Wood as an insulator?

No

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.

I used to climb up the utility pole to get on the garage roof to retrieve things as a child. I always was slightly shocked until my feet were off the ground. 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 pole.

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.

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.

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

--

JANA _____

According to

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.

jak

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

Don't ask............

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.

larry moe 'n curly wrote:

Plastic chopsticks.

John

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

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

Learning the difference without getting burned, pricelsss.

Ed

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 for!

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 ( snipped-for-privacy@misty.com)

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 product.

- Don Klipstein ( snipped-for-privacy@misty.com)

Or out!

- Don Klipstein ( snipped-for-privacy@misty.com)

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

Also kind of beyond the point.

jak

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.

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.

Hi there.. Well, a little over 35 years ago, when I was a young man, and had just gotten my Amateur Radio License, I didn't have the money for a center insulator for my low frequency 40 meter dipole, So, I built a "homemade" insulator out of fresh, new, woodstock that my dad had around... I carefully put the dipole together, wrapping it with your usual black tape, and it worked great! The SWR was 1.2 to 1, and I was happy.. A few weeks later, after a few moderate rainfalls, my SWR went sky high, for no reason! (At least, that I didn't know about yet) When I finally thought I figured out what was happening, an old timer agreed with my asessment of the problem, and, had pity on me, and was nice in giving me a ceramic glass egg insulator, and all was well after that.. As far as your question goes, especially with high voltage (as opposed to 50 watts RF) I wouldn't trust wood for a HV insulator no matter what you did to it! Stick with what you know works, i.e., ceramic glass, teflon, and the many new HV insulation techniques that have come about for reasons of saftey first, and THAT is what counts, OM.. Best luck then! Anthony, WB8MLA