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Fuse before the switch?

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  • Fuse before the switch?

    Maybe I have been doing it wrong but when I replace a 2-prong cord with a 3 prong cord I run the hot (black) to the switch first then to the fuse.

  • #2
    Yes, fuse first. What if the switch somehow shorts to chassis?
    "Yeah, well, you know, that's just, like, your opinion, man."

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    • #3
      Fuse it first!!!

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      • #4
        I'll add another vote for fusing it before the switch.
        Contrary to a very common belief, the fuse is not there to protect the insides of the amp. Instead, it's there to prevent a failure inside the amp from starting a fire either in the amp or outside of it, or to prevent a failure inside the amp from making the chassis hot to the AC line and thereby an electrocution hazard. And as the Dude says, a problem with the switch itself can cause fire or electrocution hazards if the fuse is not first.
        As one other safety note, the fuse and switch should both be in the AC mains "line" side, neither of them in the "neutral" side.
        Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

        Oh, wait! That sounds familiar, somehow.

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        • #5
          I'm not arguing with anyone, but just want to point out this seems to be a matter of opinion rather than any legal issue.
          Modern Fender practice is switch first (and several other manufacturers as well).
          "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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          • #6
            Maybe 40 years back, I remember a friend's Marshall having acrid smoke emerging from it - switching it off at the front panel didn't stop it, eventually realised we had to pull its plug.
            On examination, its ancient Bulgin fuseholder, made of Bakelite, had somehow developed a conductive path from its live side terminal to the chassis ground, so that had been freely arcing across.
            UK power plugs have a fuse built in, but a 13 amp fuse had been fitted and the arc current must have been below that.
            Of course this was before RCDs etc were commonplace - Thank goodness the grounding system was good!
            My band:- http://www.youtube.com/user/RedwingBand

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            • #7
              Originally posted by g1 View Post
              I'm not arguing with anyone, but just want to point out this seems to be a matter of opinion rather than any legal issue.
              Modern Fender practice is switch first (and several other manufacturers as well).
              Compliance regulations can vary depending on municipality, preferred organization board of standards, and more importantly – time. It's a good point you bring up. I was trying to picture the insides of some modern Fender amps, and I could figure that this would probably be the setup in models which have the mains fuse mounted internally on the circuit board. (I thought I remembered reading that UL requires the mains in to be fused before the switch, but I might be mistaken.)
              Regardless.. I think the safest configuration would have the "Live" conductor fused before connected to anything else, as close to the location where the Mains wiring enters the chassis. In most fault conditions, by limiting the area of exposure, this would minimize risk of shock or electrocution, as well as potential damage to any switches or components.
              This is why I think the "shock-proof" fuse integrated into the IEC inlet is ideal.
              If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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