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Whole house surge protectors

Discussion in 'Electronic Design' started by Ignoramus32515, Dec 21, 2005.

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  1. Just curious. A discussion that I had in another newsgroup mentioned
    whole house surge protectors. I understand that they do not provide
    100% protectiom from all surges, lightnings etc but they could be useful.

    1. Is a WHSP something that is much more than a (hopefully) beefy MOV
    in a steel box?

    2. Can I, instead of buying a WHSP, just buy properly rated MOVs and
    install them at the service panel? (from each power leg to ground,
    I suppose).

    3. We had some disagreement about whether a UPS such as APC 2200
    offers protection from surges coming from the power line. I think that
    the answer is yes.

    Any thoughts?

  2. Tim Shoppa

    Tim Shoppa Guest

    They are typically two beefy MOV's (hot1-to-ground and hot2-to-ground)
    or three beefy MOV's (above plus hot1-to-hot2) in a sand-filled metal
    box. Most also have a little LED telling you that you're "protected" (I
    think this works on a few mA leakage current through the MOV when the
    MOV has not yet failed open.)

    These are typically installed behind 15 or 20A breakers (at least the
    smaller ones designed for say 200A panels).
    You could, but you'd then face the never-ending battle of getting your
    local electrical inspector to approve something that isn't UL listed.
    MOV's hit with a big surge really do explode into tiny little pieces,
    having those pieces flying about inside your panel isn't the most
    desirable thing. Sometimes they fail shorted, other times they fail
    Putting the protection at the service panel (where presumably you've
    got a nice good low-impedance path to ground) is generally a better
    idea than installing it far away from ground.

  3. Thanks. I read some articles suggesting that WHSP are rated for higher
    voltage and are not effective for protecting electronics, only motor
    loads (see, for example,, I can provide a reference).

    I also want some clarification regarding path to ground and such.

    If an electrical surge comes through the electrical line, and a surge
    protector shunts it to ground/neutral (both wired to the same point on
    the panel), and the device that's being protected is insulated from
    ground (say, it is in a wooden cabinet), then would it be beneficial
    for this circuit to also have WHSP?

    Also, would a decent UPS such as a APC 2200 (I got four for $60
    yesterday) be sufficient? We just bought an expensive electronic
    consumer appliance and I want to protect it. Hence my question.

  4. Jim Thompson

    Jim Thompson Guest

    On Wed, 21 Dec 2005 17:59:07 GMT, Ignoramus32515

    About five years ago, we had a surge from a lightning strike at an
    electrical substation some four miles away.

    It propagated on _underground_ cabling to my house where it took out
    all the light dimmers in the house, two computers and a couple of TV

    I added a WHSP as well as little UPS's on critical items.

    So far so good... fingers crossed ;-)

    ...Jim Thompson
  5. GregS

    GregS Guest

    My electric company charges for their device on a monthly rate of
    $5. Imk pretty sure some kind of protection insurance is provided, but
    at least the intention is to protect your stuff.

  7. David Harmon

    David Harmon Guest

    On 21 Dec 2005 09:38:07 -0800 in, "Tim
    So how does that work? Putting a puny LED in series with your MOV
    is obviously a bad idea.
  8. Pig Bladder

    Pig Bladder Guest

    So, how long has that volcano under your ass been dormant?
  9. Jim Thompson

    Jim Thompson Guest

    Apparently before history.

    ...Jim Thompson
  10. ehsjr

    ehsjr Guest

    No that's pretty much it - big MOV's. My WHSP is a double pole
    circuit breaker size/shape - it goes in the service entry panel
    and takes up two positions where breakers could go. (It does
    not provide the circuit breaker function, just the surge
    You could, but it is far more practical to buy a premade unit.
    It does. 880 joules, according to the spec:

    However, think of what "protection" means. Compare it to
    a bulletproof vest. The vest stops small caliber bullets,
    but doesn't kepp one safe from highpowered rifle slugs.
    Also, it protects your chest, but doesn't cover other areas.
    With respect to the ups, the PC can be damaged by a surge
    entering on the phone or cable wires, or by a power line
    surge to a device not on the ups and thence to the PC. Or
    there can be a surge on the powerline that overwhelms the
    protection the ups provides, like the high powered rifle
    bullet overwhelms the bulletproof vest.

  11. Tim Shoppa

    Tim Shoppa Guest

    You noticed I wrote "I think this works on leakage current...". My
    belief (based largely on a mix of marketing and marketing!) is that
    the LED's that accompany MOV-based surge protectors are there to tell
    you that the MOV has not yet failed open. If the MOV fails shorted,
    a breaker trips, so the LED can't be there to tell you that the MOV
    failed shorted.

    So my guess was that the LED was lit from leakage current through the
    MOV. I have not done a close enough inspection to confirm this guess,
    and in fact I'm not sure how you wire a LED to do this function! Maybe
    the LED just tells you that power is applied and tells you nothing
    the remaining health of the MOV's. Maybe the LED is just marketing
    mumbo-jumbo and means absolutely nothing.

  12. qrk

    qrk Guest

    I've seen this company's product in use in FAA installations.
  13. Jim Thompson

    Jim Thompson Guest

  14. Riscy

    Riscy Guest

    I have designed the surge protection unit, the biggest issue I found
    that it requires good earthing arrangement, in fact very high quality
    as it critually direct surge current to ground, otherwise it

    This is difficult part of the design, if you seen standard AWG12-AWG20
    earth cable to earth at more than 1 meter than you know it likley to be
    badly installed. It need better than AWG8 earth cable to earth stake,
    length less than 1 meter.

    Any comment on that?
  15. qrk

    qrk Guest

    Only good stuff comes from Goleta! They don't call this area "Silcon
    Beach" for nuthin'. Our building, an old FAA flight services building,
    has one of these units. Nice gas arresters protecting this building.
  16. ehsjr

    ehsjr Guest

    On this side of the pond, you'd never pass an electrical
    inspection with a GEC (grounding electrode conductor)
    of the AWG12-20 sizes you mention, regardless of whether a
    surge protector is installed. #8 copper is the smallest
    you can use, and bigger services require larger GEC's.

    The 1 meter figure is damn near impossible to achieve for
    most services - the power meter is usually mounted over
    4 feet above ground level.

    In any event, you want a real good grounding electrode
    system connected with as short, large and straight a
    GEC as is practical.

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