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Tolerance rating on a 0 Ohm resistor?

  1. Dec 27, 2007 #1
    Tolerance rating on a 0 Ohm resistor???

    I'm just curious why the zero ohm "jumper" resistors I use have a tolerance rating of 5%. This doesn't really make sense to me because 5% of 0 Ohms is still 0 Ohms. I understand that even a close to ideal conductor is not going to be 0 Ohms, but why do they use a percentage of 0 to show the tolerance rather than say [tex]\pm[/tex] 0.1 Ohms??
     
  2. jcsd
  3. Dec 27, 2007 #2
    also, i just realized you can't really have a +/- on a 0 ohm, but just a + (no negative resistance), just wanted to extinguish that before someone called me out on it :D
     
  4. Dec 27, 2007 #3

    berkeman

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    Staff: Mentor

    Yeah, that's an old running joke in EE. Tolerance on a "zero ohm jumper" -- LOL.

    But as a practical matter, they do make most 0-Ohm jumpers with resistor fab techniques (well, not the old simple wire jumpers), so there will be some finite resistance associated with the jumper, and maybe for some applications, knowing the resistance will be important. The datasheet should give a more practical resistance maximum for the particular 0-Ohm jumper. If it doesn't, just use 5% of the next higher resistor in the family, usually 1 Ohm.
     
  5. Dec 27, 2007 #4
    Alright thanks for explaining that, I was afraid it was going to be some complicated statistical explanation :D
     
  6. Dec 27, 2007 #5
    A zero ohm resistor is a fancy word for a fuse. I admit they look different.
     
  7. Dec 27, 2007 #6

    berkeman

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    Staff: Mentor

    Not necessarily, in fact, 0-Ohm jumpers are never used as fuses, AFAIK. They are not built to act as fuses. The are used as option straps, usually, or as optional grounding paths for ESD cofigurability of a final PCB design based on final ESD testing.

    A fuse does have a finite, low resistance, with some tolerance. I've used low-current fuses as "blow-able" option straps in products that get configured in production to be an expensive version (fuse unblown) or a cheaper version (fuse blown). I've also used cuttable wire jumpers as cheap configuration straps in products that had multiple personalities, where the option is set once, and must never change (so no DIP switches).

    A 0-Ohm SMT resistor would be a poor choice for a fuse, because the current and voltage required to reliably blow it open would not be well constrained by the construction, and because the resulting open would be subject to corrosion and potential healing. Not good.
     
  8. Dec 27, 2007 #7
    Scusa, I should have said act as a fuse in event of short circuit.
     
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