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Help understand correct FUSING.

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  • Help understand correct FUSING.

    Hey,

    I've asked this question a couple of times and got different response. Question is simple, how do I pick the correct fuse rating.

    First response I got, told me to add up all the amperage that will be pulled over the line and use that fuse. With this scenario if I have a PSU thats drawing 20amps and a screen with 1 amp, i need a fuse on the battery of 21amps and then 20amps and 1amps fuses on the individual lines coming from a distro.

    Then someone told me, that I am not using the fuses to protect my equipment but to protect my wires. Okay, an 8gauge wire should be fused with about 45amps or so..however..in this scenario what would protect my equipment??

    which one of these is true? I am about to fuse twice, 1 to protect the wire and 1 right at the equipment, because I dont know which one of these I should listen to.

    Google is great and all, but I also want to hear some real live experienced folk.

    Thanks.

  • #2
    Others who know for certain will pipe in here I'm sure, but I think you would use a fuse that is the lower of the two amperages you are concerned with (i.e. wire & electronics). But I think in any case the electronic component would not draw more current than it is designed to, so if you fuse the circuit to protect the wire and that allows 45 amps, the device should never draw more current than it is designed to draw (21 amps).

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    • #3
      Whoever told you that you use fuses to protect the wiring is 100% correct.

      Think of it this way....
      When the fuse blows, it prevents current from flowing down that wire. If the wire is rated for 50A (as an example) and 100A of current flows down that wire, then the wire will heat up, melt the insulation and risk a fire or shock...

      You'd want a fuse on that wire somewhere between the max draw of the equipment and the current rating of the wire. I'd go closer to the max draw of the equipment to minimize the amount of current flowing through the wire, reducing the risk of overheating wire. In your case a 25A or 30A fuse on the wire would be a good choice.

      Hope that helps.
      Have you looked in the FAQ yet?
      How about the Wiki?



      Under normal circumstances, a signature would go here.

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      • #4
        Originally posted by DarquePervert View Post
        Hope that helps.
        thanks that did help. i guess i was getting confused, but because im running thicker wires for small amperage, thats what was getting me confused.

        for instance im running an 8awg wire which is rated for 50amps (meaning anything below 50A will be okay). My PSU is pulling only 20A if I fuse with a 30A at the battery (protecting the wire) and then with a 20A fuse (after distro) to the PSU with a 10awg wire (rated for 30A)..I am automatically protecting the new lower wire and the equipment..am I correct?

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        • #5
          You are correct, sir.
          Have you looked in the FAQ yet?
          How about the Wiki?



          Under normal circumstances, a signature would go here.

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          • #6
            thanks for your help. finally fuses have been demystified for me.

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            • #7
              Just to add to this your equipment has its own protection. It might not be in a visible or readily replaceable form but any equipment worth its salt always has at least one form of protection built in.
              Visit my site V8 Scimitar

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              • #8
                Put that fuse close to the battery, yes it does protect your wire. I watched a guy burn his carpet and rubber gomets to nothing because he ran no fues. He actually tried to rip the wire off the battery with his hands and burned a nasty line in his hand.

                BTW always use fuses!! Never use circuit breakers. I had another friend of mine who had a 100 amp breaker in his S10. When it was suposed to kick, it melted and fuse together. Yeah that wasnt a pretty site either...
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                • #9
                  sorry guys, quick thread revival.

                  i completely understand fusing now and the role they play in protecting wires and equipment. so much thanks for that.

                  however i have 1 more question. I know its a good idea to fuse whenever the gauge of the wire is changed.

                  lets say i bought a lower gauge wire..12awg and im trying to connect it to a 22awg wire. However at the power source i am fusing to protect the 22AWG wire which should automatically protect the 12awg wire because the fuse is so small. Can i then simply connect the 22awg wire to a 12awg because i am already protecting the 22awg wire with a fuse at the power source.

                  I would assume i can do that, however i am a bit skeptical (resistance??) .. i dont know..can anyone clear this up for me???

                  thanks.

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                  • #10
                    you can do it but why would you want to as its pointless using the thicker wire as you cant get the benefit from it.
                    Visit my site V8 Scimitar

                    SP13000, 300GB SATA HD, 1GB DDR. Opus 150, K301 screen, Cisco WIFI, AQmax GPS, RoadRunner and FreeDrive, Sony MEX-R5 head unit. 4 years installed and it just keeps running!

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                    • #11
                      Originally posted by v8 scimitar View Post
                      you can do it but why would you want to as its pointless using the thicker wire as you cant get the benefit from it.
                      because i bought a 12AWG wire by accident and i am going to use it anyway to wire up something else.

                      However one of my gauges uses a 22AWG wire thats hardwired for power, so instead of going out and buying a 22AWG..i can just use the 12AWG i already have... make sense??

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                      • #12
                        Only thing i wanted to chime in on here. Both points are true. You put in a fuse to protect the equipment and so that you dont cause a fire or damage the wires. The total current being passed through the wire will never be much higher then the max current your equipment draws. the reason i say much, is the longer the length of wire the bigger the gauge you want to use. The reason for this is because of some innefiency in the wires, some current is lost in the wire and hence needs to draw a bit more current from the battery to get it to the destination.

                        the main problem or concern i would say with what was said before. if you use a fuse of lets say 50 amps based on the wire gauge only. and your equipment only draws 30 amps and can't handle 50. Then if thers a short or for whatever reason great then 30amps goes down the wire... zap there goes your equipment.

                        But thats another big reason why you fuse at the battery AND at the equipment, most good distro blocks will have fuses built in, of which some you can put in whatever fuse you need.


                        hope that all makes sense, basically the thinner the wire, and the longer the run, the greater resistance. so you have to accommodate for that when picking out your wiring/fuses

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                        • #13
                          Originally posted by MastaShake View Post
                          because i bought a 12AWG wire by accident and i am going to use it anyway to wire up something else.

                          However one of my gauges uses a 22AWG wire thats hardwired for power, so instead of going out and buying a 22AWG..i can just use the 12AWG i already have... make sense??
                          I want to know what you intend to power with 22awg wire.
                          22awg is what's inside Cat5 network cable, and is't really sufficient for anything except carrying data....
                          Maybe an LED or two, I suppose....
                          Have you looked in the FAQ yet?
                          How about the Wiki?



                          Under normal circumstances, a signature would go here.

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                          • #14
                            good question.

                            i have an Aeroforce gauge that needs 12V switched power, it provides me a wire to connect to to give it power..this wire is 22AWG and i cant change it, because it is hardwired into the actualy gauge...i need to connect this wire to a 12V source..thats basically it.

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                            • #15
                              I thought this stuff was in the FAQ.

                              Wire has a maximum amount of amperage (current) it can carry...an example of the extreme is the light bulb...the wire in your bulb is the bare minimum allowable to not burn out...as a result you get a nice white hot burning piece of wire in that glass bulb.

                              Another example is the fuse itself. It has a piece of wire that will melt due to heat when the rated current (amps) is exceeded.

                              So lets say you have an undersized piece of wire (22gauge) and you are trying to operate your hair dryer with it...at best you will feel the wire get warm...at worst you will smell the magic smoke escaping from the wire while your hair dryer stops working.

                              Ok...so what would happen if you powered a single LED using 00 gauge welding cable...the LED will work fine, and the totally overkill wire won't even notice.

                              I doubt you can create enough current on 00 wire to melt it...think of it...welding wire...you will melt the rest of your car before the cable melts.

                              Electronic equipment contains fuses in case some kind of internal problem develops and it will cut the current before the electronic device catches on fire.

                              Your wire to the equipment ALSO needs a fuse to keep it(the wire) from melting in case a wiring problem develops away from the battery.


                              There is no problem running heavier gauge wire than the application requires...just the cost and difficulty in running the wire.

                              In the example of your gauge...it would need to be fused for the 22gauge wire...not the 12gauge wire.
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