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Spring-Loaded Switch?

Discussion in 'Electrical Engineering' started by Jones, Mar 2, 2008.

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  1. Jones

    Jones Guest

    Hello, all,

    My father's old table saw (240V) used to have a box and wall-style
    switch that he wired into it, and if I recall correctly, the switch
    seemed to be really hard to throw, and when it did, it seemed to "snap"
    really hard and fast.

    I think I remember Dad telling me that it was a special switch and that
    it had strong springs that were meant to slam the contacts together
    very fast and hard to prevent arcing and consequent
    corrosion/pitting/degradation of the internal contacts.

    Am I remembering this right, and can anyone tell me more about this
    type of switch (what it's called, etc.)? Thank-you.

  2. bud--

    bud-- Guest

    From the UL White book: "AC general-use snap switches are tested ...
    for motor loads up to 80% of the amp rating of the switch, but not
    exceeding 2 hp." These are standard wall switches.

    A "manual motor starter" is probably more rugged, would probably last
    longer, and I agree it fits the OP's description.
  3. bud--

    bud-- Guest

    According to the White book the 50 cent ones can be used for motors up
    to 80%/2HP if they are "AC general-use" (not AC-DC). One of the hidden
    tidbits in the UL standards. (Snap switches, guide category WJQR.)

    The 50 cent ones might not be the best choice for what to use.
  4. Guest

    10:39 -0600, bud-- <>
    | wrote:
    |>According to the White book the 50 cent ones can be used for motors up
    |>to 80%/2HP if they are "AC general-use" (not AC-DC). One of the hidden
    |>tidbits in the UL standards. (Snap switches, guide category WJQR.)
    |>The 50 cent ones might not be the best choice for what to use
    | Bear in mind U/L is only saying these things won't burn your house
    | down when they fail, not that they will actually work for any length
    | of time.

    Exactly. UL testing is in regards to safety, not efficacy.
  5. Tom Horne

    Tom Horne Guest

    The man has brought out a very important point here that we ignore at
    the peril of our customers dissatisfaction.

    A little history is in order here. When the Great Chicago Exposition
    was under construction to be a showcase for mans brand new servant
    called electricity the closest Chicago fire houses had horses literally
    dying from exhaustion because so many fires of electrical origin broke
    out. The insurance companies that had insured the exposition saw the
    specter of financial ruin staring them in the face. The underwriters
    who had purchased a share of the risk in return for a share of the
    premiums threatened to withdraw their support and leave the original
    insurers with the entire risk. They agreed to continue to underwrite
    the risk under specific conditions. One sample of every single item to
    be used in the electrical installations was to be delivered to a
    laboratory that they hired an engineer to set up in a nearby loft
    building. If that engineer didn't approve it for the list of acceptable
    components it could not be used without voiding the fire insurance.
    That was the birth of the "Underwriters Laboratory" and it's listing

    To make it onto the electrical materials list a device has to pass
    testing that has nothing to do with service life or fitness for a given
    use. The testing is only meant to show that the device will fail safe
    in that in failing it will not serve as an ignition source for a fire of
    electrical origin. Even the preamble to the National Electrical Code
    warns that compliance will produce "an installation that is essentially
    free from hazard but not necessarily efficient, convenient, or adequate
    for good service or future expansion of electrical use."

    When customers demand an installation that is "just whats needed to pass
    inspection I have them sign off on a letter that quotes that section and
    throws their exact words right back at them. That usually serves as the
    beginning of a discussion that leads to a more rational approach to the
    job in question. When I asked one fella to sign it he was amazed that I
    thought it necessary. When I explained that my intent was only to make
    sure he new what he had asked for he allowed as how he didn't know what
    to ask for so we went over the prints for his addition together and he
    got pricing in advance for what he decided he wanted. Long after the
    job was over I found out he is a consumer rights attorney with a great
    record of success representing the interest of the buying public in my
    state. He is also an adjunct professor at a law school and a friend
    told me he uses that letter in class.

    Perhaps the basic principal being discussed here can best be explained
    by quoting the old Yankee shop keepers warning that "Quality can be
    illustrated by the purchase of oats. If you want nice clean fresh oats
    you must pay a fair price. If you will be content with oats that have
    already been through the horse you may pay slightly less!"
    Tom Horne

    "This alternating current stuff is just a fad. It is much too dangerous
    for general use." Thomas Alva Edison

    ARTICLE 90 Introduction
    90.1 Purpose.
    (A) Practical Safeguarding. The purpose of this Code is the practical
    safeguarding of persons and property from hazards arising from the use
    of electricity.
    (B) Adequacy. This Code contains provisions that are considered
    necessary for safety. Compliance therewith and proper maintenance will
    result in an installation that is essentially free from hazard but not
    necessarily efficient, convenient, or adequate for good service or
    future expansion of electrical use.
  6. John

    John Guest

    "Jones" wrote

    Sounds like just like a common type of isolator which was common until about
    the 1950's/60's. Probably about 6" high by 5" wide by 4" deep and often
    silver in colour, and with the switch actuator lever on the right and
    designed so as to stop the front cover being opened while in the "on"

    Most switches will contain a spring to ensure that they change state very
    rapidly to minimise arcing.
  7. bud--

    bud-- Guest

    Interesting. Sounds like the 1893 Fair, which was the first major defeat
    for Edison’s DC empire.
    For some devices, like TVs, it is not possible (or desirable) for UL to
    determine if the device is actually useful.

    The same is true for industrial control panels. They are investigated
    for safety.

    I believe fuses and circuit breakers are investigated for “fitness for a
    given use” and “service life”.

    I expect more complicated devices, like GFCIs and smoke detectors to be
    fit for their intended use and have a useful service life. (Both with
    testing as required in the listing.)

    A lot of other electrical apparatus is tested for more than failing safely.

    One of the 3 UL standards I have is a 15 year old one for Snap Switches
    - the subject.
    For AC only switches the tests include the following - at rated voltage:
    10,000 operations at rated current
    10,000 operations at rated current and power factor around 0.8
    10,000 operations at rated current controlling incandescent loads
    as you know, this involves a high inrush current and IMHO
    is similar to starting a motor
    100 operations at 4.8x rated current and power factor around 0.5
    IMHO this is very similar to switching off a stalled motor with
    running current 0.8x the switch rating
    IMHO this is testing for “service life” and “fitness for use”, and is a
    reasonable test for use with on motors.

    But I still would use a spec grade switch if using it for a motor load
    approaching 0.8x rated switch current.
    I have always taken this to be a comment on the code itself. A house
    with the minimum circuits required for kitchen, laundry, bath and
    general would be safe but probably would not make a buyer happy.
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