Foglight bulbs

[ilovedmymantas]

One of my fog light bulbs had gone.

In a moment of boredom/madness I bought a couple of white xenon bulbs rated at 100W.

Now I'm wondering if the wiring will take it

[iangsi]

By using these 100W lamps instead of the standard 55W lamps you've practically doubled the current the they will draw thus causing the cable to heat up, causing the cable resistance to go up which causes more current drawn until the cable insulation melts then shorts out blowing a fuse or worse a fire, that's worse case though. Plus the extra heat inside the light fitting itself may cause some damage. But for short duration use they should be OK, just be aware how long you have them on for.
Since I fitted front fogs to my Motorsport 7 or 8 years ago I think I've only used them in anger once or twice.

[Robsey]

From memory.

The wire to the left lamp is 1.5mm csa.
This is then linked to the right lamp via a 0.75mm csa wire.
(TIS says that this should be 1.0mm if retro fitting the wiring).

So consider that you are firing 200 watts or 16.7 amps down that left hand wire.

I echo Ian's comments totally.

From my calculations, you are very close to the maximum safety limits (current carrying capacity) of the car wiring - depending on how you "bundle" or loom it.
If there is good air around the cable, then you can use the higher rating.

If the cable is enclosed or bundled with other cables, then you should reduce the rating accordingly.

Strangely the fuse (No 13) is rated at 20 amps.

1.0 mm CSA = 8.75 amps to 10 amps
1.5 mm CSA = 17.3 amps to 21 amps.

[ilovedmymantas]

thanks chaps,
I'll store them in the ever- expanding 'probably never happen' place ( same place you find the 'why did I buy that? pile)

I didn't think too much of it at the time, the mantas always had h4 100/130w headlight bulbs fitted by me instead of 55/60's and there was never a problem.
The cars didn't really have much in the way of electronics and were probably sturdy electrically due to the rally pedigree? Just a theory...

I read somewhere a while ago that the uk averages 6 days of fog a year so I don't really understand why they're needed, I can't remember the last time I used them.
Nice to have though

They do come in handy for spotting low level wildlife, and deer with their heads down(much more hurty-car damage!) when winter sea-fishing and travelling along unlit twisty coast roads

[3cav3]

Years ago I used to have a diesel Volvo 440, a rare but amazing car in everything apart from headlight output. I can't remember the exact figures but a previous owner had fitted bulbs way more powerful rating to try and improve the situation. I ran it for 18 months or so like this when suddenly the lights both stopped working. Under inspection it turned out that the bulb holders and wiring had melted. Cost quite a lot of money to replace everything, after that I will personally never run over rated bulbs.

[Robsey]

In the late 80s and very early 90s, the weather was a lot more extreme with things such as snow or fog.

Nowadays, it is strong winds and driving rain.
More chance of seeing fog patches on frosty mornings in rural areas... but then, that is morning mist, not fog.

Blame it all on me. I have retro fitted front fogs on all of our cars (except Cavalier mk2, which escaped most of my interference).
So "Rob's Law" says that -
'If you fit a gizmo to a car, then you will never need to use it'

[iangsi]

So "Rob's Law" says that -
'If you fit a gizmo to a car, then you will never need to use it'

[Robsey]

That reminds me - my left side front fog is still out.

I have some H3's in my spare bulbs box, in my car boot.
I really should pull my finger out and get some jobs done.