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Wood as an insulator?

Discussion in 'Electronic Basics' started by larry moe 'n curly, Feb 1, 2006.

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  1. Why is it safe to use wood around high voltage when it contains

    According to , wood contains
    approximately 2-15% moisture at room temperature.
  2. Lord Garth

    Lord Garth Guest

  3. Who said that it was?
    Wood is usually classified as an insulator, but don't bet your life on
    it. ;-) I would imagine that's why you see glass (or whatever they're
    made of now) insulators used even at relatively low voltages.
  4. Lord Garth

    Lord Garth Guest

    I used to climb up the utility pole to get on the garage roof to retrieve
    as a child. I always was slightly shocked until my feet were off the
    Then again, I did grow up 1 block from the Gulf of Mexico so the salt spray
    and high humidity had much to do with the conduction through the wooden
  5. Lots of people who tap circuit boards with wooden dowels to find
    intermittent problems or who carve dowels to use as screwdrivers for
    adjustments on CRT monitors or TVs that are running. So far, I've used
    only plastic or fiberglass rods for this, but dowels are a lot easier
    to buy locally.
  6. larry moe 'n curly spake thus:
    I wouldn't want to go poking with one of them thar things around a
    flyback transformer, no siree Bob.
  7. JANA

    JANA Guest

    Wood is not a reliable insulator for electrical devices! Especially for high
    voltage, don't even try it!




    According to , wood contains
    approximately 2-15% moisture at room temperature.
  8. jakdedert

    jakdedert Guest

    Water in and of itself is a lousy conductor. Nobody ever said that wood
    was a perfect insulator, even dry...just 'good enough'. If you're
    really curious, put your DVM probes on each end of a hunk of wood and check.

    If you can get a reading I'll be surprised.

    For tuning purposes, the utility of wood diddle sticks is their lack of
    inductance, moreso than a lack of conductivity. OTOH, the previous
    experiment should have demonstrated that there is no danger in using
    them to tap out faults, either.

    Just don't store them in a glass of water between uses. <g>

  9. CRaSH

    CRaSH Guest

    Wooden dowel = ok
    Lead pencil, holding onto metal ring around eraser = NOT ok

  10. Mike Berger

    Mike Berger Guest

    Look at the breadboards people built for their old high
    voltage tube projects. They're varnished. It's not just
    for looks -- it seals the moisture in.
  11. John Larkin

    John Larkin Guest

    Plastic chopsticks.

  12. default

    default Guest

    Cellulose is an insulator and what little moisture remains in the wood
    is parked in insulating cells.

    Like all insulators it has a breakdown rating of volts per mil
    thickness (highly variable in the case of wood, for both species and
    moisture content). I have no problem poking around a TV with a clean
    dry stick to look for intermittent's, but a Tesla coil working at
    100KV treats wood like it was a conductor or semiconductor.

    Wood sealed with lacquer, wax or varnish will be safer than bare wood.
  13. ehsjr

    ehsjr Guest

    Learning the difference without getting burned, pricelsss.

  14. Cleaner, drier wood is good for insulating line voltages - well, maybe
    not quite good enough for making products with wood as the main
    insulation... I would not mass-produce products using wood to hold
    bare wires with line voltage. That's something plastics and ceramics are

    I have found dowel rod from a hardware store to be a good insulator -
    so far - although I would not bet my life that it will insulate me from
    several KV or 10's of KV.

    As for old lumber that was in a basement for the past how many months or
    years? Sometimes a good insulator, sometimes not... Usually reads
    megohms to open circuit if you touch ohmmeter probes to it, but your hand
    has more contact area. Old lumber in the garage is worse if anything, let
    alone lumber that has been stored outdoors...

    As for brand-new lumber? I have seen a couple examples not do well with
    a neon sign transformer. Some lumber is not as good an insulator as the
    usual dowel rods.
    The problem is high variability!

    If should I ever have to work on a single live wire live with several
    KV, I would not stand on wood, but on a plastic milk crate or a plastic
    bucket. (Better still make a platform of a bunch tied together with nylon
    or polypropylene or other "plastic" rope/twine, so if I have to make a
    sudden maneuver to keep my footing I won't have to worry about getting my
    hands away from the high voltage before stepping onto the ground!)

    - Don Klipstein ()
  15. Water with the amount of carbonic acid formed by the amount of CO2
    dissolved in it when it is in equilibrium with the atmosphere is not that
    great an insulator!
    Touch the tips of DVM probes with your fingers and see readings usually
    in the megohms or 100's of K-ohms... Things are a little different when
    you have hundreds of times more contact area - and skin form-fits to
    contact a not-perfectly-smooth surface better than a piece of sheet metal
    will. Try with two larger coins contacting a piece of wood when assisted
    by small puddles of salt water - ohmmeter readings will usually be high
    enough to indicate "no problem" but there is a problem with high
    variability. And if you do a "study" on some sample set of a variety of
    pieces of wood, there is the chance you will miss wood types or wood
    sources that provide killer more-conductive wood, or you could fail to
    include clunkers made more conductive by location, climate or past weather
    or storage conditions or the like...
    I think plastic diddle sticks have the same advantages. The
    requirements here are lack of ferromagnetism and being no worse an
    insulator than less-conductive core materials - many ferrite cores will
    draw sparks/arcs if subjected to the output of neon sign transformers!
    Danger there is negligible even if line voltages are present. I would
    trust a piece of dowel rod from a hardware store to insulate me from 120V,
    although I would not use it as a primary insulator in a mass-produced
    - Don Klipstein ()
  16. Or out!

    - Don Klipstein ()
  17. jakdedert

    jakdedert Guest

    Wood plated with gold is also a great conductor; but that wasn't the point.
    Also kind of beyond the point.

  18. Recall that paper is basically wood, and paper has been used for over a
    century as an insulator in transformers and capacitors. In capacitors
    it's like a few thousandths of an inch for each 100 volts, so it's not
    too bad.

    So it's likely that DRY wood is a pretty good insulator.
  19. I have not seen paper capacitors that were just sheets of paper and
    foil stacked or wound up. And I have dissected lots of capacitors.

    Most paper capacitors are actually paper-oil capacitors, where a
    highly refined tissue paper web acts as a spacer (similar to what the
    spacers between the plates of a lead acid battery ), while the oil (or
    wax) soaked into all the pores performs most of the dielectric
    function. The paper is also vacuum dried as part of the process of
    getting all the pores filled with the hydrocarbon filling. Any air
    bubbles left unfilled would be places where the E-field would be
    concentrated by the abrupt drop in permitivity, causing corona that
    would degrade both the paper and the oil.
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