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Surge Protector Circuit Questions

Discussion in 'Electronic Design' started by loutiberia, Aug 29, 2005.

  1. loutiberia

    loutiberia Guest

    Hello,

    I'm hoping someone that's knowledgeable about surge protectors can
    answer this:

    I opened the case of an industrial power strip (PDU) to see what's in
    it.
    Basically, the PCB inside just has the Line, Ground, and Neutral wires
    soldered onto the PCB, and then 3 other matching L-G-N wires soldered
    on to continue on to the receptacles.
    On the PCB, in parallel to thse main L-G-N traces, are 3 surge
    protection circuits, each circuit consisting of 1 fuse, 1 thermal cut
    off (TCO), and 3 MOVs.
    All 3 surge circuits connect in the classic arrangement of several MOVs
    in parallel placed across each of the three conductive pairs; L-N, L-G,
    and N-G.

    I understand the arrangement of MOVs, thermal cut offs (TCOs), and
    fuses, but have 2 questions:

    1)
    The fuses are 2AG-224 8A 125V Fast-Acting.
    Why was an 8A fuse picked?
    Since the fuse is there for the case when the MOVs have failed closed
    and the surge circuit is always drawing current, wouldn't a lower rated
    fuse be preferred?

    2)
    The traces in the surge circuits are anywhere from .1" to .3" wide.
    The PDU is rated 20A.
    Shouldn't the traces be at least .5" wide?
    For example, what happens if a surge strikes while the PDU has
    equipment plugged in that is drawing 18A?
    Wouldn't that burn out or blast a trace path?

    Thank you,
    Lou
     
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