Originally Posted by 65chevelle300post
The factory headlight switch uses a 15 amp thermal overload breaker so I'm not sure why you would need a 30 amp resettable fuse to protect the relay power wire when 15 amps should be enough. Even with the Halogen's you won't pull that much.
Maybe Joe can explain the reasoning for this?
This isn't the factory configuration. Power is tapped from under the hood with the assistance of relays, thus the voltage level seen by the lamps will be higher. An increase in voltage results in an increase in current with the incandescent lamps.
About 2 years ago or so, I did some current measurements with the modern Wagner "drop in" halogen replacements. (This is for a factory 4 lamps system, the outer bulbs being both hi/lo combination units and the inners being HI only, with all 4 units illuminating in hi beam mode)..,
I used a fully regulated DC power supply with the voltage set at 13.3 volts. Higher then a stock set-up, but low for many of you out there with revamped electrical systems providing a closer to alternator output level across the lamps filaments (14++).
The Wagner H5001 units (the hi-beam only unit), drew 3.8 amps.
The Wagner H5006 units (the hi/lo combo units) drew 2.78 amps (with the high filament powered).
So in high beam mode, (3.8 X 2) + (2.78 X 2) = 13.16 amps @ 13.3 volts.
For even higher voltages, you're cutting it too close to the 15 amp breaker rating. A real risk is nuisance tripping. Another thing to remember with incandescent lamps is they represent a "cold" and "hot" resistance. When they are first powered, there is an in-rush of current as they look almost like a short to a power supply. Once the filaments warm, then the current levels decrease.
Low beam only H5006 units drew 2.8 amps. Low operation would result in 5.6 amps @13.3 volts.
Now, if the OP once to install (2) 15 amp breakers to protect the hi and lo feed lines to feel better about redundancy, that's up to him. I recommended the single 30 amp to cover the needs of the circuit as a whole. The 30 amp breakers with terminal mounting studs and mounting tabs are easier to come by at the local parts stores then say a 25 amp unit.
Back to one of the other original questions on wire gauge, the OP states that the longest run shouldn't be more then about 2 feet. You could use no smaller then a single 14 gauge wire to meet the needs of the whole circuit (main hi/low feed) and be okay.