MOV's In Surge Arrestors Quest. ?

Discussion in 'Electrical Engineering' started by Robert11, Aug 9, 2005.

  1. Robert11

    Robert11 Guest

    Hello:

    Two questions regarding the MOV's one finds in the typical surge arrestors:

    When the MOV clamps due to a spike, is it all over for the MOV, or are they
    typically good for many clampings ?

    When they do fail, do they usuall fail as an open, or as a short circuit ?

    Thanks,
    Bob
     
    Robert11, Aug 9, 2005
    #1
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  2. Robert11

    SQLit Guest

    "Robert11" <> wrote in message
    news:...
    > Hello:
    >
    > Two questions regarding the MOV's one finds in the typical surge

    arrestors:
    >
    > When the MOV clamps due to a spike, is it all over for the MOV, or are

    they
    > typically good for many clampings ?
    >
    > When they do fail, do they usuall fail as an open, or as a short circuit ?
    >
    > Thanks,
    > Bob



    MOV's are tested by UL once. They work the design passes. There is no more
    testing for another hit. Manufactures test the random one off the
    manufacturing line and as long as they work as rated the line continues to
    produce.

    My experience is if the MOV sees a max rating they usually fry, open. I have
    installed a lot of Class 1 and 2 surge arrestors. ( distribution and
    service ). They have fused protection and usually if a fuse blows we just
    replace the circuit board with the MOV's. Testing has shown the odds are the
    board is bad.

    I have a whole house arrestor installed and then point of use strips. Ya
    need 2 of the 3 zones for protection. The house arrestor clamps down to a
    level that the point of use ones can handle.
    I check to see if the lights are green after each lightning storm at the
    service. If the lights change color I go buy another one. I have lost 2 in
    the last 3 years. I replace the point of use ones every 3 years or earlier
    if I think it is needed. My opinion is that they are pretty cheap insurance.
    Compared with the big screen HD TV and the DVR.
     
    SQLit, Aug 9, 2005
    #2
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  3. Robert11

    Robert11 Guest

    To SqLit From OP: Re: MOV's In Surge Arrestors Quest. ?

    Hi,

    Thanks for info.

    Can you recommend a point of use type of brand and model ?

    Want to protect a new furnace circuit board that runs off a dedicated 110 V
    line.
    Has already been fried once, recently, in a lightning storm.

    It has a fuse, but have real doubts if the board has any MOV's.

    What do yo think of the Intermatic AG2401 ?

    Thanks,
    Bob
    ----------------

    "SQLit" <> wrote in message
    news:Sr6Ke.174$...
    >
    > "Robert11" <> wrote in message
    > news:...
    >> Hello:
    >>
    >> Two questions regarding the MOV's one finds in the typical surge

    > arrestors:
    >>
    >> When the MOV clamps due to a spike, is it all over for the MOV, or are

    > they
    >> typically good for many clampings ?
    >>
    >> When they do fail, do they usuall fail as an open, or as a short circuit
    >> ?
    >>
    >> Thanks,
    >> Bob

    >
    >
    > MOV's are tested by UL once. They work the design passes. There is no more
    > testing for another hit. Manufactures test the random one off the
    > manufacturing line and as long as they work as rated the line continues to
    > produce.
    >
    > My experience is if the MOV sees a max rating they usually fry, open. I
    > have
    > installed a lot of Class 1 and 2 surge arrestors. ( distribution and
    > service ). They have fused protection and usually if a fuse blows we just
    > replace the circuit board with the MOV's. Testing has shown the odds are
    > the
    > board is bad.
    >
    > I have a whole house arrestor installed and then point of use strips. Ya
    > need 2 of the 3 zones for protection. The house arrestor clamps down to a
    > level that the point of use ones can handle.
    > I check to see if the lights are green after each lightning storm at the
    > service. If the lights change color I go buy another one. I have lost 2 in
    > the last 3 years. I replace the point of use ones every 3 years or earlier
    > if I think it is needed. My opinion is that they are pretty cheap
    > insurance.
    > Compared with the big screen HD TV and the DVR.
    >
    >
     
    Robert11, Aug 10, 2005
    #3
  4. Robert11

    w_tom Guest

    UL tests protectors only for human safety. Plug-in
    protectors can fail on the first transient (which means
    ineffective protection) and still obtain a UL 1449 approval.
    UL does not care whether a protector provides transistor
    protection. Purpose of UL is human protection. UL only cares
    that the protector does not burn down the house - harm
    humans. Indeed, many protectors in some 1987 tests by PC
    Magazine did spit flames. One technique to meet UL 1449 is to
    disconnect the protector faster - leave more transient to find
    other paths such as through the adjacent computer.

    How dangerous are plug-in protectors? Others demonstrate
    the problem. Or why plug-in protectors that are also
    undersized should not be on a desk covered in paper, on the
    rug, or behind furniture in a ball of dust:

    http://www.westwhitelandfire.com/Articles/Surge Protectors.pdf
    > Do not locate a surge protector or power strip in any area where
    > the unit would be covered with carpet, furniture,or any other
    > item that will limit or prevent air circulation.


    http://www.nmsu.edu/~safety/programs/gen_saf/surgeprotectorfire.htm
    or
    http://www.ddxg.net/old/surge_protectors.htm
    > An employee arrived at the Greensport Yard in Houston this
    > morning to find the field office full of smoke. Investigation
    > led him to a melted down surge protector


    http://www.ehs.washington.edu/LabSaf/surge.htm or
    http://www.cob.org/fire/safety/surge.htm
    > From February 1994 to February 1995, two families on Brainbridge
    > Island lost their homes due to fires caused by Multiple Outlet
    > Power Surge Suppressors! Failing devices have also been
    > discovered on campus (see photo), luckily before there was a
    > fire.


    http://www.hanford.gov/lessons/sitell/ll00/2000-02.htm
    > On August 28, 1999, a Kensington Power Tree 20, model # 62162
    > multi-outlet power strip with surge protection failed and
    > started a small fire in a trailer at the Stanford Linear
    > Accelerator Center (SLAC). This graphic shows the damaged
    > power strip.


    MOVs are designed to shunt transients and remain operation.
    MOVs (properly sized) fail due to degradation - not
    vaporization. One Taiwan MOV manufacturer even defines a
    number for degradation. A 10% change in the Vb voltage. They
    provide examples of how an MOV can degrade by 10%: for the
    18 series MOVs, a 200 amp (classic 8/20 usec) transient is
    applied 10,000 times. No open circuit (vaporizing) condition
    in these tests. 18 series MOV degrades after about 10,000
    pulses. Degradation - not vaporization - not open circuit
    failure - is how MOVs fail when properly sized. An MOV that
    vaporized - well the manufacturer does not even provide specs
    for that because the protector should not be that grossly
    undersized.

    To sell ineffective and excessively profitable plug-in
    protectors, some manufacturers undersize their product. Then
    the naive will promote that grossly undersized protector with
    myths. A vaporized protector provided no effective protection
    - but did promote myths that increase sales.

    UL does not test protectors for protection. That is not
    what a UL test does. The protector can completely fail -
    provide no transistor protection - and still get UL1449
    approval because it did not threaten human life. That is all
    that UL 1449 2nd edition tests for - human safety and not
    transistor safety.

    SQLit wrote:
    > "Robert11" <> wrote in message
    > news:...
    >> Two questions regarding the MOV's one finds in the typical surge
    >> arrestors:
    >>
    >> When the MOV clamps due to a spike, is it all over for the MOV,
    >> or are they typically good for many clampings ?
    >>
    >> When they do fail, do they usuall fail as an open, or as a
    >> short circuit ?

    >
    > MOV's are tested by UL once. They work the design passes. There
    > is no more testing for another hit. Manufactures test the random
    > one off the manufacturing line and as long as they work as rated
    > the line continues to produce.
    >
    > My experience is if the MOV sees a max rating they usually fry,
    > open. I have installed a lot of Class 1 and 2 surge arrestors.
    > ( distribution and service ). They have fused protection and
    > usually if a fuse blows we just replace the circuit board with
    > the MOV's. Testing has shown the odds are the board is bad.
    > ...
     
    w_tom, Aug 10, 2005
    #4
  5. Robert11

    SQLit Guest

    Re: To SqLit From OP: Re: MOV's In Surge Arrestors Quest. ?

    "Robert11" <> wrote in message
    news:...
    > Hi,
    >
    > Thanks for info.
    >
    > Can you recommend a point of use type of brand and model ?
    >
    > Want to protect a new furnace circuit board that runs off a dedicated 110

    V
    > line.
    > Has already been fried once, recently, in a lightning storm.
    >
    > It has a fuse, but have real doubts if the board has any MOV's.
    >
    > What do yo think of the Intermatic AG2401 ?
    >


    First off absolutely nothing is lightning proof. The closer the lightning
    gets the worse the results.
    Second just protecting the furnance board is silly to my way of thinking.
    ( lets not go there right now )

    IEEE says if your going to protect from Transients, and that may or may not
    include lightning for some. It does for me. You need two of the three
    levels of protected.
    Levels are distribution, service, and point of use. Distribution would have
    the highest let through service lower and point of use even lower.
    Coordinating the zones is the key. Your situation installing the intermatic
    at the service gives you one level of protection. You still need another
    level that can withstand the 490v and clamp down further.

    What is the voltage tolerance of the equipment being damaged? Furnance
    boards are usually powered by a transformer not line power. I have not
    worked on any of the new stuff but I think that the manufactures still keep
    below 120v level for controls. Following this line the voltage was induced
    into all of the wiring in your home. Only the furnance was damaged. I lost
    a garage door opener last monsoon season, it was the only electronics, THEN,
    that was not protected by a point of use TVSS.

    Someone mentioned that the 490v clamping voltage seemed high. I tend to
    agree. But this unit is being sold as a lightning protector. Just looking
    at the voltage is not the whole story, you also need to look at the joules
    that the unit will withstand/protect.

    As a matter of prinicpal I do not care for "wired" solutions. I once worked
    for an OEM, CH. They came out with a bus connection TVSS series called
    Clipper. Yep they make wired solutions as well. Just like all of the other
    manufactures. The techy's that I worked around explained to me that TVSS
    connected to the bus are better cause the distance is shorter. Wired
    connections are longer. Programs with the APQA, Arizona Power Quality
    Association also agree with this.
    My recommendation is to look for a bus connected surge protector/tvss by
    your panel manufacture. As far as I know they all make them. Then look for a
    point of use device

    http://www.levitonproducts.com/cata...vchn=FRO&ovcpn=Froogle&ovcrn=Froogle&ovtac=PI

    this one is a pretty blue color. (humor)

    The bus connected unit should have a failure light, not that they are a
    guarntee.

    Nothing is lightning proof. Mov's are not tested for a second surge. I
    replace my equipment everyother year.

    good luck




    ========snipped=======================
     
    SQLit, Aug 10, 2005
    #5
  6. Robert11

    ehsjr Guest

    Robert11 wrote:
    > Hello:
    >
    > Two questions regarding the MOV's one finds in the typical surge arrestors:
    >
    > When the MOV clamps due to a spike, is it all over for the MOV, or are they
    > typically good for many clampings ?
    >
    > When they do fail, do they usuall fail as an open, or as a short circuit ?
    >
    > Thanks,
    > Bob



    You cannot test or detect how well your installed MOV will work.
    Throwing MOV's at your problem is not the right fix. Bond the
    duct work. That is a human safety requirement, and one possible
    source of your controller failure if it is not properly bonded.
    No exposed metal in your heating system should be permitted to
    be above ground potential.

    But, since you asked:
    MOV's fail shorted - but that is an over simplification.
    The short usually leads to an open, unless power is removed.
    There are an enormously huge number of possible paths
    for current through an MOV at the atomic level. Each path
    can be thought of as two conductors separated by an insulator.
    When the voltage across an MOV exceeds some specific level,
    one or more of these insulators has a hole torn in it, resulting
    in a short circuit (actually, a very low resistance) between
    the conductors. The energy that tore the hole is converted to heat,
    and does not reach your equipment. That's a good thing - but the
    hole is permanent. As further current flows after the hole is made,
    it is converted to heat in the MOV, and does not reach your
    equipment. How much current flows through the MOV (and therefore
    not through your equipment) is a function of path impedance,
    voltage, and how much energy the MOV can absorb. If electrical
    energy exceeding threshold is applied to the MOV for a long enough
    time, it will burn out and become open. Each time the threshold
    voltage is exceeded, at least some of the paths are destroyed,
    and the MOV's capability in trems of how much energy it can
    absorb is reduced by the amount already absorbed.

    Ed





    A shorted MOV in your point of use protector will quickly
    become an open MOV, unless a fuse blows or a breaker trips.
    An MOV *works* (not fails) by degradation.
     
    ehsjr, Aug 14, 2005
    #6
  7. Robert11

    Ben Miller Guest

    "ehsjr" <> wrote in message
    news:b3ALe.1129$MH1.639@trndny01...
    > Robert11 wrote:
    >> Hello:
    >>
    >> Two questions regarding the MOV's one finds in the typical surge
    >> arrestors:
    >>
    >> When the MOV clamps due to a spike, is it all over for the MOV, or are
    >> they typically good for many clampings ?
    >>
    >> When they do fail, do they usuall fail as an open, or as a short circuit
    >> ?
    >>
    >> Thanks,
    >> Bob

    >
    >
    > You cannot test or detect how well your installed MOV will work.
    > Throwing MOV's at your problem is not the right fix. Bond the
    > duct work. That is a human safety requirement, and one possible
    > source of your controller failure if it is not properly bonded.
    > No exposed metal in your heating system should be permitted to
    > be above ground potential.
    >
    > But, since you asked:
    > MOV's fail shorted - but that is an over simplification.
    > The short usually leads to an open, unless power is removed.
    > There are an enormously huge number of possible paths
    > for current through an MOV at the atomic level. Each path
    > can be thought of as two conductors separated by an insulator.
    > When the voltage across an MOV exceeds some specific level,
    > one or more of these insulators has a hole torn in it, resulting
    > in a short circuit (actually, a very low resistance) between
    > the conductors. The energy that tore the hole is converted to heat,
    > and does not reach your equipment. That's a good thing - but the
    > hole is permanent. As further current flows after the hole is made,
    > it is converted to heat in the MOV, and does not reach your
    > equipment. How much current flows through the MOV (and therefore
    > not through your equipment) is a function of path impedance,
    > voltage, and how much energy the MOV can absorb. If electrical
    > energy exceeding threshold is applied to the MOV for a long enough
    > time, it will burn out and become open. Each time the threshold
    > voltage is exceeded, at least some of the paths are destroyed,
    > and the MOV's capability in trems of how much energy it can
    > absorb is reduced by the amount already absorbed.



    Each one of those transient events also causes a slight reduction in the
    conducting threshold voltage. Eventually, it can reach the normal peak
    voltage, at which point the MOV begins conducting every half cycle and self
    destructs.

    Ben Miller
    --
    Benjamin D. Miller, PE
    B. MILLER ENGINEERING
    www.bmillerengineering.com
     
    Ben Miller, Aug 16, 2005
    #7
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