I have 5 hubbell 505 fixtures mounted on the front of a flounder boat and going to wire them to a 12 volt battery with alternator, the bulbs are 150 watt. I need help on wire size 12 guage? And fuse size? and how many to a circuit 3 and 2? Thanks for any help Bob

 

The current determines the wire size. 150W/12volts= 5/4amp which is 1.25 amps. The National Electrical Code specifies the wire size, but my copy ignores any current less than 15Amps (no. 14AWG). I'd say no. 18 AWG is good enough for one light and use a 2 amp in-line fuse (slow blow) with each light.

I'm not sure about the second part of your question. 3 lights means 3.75 amps. And you want to put them on one circuit with one fuse? Again, use no. 18 but this time use a 5 amp fuse, slow blow.

 

Rerun the calculation - I get 12.5 amps/bulb (12 x 12.5 = 150).

 

Uh oh! LOL, that's alcohol for you. Yes, we have 12.5 amps per bulb. So use no 14 wire and a 20 amp slow blow fuse for each light. But if you want to run three lights on one circuit, we have 3*12.5=37.5 amps.

What this means is that you use no 10 AWG to the first light on the circuit, then use no 12 to get to the next light, then use no 14 to get to the next. Wire them in parallel, not series. This involves tapping your feeder with no 14 AWG wires at each light.

 

PRS thanks for the reply, I like the 1st calculation better but was told by a friend close to the same of the 2nd post. Thanks Bob
P.S. I have 3 of the lights in the front of the boat and one on each side.
I think I will run 12 wire to 2 lts with 30amp fuse x 2 and one with 14 wire with 20 amp. Thanks again.