220 V table saws and ground

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On Wed, 9 Dec 2009 21:00:48 -0800, the infamous "CW"

That's pretty much what I said in different words, CW, unless these are automated switches, which leaves us in -exactly- the same situation I just described. ;)
-- To know what you prefer instead of humbly saying Amen to what the world tells you you ought to prefer, is to have kept your soul alive. -- Robert Louis Stevenson
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Which they are. It would be quite the waste of manpower to have someone reading a meter and changing taps 24 hours a day.
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On Thu, 10 Dec 2009 13:06:56 -0800, the infamous "CW"

What used to happen is that they'd set it up, check it later, and adjust it if necessary before leaving for the lifefime of the xfmr. ;) "Highest voltage = X, Lowest voltage = Y, we'll set taps for the average of those and that's what y'all get, forever." 120v +-5%, right?
-- To know what you prefer instead of humbly saying Amen to what the world tells you you ought to prefer, is to have kept your soul alive. -- Robert Louis Stevenson
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As said or implied by others, the variable voltage output is good for setting up the voltage at the load, but not something that would be adjusted except as the load changes. For instance, if there's a transformer on a pole leading to a farm or ranch with 2 miles of run, the the variable feature would allow for line loss over that distance and the supplied voltage would be set to give 115-120 vac at the typical load. Good feature.
--
Nonny

ELOQUIDIOT (n) A highly educated, sophisticated,
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A *BIT* ??? <Snicker>
In many places, the regulation is *terrible*. One place I lived, I was across the parking-lot from the neighborhood substation, in a building with _old_ wiring in it ( turning on some of the big tube-type electronic test gear I had would cause a _10+_ V drop in the voltage at that wall outlet. [no drop on a different circuit, that was ALL losses in the building wiring -- eek!]) I had a lab-grade line voltage monitor plugged in on one circuit, and could watch the voltage drop as the neighborhood 'powered' up in the morning. Around 3 AM 'line voltage' was circa 127-128v by 10 AM it was down around 112-113 V. This was _after_ I'd had a 'discussion' with the electric utility, resulting in a couple of real engineer (MSEE and better) types, not just a 'lineman', coming by to visit, and check out my monitoring gear; because when I first called the utility, peak sustained voltages were in the 132-133V range -- which played hob with the life of the light bulbs. :-/ They came out prepared to dismiss the crank reporting; recognized some gear that was was in their labs, and decided to take me seriously. A quick check comparing what my box displayed against their 'calibrated' box -- in agreement to within 0.1V -- and they promptly a greed that there was a significant problem. A little _manual_ transformer tweaking got things to 'borderline acceptable' at my location. *THEN* they started looking at what was necessary to 'fix it right' for the whole area.
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"Robert Bonomi" wrote:

The utility is only required to provide 120V, + 10%, - 15%.
IOW, 132V Max, 102V Min.
Multiples of 120 apply (208, 240, 277 & 480).
Which is why the utilities get away with supplying "brown out" power levels during periods of peak demand.
Over voltage problems are a little more difficult to catch since shortened life requires some period of time to document.
Lew
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In the US it's +/- 5%, ie. 114V to 126V.

They "get away" with it because there is no other choice, other than to shed customers.

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Maybe that's in your utility area, but not the last two utilities areas I've had.
Lew
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No, that is the US standard.
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Robert Bonomi wrote: ...

I only buy 130V bulbs for that reason...and in fact, the door handout "goodie bag" at annual meeting always has at least one bulb in it and _they're_ 130V-rated, too.... :)
--
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"dpb" wrote:

That is actually false economy.
Yes, you get longer lamp life which is good; hovever, you also get reduced lumen/watt output which is bad.
You are buying lumens, not hours of lamp life, so it becomes a trade off of economy vs convenience.
Lew
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Lew Hodgett wrote: ...

No, I'm buying bulbs...or actually, not buying nearly as many bulbs as would otherwise.
They output what they output (which if blown is nothing, nil, nada, until replaced). _That's_ the tradeoff.
--


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"dpb" wrote:

Actually you are buying both lamps and KWH to operate them.
If you wish to buy more KWH than are needed for the sake of convenience, that's your choice.
Lew
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Lew Hodgett wrote:

No, 75 or 100W is still 75 or 100W...
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If a 100W bulb is run on less than its nominal voltage it will consume a little less power and run less efficiently that's all. The light will be yellower but its life will be extended. If that is the choice you wish to make then that's entirely your affair and no one else's.
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On 12/10/09 6:47 PM, Stuart wrote:

Correct the bulbs resistance is fixed, increased voltage causes more amperage, reduced voltage reduces the amperage. Light output and bulb life will vary according to their ratings.
--
Froz...


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"FrozenNorth" wrote:

=============================================NOT!!!
As the voltage rating of a specific wattage lamp rating increases, so does the resistance of the filament.
This increased filament resistance provides a mechanically heavier wire which then allows for a "rough service" or "traffic signal" lamp rating.
The increased filament resistance also reduces the current flowing thru the filament which in turn reduces the lumen output.
Basic data available in any lamp catalog.
Just some of the basic engineering trade offs the lamp designer faces.
Lew
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Lew Hodgett wrote:

Please explain *CLEARLY* how increasing the thickness of any uniform substance can *increase* the resistance if everything else remains unchanged.
Hint: imagine a square wire of a fixed length, double its thickness and width, now explain to me the difference between that and four wires of the original thickness in parallel for 1/4 the resistance!
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
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Who said anything about a fixed length?
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The resistance varies inversely to the cross-section of the conductor.
AWG 12 wire resistance/foot = 1.619Ohms. AWG 10 wire resistance/foot = 1.018ohms. AWG 8 0.6405
http://www.interfacebus.com/Copper_Wire_AWG_SIze.html
Ergo, heavier wire, less resistance.
So assume that a 100watt blub rated at 130V filament consumes 0.769231 amperes of current. From ohms law, one can then derive the resistance of the conductor as (R=V/I) 156 ohms.
Now run that same bulb at 120volts, the current in the filament (per again ohms law) will be (I=V/R) 0.769231 (i.e. the same current).
However, the power consumed (P=IV) will only be 92.3 watts, thus reducing the lumen output of the bulb.
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