How come wet trees don't conduct electricity?

[Rob Votin]

Behind my house runs a string of telephone poles that carry (among
other things) the 240VAC single power that is run into each house. The
wires going from the poles to the houses are insulated and twisted
together, but the lines between the poles are bare and un-insulated;
they are simply held apart with spacers so that they don't touch.

There is more than one place where the tips of some tree branches are
actually touching these conductors. During a good rainstorm, these
trees must be completely soaked, so how come there isn't a "short
circuit"?

Is it possible that the amount of leakage current is so low that 1) it
does no harm to the tree and 2) the power company doesnt care about
the extra loss? Or is there some strange property of wet wood that I
am unaware of? Thanks.

 

[Joerg]

Hello Rob,

Behind my house runs a string of telephone poles that carry (among
other things) the 240VAC single power that is run into each house. The
wires going from the poles to the houses are insulated and twisted
together, but the lines between the poles are bare and un-insulated;
they are simply held apart with spacers so that they don't touch.

There is more than one place where the tips of some tree branches are
actually touching these conductors. During a good rainstorm, these
trees must be completely soaked, so how come there isn't a "short
circuit"?

Call your utility. Immediately. This is a VERY dangerous situation. What
if somebody touches a wet tree, falls over and dies from cardiac arrest?

Is it possible that the amount of leakage current is so low that 1) it
does no harm to the tree and 2) the power company doesnt care about
the extra loss? Or is there some strange property of wet wood that I
am unaware of? Thanks.

Wet wood does conduct. A situation like this can seriously harm or kill
someone.

How much current is a matter of voltage. But a few milliamps too much
can kill. A couple of years ago we had a tree in our county touch 10kV
lines during a storm. Boom, and the whole tree was engulfed in flames.

 

[Rich Grise]

Behind my house runs a string of telephone poles that carry (among
other things) the 240VAC single power that is run into each house. The
wires going from the poles to the houses are insulated and twisted
together, but the lines between the poles are bare and un-insulated;
they are simply held apart with spacers so that they don't touch.

There is more than one place where the tips of some tree branches are
actually touching these conductors. During a good rainstorm, these
trees must be completely soaked, so how come there isn't a "short
circuit"?

Is it possible that the amount of leakage current is so low that 1) it
does no harm to the tree and 2) the power company doesnt care about
the extra loss? Or is there some strange property of wet wood that I
am unaware of? Thanks.

If the wires are really as you describe, then they don't care about
a current path to ground because it's an isolated current loop.

Hope This Helps!
Rich

 

[DJ Delorie]

I don't know what kind of trees you have in your area, but around here
when the wind pushes rain-soaked trees into the bare wires, the pole
breakers trip. It causes power flickers throughout the rest of the
grid (off time == reaction time of breaker).

 

[Rob Votin]

Thanks for the replies Joerg and Rich.

First, I did call the utility company as soon as I bought this house,
more than a year ago (I'm in the northeast US if that makes a
difference). I was told that someone came and looked at the lines and
that it was no problem on their end. If I wanted the trees trimmed for
"aesthetic" reasons then it was my responsibility as the homeowner.

Second, the lines are definitely not an isolated current loop. There
are 4 paralell conductors on the top of the pole (middle part of the
pole has telephone and cable TV lines). Of the four lines (uninsulated
aluminum alloy by the looks of them) three of them are tapped for my
house. One of them is an un-insulated line, which comes through the
power meter to my circuit breaker panel and is bonded to a grounding
rod by the meter and also to a cold water pipe. So as far as I know,
either of the other two lines would be at a potential of 120 volts to
earth ground. Meaning some current should be flowing to ground through
the wet tree.

From the sound of things, maybe I should call the power company and
insist they take a second look. Maybe I could also go out after the
next rain storm and hook up a voltmeter from the tree trunk to the
earth to see if I measure any stray voltage? (taking the appropriate
safety precautions of course). Maybe I could also hook up a light bulb
to the tree trunk. A picture of that glowing would be worth a thousand
words to send to the power company....

 

[Rob Votin]

DJ,
..
Funny you mention that, we definitely get very brief (approx 1 sec)
power outs during very windy storms. I did not realize that whatever
types of breakers are employed down at the "street" level of the grid
are actually auto-resetting.

Being an electrical engineer this type of thing is horribly
fascinating for me, but there doesn't seem to be any good online
reference for such low level technical details. Searching the web or
how_stuff_works.com type of sites for "power grid" info usually
results in a nice pretty picture of a power plant, a house, a wire in
between and not much else in the way of technical info. Looking around
the neighborhood i see the wires and the "pole-pig" step down
transformers, but nothing else I recognize as a breaker. please excuse
my ignorance and dont hesitate to educate.

Regards,
Rob

 

[[email protected]]

Behind my house runs a string of telephone poles that carry (among
other things) the 240VAC single power that is run into each house. The
wires going from the poles to the houses are insulated and twisted
together, but the lines between the poles are bare and un-insulated;
they are simply held apart with spacers so that they don't touch.

There is more than one place where the tips of some tree branches are
actually touching these conductors. During a good rainstorm, these
trees must be completely soaked, so how come there isn't a "short
circuit"?

Is it possible that the amount of leakage current is so low that 1) it
does no harm to the tree and 2) the power company doesnt care about
the extra loss? Or is there some strange property of wet wood that I
am unaware of? Thanks.

If these get up in the primary (usually the wire on top with the big
insulators) they will come to cut it. That will arc and spark.
I couldn't get the PoCo interested in cutting the trees away from my
secondaries either (the 120/240v side).
I called and said I was thinking about cutting the tree down and asked
if they had any concerns since it might fall on the lines and they
were right out there. They whacked it down below the secondary and
told me I could cut it down now.
I still hadn't got around to it when Charlie took it out for me.

 

[Roy L. Fuchs]

I still hadn't got around to it when Charlie took it out for me.

Those damned commies! :-]

 

[[email protected]]

I still hadn't got around to it when Charlie took it out for me.

Those damned commies! :-]

Yup and a year later That Fred Flintstone's bitch Wilma cane by and
whacked me again.

 

[Abstract Dissonance]

Behind my house runs a string of telephone poles that carry (among
other things) the 240VAC single power that is run into each house. The
wires going from the poles to the houses are insulated and twisted
together, but the lines between the poles are bare and un-insulated;
they are simply held apart with spacers so that they don't touch.

There is more than one place where the tips of some tree branches are
actually touching these conductors. During a good rainstorm, these
trees must be completely soaked, so how come there isn't a "short
circuit"?

Is it possible that the amount of leakage current is so low that 1) it
does no harm to the tree and 2) the power company doesnt care about
the extra loss? Or is there some strange property of wet wood that I
am unaware of? Thanks.

rain water has anywhere from 1 M/cm to 1/10 M/cm ohms
resistance(approximately). given that a tree tends to be several meters high
theres not much of a chance for shock or much leakage. Unlike humans a tree
doesn't have a heart. I'm not sure if the current will flow through the tree
or just on its surface though and it might change the results somewhat. I
doubt theres much to worry about unless you like plain around tree's next to
powerlines when its raining?

 

[Eeyore]

I still hadn't got around to it when Charlie took it out for me.

Those damned commies! :-]

LOL !

Graham

 

[Roy L. Fuchs]

I still hadn't got around to it when Charlie took it out for me.

Those damned commies! :-]

Charlie didn't get much USO. He was dug in too deep or moving too
fast. His idea of great R&R was cold rice and a little rat meat.

MMMmmm... especially baby rat meat... Mmmmm... Stir fry...

He had only two ways home: death, or victory.

Depends on which side of Tet he was in on.

Most of 'em got Chi Chi! (FireSign Theater, Eat Or Be Eaten)

Ahhh... the smell of Napalm in the morning!

 

[Spehro Pefhany]

I still hadn't got around to it when Charlie took it out for me.

Those damned commies! :-]

Charlie didn't get much USO. He was dug in too deep or moving too
fast. His idea of great R&R was cold rice and a little rat meat.
He had only two ways home: death, or victory.


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

On Thu, 06 Jul 2006 00:50:20 -0400, [email protected] Gave us:

I still hadn't got around to it when Charlie took it out for me.

Those damned commies! :-]

Charlie didn't get much USO. He was dug in too deep or moving too
fast. His idea of great R&R was cold rice and a little rat meat.

MMMmmm... especially baby rat meat... Mmmmm... Stir fry...

He had only two ways home: death, or victory.

Depends on which side of Tet he was in on.

Most of 'em got Chi Chi! (FireSign Theater, Eat Or Be Eaten)

Ahhh... the smell of Napalm in the morning!

Looks like Hajji don't surf either:
http://www.latimes.com/news/opinion...ul05,0,5998634.column?coll=la-home-commentary


Best regards,
Spehro Pefhany

 

[Roy L. Fuchs]

On Thu, 06 Jul 2006 05:00:28 GMT, the renowned Roy L. Fuchs

On Thu, 06 Jul 2006 00:50:20 -0400, [email protected] Gave us:

I still hadn't got around to it when Charlie took it out for me.

Those damned commies! :-]

Charlie didn't get much USO. He was dug in too deep or moving too
fast. His idea of great R&R was cold rice and a little rat meat.

MMMmmm... especially baby rat meat... Mmmmm... Stir fry...

He had only two ways home: death, or victory.

Depends on which side of Tet he was in on.

Most of 'em got Chi Chi! (FireSign Theater, Eat Or Be Eaten)

Ahhh... the smell of Napalm in the morning!

Looks like Hajji don't surf either:
http://www.latimes.com/news/opinion...ul05,0,5998634.column?coll=la-home-commentary

Interesting that they make it as safe and easy going as they can for
those that aren't actually in the urban shit, and somebody still
manages to make it look like our leaders do not value the lives of
their men by claiming that all that comfy setup has cost us lives.

There are a lot of facts in that opinion piece, but the opinion that
the command and control setup over there or the logistics system that
is in place over here is slowing us or costing us should not be
entertained.

 

[[email protected]]

Thanks for the replies Joerg and Rich.

First, I did call the utility company as soon as I bought this house,
more than a year ago (I'm in the northeast US if that makes a
difference). I was told that someone came and looked at the lines and
that it was no problem on their end. If I wanted the trees trimmed for
"aesthetic" reasons then it was my responsibility as the homeowner.

Second, the lines are definitely not an isolated current loop. There
are 4 paralell conductors on the top of the pole (middle part of the
pole has telephone and cable TV lines). Of the four lines (uninsulated
aluminum alloy by the looks of them) three of them are tapped for my
house. One of them is an un-insulated line, which comes through the
power meter to my circuit breaker panel and is bonded to a grounding
rod by the meter and also to a cold water pipe. So as far as I know,
either of the other two lines would be at a potential of 120 volts to
earth ground. Meaning some current should be flowing to ground through
the wet tree.

From the sound of things, maybe I should call the power company and
insist they take a second look. Maybe I could also go out after the
next rain storm and hook up a voltmeter from the tree trunk to the
earth to see if I measure any stray voltage? (taking the appropriate
safety precautions of course). Maybe I could also hook up a light bulb
to the tree trunk. A picture of that glowing would be worth a thousand
words to send to the power company....

Ask for a signed paper that makes them liable for any potential harm from
anyone touching the tree.. That should get their attention

One could circle some steelwire around some upper part of the tree and a
ground rod. Connect it to light bulb. And wait for some rain

 

[Ancient_Hacker]

Behind my house runs a string of telephone poles that carry (among
other things) the 240VAC single power that is run into each house. The
wires going from the poles to the houses are insulated and twisted
together, but the lines between the poles are bare and un-insulated;
they are simply held apart with spacers so that they don't touch.

120 volts isnt enough to leak very much current. Now if these were
your 4400 volt lines, there would be sparks and smoke.

Most power companies are alerady too busy trimming trees near 4400 and
up lines. Maybe later in the fall they'll have some free time and can
work on your lower voltage lines.

 

[DJ Delorie]

Funny you mention that, we definitely get very brief (approx 1 sec)
power outs during very windy storms. I did not realize that whatever
types of breakers are employed down at the "street" level of the grid
are actually auto-resetting.

They're not. What happens is, when a tree hits a wire it shorts out
the power, and everyone's power drops. Then the breaker trips.
Everyone covered by the breaker gets a power failure. Everyone *else*
sees a flicker, as the short is isolated and no longer affects them.

The repair trucks drive around in storms resetting them by hand.

transformers, but nothing else I recognize as a breaker.

Go look at your power pole. Find one that has wires running off in
three directions; one of them should have a breaker on it. It's just
a rod clipped between two metal arms; it falls out (pivots) when open.

 

[Rich Grise, Plainclothes Hippie]

I still hadn't got around to it when Charlie took it out for me.

Those damned commies! :-]

Yup and a year later That Fred Flintstone's bitch Wilma cane by and
whacked me again.

You know why Fred's so terrified of earthquakes?

He doesn't want to come home and find Wilma under Rubble.

<rimshot>

 

[[email protected]]

The repair trucks drive around in storms resetting them by hand.

Do a google on "recloser"
They do reset themselves on the MV distribution lines.