YucaLandia
Aug 24, 2011, 11:28 AM
Post #28 of 29
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Re: [at7mbe] USA  Mexico Voltage Differences for Wire Size

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at7mbe's observation about the difference about my text wording "higher", and at7mb's & my earlier interchanging use of "load" and "power", all got me thinking about how my words were contradictory to the theoretical Ohms law RMS example math calculation I included:
"When the voltage is higher than 110V, the current drawn for the same wattage load is proportionally higher. e.g. A microwave oven rated at 1500W draws roughly 15% lower amperage at 127V (17 amps) versus 19 amps at 110V."
Issues arise when convolving calculations based on batteries vs. variable output power supplies, and when mixing "power", vs. "load" (R for pure resistive loads and including phase angles w/inductive loads), and my error in claiming "the same wattage load"  because the household devices wattage does not stay constant with varying voltage. Here's my attempt to correct my earlier misspeaks: Households in Mexico can have variations in AC power ranging from 110V to 137V, mainly depending on the transformer for your block and on neighbor's loads (Air Conditioning etc). Both the wattage used and current used vary with the supply voltage => Power (Watts) = I x V for resistive loads. This means that higher household voltage also give higher wattages uses: (Physics 101 calculations do fit reality). Fortunately, our home has two "127V" legs coming into the home, with one at 132V and one at 119V, and I have various meters which gives me a chance to measure actual voltages, wattages, and amperages on various real world loads Table of Measured Wattages and Amperages (RMS values) 132V..........119V.........Item 111W..........93W..........Coffee bean grinder = AC motor 0.85A..........0.81A..........Coffee bean grinder = AC motor 1008W..........827W..........Clothes Iron 7.91A..........7.25A..........Clothes Iron 996W..........810W..........Espresso Water Heater 7.81A..........7.08A..........Espresso Water Heater 42W..........36W..........Floor Fan  Low Speed 50W..........45W..........Floor Fan  Medium Speed 63W..........57W..........Floor Fan  High Speed 130W..........120W..........Plasma Screen TV with constant picture 1610W..........1419W.........."1600W" Microwave Oven As shown by 16 measurements on a variety of common household inductive and resistive loads, and with at7mb's light bulb, ammeter, and variable VOLTAGE and variable POWER supply issue, when you increase the Voltage using a variable power supply, then I increases too... Clearly, the CFE lines offer variable power, variable voltage, and variable current. So, the power used by devices increases with increasing voltage. (Said another way, neither CFE's power supplied nor the power consumed by household devices are constant with changing voltage, so P is NOT a fixed variable, and P is NOT "load".) These data also clearly show that higher household voltages also give higher reading of actual watts used, and higher amperages, which is exactly what Robt65 was concerned about. This also means that at7mb's implied claims (and my faulty math example) of higher household voltages giving lower amperages just does not work in the real world. Fine for teaching theory in an EE or Physics class using a fixedvoltage/fixedpower battery, but not in actually wiring homes in Mexico with voltages that vary from 110V  137V. Making measurements: I used a combination of 2 Fluke meters and a KillaWatt meter to cross check the voltage, amperage, and wattage measurements. at7mb also writes that : "2. if you're plagued by low voltage, the current will increase for a constant load as the voltage falls. ", but as we can see with a variety of household loads (both inductive and pure resistive loads), the opposite is true: lower household voltages give lower current loads (though his argument is true if you have very limited power  as in failing CFE power at 95V). Except for caveat 2, all of this works out, based on: theory, at7mb's experiment, and my home measurements. Fortunately, all the wire sizes advice given to Robert (above) were correct. I also measured refrigerators, computers of various kinds, microwave ovens, other fans, incandescent and fluorescent lights etc to find out their actual power usage values when operating and when "turned off"  and everything made sense for those devices. steve   Readon MacDuff Evisit at http://yucalandia.com
(This post was edited by YucaLandia on Aug 24, 2011, 1:44 PM)
