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I'd have to say no, and agree with Tim. Current takes the path of least resistance. The current will flow across one or both of the fuses until it reaches 60 amps, then it will blow. Why not just get a 120 amp fuse if you need one, instead of trying to mickey mouse it?
yes and no. If you were some miracle man who could make the wires EXACTLY the same length, resistance, etc. then you should have 120 amps of fusage. Until one goes. Then, the other will go in very short order. There's gotta be a 120 amp someplace. How about a really weak house fuse? or maybe a breaker switch? j/k best of luck finding stuff. merry xmas. out.
It really doesn't take a miracle to make (essentially) equal currents flow through each fuse. The current itself will help you achieve your goal.
If all of the current starts to flow through just one fuse, that wire and fuse will heat up. When they heat up, the resistance will go up (causing more current to flow through the other fuse). This effect will cause the wiring to auto-balance the current.
As long as the parallel wires are about the same length and gage (duh), the 2 fuses will act like a single 120A fuse.
While Kevin doesn't have his facts straight, he does bring up a very good point: Get yourself a 120A fuse (fusible link).
I agree with 5ubtle, that any differences in using two smaller fuses rather than one larger one will be insignificant. The differences between using one or two smaller fuses are so minute that unless you are designing a circuit to conform to military specifications or for the environment of space (NASA), I would not worry about it (I presume your circuit is not going into the space shuttle).
Two analogies I would offer are:
1. Two resistors of equal value connected in parallel in order to achieve a greater power rating. For example, two 100 ohm 1/4 watt resistors connected in parallel will equal one 50 ohm 1/2 watt resistor. Will anyone be concerned that one of the 0.25 watt resistors is actually 0.235 watts, and the other 0.249 watts? If you’re only passing 0.2 watts through the resistor pair, which is now rated for 0.5 watts, so what if the resistor power combination is now 0.484 instead of 0.500?
2. Two smaller gauge wires connected in parallel can be used to take the place of one larger gauge wire. For example two 10 ga. wires connected in parallel will have more wire conductor area than one 8 gauge wire, so it would handle more current (presuming the same voltage drop) than one 8 gauge wire – actually more like a 7 gauge wire (good luch finding any 7 gauge wire!). This is determined by taking the area of a 10 gauge wire (10383.61 CM, or “circular mils”), then doubling it (because you are using two wires in parallel) and comparing that figure to the corresponding wire gauge. 8 gauge wire has an area of 16512.25 CM and 7 gauge wire has an area of 20822.49 CM. Two 10 gauge wires in parallel will have an area of about 20767 CM, well over the area that 8 gauge wire has, and just under 7 gauge.
If I wanted to protect a circuit with a 120 ampere fuse, I think I would use the two fuse circuit because it is a lot less expensive and, probably more important, easier to find replacement fuses.
Two 60 ampere “maxi fuses” wired in parallel would be ~ $15 (two “maxi fuses” at $3.50/each and two “maxi fuse” holders at $4.00/ea [from Hosfelt Electronics]). Any time the fuse blows, it’ll only cost about $7 to replace both fuses. Compare this to one large fuse, for example a 100 ampere fuse ($15 from Crutchfield) plus the fuse holder ($45 (wow) from Crutchfield), and total cost will be about $60. Quite a difference from the two fuse circuit for $15. Subsequent fuse replacement will cost $15, or double the cost of two Maxi fuses. Also, unless you have a good supply of spares, Maxi fuses are much more common (Pep Boys carries 20 to 60 ampere values), making replacement easier.
I do not generally like circuit breakers for electronic equipment. Most importantly, they do not open (or trip, or “blow”) nearly as quickly as a fast acting fuse (as opposed to a slow-blow fuse). This offers better circuit protection. Specifications for one circuit breaker manufacturer states that it will trip their 3-15 ampere models when the following overcurrent current levels are reached.
Using the above table, if 135% of the rating of their 15 ampere circuit breaker is passed through it (20.25 amperes), it is rated to trip within an hour. A 15 ampere fuse will open almost immediately if you pass the same amount of current (20 amperes) through it.
A resettalbe circuit breaker (such as is used in the power window and seat circuits of my ‘91 Z28) will not permanently remove the load from the circuit when tripped, so this is the worse type, since if an overload condition is reached, it will constantly cycle on/off until the fault is corrected. This presents a fire hazard from the wiring overheating/burning in my opinion.
If you’re really cheap, you can use a piece of solder to make your own fuse. I’ve seen this done in Central America, and yes, it does work. However, accuracy (point at which it will open) is more difficult to achieve. But if you’re in a hurry, it’ll be better than using tin foil or no fuse at all.
I maintain that a two fuse system, wired in parallel, using two equally rated fuses will not perform the same as a single fuse system. In the two fuse system, as the current approaches the combined rating of the fuses, it would not take much variance in contact resistance or inconsistancy between fuses to present a load sharing senario that would cause an inaccurate circuit opening to occur. The operation of the circuit is unpredictable, and therefore, unable to be characterized for proper circuit operation over a given current window. For this reason, using two fuses in parallel to achieve a greater trip threshold is considered poor design practice in the electrical engineering arena. You will not see a parallel fuse configuration implemented in any circuitry designed by a professional engineer.
Tim, All very intelligent information, but once again try not to be so ****. This guy is probably not making a design to be implemented in mass production. More than likely, he is having difficulty finding a 120A fuse and wants to use the two 60A fuses which he already has.
The "variance in contact resistance or inconsistency between fuses" you mention will cause a difference, but it would be a "fail safe" failure. More than 120A would never be allowed to pass. He runs the risk of having nuisance fuse blows. Big deal. He has to run to parts store before he can crank the tunes. It's not like the failure causes a fire.
The best solution to the problem would be to use a fusible link. A fusible link is a short length of a smaller gauge wire that will open in the event of a short circuit, yet allow larger amounts of current to pass than blade or AG fuses are rated for, while having a minimal voltage drop across it, due to its short length. Fusible links, not dual parallel fuses, are used in all autos, including third gens, to fuse high current circuits - and for good reason.
two fuses parallel together will act as the sum of the value or very close. car audio amp manufactors will parallel fuse at its 12v input. kicker for example on some of there amps have 3 30amp fuse paralleled together to get the sum. that is cheaper for them then give everyone a 90 wafer fuse. some have two 20,or two 25 etc. hopes this helps.
If it is for a car audio system and you're blowing 120 amp fuses then if I were you I'd be looking at why they are blowing and not if I can make a cheap 120 amp fuse substitute.
StuartMoss & ChrisFrerick are both correct here.
This is done in industry all the time.
Electricity doesn't "take the path of least resistance" as in all or nothing. It splits and more current will flow through the least resistance and less through the greater resistance proportionatly.
As Stuart points out, Ohms law rules here. Use the same brand, size and style fuses to minimize differences and you will get the result you are after.
IROCKZ4me has it right. Since both fuses are connected in parallel, the voltage drop across both fuses will be the same. Remember, the input and output nodes are connected together. V=IR. So, unless there is a large difference in resistance, the current will be approximately the same through each fuse. And it isn't an unstable circuit. If it was, every microprocessor made wouldn't work. EEs use a concept called legging that is equivalent to the discussion above where a large inverter, for example, has two legs of size W/2 and W/2 connected in parallel vs. a single leg of W width. There are literally millions to billions of locations across the chip where this is done.
Look people, tim is 100% correct, you can't be 100% sure what the trip point will be in a parallel fuse set-up. It'll be near 120A, but thats all you can guess.
However, as was said by someone, it is a fail safe set-up. More than 120A won't go through. And that is the important part.
So let;s just agree tim is 100% correct, but also a little ****. It will work, but it not an ideal answer.
...ed
ps. I do design stuff for NASA. I'm a circuit design engineer for BAE Systems (formerly lockheed martin) in missle and space electronics doing ASIC design. Some of the work my area has turned out include all the chips on the mars pathfinder mission, as well as the RAD750, a radiation hardened version of the powerPC processor. AFAIK the next real design work i do will be on some IOs that will be going on chips for NASAs X2000 project. I just thought it was funny that somebody mentioned ckt design and NASA...lol
I understand that what Tim is saying does make a lot of sense, but...
Tim, you said that nothing designed by a professional engineer uses multiple parallel fuses.
My MTX PRO504 car amplifier uses two 30-amp ATC fuses in parallel. My MTX PRO3002 also has three 30-amp fuses. My assumption is that this is done to make replacement fuses inexpensive and easy to find.
While the folks at MTX certainly aren't NASA engineers, I'm sure they know what they're doing.
While we're on the subject, I'm interested in everyone's comments on something very similar to this.
When I finally get around to properly installing all of my car audio equipment, I want it to have as much power as possible, of course.
I'd like to use 2- or 1/2-gauge power cable from the battery to the amplifiers, but it is expensive. I have several 4-gauge wiring kits that I got for free.
My plan is to run two 4-gauge power wires, each with its own separate fuse, from the battery to the trunk. They will both go to a distribution block that has two 4-gauge inputs. (Four 8-gauge fused outputs supply the amplifiers from there.)
Both 4-gauge wires will be the same brand, as well as the fuses and fuse holders. They will be the exact same length, and run directly alongside each other, going straight to that one distribution block.
I know that one wire (or fuse) might have a little more resistance than the other, but I believe the end result will be much better than using a single 4-gauge cable. Anyone care to comment?
How many channels do the amplifiers that have the multiple fuses have? It's possible that each fuse powers a pair of or a single channel. If the fuses are truly paralleled to source one load, then if an audio system gang of fuses blew prematurely it's really no big deal. I was just making the point that the characterization of wiring fuses in parallel is unpredictable.
As for the multiple larger gauge parallel wires in place of one smaller gauge wire, that's a great idea. What you may want to do, before you run all of the wire, is calculate the maximum steady state current you will require & load the wires - or run your amps at the maximum output level you will be using and excite them with a sinusoidal input & sweep the audio frequency range while measuring the voltage drop from the battery to the amps & see if the drop is low enough to tolarate. If you don't have an AF sine wave generator, there is a CD available that has frequency ramps, white & pink noise sources, etc. recorded on it that are great for maximum output & resonance testing & also to try & set up a system for a flat response - hard to do in a car - as well.
Re: Will two 60 amp fuses wired in parallel act as a 120 amp?
Originally Posted by de bayou 'Gator
Don't try 2 60-amp fuses in parallel. The result is the same as 1 30-amp fuse, which will quickly become toast.
Two 60-amp fuses in SERIES might work. Ideally, though, use 1 fuse of the necessary rating.
Holy necro posting, Batman.
And you are so very, very wrong.
Two fuses of the same rating wired in parallel will double the rated current, though it's not a very effective way to do this, and is not recommended, even though there are devices, such as the aforementioned amplifiers that do this.
Two fuses of the same rating in series will be the same current rating.
Re: Will two 60 amp fuses wired in parallel act as a 120 amp?
Originally Posted by de bayou 'Gator
Don't try 2 60-amp fuses in parallel. The result is the same as 1 30-amp fuse, which will quickly become toast.
Two 60-amp fuses in SERIES might work. Ideally, though, use 1 fuse of the necessary rating.
tell me you are just trolling people? If not please do not give advice till you have at least read a book or two on basic electrical theory. I’m not trying to be mean I’m trying to save lives.
Re: Will two 60 amp fuses wired in parallel act as a 120 amp?
Originally Posted by Samuel Lorenz
tell me you are just trolling people? If not please do not give advice till you have at least read a book or two on basic electrical theory. I’m not trying to be mean I’m trying to save lives.
Are YOU trolling people? That response from that guy was 5 years old
Re: Will two 60 amp fuses wired in parallel act as a 120 amp?
Originally Posted by Samuel Lorenz
I’m not trying to be mean I’m trying to save lives.
Oh great , another newbie keyboard crusader ..... Dude , how's about building up a bit of forum cred before heroically running in to save us from long dead ancient threads ?
Re: Will two 60 amp fuses wired in parallel act as a 120 amp?
Real engineers sometimes do dumb things. My Promariner Pronautic 1260p battery charger has exactly this configuration (two paralleled 40A ATC fuses in sockets) to protect its 60A output circuit. After it ran well for two years, the fuses blew while it was running at about 60A. I replaced the fuses and it works fine again. I think it is probably the ATC sockets that caused the current imbalance! The variation of fuse resistance is probably minor if they come from the same lot.
Originally Posted by Tim Burgess
I maintain that a two fuse system, wired in parallel, using two equally rated fuses will not perform the same as a single fuse system. In the two fuse system, as the current approaches the combined rating of the fuses, it would not take much variance in contact resistance or inconsistancy between fuses to present a load sharing senario that would cause an inaccurate circuit opening to occur. The operation of the circuit is unpredictable, and therefore, unable to be characterized for proper circuit operation over a given current window. For this reason, using two fuses in parallel to achieve a greater trip threshold is considered poor design practice in the electrical engineering arena. You will not see a parallel fuse configuration implemented in any circuitry designed by a professional engineer.
Re: Will two 60 amp fuses wired in parallel act as a 120 amp?
I'm going to run 2 smaller wires in place of a bigger wire just to **** people off. And I'll change my license plate to "2 WIRE" because I like to live dangerously.
Ooooh... livin' on the edge now. What an adrenaline rush.
Re: Will two 60 amp fuses wired in parallel act as a 120 amp?
Originally Posted by QwkTrip
I'm going to run 2 smaller wires in place of a bigger wire just to **** people off. And I'll change my license plate to "2 WIRE" because I like to live dangerously.
Ooooh... livin' on the edge now. What an adrenaline rush.
Perfectly acceptable as long as you know how many of what size equates to a different size. And pissing people off is fine too as long as they're wrong. This site has a calculator for multiple same size wires AND different size wires to get the effect of a single larger wire. For example two 10 AWG wires is the equivalent of a single 7 AWG wire. Three of them will get you to a single 5 AWG wire.
12-20-2000, 09:20 PM
I apologize. 
Oh great , another newbie keyboard crusader ..... Dude , how's about building up a bit of forum cred before heroically running in to save us from long dead ancient threads ? 
