automotive wiring spec help

[steveo3002]

need to wire in some fog lamps , 60 watt bulb , so 60 divided by 12v =5 amp?

how much over 5 do i need to go as a saftey margin?

 

[Barking Mat]

Two bulbs ? 10 amps + ?

 

[steveo3002]

yes 2x bulbs =10a draw, i was assuming i need to add xx % for a saftey buffer or is that not the case

 

[ajlelectronics]

yes 2x bulbs =10a draw, i was assuming i need to add xx % for a saftey buffer or is that not the case

For continous operation, yes. If you buy from Vehicle Wiring Products, they list on the current rating of their cable to make it easy to choose. Really, anything 20A rated or above will do.

 

[Barking Mat]

I'd go to 12 or 15 amps, try 10 amps, if it does blow just stick the next higher current fuse.

But don't forget, a fuse is to protect the wiring, not the appliance, what size wire do you need at 10 or 15 amps at 12 volts, is more the question.

 

[Barking Mat]

12V Wire Size Calculator + Chart: What Size Wire You Need?

12V circuit is a low-voltage electric circuit. It’s primarily used in most batteries. To produce larger amounts of electric power (wattage), we usually need quite a lot of amps. That means we need relatively big 12V cable sizes. Now, how do you figure out what size wire you need for a 12V...

learnmetrics.com

 

[steveo3002]

, what size wire do you need at 10 or 15 amps at 12 volts, is more the question.

that was the question

 

[Barking Mat]

that was the question

Yes.

 

[Barking Mat]

that was the question

Depends on wiring length, I would have thought 2.5 / 3.0 sufficient.

 

[tigdlo]

I start with continuous current, then choose the fuse size and then the cable that will easily blow that fuse without melting.

eg, 5amp continuous current, 10 amp fuse, 20 amp cable but may be larger than that due to acceptable voltage drop. The current rating of any connectors or relays also needs to be taken into account.

 

[piman]

Hello Steveo,

a 10 amp wire will carry the 10 amps of the lamps quite safely. However if you double the cable size your lamps will be brighter as they get more voltage.. (voltage is a significant fcator for the output of incandescent lamps)
A thin wire loses more voltage (Voltage drop) than a thick wire for the same current and distance.

Alec

 

[Dilkris]

Round about now I reckon steveo3002 will be wishing he never asked the question......

 

[Chippie]

Round about now I reckon steveo3002 will be wishing he never asked the question......

I find that endemic with a certain model engineering forum I used to frequent….armchair experts abound there….asking 1 question elicits about four pages of answers….hence why I stopped posting. Not saying that here is no different, there are a lot, I mean a lot, of people on here go out of their way to explain even to a simpleton like me…every day a skool day… but to answer the question….2.5mm cable is more than adequate and a 15A fuse would be sufficient…considering the inrush of the lamps..,

 

[steveo3002]

Round about now I reckon steveo3002 will be wishing he never asked the question......

i went with nearest i had that the calculator said that was posted above
cheers all , theyre working and no smoke came out

 

[MetalMonkey]

If you already have filament bulbs as headlights, just use the same gauge of wire or larger? It really is as simple as that.

Not really. Depending on where the lights are mounted, how they are switched and where the supply is, length can also plays a factor in selecting cable size.
It can also be difficult to determine the gauge of existing cable in situ.

Depending on how the circuit has been designed, typically both fog lamps will be fed from the same circuit so the supply cable must carry the current for both bulbs.
Headlamps can sometimes be wired individually on separate circuits to provide redundancy, so the cable to the fitting might only be sized sufficiently for the one bulb.

If buying new cable it is far easier to just calculate what is required and buy the correct stuff rather than just guessing.
No problem in going up in size, other than cost and any issues in terminating if it is going into a specific connector designed for a smaller cable.

 

[Matrixx]

I would have said 1.5mm cable with a 10A fuse, the fuse will not blow at 10A, and the cable is rated for 15A and you dont need to account for inrush and unless your car is 20m long i wouldent worry about volts drop etc.