High current fuses

[Rukahs]

I was thinking about the 175A fuses I have in my car on either end of a 17 foot line of 0ga, and I thought "whats the point?".

I fully understand that fuses are to protect the wiring, and for smaller currents this makes sense, you can blow a 10A fuse in half a second before the wire heats up at all. But 0ga can handle 1000+A surges and 500A constant is probably not unrealistic, especially for shorter lengths.

So thinking about my wiring, if it ever gets cut and wire gets exposed and shorts to the chassis, the fuse won't notice a thing because the few strands that actually touch the frame will just melt instantly. 0ga isn't some crappy wire that can melt, its welding wire, its the kind of stuff that houses get power from, the only difference being number of strands for flexibility sake.

My 175A fuses will take over 10 seconds to open drawing 300A, and 1 second to open drawing 1000A. Drawing 300A continuous is ridiculous, and 1000A is silly to the point of me actually pushing the stripped end of the live wire into the chassis.

Just an esoteric diversion into high current fusing.

Click to read more...

 

[bubbagumper6 5,000+ posts]

ok

 

[gotparts90 10+ year member]

I have seen very large wire turn into light bulb filament, use a fuse. The wire will ground out and may weld itself to the chassis.

 

[grassroots 10+ year member]

well allowable ampacities are based on the type of insulation as well as circular mil. and even the thickest of insulations (THHW, THWN-2, ect) can only carry 260 amps and that's in free air temperatures 86F (don't forget how hot it gets under the hood). i'm not sure what most car audio brand wires use as insulation, but i doubt it's rated as high as res/com/industrial wire. (except welding wire)

i do agree somewhat with your statements though. the length of wire used in cars is extremely short and the majority of people (at least on this website) considerably oversize their wire anyways.

you should still have a fuse on your power wire just in case of a direct short to your chassis. the strands don't always "melt instantly" and i would rather a fuse blow than have your wiring catch on fire or possibly have a battery explode.

 

[gotparts90 10+ year member]

well allowable ampacities are based on the type of insulation as well as circular mil. and even the thickest of insulations (THHW, THWN-2, ect) can only carry 260 amps and that's in free air temperatures 86F (don't forget how hot it gets under the hood). i'm not sure what most car audio brand wires use as insulation, but i doubt it's rated as high as res/com/industrial wire. (except welding wire)
i do agree somewhat with your statements though. the length of wire used in cars is extremely short and the majority of people (at least on this website) considerably oversize their wire anyways.

you should still have a fuse on your power wire just in case of a direct short to your chassis. the strands don't always "melt instantly" and i would rather a fuse blow than have your wiring catch on fire or possibly have a battery explode.

Hi sparky! yeah car audio wire ***** for insulation but its pretty so the kids will buy it. I just order welding cable.

 

[Rukahs]

I would love to see 1/0 or 4ga glow like a filament.

Also point of note I do have fuses on both ends of my battery interconnect cable, I don't have a solid state battery isolator, but what made me think was open times for ANL fuses are really long. If you had a solid state isolator and a ANL fuse with the same rating, you'd break the isolator before the fuse would open.

http://www.cooperbussmann.com/pdf/0810938a-26c4-44e2-a299-8962dd6ea9a7.pdf

Also along with oversizing wires people over estimate current draw as well. Your 500 watt amp isn't ever drawing 500 watts continuous. In my car with a 90w x 4 and 750w x 2 running at too **** loud i saw 90amp peaks and about 30~50 amp continuous not the (90 * 4 + 750 * 2) 1860watts / 12volts = 155amp estimated

 

[smoka 10+ year member]

My 175A fuses will take over 10 seconds to open drawing 300A, and 1 second to open drawing 1000A.

According to your pdf you linked to, your 175a fuse will take 10s @ 220a or 0.5s @ 1000a.

Also a short across a battery can generate 10,000+amps. So you are talking nearly instant times for the fuse to blow.

There is absolutely no drawbacks of oversizing your wires (except for your wallet).

 

[n2audio 5,000+ posts]

Also a short across a battery can generate 10,000+amps. So you are talking nearly instant times for the fuse to blow.

I think you'd have to have a car with no engine to fit a 10,000A battery under the hood.

Ya ever seen a CA rating?? 800, 1000A? That's a short across the battery.

 

[smoka 10+ year member]

I think you'd have to have a car with no engine to fit a 10,000A battery under the hood.Ya ever seen a CA rating?? 800, 1000A? That's a short across the battery.

Cranking amps and short circuit current are NOT the same. Though 10ka might be an exaggeration, its probably more like 3-4ka short circuit for a group 31 batt.

Cranking amps the batt can do safely for short bursts, but short circuit will damage the batt.

 

[n2audio 5,000+ posts]

Other than just being completely discharged I don't see why a short would be much more damaging than leaving the headlights on.

I'll be researching both those issues...hopefully I can find some legitimate info.

 

[McIntosh 10+ year member]

well allowable ampacities are based on the type of insulation as well as circular mil. and even the thickest of insulations (THHW, THWN-2, ect) can only carry 260 amps and that's in free air temperatures 86F (don't forget how hot it gets under the hood). i'm not sure what most car audio brand wires use as insulation, but i doubt it's rated as high as res/com/industrial wire. (except welding wire)
i do agree somewhat with your statements though. the length of wire used in cars is extremely short and the majority of people (at least on this website) considerably oversize their wire anyways.

you should still have a fuse on your power wire just in case of a direct short to your chassis. the strands don't always "melt instantly" and i would rather a fuse blow than have your wiring catch on fire or possibly have a battery explode.

WTF??? Someone actually knows what they're talking about on this website? Will wonders never cease? Ask anyone else here: 1/0 is good for 300 (or even 800 amps). The NEC is all wrong because AC amps are different from DC amps. Tables 310-16 and 17 don't apply to cars. That's only for AC. Don't get them started with the length issue. They also firmly believe a short wire has higher ampacity than a longer wire. I'm not talking voltage drop, ampacity. I^2 R ignores short wires. Single conductor in free air @86F vs underhood temps make no difference. These children are smarter than that. A few shorted strands couldn't possibly draw that much current. These kids are too sharp to fall for that line of BS. They love that 1000W amp with the 60 amp fuse though. They be bumpin' with 1000W for sure. 150+dB as well. Ohm's law doesn't apply to car audio. I guess it should be renamed Ohm's postulate.

 

[ultimate157 5,000+ posts]

Other than just being completely discharged I don't see why a short would be much more damaging than leaving the headlights on.
I'll be researching both those issues...hopefully I can find some legitimate info.

I'm unsure about the internal damage possibilities to a battery after a dead short, but there is definitely enough current and heat generated to weld objects to the terminals, as well as likely melt the casing around the terminals.

 

[smoka 10+ year member]

Other than just being completely discharged I don't see why a short would be much more damaging than leaving the headlights on.
I'll be researching both those issues...hopefully I can find some legitimate info.

Your headlight is a small finite load, a direct short is an infinite load. This infinite load is going to produce a huge amount of power very quickly. Without a proper way to displace the heat that is generated, the batt will melt.

 

[mgcauctions09 10+ year member]

Mcintosh is back ****!

 

[MakeshiftAudio 10+ year member]

WTF??? Someone actually knows what they're talking about on this website? Will wonders never cease? Ask anyone else here: 1/0 is good for 300 (or even 800 amps). The NEC is all wrong because AC amps are different from DC amps. Tables 310-16 and 17 don't apply to cars. That's only for AC. Don't get them started with the length issue. They also firmly believe a short wire has higher ampacity than a longer wire. I'm not talking voltage drop, ampacity. I^2 R ignores short wires. Single conductor in free air @86F vs underhood temps make no difference. These children are smarter than that. A few shorted strands couldn't possibly draw that much current. These kids are too sharp to fall for that line of BS. They love that 1000W amp with the 60 amp fuse though. They be bumpin' with 1000W for sure. 150+dB as well. Ohm's law doesn't apply to car audio. I guess it should be renamed Ohm's postulate.

Oh my fucking god I want to buy a ban for you. My whole argument last time was based on ohms law.

Your trolling is succeeding.