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Multiple Power Strips Connected In Series

Discussion in 'Electronic Basics' started by Sean, Oct 20, 2004.

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  1. Sean

    Sean Guest

    Hi,

    I've known this was 'taboo' for as long as I can remember. What I'd
    like to know is why is it a bad idea to connect multiple power strips
    (with surge suppression and/or line filters) in series; especially
    when using computers.

    I found several references which say not to do it, but no simple
    practical explanation as to why.

    The only way I can think to demonstrate it is to get a half a dozen of
    them and connect them up in series, and stick meters at the wall,
    between each, and at the end. I suspect that doing so will show some
    form of degradation, but what I'm not sure what it will be or why it
    will occur.

    Any detailed explanation and or pointer to a web site where this is
    explained would be appreciated.

    Thanks a 10E6!
     
  2. rayjking

    rayjking Guest

    Hi,

    One reason is due to the fast rise of current in transients the inductance
    of the added length of wire defeats the transprotection.
    One inch of wire ( type used in the power strips ) is about 19nh. if you add
    the 1000 amps possible and the length of wire at a high di/dt then many
    volts can be generated and addition the phone leadin may have lower
    impedance ( more current ) than the power leads due to the transmission line
    effect of the telephone line.

    Ray
     
  3. John Larkin

    John Larkin Guest


    There's really no reason not to. If they all have circuit breakers,
    which most do, the upstream guys will trip if they're overloaded by
    the total load. If you put the lighter loads towards the end of the
    string, voltage drop along the total length of power cord will be
    minimized. As far as length goes, it's not much different from a long
    extension cord.

    John
     
  4. Sean

    Sean Guest

    Here's what I found in groups:

    ----------

    http://groups.google.com/groups?q="...afe=off&selm=&rnum=1

    Putting power strips in series only degrades their performance.

    http://groups.google.com/groups?q="...7l1ag$-cruz.ca.us&rnum=2

    Someone wires 5 power strips in series and you're at the end.

    http://groups.google.com/groups?q="...elm=&rnum=4

    - Multiple AC power strips in series.

    http://groups.google.com/groups?q="...selm=&rnum=6

    "Does 5 power strips in series violate some kind of NEC code or
    ordinance"?

    http://groups.google.com/groups?hl=...5%40bgtnsc06-news.ops.worldnet.att.net&rnum=4

    {Dialog where a power strip is diagnosed as a problem}

    http://support.jp.dell.com/docs/systems/ph2o/solving.htm#1111403

    Check for interference— Electrical appliances on the same circuit or
    operating near the computer can cause interference. Other causes of
    interference: power extension cables, too many devices on a power
    strip, or multiple power strips connected to the same electrical
    outlet.

    OPNAV INSTRUCTION 5100.19D VOLUME II CHANGE TRANSMITTAL 1 30 AUGUST
    2001 - C0804

    s. Use onlt Navy-approved power strips for computer equipment,
    printers, and peripherals. Never use power strips in series
    (connected to one another).

    ---------------

    I see no hard evidence one way or the other at this point.

    Most computers have switching power supplies, is there any evidence
    that the combination of line filters and or surge suppressors
    adversely affects them?

    I have seen UPS devices have problems if they are fed anything but
    current streight from the wall socket. They detect a small flux in
    the supply as intercepted by the power strip and switch into battery
    mode.

    I'm beginning to think that this has all the makings of an urban
    legend. Maybe it is time to contact MythBusters.
     
  5. Rich Grise

    Rich Grise Guest

    The breaker in the first strip has to handle the whole load, so
    when you add the 14th computer, the whole string goes down. ;-)

    Cheers!
    Rich
     
  6. Rich Grise

    Rich Grise Guest


    Right. So be sure to pile up all of your electrical appliances next to
    the wall outlets. ;-)

    Cheers!
    Rich
     
  7. Sean

    Sean Guest

    Here's another source:
    http://www.eeel.nist.gov/817/817g/spd-anthology/files/Text Part 4.doc

    From "Coordination: 1980" - F.D. Martzloff

    Fact 3.
    Without substantial connected loads in the system, the open-circuit
    surges appearing at the service entrance propagate along the branch
    circuits with very little attenuation.

    Conclusion 4.
    Coordination of surge suppressors requires a finite impedance to
    separate the two devices, enabling the lower voltage device to perform
    its voltage-clamping function while the higher voltage device performs
    the energy-diverting function.

    Conclusion 5.
    The concept that surge voltages decrease from the service entrance to
    the outlets is misleading for a lightly loaded System. Rather, the
    protection scheme must be based on the propagation of unattenuated
    voltages

    Conclusion 6.
    Indiscriminate application of surge protectors may, at best, fail to
    provide the intended protection and, at worst, cause disruptive
    operation of the suppressors. What is needed is a coordinated
    approach based on the recognition of the essential factors governing
    devices and surge propagation.

    There is a wealth of papers concerning surge suppression available tn
    the directory of the example above, that I am trying to sort through.

    More Later [YMMV]
     
  8. w_tom

    w_tom Guest

    What does a surge seek? Destructive transients are
    typically longitudinal mode. IOW they seek earth ground. If
    not earthed at the building entrance, then they will seek
    earth ground destructively through household appliances. Too
    many fail to learn of multiple types of transients. The
    destructive transient is not stopped, blocked, or absorbed.
    And yet that is what a plug-in protector must do. Is that
    plug-in protector going to stop what miles of sky could not?

    Introduction to protection principles in "Pull the wall plug
    or not?" in nz.comp on 7 Sept 2004 at
    http://tinyurl.com/5ttwl

    For more technical sources, then three consecutive posts: "
    Belkin Surgemaster worth the money?" in the newsgroup
    uk.comp.homebuilt on 29 Sept 2004 at
    http://tinyurl.com/6zfps

    Surge protection demonstrated by a simple example:
    "Whole house surge suppressors" in alt.home.repair on 12 Jul
    2004 at
    http://tinyurl.com/6gl67
    Transients first form a complete electrical path from cloud
    to earth. Only after current is passing through everything,
    then something in that path fails. Destructive transients seek
    earth ground. Earthing - and not some protector - defines a
    protection 'system'. A surge protector is only as effective
    as its earth ground. Too many forget about essential earthing
    and instead hope what they see on retail shelves is actually
    protection. No earth ground means no effective protection.

     
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