Conference 7.286::home_work

    Re: .5
    
    You can buy whole-house surge suppressors.  I have one, made by
    Intermatic; it attaches to the circuit breaker panel.  It's rated
    for a whopping amount of surge current, but nothing will really
    protect against a direct hit.  Still, such a device would be well
    worth the small ($40 or so plus installation) investment for you.
    
    				Steve

    We had a bout with a nearby strike a few months ago (just got the
    check, finally). 
    
    In my case, I don't think the whole-house protector would have helped,
    because I don't think anything came in via the power wiring.. I think
    what happened is the local magnetic field induced common-mode spikes in
    anything that had a long wire attached, or induced a differential
    voltage between any two wires leading to a single unit: 
    
     The VCRs (which have both power and cable) were toast.
     Stereo power amp sustained output-circuit damage (long speaker
       wires
     Modems and phones which had a wall cube blew up somewhere in the
       phone-input stage (power and phone to the unit).
    
    So, the current plan being implemented in my house is: 
      1.) whole-house suppressors on power and also phone at the power
          service entrance.
      2.) single-point, common ground suppressors for anything that has
          more than one cable attached to it. (e.g. phone suppressors
          plugged into the same outlet as the computer, before the 
          power fans out into the UPS, socket strips, etc).
      3.) MOVs to chassis on both sides of speaker leads.
    
    ...tom
     

    BTW, the intermatic suppressor functions by providing a path for some
    of the energy; it is placed in parallel on a branch leg, so it isn't
    actually in the line of fire to the other branches.
    
    One can also have an electrician install a much larger GE suppressor in
    either the meter box or the breaker panel; this unit is designed to go
    directly across the incoming line. This is expensive, and probably not
    worth it for most situations (you have to be really careful about
    grounds in this case, and most electricians DO NOT understand
    lightning grounding)..
    
    Don't make your own phone-line suppressors out of MOVs; they can cause
    fires in the event of a "line-cross" fault (where a power line manages
    to contact a phone line). The phone-line suppressors that you buy have
    fuses and fusible paths to sacrifice themselves in case of such an
    incident..
    
    ...tom

Re: .8

The Intermatic suppressor I have is wired to both hot lines, neutral and
ground in the panel box.  I don't quite see how it could fail to protect
all of the branches.  It is the size of a surface-mount outlet box,
epoxy-filled and rather heavy.

				Steve

	re -last few.

	Do you need one intermatic for each leg in a house with
	a gnd and two legs?

	Does anyone have a schematic for a phoneline surge prot?

	Thanks
	Pete

    No, just one; it protects both legs.
    
    			Steve

    The Intermatic is better than nothing (I do have one), but its
    protection is somewhat limited because of all the inductance between it
    and the branche circuits. So, it primarily functions by absorbing energy
    later in the surge rather than by killing off the leading edge. 
    
    It wouldn't surprise be to still be able to see several KV for a
    microsecond on the house circuits with this arrangment. All that means
    is that solid-state things may still need some protection, but you
    probably won't have catastrophic mechanical damange (like the wall-cube
    I have that shorted its primary..)
    
    ...tom

Tom,

Could you please explain regading the inductance?  Where does it come from?
(the breakers themselves?) 

				Steve

    The long wires that connect the suppressor to the breaker.
    
    The way to connect a surge-suppression device for maximum effectiveness
    is to run the circuit being protected "through" the suppression device,
    thus:
    
        ---------  -------------
                 \/
        line    +--+       load
                |  |
                |  | suppressor
                +--+
                 /\
       ----------  -------------
    
    This minimizes the common inductance between the line circuit and the
    load circuit. In practice, this means making the leads as short as
    possible, although there are both varistors and clamp diodes available
    with four wires so that you can actually run the load through the
    package of the device.
    
    So, for maximum effectiveness, you'd want to mount the suppressor on
    the side of the box where the neutral and ground bus bars are, and wire
    straight in to the nearest breaker from there. This is usually
    "inconvenient", because there is a lot of congestion in that area of
    most breaker panels, and the high-amperage breakers tend to gravitate
    there as well.
    
    There is also a second-order problem in that the leading edge of the
    surge may also see sufficient inductance in the sharp bend where the
    breaker connects to the bus-bar (and also in the internal wiring of the
    breaker) to limit the effectiveness of the suppression device.
    
    ...tom