100W Bulb on 14 gauge wire?

I Just bought a pair Hella Black Magic 1000's they come with 55w Bulb and a comple harness with 14 gauge wire. Is it possible to use 100w bulbs or would i have to change all the wiring?

Thanks

 

Two 55w lamps pull 9.2a.
80% rule dictates that the fuse be rated at 12a, wire should be rated for 15a continuous (and you'd run a 12.5a fuse).
14ga is good for 17a in a raceway, more in free air, but given the heat under the hood of a vehicle, I generally use the lower limit.

Kicking the lamps up to 100w each brings your total continuous draw to 16.7a, divide by 0.8 and we have a requirement for a 21a fuse. Wire capacity would need to be 26.3a. I'd run a 20a fuse on that, but I'd still stick with nothing smaller than 10ga.

 

I can see why you would de-rate for continuous use using 80% factor but why are you doing it twice? You would only de-rate the wire and size your fuse accordingly. 16.7A/.8=20.875 which would technically correspond to 14AWG or possibly more depending on the insulation and I would just use the closest fuse, 20A. I don't see why you are getting 26.3A unless you are also de-rating for ambient temperature, but then I don't see where you are getting the de-rating factory for that either

 

Derate the fuse so the continuous load is no more than 80% of the fuse rating.
The wire is derated by the same factor for safety, since the fuse CAN allow full current to flow without blowing.

14ga is good to 32a only in free air. It's limited to 17a when enclosed... and actually limited to 5.6a for "transmission" (of course, voltage drop over long runs is the driving factor on that).

Like I said... I always use the lowest rating to give me a "fudge factor" given the high underhood temperatures, and the potential cost/inconvenience of a burnout (and personal risk in the event of an underdash "event".)

I won't use anything smaller than #18 in a motor vehicle or motorcycle, simply for durability in the high vibration environment. I know factory harnesses go down to #20, but those harnesses are laced and tied and aren't likely to fail from movement/vibration.

 

Either way... with a 20a fuse, he's going to need more than #14. No reason not to go with #10 since it needs to be rewired anyways.
If he had an existing #12, I might be tempted to say "You're close, but it'll live"

 

I would bet, given we are dealing with automotive wire and not something like thhn, that the insulation rating would be high enough that a 14 would be fine for a continuous 20A circuit. I'm not sure what the insulation is but I would probably run a 12, 10 wouldn't hurt but is a bit overkill

 

So I checked the wire harness again today, i see the Positive cable coming from relay and fuse box is 10 gauge, everything else is 14 very good quality wire from hella.

Would this make any difference? or still every single wire has to be 10 - 12 gauge at least?

Thanks

 

No, the wires that run to the coil inside the relay can be small, the other two wires the go to the power and to the lights should be bigger

 

The 10 to the relay is fine.
14 going to each individual light is fine, you just need to go heavier where they combine into one wire.

Also, don't forget the ground wire. It/they need to be as large as the supply wire. One 14ga ground wire can't "drain" the feed from two 14's.