My boat came with 16 AWG duplex going to a standard incandescent tri/anchor light. As part of my refit I'm putting a Lopolight LED tri/anchor up there. I would also like to switch to 20 AWG signal wire. Here's my argument.
The mast is 50' and the max LED current is 0.3 amps.
16 AWG has 4.00 Ohms/1000'
.3amps * 4 * (50*2)/1000 / 12V = 1.00% voltage drop
18 AWG has 6.48 Ohms/1000'
.3amps * 6.48 * (50*2)/1000 / 12V = 1.62% voltage drop
20 AWG has 37 Ohms/km (1' is 0.0003048km)
.3amps * 0.0003048km * (50*2) * 37 / 12V = 2.8% voltage drop
20 AWG weighs a lot less:
Marinco 124902 18/2 Duplex weighs 49 lbs per 1000 feet
Marinco 189303 20/2 Signal weighs 18 lbs per 1000 feet
NMEA 2000 cable uses 22 AWG and is Coast Guard certified under 46 CFR:
https://www.nmea.org/Assets/nmea2000%2022%20awg%20update.pdf
Lastly, the LED has a voltage-voltage regulator so that 2.8% voltage drop doesn't really matter.
Am I missing anything?
Signal wire in a mast ?? Too much vibration. Rule of thumb for mast wire is 14 AWG minimum. The 16 AWG in the mast already is very aggresive.
To save 1.55 lbs, I can see how that's attractive. But if you apply this logic across your entire boat, your going to have an unrealiable electrical system in a short time period.
You have so many projects running in your boat, why don't you let that one be.
That 2.8% voltage drop is going somewhere, i.e. becoming a little heat radiating off the 20 AWG mast wire. Therefore, I think, you'll be using slightly more battery power to get the same juice to your masthead light. Plus you'll have less room for install error or corrosion where those lighter wires connect. Is all that worth a weight savings of about 1.5 pounds (stretched between mast head and step)?
Grumble. You're probably right but I still have to work the problem.
You would think that UL 1426 tinned boat cable "with ultra flexible (Type 3/Class K) stranding to resist fatigue due to vibration and flexing" would be enough. The voltage drop is less than the 3% ABYC/CG reqs.
But is it worth 1.5 lbs? No, it isn't.
At a 20 degree heel with a 50' mast the rotational inertia (for pitching) for a thin rod is:
m L^2 = 1.5 * 50^2
But the mast and sails probably weigh 150 lbs. So this extra wire is about 1% of the total inertia.
For heel, those 1.5 lbs can be replaced by a point mass at 25'. The torques are:
1.5 * 25 * sin(20)
x * 6 * cos(20)
x = 1.5 * 25 * tan(20) / 6
= 2.27 lbs on the rail
= epsilon.
16 AWG it is.
Are we sailing a laboratory? I guess I'm impressed with this, don't know yet.
What you've got is a 50' of wire with a .3 ma load (the Lopolight) hanging on it. That wire shares space with your N2K cable in a conduit. Conceptually, I don't have any difficulty at all with using #22 if it weren't for the fact that #22 is frail to begin with...but #20 or #18 is fair game if the install takes that fragility into account. Remember, the made-up cable includes it's sheath which is usually more than adequate to make up for ALMOST any frailty. it's not the vibration or radiation or whatever that can do you in, it's the weight of the cable itself, and that can be mitigated. There is no rule of thumb that I'm aware of that specifies #14, either, specific to mast work. ABYC voltage drop tables may take you to that conclusion, but it wont be specific to mast wiring.
Anyway, unless I'm missing something, how does powering the Lopolight have anything to do with NMEA cabling?
I, myself, tend to err on the side of most favorable results. I'd go with # 18 for the Lopolite and stick with mfgr's spec for the N2K
Howard
I must have gotten up way too early this morning.I seem to be the one who made the connection between the NMEA cable and the Lopolite..My bad.
Howard
Howard, I was just surprised to read that N2K micro uses 22AWG for power. However those wires are in a 5 wire bundle with shielding: pretty strong. Simrad makes a lighter version of N2K micro specifically for the mast run. It's hard to find in the US but Chicago Marine has it.
As for the LED power, the big weight difference is between Marinco Duplex and Marinco Signal. The weight difference between Marinco Duplex 16AWG and 18AWG is really small, 51 vs 49 lbs/1000'. Just to further confuse things, there's also flat and round with round duplex being slightly lighter. Go figure.