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Fusing on NPN outputs

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  • Fusing on NPN outputs

    Your connection drawings show a fuse in the output common. This drawing is for a BX-DM1E-36ED13, but I think others are the same if I remember.

    The drawing isn't incorrect in and of itself, but in practice, people wiring NPN I/O will still tend to ground the negative rather than the positive output of their DC supply, just as you would in a normal system. (Now don't get me started on using ground as your "true" signal) But, if the user grounds the negative side, then your fuse is showing on the grounded side, which is improper.




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  • #2
    It is a reference drawing that is used all over our products. Some folks ground the negative and some folks don't. We expect the user to take some amount of responsibility to figure out where the fusing belongs and adjust the location accordingly.

    On a personal note, if it were my panel I would have each output fused individually. But that is my preference. Your mileage may vary.
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    • #3
      Originally posted by Do-more PE View Post
      It is a reference drawing that is used all over our products. Some folks ground the negative and some folks don't. We expect the user to take some amount of responsibility to figure out where the fusing belongs and adjust the location accordingly.
      Yeah, I get that, and that would be about where I'd be too. Only problem is showing it is neither fish, fowl, nor herring. Maybe delete the fuse and substitute a note about overcurrent protection, or add a footnote with a reference next to the fuse.

      On a personal note, if it were my panel I would have each output fused individually. But that is my preference. Your mileage may vary.
      Yeah, I know a lot of people do that. I personally have never done it (I don't even protect per module). I might protect output power separately from input power but that would be about it. Maybe I just got lucky but in about 30 years of this stuff, I've yet to have a scenario where individually fused outputs would have made a problem less damaging or easier to diagnose. 'Your mileage may vary' is definitely correct! [shrug]

      Also in 30 years: I so rarely use NPN that this is the first time I've noticed it was shown that way! (I also don't run 120V to my light fixtures and switch the neutral)

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