Conference 7.286::home_work

    RE: .0
    
    My only problem with the house would be the "look" from the power lines
    i.e. the large towers would detract from the landscaping. As far as
    the heath risk......its BS.
    
    Marc H.

There are lots of studies, none conclusive enough for power companies to
agree there is a problem.

BUT whether there is a problem or not, there is a perceived problem, and
that makes the house a) more difficult to sell, and b) a bargaining chip to
knock the price down may thousand.

If it were me buying the house, I would want the lines at least 150 to 200
feet from living quarters, and then I'd want to know I was going to stay
there a long enough time to build equity, and that there was little chance
I'd want to sell in a hurry.  Lines can help delay the sale of a house by
months.

Stuart (who had power lines near his last house, and lived in an area where
there were mega power lines too, which really caused houses near those to 
be nearly unsaleable).

i growed up wiht a powar lin running rite besid my hous.  I lived their for 
nineteenth yeers and didnt not notice anny problums.


Actually, I grew up next to the Northeast Utilities lines that run from the 
Cobble Mountain substation over to the Northeast Utilities lines along the 
Westfield River.

I was sicker when I lived in West Springfield prior to that (normal 
childhood diseases) and never had any "health problems" to speak of in the 
19 or so years I lived next to the power lines.  My mother just sold the place 
about 14 years ago but my kid brother built a new house right next door (which 
he sold about 3 years ago)

I lived there from '54 to '73.

I think too many people associate power lines with the National Inquirer's 
alien reports.

     I think I'd be more concerned if I was placing children in such a
situation than healthy adults.  Of course, if I went outside with a 
flourescent light tube and it glowed in my hands, I would not live there
at all.

     I've read enough to reasonably believe that large E.M. fields affect 
health negatively, but not enough to know how much of an effect that might be.

                                   Greg

    One more vote for "perception is concern enough", especially in
    terms of resale potential.
    
    1. If there's a need to sell the house soon, it could be at a loss
    (even if the perceived risk is used to reduce the price for this
    purchase)
    
    2. If the house is held for a longer time, it's a real gamble:
    either further studies will show no risk (in which case it could be
    a gamble that paid off), or further studies will verify the risk (in
    which case you've bought a house in Love Canal).
    

	    Just read an article a few weeks ago about this.  The scientist
	performing the research `proved' that the electro-magnetic fields 
	generated by low frequency radiation did not affect the magnetic
	`whatever they ares' inside our cells.  He contends power lines are
	NOT a health risk.  
	   But I bet this guy doesn't live under any high voltage wires.

					Tim

    
    I have lived next to smaller power lines for almost 10 years. They are
    about 200 feet from the house. I have been sick a lot more these past
    10 years that before. Whether or not this has been caused by the 
    power lines is difficult to tell. Our radio and TV reception is
    poorer than neighbors that live a further than we do from the lines.
    We have lots of traffic from snowmobiles, dirtbikes and other OTRV's
    that think the power lines are a highway. And because the power 
    company has a ROW for the power lines, a local developer did NOT need
    my permission to work on my land which was part of the ROW. All in all
    I would not choose such a location again.
    
    Harry
    
    

    
    If you're reading this on a large color monitor, just turn it around
    and read the German & Japanese EMR compliance notices.  Digital
    has to comply with these to do business in other countries.  Note
    that the US notice only applies to FCC (broadcasting intereference).
    
    Prior to the establishment of national standards for emissions,
    many European countries prevented pregnant women from working on VDT's
    that had higher emissions.  Sweden was the first country to introduce
    laws on this, and many EEC countries followed.  I'm not 100%
    sure but I believe that California also legislated on this.  The
    result has been the development and marketing of low-emissions VDUs.
    The jury is still out on this, but they decided to err on the side of
    caution.  
    
    Kind of strange that it's supposed to be dangerous to sit in front of a
    device that has relatively low fields compared to a power line, yet the
    authorities allow power companies to string lines right OVER houses in
    places like the UK.  I don't mean "close to" I mean that the high
    tension lines can be right over your roof with a pylon in your back
    yard if they want it.
    
    I suspect that even if there WAS a risk here, there are some strong
    vested interests in maintaining uncertainty.  It can only mean cost for
    the transmission companies.  
    
    Regards,
    
    Colin

The inverse square law applies, so even though currents are a lot 
higher in high tension lines, it takes a *lot* less in a VDT to produce 
similar EM levels compared to power lines hundreds of feet away. 

We dumped our electric blanket a few years back, in favor of a down 
comforter, largely due to uncertainties around this issue. Never 
regretted it (down comforters are comfy). We'll probably never buy a 
house that's situated under a large electric blanket.

    The discussion around the "hazards" of 60Hz would best be on the
    Montel Williams show....thats the level of techno-babble they operate
    on. Just shows how much of a "high tech" company we aren't.
    
    Marc H.

Usually when you read reports of "hazards" of power lines, it's the magnetic
field that gets the blame for the alleged harm.  However, these lines are
high *voltage*, and magnetic field is proportional to the current.  Because of
I�R losses the power companies try to reduce the current as much as possible
(which is why they run them at such high voltage to begin with)

Typically a major line will carry 345,000 volts at a couple thousand amperes
worst case.  But the lines are dozens of feet in the air and dozens to hundreds
of feet away.  The inverse square law applies so it's almost certain that 
various electric devices in the house will be generating stronger magnetic
fields because they're closer.  (*especially* electric blankets)  Remember
the lines are carrying only about 10 times the current of the full rating of a
typical 200A residential service.

Having said that, the power companies do or did spray their right-of-ways
with herbicides to keep the trees down, including a relative of Agent Orange.
This may have caused problems in the past, but the magnetic fields are
innocent.

-Mike

 As far as I know,  the jury is still out on whether proximity to high
voltage power lines has detrimental affects on ones health.  I do know
that a municipal council rep.  made quite the crusade about the power
lines near her house and over top of the local primary school.  The 
bottom line was that she really didn't achieve any headway against the
power company but did sell her house to be "true" to her principals.
Unfortunately,  due to the media coverage and the now generally accepted
perception that high power lines *may* affect your health,  she ended up
selling her house about $35K under market value.

My best friend recently bought a house so near the power lines,  that with 
a good throw,  I could hit the tower with a stone.  The builder offered
a $5k discount due to the location of the power lines.  Considering that 
they intend to stay there for 20 or more years,  I'm not convinced that 
it was the wisest decision.  Keep in mind that both of their daughters will
now live quite close to the power lines and also attend a school where the
lines cross over top of it.

From a resale and health points of view,  I would rather err on the side
of caution and pass on properties near these "hazards".

Roy

Two more considerations:

It can't help your TV and Radio reception, and...

It has been shown that there are significantly more UFO sightings
near high-tension power lines.

-steve-

I'm surprised nobody has mentioned the safety issues.  A severe ice or wind
storm can bring a live 440KV wire into your yard.  *You* may know enough to
stay away, but will your kids?

Also, in the few "studies" that I've seen reported, the range of influence
is usually about 100 yards.  That is, the reports that many think are
blowing the situation out of proportion say that there's no problem if
you're 100 yards away from the power lines.  So if the house is far enough
away, you don't have to worry about the health effects whether or not you
believe the reports.

Personally, I find power lines ugly, and would not buy such a house just for
asthetic reasons.

    
         Coincidentally, the May issue of Consumer Reports has an article
    addressing this very matter.  Take a look at page 354.
    
                                   Greg

    
      Nothing conclusive on this yet, there are varying studies and
    results globally. However, a court case recently in New York I believe
    (may have been for new transmission lines going thru a previous clear
    area) resulted in the utility company paying homeowners a determined
    amount of money because the "perception" of a problem would de-value
    the property. They had to compensate for the difference in $$. Don't
    quote me on this though.
    
      I would be more concerned with underground transmission, than
    overhead, obviously which source would be closer to a person??
    
      Prudent avoidance is the buzzword in this area, since no one is
    really sure.
    
        Mark

     Hello again,
    
    Thanks for all your replies. I have made copies of them all and gave 
    them to my friend, who is going to make a offer on the house anyway
    but he is going to use the power lines as a bargaining chip in his
    favor (even though he does not consider the high tension lines to 
    be a problem.) Please keep any information or opinions coming on
    the subject of power lines. I would like to hear more.
    
                              Thanks,
                             George
    

>     I think I'd be more concerned if I was placing children in such a
>situation than healthy adults.  Of course, if I went outside with a 

If you read my previous reply, you'll see that I was one of those children 
you're so concerned about.  I was 9 years old and my two brothers were 7 
and 5.  Neither one of them has any space alien related problems, either.

>storm can bring a live 440KV wire into your yard.  *You* may know enough to
>stay away, but will your kids?

Have you ever seen a high voltage line when it gets close to the ground?  
If you had, you wouldn't make foolish statements like the one above.

A wire with that much voltage on it will self destruct when it gets near 
an object with the opposite potential.  This includes, the ground and the 
pole that supports it.  

>If you read my previous reply, you'll see that I was one of those children 
>you're so concerned about.  I was 9 years old and my two brothers were 7 
>and 5.  Neither one of them has any space alien related problems, either.

You just *think* you don't have space alien related problems.
There's a shrink from Harvard who can set you straight.

>If you read my previous reply, you'll see that I was one of those children 
>you're so concerned about.  I was 9 years old and my two brothers were 7 
>and 5.  Neither one of them has any space alien related problems, either.

AHA! THAT EXPLAINS IT ALL! 

Stuart :-)

	   The whole potential problem could be eliminated by transmitting
	filtered DC instead of AC over those lines.  DC doesn't generate
	EMF (no field collapse) so would eliminate any potential low fre-
	quency hazards.  There is a good deal of line loss due to the EMF
	generated along HiV transmission lines.  Running DC would eliminate
	this loss, could be done over existing wires, and would save the
	utilities companies big bucks over the long run.
	    There is the initial expense of installing DC to AC inverters
	(You can't transform DC).  I'm sure the equipment is not cheap.
	But it can and has been done on a transmission line into the US 
	from Canada.
	    And Skip, stating that HiV lines will not harm anyone because
	they never harmed you is not justifiable logic.  That's like saying
	cigarettes will not cause cancer because "I've been smoking for 25
	years and I don't have cancer."  And just like the tobacco companies,
	if big business wants to cover something up, they can and will.
	    And lastly, abbreviating Hi Voltage to HiV was a freudian slip
	that I opted not to change.  I didn't mean to insinuate that you
	would get AIDS if you live under those wires.  Leukemia, maybe, but
	not AIDS.

					Tim

    RE: .22
    
    No...the field from DC lines is constant, but still large. I'm sure the
    same chicken littles would discover that a constant B field was bad
    too.
    
    MarcH.

Neither of my brothers (ages 47 and 45) have any medical problems.

My neighbor on the other side of the power lines (age 49 next month) 
doesn't have any medical problem, either.

We all spent at least 20 years living next to these power lines and my 
youngest brother spent closer to 30 years there.

    If the risk were such that any population of (say) 10 or fewer
    exhibited health problems, there would be no doubts. That "neither
    me nor my immediate neighbors" have not had problems isn't very
    instructive, statistically. (Though it may be quite comforting to
    you.)
    
    From the Consumer Reports article (right up there with JAMA,
    right?), the most suggestive linkage is with some forms of leukemia,
    which have a normal risk of less than 1:20,000 (per year, I think).
    So if risk were doubled, you'd still only see one additional case in
    10,000 people per year. You'd have to poll a lot of neighbors to see
    anything to worry you...
    
    Put another way -- I drove to work today. Didn't have an accident.
    Didn't have one last week, either. Haven't had one all year.
    Therefore, there is no risk of traffic accidents, right? ...
    
    By the same token, you have to wonder, when a New Hampshire school
    district spends $100,000 to reduce the risk of EM exposure in a high
    school, if the same money might have been used to reduce risks in
    other areas with much higher hit rates.

    RE: point about lead is a good one.
    
    The Romans didn't know lead was bad because they did not live long
    enough.  With a mean lifespan of 32 years, there wasn't enough time for
    them to associate the use of lead with a health risk. Most of them died
    from something else, but their bones contained large amounts of lead.  
    
    This is part of the problem of isolating effects of any part of the
    electomagnetic spectrum on living organisms. A few decades ago we had
    no idea of the health risks associated with UV light.  Now we know it's
    a cause of certain forms of skin cancer.  These effects emerge because
    we are living much longer, and it's possible that more effects related
    to other parts of the spectrum will emerge over time.   It also depends
    what you define by "health".  Recently, there's some good evidence that
    certain forms of seasonal depression may be linked to the absence of
    sunlight.  So, if light can affect health, why not other parts of the
    electromagnetic spectrum?  
    
    (When I joined DEC I worked with a chap by the name of Ted Humby, who
    during WW1 worked with Arthur C. Clarke on the development of Coastal
    Radar.  One of his war stories was how they discovered the unpleasant
    effects of microwave radiation.)
    
    The other problem is that few animals live as long as we do, so we
    can't reproduce the effects of dosages except by using elevated dosages
    over a short period.  Scientists are beginning to doubt that this is an
    effective way of reproducing "real life effects" and that smaller doses
    over much longer periods may be worse for some health risks.

    Given this history,  the riskiest thing you can do these days is to
    make statements like "there's no risk...".   Marie Curie wouldn't
    have handled radium if she'd known about radiation.
    
    Rgeards,
    
    Colin
    

    Re: .26
    
    No not agree. But, its your choice.
    
    Marc H.

I just happened to be browsing a World-Wide-Web information resource 
provided by the University of Pennsylvania Department of Oncology
(http://cancer.med.upenn.edu/) and found a FAQ (Frequently Asked Questions)
list about "Powerlines, EMF and Cancer".  The full FAQ can be found using a 
WWW browser (Lynx, Mosaic - see SOFBAS::INTERNET_TOOLS note 448) at URL:

     http://archive.xrt.upenn.edu/0h/faq/powerline_faq#

It's too long to post here, but I've put a copy of the current version at:

     TLE::FORD$:[LIONEL.PUBLIC]POWERLINE_FAQ.TXT

Here's the table of contents.  Note that question 28 is especially relevant
to the base note.

				Steve


 1. Why is there a concern about powerlines and cancer? 
 2. What is the difference between the electromagnetic (EM) energy associated 
   with power lines
   and other forms of EM energy such as microwaves or x-rays? 
 3. Why do different types of EM sources produce different biological effects? 
 4. What is difference between EM radiation and EM fields? 
 5. Do power lines produce EM radiation? 
 6. How do ionizing EM sources cause biological effects? 
 7. How do RF, MW, visible light, and IR light sources cause biological 
   effects?
 8. How do the power-frequency EM fields cause biological effects? 
 9. Do non-ionizing EM sources cause non-thermal as well as thermal effects? 
 10. What sort of power-frequency magnetic fields are common in residences and 
   workplaces? 
 11. Can power-frequency fields in homes and workplaces be reduced? 
 12. What is known about the relationship between powerline corridors and 
   cancer rates? 
 13. How big is the "cancer risk" associated with living next to a powerline? 
 14. How close do you have to be to a power line to be considered exposed to 
   power-frequency magnetic fields? 
 15. What is known about the relationship between "electrical occupations" and 
   cancer rates? 
 16. What do laboratory studies tell us about power-frequency fields and cancer?
    1. Are power-frequency fields genotoxic? 
    2. Are power-frequency magnetic fields cancer promoters? 
    3. Do power-frequency magnetic fields enhance the effects of other 
   genotoxic agents? 
 17. How do laboratory studies of the effects of power-frequency fields on 
   cell growth, immune
   function, and melatonin relate to the question of cancer risk? 
 18. Do power-frequency fields show any effects at all in laboratory studies? 
 19. What about the new "Swedish" study showing a link between power lines and 
   cancer? 
 20. What criteria do scientists use to evaluate all the confusing and 
   contradictory laboratory and
   epidemiological studies of power-frequency magnetic fields and cancer? 
    1. Criterion One: How strong is the association between exposure to 
   power-frequency fields and the risk of cancer? 
    2. Criterion Two: How consistent are the studies of associations between 
   exposure to power-frequency fields and the risk of cancer? 
    3. Criterion Three: Is there a dose-response relationship between exposure 
   to power-frequency fields and the risk of cancer? 
    4. Criterion Four: Is there laboratory evidence for an association between 
   exposure to power-frequency fields and the risk of cancer? 
    5. Criterion Five: Are there plausible biological mechanisms that suggest 
   an association between exposure to power-frequency fields and the risk of 
   cancer? 
 21. If exposure to power-frequency magnetic fields does not explain the 
   residential and occupations studies which show increased cancer incidence, 
   what other factors could? 
    1. Could problems with dose assessment affect the validity of the 
   epidemiological studies of power lines and cancer? 
    2. Are there other cancer risk factors that could be causing a false 
   association between exposure to power-frequency fields and cancer? 
    3. Could the epidemiological studies of power lines and cancer be biased 
   by the methods used to select control groups? 
    4. Could analysis of the epidemiological studies of power lines and cancer 
   be skewed by publication bias? 
 22. What is the strongest evidence for a connection between power-frequency 
   fields and cancer? 
 23. What is the strongest evidence against a connection between 
   power-frequency fields and cancer? 
 24. What studies are needed to resolve the cancer-EMF issue? 
 25. Is there any evidence that power-frequency fields could cause health 
   effects other than cancer. 
 26. What are some good overview articles? 
 27. Are there exposure guidelines for power-frequency fields? 
 28. What effect do powerlines have on property values? 
 29. What equipment do you need to measure power-frequency magnetic fields? 
 30. How are power-frequency magnetic fields measured? 

re .26:

>    So, if light can affect health, why not other parts of the
>    electromagnetic spectrum?  
    
Perhaps, but if this turns out to be so we'd still be barking up the wrong
tree by going after those power lines.  The fields from the electrical
devices all around us, motors, lights etc. exceed that from the power lines,
unless you live in a tree house in one of the pylons...

-Mike

One time I was the passenger in a car over which we were transporting an aluminum
canoe, inverted on the car roof and tied down to the rack.

Every once in a while, I'd reach my hand out the window and touch the canoe
just to make sure it seemed secure.  At one point, we were driving under
power lines that were crossing the road, and I felt an electric shock !

/Eric

    The May issue of "Consumer Reports" has an article on this issue.
    
    				Steve

>tree by going after those power lines.  The fields from the electrical
>devices all around us, motors, lights etc. exceed that from the power lines,

	    If you hold up a flourescant lamp under Hi Voltage lines, it
	will glow.  Can you do this near `any' device all around you?  Me
	thinks not.  This leads me to believe that your statment is not
	necessarily accurate.
	   As to the fields being the same between AC and DC, I'm not so
	sure about this.  There's no field collapse with the DC, which could
	make a big difference.  A condensor coil on a car:  12 Volts DC in,
	10,000 Volts out.  The points (or elect. ignition) break the circuit
	which collapses the magnetic field built up inside the coils. This
	in turn produces a hefty voltage for the spark.  No collapse...
	nothing.  Relevent?  Maybe no, but it is another way of looking at
	this.
					Tim

    Re: .32
    
    I can make a flourescent lamp glow by running my hand along the
    tube.  Does that make me dangerous?
    
    
    I read the Consumer Reports article last night.  It appears to me to
    be a balanced and well-researched work.  I recommend it in conjunction
    with the FAQ I mentioned a few replies back.
    
    					Steve

    ER: .32
    
    The "collapsing" field does not produce the high voltage. Transformer
    action does. 
    
    Marc H.

    I've found fishing under these lines is better.  Just the hum 
    bothers you.....(+:}
    

    RE:-1
    
     Watch out for electric eels though.

    
    re: 35
    
    Strange you should mention that.  There's been a long running study at
    Cambridge (UK) looking at the way fish can generate electric fields.  It
    turned out that it's not just the electric Eel - many species of fish
    can generate or detect very low power fields.
    
    Some fish detect the fields generated by other fish, and use this
    ability to find and catch their prey.  Perhaps they're attracted to the
    field generated by the power lines, thinking there's a whopping meal
    lurking there.....
    
    

    SO maybe I should cast my worms onto the power line and energize them
    before putting them in the water.   I'll have to try that (+:}....
    
    But the Bass do seem to hang around the area I am talking about...
    

>>>    I can make a flourescent lamp glow by running my hand along the
>>>    tube.  Does that make me dangerous?
    
    Anyone who caresses electrical appliances is potentially dangerous
    in my book...


    ... sorry. :-)

    Kevin

>    The "collapsing" field does not produce the high voltage. Transformer
>    action does. 

	    Not exactly.  Take a big coil with plenty of windings on
	it and connect it to a 6 Volt battery.  Disconnect the power;
	the field collapse will produce a voltage far greater than the 
	6 volts placed across the coil.  But that wasn't my point.
	    I believe that low frequency radiation might produce a health
	risk from continuous exposure.  I could be wrong, and we may never
	know for sure.  I assume that no frequency (DC) radiation does
	not pose the same supposed risk.  Again, who knows?
	    I do know that there are two kinds of line loss, resistive 
	and reactive.  Loss do to the resistance of the wires is mini-
	mized by transmitting extremely high voltages.  Reactive line
	loss can only be produced by transmitting AC.  Conservation of 
	matter and energy:  It has to go somewhere!

					Tim

    Latest from the Johnson Smith catalog, home of the poo-poo cushion and
    the x-ray-spex:
    
    ARE YOU SAFE FROM ELECTROMAGNETIC RADIATION?
    Test Computers, Clock Radios, Televisions, Microwaves
    
    Invisible electromagnetic radiation can be avoided when you know where
    it is!  All electrical appliances emit different amounts of
    electromagnetic radiation.  Radiation that is stronger the closer you
    get to it.  Discover the hot spots in your home or office with this
    easy to use Electromagnetic Field (EMF) Detector.  Now you can
    accurately measure the level of EMF's emitted by all common electrical
    appliances & equipment in your home or business so you can avoid the
    risk.  Easy to read LED scale measures 1.5 to 30 milligauss.  Manual
    included.
    
    3467 Radiation Detector......................................$34.95
    
    (813) 747-2356
    

Consumer Reports tested an EMF meter sold to consumers (more expensive than
the one from Johnson Smith) and said that it was nearly impossible to get
a consistent and accurate reading from it.  Here's what the FAQ says:

29) What equipment do you need to measure power-frequency magnetic fields?

Power-frequency fields are measured with a calibrated gauss meter. The meters
used by environmental health professionals are too expensive for "home" use.

A unit suitable for home use should meet the following criteria:

   A reasonable degree of accuracy and precision, plus/minus 20% seems
   reasonable for home use.
   True RMS detection, otherwise readings might be exaggerated if the waveform
   is non-sinusoidal.
   Tailored frequency response, because if the unit is too broadband, higher
   frequency fields from VDTs, TVs, etc. may confound the measurements.
   Correct response to overload; if the unit is subjected to a very strong
   field, it should peg, not just give random readings.
   The presence of a strong electrical field should not affect the magnetic
   field measurement.

Meters meeting these requirements are quite expensive, $600 would probably be
the bare minimum. These meters are not suitable for the non-technically trained.

There is an understandable reluctance to recommend any unit with unknown
characteristics to a person whose technical abilities are also unknown, and no
peer-reviewed articles on inexpensive instruments appear to be available. The
suggestions that one wind a coil and use headphones or a high impedance
multimeter are misguided. A clever physicist or engineer can anticipate and
correct for nonlinearities and interferences, but for the average person, even
one technically trained, this is unreasonable.

Never mind power lines, what can I do to minimize the danger of X-ray specs?

    RE: .41
    
    "Sold by Johnson & Smith"
    
    Ha Ha Ha......
    
    Case closed.
    
    Marc H.

>
>>    The "collapsing" field does not produce the high voltage. Transformer
>>    action does. 
>
>	    Not exactly.  Take a big coil with plenty of windings on
>	it and connect it to a 6 Volt battery.  Disconnect the power;
>	the field collapse will produce a voltage far greater than the 
>	6 volts placed across the coil.  But that wasn't my point.

"coil" "transformer" what's the difference?

> "coil" "transformer" what's the difference?

	    A transformer is made up of two or more coils and (usually) a
	core.  A single coil does not a transformer make.  

					Tim

Correct me if I'm wrong, but what is an autotransformer if it is not a
single coil transformer.  My recollection is that it is a single coil
with various taps that can be used to step-up or step-down voltages.

John

That is correct, an autotransformer is a single coil with multiple taps
and can be used to step voltages up or down if electrical isolation isn't
needed.  The ignition coil of a car is an autotransformer.

-Mike

>Correct me if I'm wrong, but what is an autotransformer if it is not a
>single coil transformer.  My recollection is that it is a single coil
>with various taps that can be used to step-up or step-down voltages.


OK .... let's see what I can remember of electrical theory some 20 years
ago ...

An inductor (fancy name for a coil) will pass a continuous unvarying DC 
current through it as if it was just a piece of wire.  If you should break 
that flow, the collapsing magnetic field will induce an emf back into the
coils ... the effect being that it will use the energy of the collapsing
field to try to preserve the field, and hence maintain a constant current.
Thus the EMF across the open coil will increase until the field collapses
completely, since no current can flow (remember it is now an open circuit).
Thus the momentary EMF will go very high, depending on the inductance ...
or if you will magnetic inertia ... of the coil ... which is why iron is
used as a core.  However, the higher the voltage, the lower the available
driving current ... (Power = EI and good old mr Ohmstead and all that!)

Now in a car igniton coil, (which incidentally is often an Autotransformer)
that voltage spike is increased by transformer action from around a few
hundred volts, to several thousand volts.

Now where were we before this diversion ?

Stuart

>needed.  The ignition coil of a car is an autotransformer...............
..... that creates one hell of a spark when the field collapses.

    The ignition "coil" in your car is not an autotransformer. It is a
    straight forward transformer.
    
    Marc H.

re .51:

No, it is almost always an autotransformer.  It has only 3 electrical
connections, to ignition module/points, +12V, and HV.  A 'regular' transformer
has a minimum of 4 contacts, 2 for each coil.

The description of how a 'coil' works is correct, but there are 2 parts to
it.  A rapidly changing current in a coil generates a changing magnetic field
(and cutting off the current generates a very rapid change in a current, and
also a rapidly changing magnetic field)

A rapidly changing magnetic field induces a current in a coil.

The coils in the first and second part can be the same coil (simple
inductor) or separate (transformer with isolated coils).  An autotransformer
can be thought of as a regular transformer where a portion of the coil
plays the part of both coils.  A simple inductor can be thought of as a
transformer with the entire single coil playing both parts.

-Mike

    RE: .52
    
    Wrong. One primary lead is connected to a secondary lead, which in turn
    is connected to ground.
    
    Marc H.

What is this, College Bowl with MIT and RPI?

    I graduated from WPI...please, not MIT.
    
    Whats that old line? "You can always tell a MIT engineer......but you
    can't tell him much."
    
    Marc H.

re .53:

>    Wrong. One primary lead is connected to a secondary lead, which in turn
>    is connected to ground.

I suppose that by now some cars ground the supply end of the coil, but the
stuff I've worked on have all been autotransformers fed +12V with no ground
connection other than the case of the coil itself.

-Mike

    -mike,
    But your experence has only been on Ramblers.
    
    :-)
    
    TMW

    RE: .56
    
    Huh????
    
    Car ignition systems are pretty straight forward. Even the so called
    "electronic" systems subsitute a transistor for the points. The idea,
    though, is the same. A collasping field in the primary is transformed
    to a higher voltage (turns ratio) by the secondary. The new electronics
    just replace the old mechanical parts.
    
    By the way, a good application of autotransformers is a variable source
    for ac, called by the trade name "variac". The advantage of the
    "variac" is that you can control the ac voltage without the power
    waste from conventional variable resistors.
    
    Marc H.

re .57:

Yes, but I also have a Slow-Par now.  It has one of them new-fangled Commie
inspired electronic doodads hooked where any proper vehicle would have points.
:-)

re .58:

If all electronic ignition systems are wired just as the old point systems with
the points replaced by a transistor, .53 is wrong.  Points switched the
connection between the coil and ground, not between the coil and +12V.  (easier
to design the distributor that way)  The other low-voltage coil lead goes to
+12V (through a resistor w/points and some electronic systems)

But why the fuss?  An autotransformer is just a transformer with a section of
coil fulfilling both the role of primary and secondary.  An autotransformer
is also a tapped coil.  It's all the same thing.

-Mike

    There is no better way to derail a discussion with engineers than to
    start talking power supplies.  They love that stuff better than sex.
    

    RE: .59
    
    The problem with an autotransformer for a ignition system, is that the
    wire that carries the primary circuit is heavy ( many amps), whereas
    the wire that provides the high voltage is fine since the current is
    low and the turns have to be many.
    
    An autotransformer uses heavy turns , since the current could be high
    from one end to another.
    
    Re: .60
    
    Sex? Electronics is much more fun, and satisfies.
    
    Marc H.

>    
>    The problem with an autotransformer for a ignition system, is that the
>    wire that carries the primary circuit is heavy ( many amps), whereas
>    the wire that provides the high voltage is fine since the current is
>    low and the turns have to be many.
>    
>    An autotransformer uses heavy turns , since the current could be high
>    from one end to another.
>    

Nope ... An autotransformer can use whatever size wire is necessary on each
portion of the winding, and splice them together at the "tap".  This is
common in specialty transformers, less common in general purpose 240/120
transformers.

    RE: .62
    
    	I'll end the discusion.....folks that are really  interested can
    read up on the subject.
    
    Marc H.

	Back to the discussion:

	When I lived in a development that had HT lines running thru it,
	my then 13 yr old stepson reported that whenever he walked under the
	lines, he would feel buzzing in his head.

	It only happened when he walked under them, not when we drove under them
	in a metal car...

	So I say inverse law or not, the human body DOES feel the effect of them
	at ground level.

	Fortunately we lived a few hundred feet away from them.

	BTW, this was 18 years ago. 

	Bob

    Yeah but... that could be just a mechanical sound.  Heard only when
    quietly walking by, not when masked by the sound of the car.
    
    	Dave.

Could be loose filling in teeth too!  Many people complain about hearing
a radio in their fillings when near a radio transmitter!

Stuart

>	When I lived in a development that had HT lines running thru it,
>	my then 13 yr old stepson reported that whenever he walked under the
>	lines, he would feel buzzing in his head.


Did you hear the same thing?