Cable Size Calcuator*

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Standard automotive cable ratings
Thinwall automotive cable ratings
Tinned automotive cable ratings
Automotive battery/startercable ratings
Some suppliers list 40mm2 / 240A cable, others list 35mm2 with the same 240A rating.

Automotive mini blade fuse ratings
Amps Continuous2357.51015202530
Amps Fusing (blow)4610152030405060
ColourGreyVioletTanBrownRedLight BlueYellowWhiteLight Green
Automotive standard (midi) blade fuse ratings
Amps Continuous3457.51015202530
Amps Fusing (blow)6810152030405060
ColourVioletPinkTanBrownRedLight BlueYellowWhiteLight Green
Automotive maxi blade fuse ratings
Amps Continuous20304050607080
Amps Fusing (blow)406080100120140160
Warning: Your selected fuse's rating (blow) must ALWAYS be a LOWER value than the capcaity of the cable you choose.

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Safety margin:
Cable Run (m):

Info & Warnings

Results - colour coded!
Not suitable For cables: Amps rating is below required amps.
For voltage drop: Drop is greater than 10% of available voltage
For fuses: Continuous fuse rating is either below required amps (fuse will blow instantly), or way above it (the fuse rating is too high to provide useful protection).
The fusing (blow) rating of the fuse must always be lower than the rated capacity of the cable, otherwise the cable may melt before the fuse blows. That's generally considered a Bad Thing.
Probably OK For cables: Amps rating is above required amps, but below amps + safety margin ().
For voltage drop: Drop is greater than 5% of available voltage
For fuses: Continuous fuse rating is next-size-up from required amps. This may be too high, although some loads (EG elecrtic cooling fans) can require oversized fuses to handle the startup kick.
OK For cables: amp rating within your safety margin ()
For voltage drop: Drop is less than 5% of available voltage
For fuses: Continuous fuse will handle required amps but isn't too much over.
Probably overkill For cables: Amps rating more than twice your required amps + safety margin.
Not for fuses: There's a reason way-too-big fuses are marked in red for danger / death / chaos / car on fire.

Note that by default, Volts will remain fixed and Amps & Watts will change when you move sliders.
This is because watt rating is usually based on a nominal supply voltage, and indicates a given load.
Therefore we assume the load stays constant, and will therefore draw a varying current as voltage changes.
You can override this by locking ONE of the values (Volts, Amps, Watts) above.
* = Warning: Do not trust your safety to Javascript calculators!
This was primarily designed to provide approximations for basic automotive wiring.
For cables bundled together, run in enclosed spaces, etc. etc. you should de-rate. If you don't know what I'm talking about then you should probably read up on it or ask an adult.
Numbers are based on random info found on the internet and are probably wrong.
This is experimental code. You should not trust it. It may be an elaborate hoax.
The warranty just expired.
If you found this useful why not pop some pennies in the pot at or, if that's not your bag, the good folks at Hampshire & Isle Of Wight Air Ambulance always need petrol money for their helicopter.

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