what AWG for mast head light?

[Spot]

The issue seems to be the intuition of knowing LED's are lower current devices combined with not enough understanding of DC circuit theory and/or regulatory requirements. I do not claim expertise on these, I can also make mistakes with the best of them. Here is what I understand as of now:

The spec's seem simple: Nav lights=critical system=<3% voltage drop round trip and 16 AWG min (ABYC) and <3% voltage drop round trip and 14 AWG min (CRF).

OP's P+B 2NM all-around white series 580 2.8W 9-28v LED would pass voltage drop round trip on 18 AWG, simple enough to verify, no need to guess... but 18 AWG is not allowed for navigation lights per ABYC and CRF. The choice of 14 AWG for this application seems like a winner.

Fair winds and following seas to all,

[Bycrick]

For what little it’s worth, I have two wire-sizing apps. Both have as input the "one way" run length. I can’t see that it makes much difference, unless you don’t bother to read the instructions for the table/app, or can’t multiply by two where necessary.

[DeValency]

Originally Posted by Bycrick

For what little it’s worth, I have two wire-sizing apps. Both have as input the "one way" run length. I can’t see that it makes much difference, unless you don’t bother to read the instructions for the table/app, or can’t multiply by two where necessary.

What a relief... now I don’t need to ask MIT to change the electrical engineering department text books... 🙂

[CharlieJ]

@Bycrick
I also have two wire sizer apps:
1. WireSizer-calls for "circuit length", circuit being to and from the load from the source
2. Circuit Wizard by Blue Sea Systems- requires "Length of Conductor" and further defines this as "The total length of the conductor-the combination of supply wire and return to complete the circuit."

GordMay in #10 quoted the formula for calculating wire size from the ABYC Electrical Standard. In the formula, the circuit length is defined as from the source to the load and returning to the source.

Spot in #15 correctly depicted a circuit as a supply and a return, both conductors having small, but not insignificant, resistance.

I continue to beat this horse because @DeValency is adamant in declaring that, for calculating DC voltage drop, only the length one way is used. This is wrong and his erroneous statements may lead an electrical novice down the wrong path.

[GordMay]

Originally Posted by Bycrick

For what little it’s worth, I have two wire-sizing apps. Both have as input the "one way" run length. I can’t see that it makes much difference, unless you don’t bother to read the instructions for the table/app, or can’t multiply by two where necessary.

Please share a link.
Personally, I've never seen such.

[Bycrick]

The two apps are DC Wire Sizer and the iNstall app from Gemeco. In most cases, people run two wires together, so it’s "easier" to specify the length of the run and have the app multiply by two. I can’t remember the last time I just wanted to size a single wire.

[CharlieJ]

@Bycrick
But the point that @DeValency is erroneously making is that a "circuit" is only one way. Yes, DC Wire Sizer does the math for you but it is circuit length which is to and from the load from the source.

[CharlieJ]

@Bycrick
And this from the User’s Guide for Wire Sizer:

How to Use

You may specify the circuit voltage (DC only), current (in amps), and total circuit length (round trip, from the electrical source, to the load, and back) by "flipping" through the options in the top spinner. In the bottom spinner you can see the gauge of wire needed for different percentages of voltage drop. Wire gauge recommendations are for commonly available SAE, AWG, and ISO/Metric wire sizes

[DeValency]

For all the ABYC experts here... this is really amusing, but to close the case, at least at my end;
Just do the math, calculate the current (100mA for 1W LED) density per conductor cross cut in sq.mm and you’ll find out how far are you from the anachronistic 14 AWG.
That’s unless you decided to place a fully illuminated Christmas tree on your masthead.

Out.

[Bycrick]

Choosing a wire for its physical properties isn’t anachronistic: it’s good engineering. Resistance/voltage drop is just one of the considerations, and often not the most important one.

[Icarus]

Originally Posted by BAD ORCA

i bought a new LED mast head anchor light, now i need to order the correct gauge wire.

according to the blue sea chart im assuming i can use the 10% (non critical) specifications. I guesstimate 50 ft mast height and roughly another 15-20ft to the nav desk so 70 ft total. do i use this as my estimate for my total wire run length or is it double that length (round trip) so 140 ft? 140 round trip would put me at 10 AWG wire for a single LED anchor light. does that sound about right?

10 AWG can carry max 15A
12 or 13 AWG would be better

[s/v Jedi]

Originally Posted by Icarus

10 AWG can carry max 15A
12 or 13 AWG would be better

10AWG can carry 60A so 4x as much as you think...

[DeValency]

Originally Posted by s/v Jedi

10AWG can carry 60A so 4x as much as you think...

And about 200x the current required to power a masthead LED light.

[GordMay]

Originally Posted by Icarus

10 AWG can carry max 15A
12 or 13 AWG would be better

#10AWG is rated 30A NEC (60A @ 86 deg. F/ or 51A @ 122 deg F, per ABYC)
#12 would be lesser, rated 20A NEC, (45A/38.3 ABYC)
#13AWG is not a standard size.

[Spot]

Originally Posted by DeValency

And about 200x the current required to power a masthead LED light.

This we can agree on!

If the P+B Series 580 light is ran at is lowest operating voltage 9v and is consuming its spec of 2.8W and w=v*a so 2.8=9*a yields .311 amps. As the volts increase, if the watts stay the same then the amps decrease, making the device easier to wire with smaller gauge wire.


***


This problem is not just AWG and amps. It's AWG and amps and length of wire and allowable voltage drop and minimum wire size allowed per the specification used to validate the installation.

For the 'Muricans we get ABYC and CRF. Both are 3% max drop for nav lights. They both have a minimum wire gauge and exceptions to minimum that do not include nav lights if I am reading them correctly.

The formula for voltage drop is amps*overall wire length*resistivity of that gauge wire. Easiest for me to do online but I can also do the math at home.

Picture below is me using the online calculator to fill in a small table. I did spot check some of the numbers and online agrees with by hand. If there is something wrong with my thinking or my math or my understanding of specs, I am open to discuss and learn as I am in the middle of a while boat rewire and would like to get it right.