10AWG for a 1amp nav light? AWG Overkill?

[Shrek6737]

Hello,
I am working on rebuilding a project boat and I am currently planning out electrical work and wire costs. The boat is a 17ft 1978 Hammond with a Merc 470. I measured out the round trip (fuse panel to dash switch control to nav light and back) for the light and it calculates out to about 54.6 feet. I am using the ABYC 3% voltage drop chart for awg determination. Since the nav light only pulls about .7 amp (per spec sheet) I default to the 5 amp setting on the ABYC chart. All these numbers on the chart are pointing to a 10AWG wire. To me this seems crazy overkill even for a 3% volt drop.

The original wiring in the boat, which I am assuming was built in 1977 range has 12 AWG for all the non-engine related electrical. The battery feed to the switch panel currently has an 8 or 6 AWG wire for a 36 ft round trip run.

All of the charts I seem to find for selecting AWG seem to keep coming up the the numbers above (10AWG) but that just seems crazy overkill to me. Is 10AWG correct and I'm just going to have to chunk out some $ for bigger wire or is there something I'm missing?

 

[dingbat]

Hello,
I am working on rebuilding a project boat and I am currently planning out electrical work and wire costs. The boat is a 17ft 1978 Hammond with a Merc 470. I measured out the round trip (fuse panel to dash switch control to nav light and back) for the light and it calculates out to about 54.6 feet. I am using the ABYC 3% voltage drop chart for awg determination. Since the nav light only pulls about .7 amp (per spec sheet) I default to the 5 amp setting on the ABYC chart. All these numbers on the chart are pointing to a 10AWG wire. To me this seems crazy overkill even for a 3% volt drop.

The original wiring in the boat, which I am assuming was built in 1977 range has 12 AWG for all the non-engine related electrical. The battery feed to the switch panel currently has an 8 or 6 AWG wire for a 36 ft round trip run.

All of the charts I seem to find for selecting AWG seem to keep coming up the the numbers above (10AWG) but that just seems crazy overkill to me. Is 10AWG correct and I'm just going to have to chunk out some $ for bigger wire or is there something I'm missing?

Should be using 10% unless your powering sensitive electronics. Having said that, most modern electronics have no problem with a 10% drop

A 54’ long circuit on a 17’ boat?

My boat is 22’-6”. Longest circuit on the boat is the distribution panel at the helm…31’. Longest lighting circuit is less than 15’ - 16 ga wire

 

[Shrek6737]

Should be using 10% unless your powering sensitive electronics. Having said that, most modern electronics have no problem with a 10% drop

A 54’ long circuit on a 17’ boat?

My boat is 22’-6”. Longest circuit on the boat is the distribution panel at the helm…31’. Longest lighting circuit is less than 15’ - 16 ga wire

I'm also wondering if I'm measuring or calculating the distances wrong. An example is the switch panel to/from the fuse panel. Measured 18ft, routing from port side battery area (in stern), to transom, across transom, along starboard rail, and down to panel. I had 94+24+16+16+36+16+16=218" = 18.1'. Having typed all this out, I think I added some extra length to go around (don't know what to call them) 2 equal size pillars that the engine bay venting goes through. The current wiring goes "through" one of these (essentially switch panel starboard side rail strait across transom to battery). If I go that route, now that I've processed all of it a bit more, I can probably axe 3' of calculated length per run.

I am using 3% drop due to USCG/ABYC saying critical loads. Blower, nav lights, horn.

 

[dingbat]

Your over estimating a bit in your length and using a 5 amp (chart) instead of 0.7amp actual load.

If you use the actual values the wire size calculator comes up with a 16 awg wire for a 1 amp load

Circuit Wizard - Blue Sea Systems

circuitwizard.bluesea.com

 

[Scott Danforth]

your boat is only 17 feet. no way your total length of wiring is 54 feet to a nav light. if your nav light is at the helm, and your circuit breaker and switch is at the helm, your looking at 20 foot max lenght

my boat is 26 feet long, max length of run on any circuit in my boat is 22 feet total and that is the blowers. bow light is only 20 feet

3 batteries in the stern. 1 for engine, 2 for house
00 gauge wires from the engine battery to the block/starter, 6 gauge wires to the helm for engine wiring. 12 gauge back to the engine for fuel pump/ignition/etc. 12 gauge to the bilge pump, 14 gauge to the blowers
4 gauge wires from the house batteries thru a 100 amp circuit breaker to the helm power distribution center
16 gauge to all the nav lights
16 gauge to the horn
16 gauge to all the courtesy lights
18 gauge to all the alarm triggers
6 gauge to the amplifier/stereo

while I could have run lighter wires, I do not run anything less than 18 gauge for the pure mechanical strength

also, you should be calculating voltage drop with actual load

 

[Shrek6737]

your boat is only 17 feet. no way your total length of wiring is 54 feet to a nav light. if your nav light is at the helm, and your circuit breaker and switch is at the helm, your looking at 20 foot max lenght

my boat is 26 feet long, max length of run on any circuit in my boat is 22 feet total and that is the blowers. bow light is only 20 feet

3 batteries in the stern. 1 for engine, 2 for house
00 gauge wires from the engine battery to the block/starter, 6 gauge wires to the helm for engine wiring. 12 gauge back to the engine for fuel pump/ignition/etc. 12 gauge to the bilge pump, 14 gauge to the blowers
4 gauge wires from the house batteries thru a 100 amp circuit breaker to the helm power distribution center
16 gauge to all the nav lights
16 gauge to the horn
16 gauge to all the courtesy lights
18 gauge to all the alarm triggers
6 gauge to the amplifier/stereo

while I could have run lighter wires, I do not run anything less than 18 gauge for the pure mechanical strength

also, you should be calculating voltage drop with actual load

Yeah I for sure wont be running anything lighter than 18 for the same reason. I'll probably push that up to 16 just as extra caution.

The 20ft length you menton, is this round trip or one way? The 54ft I came up with (need to re-measure it anyway) was a round trip so from source through switch to light and back.

The circuit wizard dingbat suggested is for sure giving better awg than using the charts. My guess is since charts are loads above 5 amps.

My main goal for the wiring is to do it as recommended by ABYC and USCG for safety factor. But i have a feeling that's going to hit the budget hard. Break Out Another Thousand. Lol

 

[Scott Danforth]

99% of boat manufacturers are running 16 gauge to the nav lights on boats much bigger than yours.

 

[Fossil Fueler]

I agree 16 ga wire is fine. Just remember, use marine grade tinned copper wire. Don't be the guy using cheap Chinese "copper clad" aluminum speaker wire even for speakers. Even American made pure copper wire without the tin coating on each strand will be subject to copper oxide growth in marine applications. Copper oxide is green in color and is an insulator, ie it does not conduct electricity.