3 way switches

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Re: 3 way switches

Karl,

Correction on square of distance taken.

Are you saying the news is offering stories of the guy with three feet that he got from living under power lines on the one hand and on the other hiding actual correlations with maladies?

Is this orchestrated diabolicalness? It's even worse than I thought.
 
Re: 3 way switches

Originally posted by physis:
I'm sorry Al, and Hal, Ive been calling Al Hal.
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Sam, this could be associated with all the EMF you're exposed to. :)

Roger
 
Re: 3 way switches

Physis. right on. The papers will print anything sensational but unless an investigating reporter gets involved they will take press releases from "respected" institutions at face value.

And by the way, we are not all bathed in EMF at the levels that are associated with disease. A correctly wired building, no matter how much electronic equipment it has, usually measures from zero to 0.2 mG in the general spaces. In rooms with 2-traveler 3-ways it can be up in the 3-8 mG range, just as when a building is within 50' of a high current transmission line.

Linemen and substation workers (and tree trimmers) get a dose. So do sewing machine operators (from motor in their laps) where higher Alzheimers was found. And welders, etc.

But basically, most of us don't get much of a dose. Just watch that fish stuff.

Karl
 
Re: 3 way switches

Karl, it's a pleasure.

No offence but I'm still checking on the square of the distance thing. I'm looking at gauss's law applied to a sphere and it looks geometric to me. The only reference I have is excruciatingly scientific and I admittedly can't readily reduce this stuff to practicle terms. I don't doubt you're right but I like learn from my ignorance. Idn't that just too autruistic?

Linemen and substation workers
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You mean, ...... Charlie? :(
 
Re: 3 way switches

Sam,

The fall of the field strength with the square of the distance from the point of origin is correct for a field only from a single source. The elusive image is that the magnetic field we are discussing exists in the space between two conductors. There are two fields present, and they sum.

In all of the threeway setups that have been touched on in this thread, the current out equals the current returned (assuming a complete circuit through load or loads and the absence of a ground fault). If the conductors are close together (in the same cable or raceway), the actual volume of space between the two currents where the field sums is tiny. As the two conductors are seperated further and further, it becomes possible for things and people to be between them in the presence of the summing magnetic field.
 
Re: 3 way switches

You guys are gonna think I'm crazy.

MAGNETIC FIELDS AND CURRENTS

The Biot-Savart Law

dB=(uoi/4pi)(sinAdl/rr)

d = distance
B = magnetic field
uo = permiability constant
i = current
l = wire length (I think this is meters)
r = distance from assumed point charge to a point in the magnetic field
A = angle between r and the direction of the element

I'm messed up on r. And the element's a little unclear.

there are two fields present, and they sum
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The current only goes in one direction (at a time) and therefor the same is true for the field. The appearance of two fields comes from the way the conductors are routed.

[ November 05, 2004, 12:32 PM: Message edited by: physis ]
 
Re: 3 way switches

Al,
In all of the threeway setups that have been touched on in this thread, the current out equals the current returned ...
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No it doesn't, at least not in the same cable. When two conductor NM is installed as the travelers between 3-way switches, only one of the conductors in that cable is current carrying, the other conductor is part of another cable some distance away.
Don
 
Re: 3 way switches

This is why, although it may not be obvious at first, side jobs aren't always a good idea. :D
 
Re: 3 way switches

I guess I need to call them and see if they are still feeling ok now that their lights work.
Nope,,,,,better not.
 
Re: 3 way switches

Jap, I'm glad you started this. I run 3 ways with the neutral in the cable only as a matter of standardized practice so my life is easier at trim out. I have honestly never given an ounce of thought to the considerations that came up from all the trouble you started here, in association with 3 ways that is.

Dude, you might have made the world a better place!

I was going to reread your original post until I remembered how painful it was the first time. :p

[ November 05, 2004, 04:01 PM: Message edited by: physis ]
 
Re: 3 way switches

Hi Don,

Part of my statement is that this thread is about conventional "grouped conductor" threeways as well as legacy K&T methods and also the 14/2 Travelling Bus, i.e., "separate conductor" threeways. When load(s) are connected, a current is established in the circuit from the high side of the source to the low side. The magnitude of the current is the same throughout the circuit, given one load, regardless of whether the individual conductors are grouped by cable or are separate.

The other part of my statement is about the space between the conductors. Along an imaginary straight line drawn between the two conductors, there will be two fields, from each conductor, and the direction of the field will be the same. The two magnetic fields sum arithmetically. As one selects points not on the imaginary line, a vector summing is required.

When the selected point is a large distance away from the conductors, when compared to the distance between the conductors, the direction of the field is effectively opposite, and cancels.
 
Re: 3 way switches

I too believe in the KISS system on 3 ways.While in a few rear cases you could save a wire ,it just isn't worth the chance of a misplice. It also makes life easier to take the 4 way out of the chain to trouble shoot.
 
Re: 3 way switches

Originally posted by jimwalker:
I too believe in the KISS system on 3 ways.While in a few rear cases you could save a wire ,it just isn't worth the chance of a misplice. It also makes life easier to take the 4 way out of the chain to trouble shoot.
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I'm not sure what the KISS system is but that is exactly what I did,first I asked them which switch they used the most,pulled it out,it was a 4 way,tied the 2 reds together and the 2 blacks together and waaaaalllllllaaaaaaaaaa! emf city.
(just kidding)
 
Re: 3 way switches

I said above, that the magnetic field decreases with the square of the distance. I'm confusing an electric field with a magnetic field. I'm sorry to create a confusion.

As Karl said, the magnetic field falls off as the inverse of the distance when the current is long and straight and by itself in the universe.

[ November 05, 2004, 04:48 PM: Message edited by: al hildenbrand ]
 
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