House wiring? (slightly off-topic)

[Scott Gravenhorst]

Robert Donker <RobertD at concur.com> wrote:
>If you test a 100 watt bulb you'll find it always draws a 100 watts, to keep
>it's side of ohm's law balanced, it must draw more current (generate more
>heat) at a lower voltage. This proves true in the lab, you can quickly burn
>out a bulb buy lowering the AC voltage. Sort of. The reality is its in a AC
>environment. This means it will behave like an frequency dependant impedance
>(like a speaker for example) and the actual current draw is a more
>complicated to calculate. However the ohm's law still rules. If the watt's
>remain the same and you lower the voltage the current draw will increase.

This is incorrect.  There may be a change in the resistance of 
the filament depending on how hot it is, but not enough to account
for what you are saying.  Also, there is very little inductance
given to a filament.  And at 60hz, the inductance would have
to be very large for AC maths to matter here.  A filament is 
pretty much just a resistor, granted as I said, not a perfect one.

The maths for ohm's law say    I = E / R.

It is clear from this that if you halve the voltage, the current
will also be cut in half (assume that R doesn't change).  There 
is no guarantee of a 100 watt bulb always consuming 100 watts of
power.  Only at it's rated voltage will it perform that way.


>-----Original Message-----
>From: Glen [mailto:mclilith at ezwv.com]
>Sent: Wednesday, December 27, 2000 11:05 AM
>To: Robert Donker; 'IXQY at aol.com'; synth-diy at node12b53.a2000.nl
>Subject: RE: House wiring? (slightly off-topic)
>
>
>At 12:44 PM 12/27/00 , Robert Donker wrote:
>
>>You have a relatively new house showing what is an extraordinary behavior
>on
>
>>your AC. This is more likely a low AC voltage (remember, a 100 W bulb @ 100
>
>>volts draws 1 amp, a 100 @ bulb @ 50 volts draws 2 amps) causing excessive
>
>>current in the lights. 
>
>
>
>I'm not sure I understand how you intended that to be interpreted. If I
>
>understand you correctly, you have just stated that a 100 Watt bulb
>
>connected to a source of 100 Volts would pass one Ampere of current. (So
>
>far, so good.) You also seem to say that very same bulb when connected to
>
>only 50 Volts would then pass 2 Amperes of current. If this is the meaning
>
>you intended, it is totally incorrect. The same bulb will actually pass
>
>less amperage when connected to a lower voltage source.
>
>
>
>Perhaps you intended to say the right thing, but it just ended up being
>
>worded in a confusing manner?
>
>
>
>
>
>As for the original problem of the man's light bulbs blowing too often, I
>
>suggest he contact a qualified electrician in his area, or his local power
>
>company for advice. There are many things which could contribute to such a
>
>situation, and it is not easy or prudent to try and troubleshoot this via
>
>an email mailing list. I can vouch for the "poor ground/neutral scenario"
>
>that another poster mentioned. That is certainly one possibility. I've seen
>
>it happen myself, but I'm sure there are others possible causes as well. In
>
>the case that I saw, some aluminum wiring had disintegrated inside the
>
>cable between the electrical meter and the breaker box. The resulting poor
>
>connection gave all sorts of crazy voltage problems, and it was a definite
>
>fire hazard as well.
>
>
>
>Since this is such a high-stakes diagnosis, I would definitely contact a
>
>fully qualified professional in my area to handle the job. If you have any
>
>serious wiring problems, it could possibly pose a serious fire hazard for
>
>your home. It might not simply be a threat to your light bulbs and
>
>synthesizer gear that we are talking about. Let's hope that you've just
>
>been buying a poor grade of light bulbs lately, but to be sure, have the
>
>situation checked by a professional to determine what is really happening.
>
>
>
>
>
>Good luck,
>
>Glen
>

-- Scott Gravenhorst : On The Edge, but the Edge of What?
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