20A. use stranded wire, not solid. are the flourscent bulbs made for 12vdc??

if you took 2 wires from the old lamp and connected them to the new lamp, (center to center and base to base) they would be wired in parallel, not series.

when you are comparing wattage of bulbs, the calculation is voltage x current = watts (power)

bernie

davidsmith wrote:The best rule of thumb for electrical wire size is #14 15 amps #12 20 amps #10 30 amps and #8 40 amps. When I wired my house this was the code. It would take a really big boat to exceed the recommended length of run for these wire sizes.

I believe thats specs for solid wire in an alternating current application. It may be close, but its definately not an analog for stranded wire in a direct current application.

DC voltage drop = current times resistance. Obviously different conductors will have different resistance properties. Make sure you select one that will still deliver the appropriate level of power (watts) to the lighting you are trying to run.

Its all in my book. "Phase Angle and You, A Guide To Inductive Reasoning"

"Jumping" off a light doesn't mean they're in series.

If they powered up a 120V fluorescent. bulb, they're definitely NOT in series.

Doing part in series an part in parallel is a No No as well.

Quite frankly - if you don't know the difference, then you should NOT be wiring your boat (unless you're looking for insurance money).

I have a problem with stating that a given wire size will handle x amount of current. There are more variables involved to be making such generalized statements. It really depends on the cicuit in question, and typically every circuit is different. Even if the loads are the same current wise, wire runs locations, bundling, run lengths, and critical/non-critical considerations need to be taken into account. For example: technically 14 AWG wire will only carry 15 amps safely to a load that is 12.5 feet away. That's 25 feet of wire (in general 12.5 feet from supply to load and 12.5 feet back). That's for a 10% voltage drop circuit for non-critical systems like lighting. For critical systems circuits such as blowers, bilge pumps, nav lights etc., at 3% drop allowance, 14 AWG wire will only carry 10 amps for 10 feet of wire. That's a load that is 5 feet away from supply voltage. Same holds true for all other AWGs mentioned above, not including considerations to cable bundling and those running in engine compartments which reduce current handling capacities due to increased temperatures. The key is knowing the load, the distance of run (back and forth), critical circuit or not, and the route the wire will take. Then and only then can you correctly determine which size wire to use.

Ampacity of wire as stated is for solid wire. Actually multi-strand wire is rated somewhat higher. but for sure can carry what folks have stated given appropriate length analysis.

Capacity Chart
This chart is a simple "max capacity" chart for a short wire run. Increase the wire size for long runs - for example the wires running to the back of a vehicle to power the taillights may need to be one size larger to account for the length.

Gauge 110V 12V
22 5A 5A
20 7.5A 8A
18 10A 10A
16 13A 20A
14 17A 40A
12 23A 60A
10 33A 100A
8 46A 150A
6 60A ??A
4 80A ??A


Stranded vs. Solid Wire
This one is a bit of a mind-boggler, but it's important. When electricity flows through a wire, it mostly flows on the surface of the wire, not through the middle. This effect is more pronounced on high frequency AC than it is on DC or low frequency AC. This means that a "wire" of a given size that made up of many smaller strands can carry more power than a solid wire - simply because the stranded wire has more surface area. This is one reason why battery cables in your car and welding cables are made up of many very fine strands of smaller wire - it allows them to safely carry more power with less of that power being dissipated as heat. However, this "skin" effect is not as pronounced in a typical 12V DC automotive application, and the wire and cable used there is stranded for flexibility reasons.

When looking at a chart or description of wire capacity, take note of whether it is referring to stranded or solid wire - some charts may not specify but instead assume a default based on the typical wiring used in a given application. For example, almost all automotive wiring is stranded while almost all home wiring is solid. For most applications, flexibility or the lack thereof will be more important, but for very high frequency AC applications, stranded wire might be a requirement.

Pretty neat wire calculator.
http://www.powerstream.com/Wire_Size.htm