Wire gauge for masthead light

[Brian S]

Hey, guys, my friend is replacing his masthead light fixture on a 20' boat. It has 2 bulbs so you can use both for anchoring (360º) or just the forward one for motoring. There's a 3 conductor cable running up to the masthead, and it seems to be single strand wire.

I thought marine wire ought to be stranded tinned wire.

So, if we were going to replace this cable run, what is the recommended wire gauge?

Thanks,
Brian

 

[woodster]

you can get by with 16 ga. if you use led bulbs but it has been said that 14 ga. is better in the long run just in case you have to replace a bulb for some reason or another to a conventional bulb .......... "Your boat your choice." author Stu Jackson.......

 

[jibes138]

you can get by with 16 ga. if you use led bulbs but it has been said that 14 ga. is better in the long run just in case you have to replace a bulb for some reason or another to a conventional bulb .......... "Your boat your choice." author Stu Jackson.......

Unfortunately the pigtail from the LED is like 22 gauge or smaller. I just finished this on my boat. Splicing 14 gauge to 22 gauge is overkill. The holes in my mast (slots) would not accept 14 gauge wire but did take 16 so I used that. It would be better if the fixture had bigger wires to splice properly.

 

[Brian S]

I looked it up in my Don Casey book, and assuming the replacement fixture still uses incandescent bulbs (my friend hasn't said anything about going to LED) I think he can use 14 gauge.

 

[Brian S]

Oh, and the chart only lists 16 gauge and bigger, because although 18 gauge might have enough current capacity, it is too delicate for boat applications.

 

[kjretlaw]

Here's a great link for a voltage drop calculator, the wire is priced right.

http://www.genuinedealz.com/voltage-drop-calculator

I have no affliation with this company but recommend them.

 

[Ken Cross]

don't worry about the 22 guage pigtail

Unfortunately the pigtail from the LED is like 22 gauge or smaller. I just finished this on my boat. Splicing 14 gauge to 22 gauge is overkill. The holes in my mast (slots) would not accept 14 gauge wire but did take 16 so I used that. It would be better if the fixture had bigger wires to splice properly.

Unlike plumbing, wire gauge doesn't need to be the same throughout the run. The goal is to reduce losses at the end point of the run. The short pigtail is negligible in terms of loss because it's so short.

Even 747s have splices with different wire sizes. Just be sure to make good waterproof splices. To crimp larger wire into a smaller splice, strip it long and double it over to add volume in the splice.

The reason for the waterproof splice way up there is not because you will dunk it, but to prevent corrosion because of humid air.

I hope this helps
Ken

 

[jibes138]

Yeah I get it about the voltage losses but my real beef is the pigtail isn't even tinned wire. If you strip more wire you find they only tinned the stripped ends they give you for connection points. So then you get out the soldering iron and tin the rest of the wire you expose meanwhile knowing the un-tinned wire will be subject to creeping corrosion, and with small diameter stranded wire the corrosion will be more apt to cause a failure sooner. Seems like a lot of these so called marine products are cheap crapola yet cost a small fortune. You can't compare this stuff to aerospace. I spent 35 years in aerospace manufacturing so I have some expertise in the subject matter. Make sure you use adhesive lined shrink tubing and adhesive lined crimp terminals to keep water out. Masts are not water tight so the wiring will likely be exposed to rain and salt spray.

 

[Ken Cross]

I agree that suppliers shortcut on component quality. Actually the un-tinned wire needs to stay that way. If you wick solder up the wire it will be brittle. Then it's just a matter of time before it breaks. I share your frustration, but the best we can do sometimes is just to make sure the stuff we do is as good as possible. One thing I have tried is to put a product called "Liquid Electrical Tape" under the shrink and shrink it down while it's still wet. The idea was to squeeze it up under the insulation. I don't know if it helped, but the connections I did that way haven't failed yet.

Ken