determining fuse ratings

[G.I.jonas]

I did search but didnt find just what im looking for.Wondering if there is a thread or link for info regarding what size fuse to use for certain circuits.Or how to determine the proper rating for a certain circuit.Im not great with wiring but i do remember something to do with watts divided by volts=amps or something?

[COZY Z COLE]

Here's a guide....http://www.241computers.com/ford/ContentExpress20-12-9.html.

 

 

 

LARRY

[G.I.jonas]

That does give a good general idea,wondering if there is something with a little more info on calculating the figures manualy,thanks

[lammbn]

V=IR (Volts= Current x Resistance). find out how much resistance you have with a multimeter (edit: Oh yeah, do this with the key on so that all circuits are open). Divide your systems operating volts (usually around 13.5v from the alternator with the car running) by the resistance and it should give you the amperage it will pull. if you are using this info for a fuse you should use a slightly higher rated fuse. hope this helps!

[Pop N Wood]

House fuses are determined by the size of the wire feeding the circuit. You can easily find tables listing what size fuse to use with what guage of wire.

 

IMO you should do the same thing with car wiring.

 

But keep in mind that fuses are sized to protect the wiring and not whatever is connected to it. If you have a sensitive piece of electronics, then you need to either size the wire to that part accordingly or include a separate in line fuse right at the part. Stereos and other such electronics are such part.

[Teekass]

House fuses are determined by the size of the wire feeding the circuit. You can easily find tables listing what size fuse to use with what guage of wire.

 

IMO you should do the same thing with car wiring.

 

But keep in mind that fuses the circuit to protect the wiring and not whatever is connected to it. If you have a sensitive piece of electronics, then you need to either size the wire to that part accordingly or include a separate in line fuse right at the part. Stereos and other such electronics are such part.

 

Hey Pop, I think about fuses and wire ratings the same way. Have you ever wondered why Datsun put an 80 amp fuse link on that 10 gauge wire? When I replaced my fuse links with a maxi-fuse block, it didn't give me warm fuzzies putting that big of a fuse on that size wire.

 

 

Sorry, didn't mean to hijack the thread. gijonas, I think the calculation you mentioned in your first post is how to determine the amperage draw of a light bulb (or bulbs). Watts/Volts=Amps

[deja]

V=IR (Volts= Current x Resistance). find out how much resistance you have with a multimeter (edit: Oh yeah, do this with the key on so that all circuits are open). Divide your systems operating volts (usually around 13.5v from the alternator with the car running) by the resistance and it should give you the amperage it will pull. if you are using this info for a fuse you should use a slightly higher rated fuse. hope this helps!

 

That works in theory but there is surge current to worry about. Most electrical devices have a huge inrush of current when they are turned on, especially motors. Hook a couple of these on the same circuit and you'll blow fuses a lot of fuses if the rating isn't a lot higher than the static load determined by measuring resistance. Slow blow fuses help, but are no guarantee Like was said above, fuses protect against fire, size the fuse for the wire gage they are feeding, not the end devices. If you devices draw too much current for the wire to handle you need to rewire the car.

[ZDrifter]

A good rule is a fuse should be 10% bigger then the circuit amperage pull. Hope this helps you out.