Proper Fuse ? for Halogen lights

[DIY1111]

Running (2) 50 watt, 12 volt Jabsco flood lights. Using 18 gauge marine rated wire. The longest RUN from the (+/ fuse ) source to the light is 14'. The (-) is 10'.

Want to be sure I use the right amp fuse.

Many sources online say; voltage / volts X 1.2 is how you calculate it. BUT, I know that gauge and length of wire matters.

Knowledgable advice requested...

 

[Scott Danforth]

50 watts at 12 volts is 4.2 amps. both lights together 8.4 amps. 8.4x1.2 is 10 amps

18 gauge wire is a bit light for 10 amps, would be better with 16 gauge

 

[mike_i]

Double the length of the wire. 25' run I say 10 gauge.

 

[DIY1111]

Already ran the 18 gauge. 16 gauge was going to be a problem due to tight spacing/ splicing. I’d rather buy LED floods than rewire.

So, 10 amp fuse? Ok.

Mike - not sure, are you saying 10 gauge wire ?

i had a 5 amp fuse in there and it was blowing after 30 seconds. Switch is fine. Lights are new. 12.48 volts just about everywhere.

Hoping the 10 amp fuse does the trick.

 

[dingbat]

Already ran the 18 gauge. 16 gauge was going to be a problem due to tight spacing/ splicing. I’d rather buy LED floods than rewire.

So, 10 amp fuse? Ok.

Mike - not sure, are you saying 10 gauge wire ?

i had a 5 amp fuse in there and it was blowing after 30 seconds. Switch is fine. Lights are new. 12.48 volts just about everywhere.

Hoping the 10 amp fuse does the trick.

Fuses are thermal devices. Tripping from over temp.....10%+ Voltage drop.....Not good.

10 amp on #18 awg is marginal at best. Throw in a bad crimp or solder joint or two and....

 

[DIY1111]

Understanding electrical is not my area of strength. The mechanics and workmanship of the project are solid. Help me to understand - what is the optimal fuse for this situation ?

FYI - The OEM, (2) wires from the lights are like 22 gauge - real thin. All crimps are solid with shrink tubing over connectors.

 

[DIY1111]

The manufacturer specs 14 gauge with a 6 amp fuse. Seems odd - no matter the length of the run - it can be 5' or 30' ?

I'm at about a 10' (+) and maybe 6' (-) run.

 

[Scott Danforth]

The manufacturer specs 14 gauge with a 6 amp fuse. Seems odd - no matter the length of the run - it can be 5' or 30' ?

I'm at about a 10' (+) and maybe 6' (-) run.

14 gauge is much heavier than 18 or 16 gauge.

not sure how you get a 6 amp fuse with 2x50 watts on a 12 volt system. each light draws 4.2 amps for a total of 8.4

 

[mike_i]

check out this link
https://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

Already ran the 18 gauge. 16 gauge was going to be a problem due to tight spacing/ splicing. I’d rather buy LED floods than rewire.

So, 10 amp fuse? Ok.

Mike - not sure, are you saying 10 gauge wire ?

i had a 5 amp fuse in there and it was blowing after 30 seconds. Switch is fine. Lights are new. 12.48 volts just about everywhere.

Hoping the 10 amp fuse does the trick.

 

[mike_i]

In your first post you said you had a 24' run, now you say 16', that does make a difference. The 6 amp fuse is per light, right? Not one 6 amp fuse to run both lights. Depending on your needs and $$$ LED's wouldn't be a bad idea.

The manufacturer specs 14 gauge with a 6 amp fuse. Seems odd - no matter the length of the run - it can be 5' or 30' ?

I'm at about a 10' (+) and maybe 6' (-) run.

 

[dingbat]

14 gauge is much heavier than 18 or 16 gauge.

Yep, to the turn of 3.3 X larger.

14 gauge has a 2.5 square millimeter cross section.
18 gauge has a 0.75 millimeter cross section.

 

[Scott Danforth]

and 16 gauge is 1.5