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Household wiring

Discussion in 'Electrical Engineering' started by Poh, Aug 30, 2004.

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  1. Poh

    Poh Guest


    I suspect that this may not be the place to answer my question, and if it
    isn't I apologise now, but I couldn't find any more appropriate group.

    I want to board up the loft floor to create some storage space, but in
    addition to the upper-floor lighting circuits, I have found a network of
    rusting, metal conduits with old electrical wiring inside (three single
    cables, not sheathed). BTW, the house is circa 1920s. I have found four ends
    to the wiring, where it has just been cut (not terminated) and the wiring
    left exposed. I want to rip the whole lot out, but obviously want to
    individually check each run to ensure that it isn't live before I do so.
    What is the best, economic method for me to do this? Can I get a simple
    tester to check live cables (even if they are not under load)?

    Thanks for any pointers

  2. Miles

    Miles Guest

    Your best advice is to get an electrician to look at it.

    Electrical engineering newsgroups are just that, for discussing electrical
    engineering. Any advice you get here could be flawed because no-one knows
    whether you've told them all the facts, and giving advice with only half the
    facts is just plain hazardous.
  3. Bob Peterson

    Bob Peterson Guest

    best advice we could give you is for you to contact a competent electrician.
    Nothing we could tell you would allow a complete novice to safely test or
    remove these circuits.
  4. Kilowatt

    Kilowatt Guest

    They make a 20-40$ tester that you can touch to the insulation to see if the
    circuit is hot.
  5. Kilowatt

    Kilowatt Guest

  6. Louis Bybee

    Louis Bybee Guest

    The device at the link below is a very useful tool, but if you rely on such
    a tool alone to protect you from contact with a live electrical circuit at
    some point you may be in for a possibly lethal surprise.

    Devices such as this do malfunction, have dead batteries, etc. Most of the
    electricians I see using non-contact voltage probes have established
    routines they use each time before using one to declare a circuit safe. With
    many that includes an additional meter. Interestingly enough they can
    indicate voltage where lethal current isn't present.

    Most of the people frequenting this group have, or should have the common
    sense and knowledge to use a non-contact voltage probe safely, but I cringe
    at the thought of them in the hand of an inexperienced person.

    Remove the two fish in address to respond
  7. Poh

    Poh Guest


    Thanks for the pointers. I suspected that many would suggest getting an
    electrician to do this for me, which is probably the best advice, but I had
    rather hoped that there would be a simple way for me to check it out myself,
    especially given that the old wiring is _almost_ certainly not live.
    However, I suppose I should bow to conventional wisdom and get the 'phone
    book out...

    Many thanks

  8. Kilowatt

    Kilowatt Guest

    That is why we push them in a known hot outlet before we test with them.
    The OP has what to me sounds like abandoned conduits.
    This little tester will most definitely tell him if the conduits are live or
    The circuit is either on or off.
    Yes I would trust it.
    In the past I did weekly
  9. Louis Bybee

    Louis Bybee Guest

    Good plan.

    You've hit the precise problem, "sounds like". I believe it's near
    impossible to evaluate someone's situation from an EMAIL posting. It's
    additionally difficult when the posts requesting help or information lack
    even the basic information to paint an outline of a picture. The "abandoned"
    conduits could in fact contain some working circuits with an extention into
    the area in question. A "sleeping" circuit can be cut, bare and open, or
    otherwise appear to be unused. These "sleeping" circuits could take the form
    of a switched hot (you just know that someone will switch it at the precise
    moment you are up in the attic tied up in it [hmmm.... I wonder what this
    switch does?]), switched via a photo cell, a neutral coming live after its
    normal path back to the panel is interrupted, etc.

    Even if one doesn't get hurt in the process, arbitraily removing the wiring
    before varifying it is truly abandoned could leave systems that you might be
    unaware of in an inoperative state.

    See the above paragraph.

    Each person has to assess their comfort zone individually. I have
    investigated numerous instances of electrocution, and electrical burns where
    the person in question "trusted" a circumstance where it might not have been
    the best choice to have made. I've even heard, "but I've done it hundreds of
    times before without any problems" during the investigations.

    I would advise the original poster to do the work himself if he has the
    skills, and knowledge to accomplish the task safely, but it could be in his
    best interest to at least have an experienced person evaluate the situation,
    and possible offer suggestions on how to best accomplish what he's after.

    Remove the two fish in address to respond
  10. Kilowatt

    Kilowatt Guest

    It will only take a 20$ tester to find out was my point.
    Do you think I am wrong?
    He should try?

  11. Louis Bybee

    Louis Bybee Guest

    Today's ad in the local paper lists a Greenlee Non-contact Voltage Probe for
    $13. From the ad it appears to be one of the better quality models.

    Wrong is such an all encompassing word. Who am I, or anyone else for that
    matter, to pronounce you wrong. The posts/information I have noticed from
    you strike me as being from a literate, and knowledgeable individual. I
    don't really know you, or first hand the facts surrounding the OP's
    situation. While I wouldn't presume to classify you as wrong it always makes
    me a bit nervous when offering advice on potentially hazardous subjects
    where the person posting the question appears to be unsure of the basics.
    Advising long distance always presents the hazard of the information being
    misunderstood completely or in part, and the advisee electing to not follow
    certain portions of the advise they may in their estimation deem to be in
    excess or unnecessary. It's just so easy to get "crosswise" with an
    electrical project where the safe return from an unintentional error may not
    be possible.

    That said I do believe that many individuals posses the intelligence and
    understanding to accomplish doing their own electrical work, or are capable
    of learning. Some with no assistance needed. Others might need help/hand
    holding of various levels. Some might prompt an evacuation of entire
    neighborhoods simply by considering picking up a tool. :-] I suspect
    that the OP would be the best judge of the level of assistance/advise he
    needs. I do believe however, that people offering electrical advice have at
    least some burden to suggest bringing in knowledgeable assistance where it's
    painfully apparent the person seeking assistance might be in over their
    head, or lack the understanding to proceed safely.

    Remove the two fish in address to respond

  12. Guest

    The tester gives a positive indication that the circuit is live.
    It does not give a positive indication that the circuit is dead.

    The beeping tells you to treat the circuit as live.
    The lack of beeping does not tell you to treat the circuit as dead.

    The op is clearly looking for a tester to tell him "it is safe for
    you to work on this circuit, because it is dead". That's not
    how he worded his question - but it is clear that is what he
    has in mind. The Greenlee tester can tell him it is not safe
    for him to work on the circuit - but it cannot tell him it is safe.
  13. Ben Miller

    Ben Miller Guest

    The correct procedure is a three-step process:

    1. Test on a known live circuit to see that it responds.
    2. Test the circuit of interest.
    3. Test on a known live circuit again to see that it is still working.

    This applies to ANY voltage test where you are confirming that a circuit is
    dead, regardless of the type of instrument (meter, voltage tester, etc.).

    Ben Miller
  14. Louis Bybee

    Louis Bybee Guest

    Agreed. The three step procedure you've listed is a sound practice, but two
    possibilities still concern me.

    In the hands of an inexperienced person it still could be inadequate. It
    doesn't address the possibility of checking a conductor that might be
    switched, or under automatic control. It also doesn't account for this same
    inexperienced individual placing the probes on an insulated surface that
    appears to be part of the conductor (I watched an engineer do just that
    once, and then begin to disassemble what was in actuality a live bus

    Second, it is possible for a non-contact voltage probe to lie, or
    misrepresent voltage as being present. Admittedly the lying is possibly in
    your favor, but still confusing to the unknowledgeable person. Wires, and
    other conductors that are under the inductive influence of a live current
    carrying conductor can induce a low potential voltage signal in surrounding
    conductors not connected to a live source. This signal will report as live
    on non-contact, and even high input non-loading meters.

    The three step procedure you suggest is sound in the hands of an experienced
    person, but I would still counsel the inexperienced to at least consult an
    electrician/engineer before engaging in activities that could end up being a
    one way dead end street.

    Remove the two fish in address to respond
  15. Ben Miller

    Ben Miller Guest

    I agree completely. I wasn't promoting that an amateur do this at all! I saw
    several posts that mentioned verifying the tester before making the
    measurement, and I wanted to emphasize that you need to verify it again
    after making the measurement, to be sure it didn't just die coincidently.

    Ben Miller
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