Minimum wire size

Before I found out that ABYC specifies a minimum wire size of 16 gauge I bought a 500' roll of 18/2 wire. I am wondering how important it is to stick to that recommendation. The application that I intend to use it for are LED running lights with a negligable current running to it so even 18/2 is overkill.
If it is going to mess me up down the line with resale or anything else then I rather eat the money for the 18/2 and buy 16/2 but it seems a little silly.
Any thoughts?

 

What are you wiring? How long is the longest run from the panel going to be (voltage drop = current x ohms per foot)? 18 AWG is 6.48 ohms per 1000'. What is the total load per circuit? Running lights (bow light)? Is the wire AWG or SAE? How many conductors will be bundled together (this effects amperage capacity)? Do you really need 6 pounds of wire (AWG) for this job?

 

Thanks PAR, that is the thing, load sizing wise I could be running a lot smaller wire but the smallest marine grade wire that I could get easily is 18/2.
I am running maybe 50mA on a 100' run (2 x 50). My aprehention to just go ahead and use the 18/2 is that ABYC dictates that the wire size should be no smaller than 16 gauge and I don't know if this may give me problems down the line with things like insurance or resale.

 

arjan
When sizing your wire, keep in mind, you have to count both directions in your run. i.e. If it is 50' from source to load then you have to size for 100'.
I think ABYC only limits to that size because of the difficulties in properly ending and protecting (fusing)the wire. It is certainly not a problem if done right. The problems are:
-Attaching a wire end to such a small cross sectional wire without breaking too many of the relatively few strands.
-Getting proper crimping pressure on such small wire with the typical termanals yacht buiilders use.
-Restraining the wire well next to the terminals so that no movement or strain occurs causing breakage of small cross sectional wire.
-Water proofing the exposed wire near the terminal because, again, the corrosion would cause resistance in such small wire very quickly.
-For such small loads you need to use a fuse, in place of or after a breaker. Typical breakers used on yachts would not be sensative enough for such a small load.

I am taking a risk saying this, but I would be suprised if that effected anything as far as insurance or sales of the boat---as long as you did a proper installation. Many boats have much smaller control wires than 18 ga in them.

 

Don't downgrade your system.....

Smaller gauge wire requires a higer current to produce the same voltage over distance. That creates heat. Heating and cooling create corrosin at connections. Corrosion at connections create more resistance. 18 gauge might never bother your system. Or you might be chasing annoying little problems. Your choice.

 

6.48 ohms / 1000'= .6 ohms for a round trip run of 100'. Voltage drop is amps. X resistance. .6 X .050 amps. = .03 volts of drop at the end. Don't sweat it. You can tie all the LED only, lights together and be very safe with a 1 amp. fuse. 10 of those LEDS = .324 volts drop if you tied all 10 at the end of a 100' cable

 

Actually, Cyclops, ABYC and Lloyds require the next size up on a .03 voltage drop. It is also general practice to increase wire size at 3% and over for lower draw circuit like bow, nav, blowers, electronics, etc. and 10% or over on heavy draw stuff.

In his application, using nothing but LED's he'll have no problem, but his concern was about resale value and legal requirements. The resale value will likely not be effected as a surveyor would see marine rated wire and wouldn't pull a load check on each these types of circuits. Which leaves the legal questions, which seem to answer themselves after some simple math, but the law may not allow this, only conformity. The idea being if a LED unit was replaced some time after this boat was sold, believed in compliance, with a standard nav unit. Typically navigation lights come in 10 and 20 watt sizes and draw about 3/4 to 1.5 amps this assumes it's not a combo unit like a masthead/foredeck flood which can draw more. This could cause the need for the bigger gauge wire.

Frankly, I think LED lighting is new enough on the market, that most codes don't cover their application yet. Use the 18/2, your insurance man could hang you in the event of an electrical issue regarding damages on or near this circuit, but this seems an unlikely event. I'm not sure what kind of deal you got on the 500' roll, but 400' of extra wire is hard to use up unless you do this sort of thing for a living. It's a judgment call and you can make the decision reasonably, but 100' of 16/2 duplex (with sheathing) retails around 50 bucks or two rolls of 100' 16 gauge for about 35 bucks. This is for Ancor AWG marine grade type 3 (tinned copper) wire.

 

Par. How does ABYC resolve AC and starting motors wild current draws. Even P&L companies allow a slight warming of wires at maximum load. The wires are protected for maximum current on land. Why such a high safety factor in boats. Modern bowriders use CB's to protect ckt's at P&L current levels.------------------------------I went to the U S C G builders wire and current capacity tables. They list 18ga. 140F wire as 10 amp. 200F wire is rated at 25 amp. outside of engine areas and------ 18 ga. 140F wire is rated 5.8 amp. in engine areas. Obviosuly the ABYC is off in another world. Does the ABYC have a legal USA code of enforcement ? Who is legal in a court of law?-------------------------I went to the ABYC web site and read their own statement of what they do. Have meetings on a subject with anybody in the boat business, discuss, have another meeting. They state that we should follow C F R ? regulations.--------18 ga. wire is legal to use. That is why you could buy it and it was labeled O K for marine use.

 

WOW! Much ado about very little. When I put nav lights on Bietzpadlin I used both LED and standard incandesant. I use the LEDs when I sail at night but turn on the incandesants when I am motoring. If the wire is too small and the run is long then the lights will not be as bright as they ought. With 6+ ohms /1000 feet you could short the ends of a 500 foot circuit together and only draw 2 amps.

 

I'm in agreement with you Cyclops, ABYC recommendations are difficult to understand, Lloyds is much better at it. Even SAE has lower ratings the ABYC for the same gauge wire which has 20 - 30% less strands and diameter.

Having a product label for marine use doesn't cover it's installation. Winning or not in a court battle has little to do with truth or the search for it. Generally it boils down to which court jester has the most believable story. The money invested in these jesters, unfortunately, usually produces the results desired. In a real world situation, the insurance company will show up with several jesters.