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Old 20-11-2020, 10:37   #1
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what AWG for mast head light?

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?
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Old 20-11-2020, 10:51   #2
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Re: what AWG for mast head light?

A #10 AWG wire is good for (3% Vdrop) 300 Amps per Foot, so 2.14 Amps over 140 Ft. (round trip) at 12V nominal.
Wire Size Chart ➥ https://www.cruisersforum.com/galler...r&imageuser=79

See also, Ohm's Law & Boats ➥ https://www.cruisersforum.com/forums....html#post1256


Wire length is always round trip total.
You can use 10% Vdrop, but I prefer 3%. You'll find the formula in the above link.
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Old 20-11-2020, 11:07   #3
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Re: what AWG for mast head light?

Quote:
Originally Posted by GordMay View Post
A #10 AWG wire is good for (3% Vdrop) 300 Amps per Foot, so 2.14 Amps over 140 Ft. (round trip) at 12V nominal.
Wire Size Chart ➥ https://www.cruisersforum.com/galler...r&imageuser=79

See also, Ohm's Law & Boats ➥ https://www.cruisersforum.com/forums....html#post1256


Wire length is always round trip total.
You can use 10% Vdrop, but I prefer 3%. You'll find the formula in the above link.
Thanks. according to that chart i can use 16 AWG wire.

5 watt bulb / 12 volts = .41 amps * 140ft = 57.4
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Old 20-11-2020, 11:24   #4
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Re: what AWG for mast head light?

It may be that the tables say you can do this... but my experience says that is a bad idea. In my opinion, anything less than 14 ga for mission critical applications (and I consider nav lights to be mission critical) is penny wise pound foolish. In real life, imperfect connections, creeping corrosion (especially up the mast) and higher current flows than those predicted on data sheets result in a need for beefier cables than the tables suggest.

Why wouldn’t you build in a little safety margin there and go a size bigger than the ‘perfect tables’ suggest?
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Old 20-11-2020, 11:24   #5
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Re: what AWG for mast head light?

Quote:
Originally Posted by BAD ORCA View Post
Thanks. according to that chart i can use 16 AWG wire.
5 watt bulb / 12 volts = .41 amps * 140ft = 57.4
Indeed, # 16AWG is more than adequate for such a small load, electrically.
For mechanical reasons (robustness), you might consider over-sizing at #14 AWG.

I think Nsboatman might be sympathetic to the basic premise, expressed in the Ohm’s Law & Boats article. I also, agree with the author.
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Old 20-11-2020, 11:41   #6
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Re: what AWG for mast head light?

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Originally Posted by NSboatman View Post
It may be that the tables say you can do this... but my experience says that is a bad idea. In my opinion, anything less than 14 ga for mission critical applications (and I consider nav lights to be mission critical) is penny wise pound foolish. In real life, imperfect connections, creeping corrosion (especially up the mast) and higher current flows than those predicted on data sheets result in a need for beefier cables than the tables suggest.

Why wouldn’t you build in a little safety margin there and go a size bigger than the ‘perfect tables’ suggest?
thank you, i couldn't agree more and thats exactly what i would do. i plan to use 12 AWG. its nice to be able to calculate a base umber though so i know where to start at.
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Old 20-11-2020, 13:40   #7
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Re: what AWG for mast head light?

@Bad Orca
To be compliant with ABYC Standards, the navigation lights must be served with conductors that produce <3% voltage drop.

Calculation shows that AWG 16 would be sufficient for a 0.5A (guess) load at 12VDC and 140' circuit and would yield a 2.43% voltage drop. FWIW, the CFR does not allow any branch circuit wiring <AWG 14. Your choice of AWG 12 will work just fine.
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Old 20-11-2020, 14:53   #8
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Re: what AWG for mast head light?

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@Bad Orca
To be compliant with ABYC Standards, the navigation lights must be served with conductors that produce <3% voltage drop.

Calculation shows that AWG 16 would be sufficient for a 0.5A (guess) load at 12VDC and 140' circuit and would yield a 2.43% voltage drop. FWIW, the CFR does not allow any branch circuit wiring <AWG 14. Your choice of AWG 12 will work just fine.
Thank you, i appreciate the ABYC clarification. I was not aware but really would like to be compliant as much as i possiby can. The only issue i may stray from intentionally is the use of yellow wire on my DC side but thats a whole other thread topic. much thanks.
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Old 21-11-2020, 09:56   #9
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Re: what AWG for mast head light?

not to start A recalculate moment but new Led light are 4 to 24v so I think they are not as VD sensitive , wiring should be sized to support a standard incandescent , my led mast head sure creates a lot of radio interference RF I think fair winds
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Old 21-11-2020, 10:38   #10
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Re: what AWG for mast head light?

The ABYC standard (E-11.14.2.6) calls for the 3% table to be used for essential items (panelboard or switchboard main feeders, bilge blowers, electronic equipment, navigation lights, and etc). and the 10% table for non essential items ( lighting, other than navigation lights, entertainment, fans, and etc)

The conductor size necessary to keep voltage drop below the maximum permitted level may be calculated by means of the following formula:

CM = (K x I x LCM) ÷ E

Where:
CM = Circular mil area of conductor.*
K = 10.75 (constant representing the resistivity of copper)
I = Load current in amperes
L = Length of conductor from the positive power source connection to the electrical device and back to the negative power source connection, measured in feet.
E = Maximum allowable voltage drop at load in volts

(e.g., for a 3% voltage drop at nominal 12V, E= 0.03 x 12, E = 0.36;
for a 10% voltage drop at nominal 12V, E = 1.2

* Use ABYC TABLE XI or TABLE XII (or my Wire Size Chart) to convert circular mils (cm) to conductor gauge.
If the cm area falls between two gauge sizes, the larger conductor shall be used.

My Wire Size Charthttps://www.cruisersforum.com/galler...r&imageuser=79

ABYC E-11 July, 2008 (out of date) ➥ http://www.blackfinforums.com/sites/.../abyc-e-11.pdf

CharlieJ: Does the CFR differ from ABYC, which allows #16AWG (& some #18 in specific exceptions)?
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Old 21-11-2020, 10:53   #11
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Re: what AWG for mast head light?

Quote:
Originally Posted by patrick brooks View Post
not to start A recalculate moment but new Led light are 4 to 24v so I think they are not as VD sensitive , wiring should be sized to support a standard incandescent , my led mast head sure creates a lot of radio interference RF I think fair winds
The only light on top of my mast is an anchor light (the new one). my deck and steaming light are mid mast at the spreaders. im hoping the anchor light doesnt interfere with VHF but it would be a simple task to shut it off if i needed to use the VHF.
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Old 21-11-2020, 12:13   #12
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Re: what AWG for mast head light?

No need to double it, the length for your calculations, it is on the other side of the load.
LED, I'd not worry about wire size other than for strength not current carrying capacity.
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Old 21-11-2020, 13:25   #13
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Re: what AWG for mast head light?

Quote:
Originally Posted by Cadence View Post
No need to double it, the length for your calculations, it is on the other side of the load.
LED, I'd not worry about wire size other than for strength not current carrying capacity.
Did anyone mention use a tinned copper wire!
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Old 21-11-2020, 15:20   #14
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Re: what AWG for mast head light?

Just a comment: most modern LED lights have on-board circuitry that claim full light output at voltages from (typically) 10-30 VDC. This being the case, worrying about small voltage drops seems unnecessary.

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Old 21-11-2020, 15:55   #15
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Re: what AWG for mast head light?

Quote:
Originally Posted by Cadence View Post
No need to double it, the length for your calculations, it is on the other side of the load.
LED, I'd not worry about wire size other than for strength not current carrying capacity.
Voltage drop and capacity is figured for the entire run, not just one side to load. Each wire acts as a resistor in the circuit.
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