A few Simple Earthing/Grounding + Screening/Shielding DOs and DONTs

Discussion in 'Pro Audio' started by Jim Gregory, Feb 16, 2005.

  1. Jim Gregory

    Jim Gregory Guest

    I have read in this litany recently several confusing or contradictory
    remarks about Earth/Ground loops and even alarming advice to disconnect a
    link designed to ensure safety!
    It led to my chipping in with the following.....

    Simple Earthing rules for a) safety and b) good practice

    Before wiring up a studio/Control Suite, trace for reliable Earth or Ground
    point as being permanently
    intact and done in a proper or fatter gauge, all the way from your incoming
    supply board.
    If poss, have two or three supply rings, separate ground ring bus/ses of
    supply outlets for programme equipment
    from ground ring bus of those needed just for utility purposes.
    Observe industrial/domestic wiring regulations issued by relevant
    Electricity Authority.

    Use RCD breakers on each ring - to trip should a leakage fault
    situation arise.
    These trip fast, actually in 2 cycles of AC. You can simulate such a fault
    with the Test button which
    should be pressed at least once a fortnight if poss.
    Always ground each bay or rack (bond it to supply outlet ground so it's
    always safe, never ever compromise its ground status) and every piece of
    rack-mounted or free-standing equipment that has a metal case or fascia or
    connector shields (unless it is "domestic" and has a 2-pole mains lead/cord,
    say, fig-8), to a clean ground.

    Ensure main mixer's tech ground and monitor amps are grounded close to one
    another. This is the production area nucleus.

    Never bother to attach the screen of a "balanced" output circuit at the
    detachable plug-in connector, unless cable is going via Source jackfield.
    See next....

    Always attach the screen at the detachable plug-in connector to the
    "balanced" input (mic or line) cct and at the Destination jackfield.

    On jackfields never link sleeve of upper jack to sleeve of lower jack if
    normalling exists between them!
    Buy both screened and unscreened (or better, screen terminated at one end
    only) patchcord types.

    On mic XLR leads, but only at the mic skt end, if available, connect shell
    tag to screen at pin1.
    This avoids stray capacitance, etc.

    Ask your techie to:
    Check out, on amplifiers that are hum-prone, that the input screen is
    traceable to a point nearest 0V (common rail of dual polarity PSU or of
    single rail PSU)
    of storage electrolytic, which if single rail is often made to chassis.

    Try to add Earth/Ground lift toggles connecting/isolating pin1 at o/p XLRs
    of portable mains-operated gear, and at DA o/ps where necessary or when

    Jim Gregory, Feb 16, 2005
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